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CALDERWOOD & HARKNESS LLP

INTERNAL MEMORANDUM — ATTORNEY WORK PRODUCT

PRIVILEGED AND CONFIDENTIAL — PREPARED IN ANTICIPATION OF LITIGATION — DO NOT DISTRIBUTE OUTSIDE OF LITIGATION TEAM

TO: Wendy Schultz, Lead Associate; Alan Ngo, Responsible Partner

FROM: Omar Siddiqui, Associate

DATE: October 10, 2024

RE: Prosecution History Estoppel Analysis — U.S. Patent No. 10,891,193

MATTER: Optiwave Semiconductor Corp. v. Lumicore Technologies, Inc., Case No. 2:24-cv-00319-JRG (E.D. Tex.)

SUBJECT: Analysis of Prosecution History Estoppel Risks for Doctrine of Equivalents Contentions on Claims 3 and 7 of U.S. Patent No. 10,891,193 ("the '193 Patent")

ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL — PREPARED IN ANTICIPATION OF LITIGATION. This memorandum constitutes attorney work product prepared in anticipation of litigation and is protected from disclosure under the work product doctrine. This memorandum also contains information protected by the attorney-client privilege. It should not be disclosed to any person outside of the litigation team without the prior approval of the responsible partner.

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I. PURPOSE AND EXECUTIVE SUMMARY

A. Purpose of Memorandum

This memorandum analyzes the prosecution history of U.S. Patent No. 10,891,193 (the "'193 Patent"), titled "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate," to determine the scope and impact of amendments made during prosecution on Optiwave Semiconductor Corp.'s ("OWS") ability to assert infringement under the doctrine of equivalents ("DOE") for Claims 3 and 7 of the '193 Patent. The analysis is undertaken in the context of OWS's pending patent infringement action against Lumicore Technologies, Inc. ("Lumicore"), Case No. 2:24-cv-00319-JRG, before the Honorable Judge J. Rodney Gilstrap in the Eastern District of Texas.

Specifically, this memorandum addresses three interrelated questions. First, it assesses whether the Festo presumption of surrender applies to OWS's doctrine of equivalents contentions for Claims 3 and 7 in light of a narrowing amendment made to independent Claim 1 during prosecution of the '193 Patent. Second, it evaluates whether any recognized exceptions under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), are available to rebut that presumption, with particular attention to the "tangential relation" and "unforeseeability" exceptions. Third, it provides strategic recommendations regarding the viability of DOE contentions served in OWS's P.R. 3-1 Infringement Contentions (served September 16, 2024) and the risks that must be addressed in Dr. Caroline Ashford's forthcoming expert report on infringement, which is due June 15, 2025 under the Court's current scheduling order.

This memorandum is a companion to the separate prosecution history estoppel analysis for the '015 Patent (U.S. Patent No. 11,402,015), which addresses DOE contentions for Claim 12 of that patent and is the subject of a separate memorandum dated October 12, 2024. The two analyses should be read together and positions coordinated to ensure consistency before the Court.

B. Summary of Conclusions

During prosecution of the '193 Patent, the applicant (OWS, through its prosecution counsel Cascade IP Advisors, LLC, lead prosecution attorney Dr. Martin Chu) narrowed the term "coherent detection module" in independent Claim 1 — from which both Claims 3 and 7 depend — in direct response to a § 102(a)(1) anticipation rejection over Takahashi et al., "Dense WDM Silicon Photonic MUX," IEEE Photonics Technology Letters, March 2014 ("Takahashi"). The amendment added specific structural limitations to the "coherent detection module" in order to distinguish the claimed invention over Takahashi's disclosed coherent receiver configuration. As detailed below, the amendment added three distinct structural requirements: (1) a polarization-splitting optical hybrid mixer; (2) at least four output ports, each coupled to a respective transimpedance-amplified balanced photodetector pair; and (3) monolithic integration of the entire coherent detection module on the silicon substrate.

Under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), a narrowing amendment made for a reason related to patentability creates a presumption that the patentee has surrendered all equivalents between the original claim scope and the amended claim scope. Because the amendment here was unambiguously made to overcome a § 102 rejection — the paradigmatic patentability-related amendment — the Festo presumption applies. The presumption, if unrebutted, would bar OWS from asserting DOE for Claims 3 and 7 with respect to the "coherent detection module" limitation as it relates to Lumicore's accused products.

However, our analysis identifies arguments under at least one, and potentially two, of the three recognized Festo rebuttal exceptions:

Tangential Relation Exception (Moderate Strength). The amendment bore only a tangential relation to the specific equivalent at issue in Lumicore's accused products. The amendment was designed to distinguish Takahashi's fundamentally different coherent receiver — a single-polarization, non-monolithic, non-TIA-amplified design — and not to foreclose alternative polarization-diversity architectures that employ separate polarization-splitting components upstream of integrated hybrid mixers. The prosecution remarks emphasized all three added structural features equally, and the specific structural path taken by Lumicore (an external polarization beam splitter preceding two single-polarization 90° optical hybrid mixers) was not the type of design the amendment was intended to exclude.

Unforeseeability Exception (Weak to Moderate Strength). The specific equivalent now at issue in Lumicore's LumiLink 400G-ZR+, LumiLink 800G-DR8, and LumiEdge 1600G-LR products — namely, a monolithically integrated coherent detection architecture using two separate single-polarization 90° optical hybrid mixers preceded by a monolithically integrated polarization beam splitter, all fabricated on a single silicon die — may be argued to have been unforeseeable at the time of the amendment. While the general concept of polarization diversity using separate receivers was known in bulk-optics telecommunications, the specific monolithic silicon-photonic implementation that Lumicore developed in 2021–2022 was not a standard design approach in the literature at the time the amendment was filed (estimated 2018–2019). This exception faces a higher bar under Federal Circuit precedent, but it should be preserved as a supporting argument.

Overall Risk Level: MODERATE. The DOE contentions for Claims 3 and 7 are viable but carry meaningful vulnerability at summary judgment and at trial. There is a near certainty that Lumicore's counsel at Hawthorne Vega & Cruz LLP (lead partner Catherine "Kate" Rourke, supported by Darren Cho) will move for summary judgment on prosecution history estoppel grounds, and we estimate the probability of the Court granting such a motion at 40–50%. If summary judgment is denied, the DOE contentions have a reasonable likelihood of success at trial, particularly before a jury. Even if the DOE contentions are ultimately barred, OWS retains literal infringement contentions for Claims 1, 10, 15, and 18 of the '193 Patent, though the loss of the DOE fallback increases the stakes of the Markman ruling on several disputed claim-construction terms.

II. BACKGROUND

A. The '193 Patent Overview

The '193 Patent, titled "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate," is one of two patents-in-suit arising from OWS's silicon-photonics transceiver technology platform. The key identifying information for the patent is as follows:

• Patent Number: U.S. Patent No. 10,891,193

• Title: "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate"

• Filing Date: April 7, 2017 (non-provisional application)

• Issue Date: January 12, 2021

• Original Assignee: Optiwave Semiconductor Corp. ("OWS")

• Current Assignee: Optiwave Semiconductor Corp.

• Named Inventors: Dr. Jian-Wei Huang (OWS Chief Technology Officer) and Dr. Nikolai Petrov (OWS Vice President of Engineering, Photonics Division)

• Priority Claim: Claims benefit of U.S. Provisional Application No. 62/499,117, filed April 7, 2017

The '193 Patent is a member of a patent family that also includes U.S. Patent No. 11,402,015 (the "'015 Patent"), which is the other patent-in-suit in this action. The '193 Patent and the '015 Patent share the common provisional application, U.S. Provisional Application No. 62/499,117, filed April 7, 2017. The two non-provisional applications were filed separately and do not stand in a continuation relationship — they are co-pending applications claiming priority to the same provisional. While the two patents share overlapping portions of the specification and disclosure, they claim different aspects of the OWS transceiver technology. The '193 Patent is directed primarily to the coherent optical transceiver architecture, with particular emphasis on the coherent detection module and its integration on a silicon substrate. The '015 Patent is directed primarily to the optical coupling and grating structures used to couple light into and out of the silicon-photonic transceiver chip, with particular emphasis on a two-dimensional sub-wavelength grating coupler.

The '193 Patent specification describes a coherent optical transceiver fabricated on a silicon-on-insulator (SOI) platform using complementary metal-oxide-semiconductor (CMOS)-compatible fabrication processes. The specification discloses the integration of a transmitter and receiver on a common silicon substrate, with the receiver portion including a coherent detection module that employs a polarization-splitting optical hybrid mixer to separate and mix the incoming optical signal with a local oscillator signal for coherent detection. The specification describes multiple embodiments, including both polarization-splitting hybrid designs and, in less detail, alternative polarization-diversity approaches, though the claims as amended are directed specifically to the polarization-splitting optical hybrid mixer configuration.

B. Asserted Claims of the '193 Patent

In this litigation, OWS asserts Claims 1, 3, 7, 10, 15, and 18 of the '193 Patent against all three of Lumicore's accused products: the LumiLink 400G-ZR+, LumiLink 800G-DR8, and LumiEdge 1600G-LR coherent optical transceivers. These claims were identified in OWS's P.R. 3-1 Infringement Contentions served on September 16, 2024.

Claim 1 is the primary independent claim and recites the coherent optical transceiver architecture as a whole, including the "coherent detection module" limitation that is central to this analysis. Claims 3 and 7 are dependent claims, each depending directly from independent Claim 1. Claim 10 is a second independent claim directed to a method of coherent optical signal detection. Claim 15 depends from Claim 10. Claim 18 is a third independent claim directed to a coherent optical transceiver system.

The doctrine of equivalents is asserted specifically and exclusively for Claims 3 and 7 of the '193 Patent, in addition to the literal infringement contentions for all six asserted claims. (DOE is also asserted for Claim 12 of the '015 Patent, which is the subject of a separate memorandum.) For Claims 1, 10, 15, and 18, OWS's infringement contentions rest solely on theories of literal infringement.

The specific limitation at issue for the DOE contentions on Claims 3 and 7 is the "coherent detection module" limitation recited in Claim 1 and inherited by Claims 3 and 7 as dependent claims. In addition, Claim 7 recites a specific limitation regarding signal processing within or coupled to the coherent detection module, which, while literally met by the accused products, interacts with the Claim 1 amendment in a manner that requires analysis, as discussed in Section VII.B below.

C. The Accused Products

OWS accuses three Lumicore coherent optical transceiver products of infringing the '193 Patent:

1. LumiLink 400G-ZR+ Coherent Optical Transceiver. This product was launched by Lumicore in Q3 2022 and generated fiscal year 2023 revenue of approximately $94.8 million, based on Lumicore's public filings and discovery productions. The LumiLink 400G-ZR+ is a pluggable coherent transceiver designed for data center interconnect (DCI) applications at distances up to 120 km, supporting 400 Gbps data rates using dual-polarization quadrature phase-shift keying (DP-QPSK) modulation. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.

2. LumiLink 800G-DR8 Coherent Optical Transceiver. This product was launched by Lumicore in Q1 2023 and generated fiscal year 2023 revenue of approximately $128.4 million. The LumiLink 800G-DR8 is a pluggable transceiver supporting 800 Gbps aggregate data rates over eight wavelength channels, using coherent detection on a silicon-photonic platform for data center and campus network applications. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.

3. LumiEdge 1600G-LR Coherent Optical Transceiver. This product was launched by Lumicore in Q4 2023 and generated fiscal year 2023 revenue of approximately $41.7 million. The LumiEdge 1600G-LR is Lumicore's highest-bandwidth coherent transceiver product, supporting 1.6 Tbps aggregate data rates over long-reach (LR) distances for telecom metro and backbone networks. The product was launched after OWS's pre-suit notice letters (January 15, 2023 and May 15, 2023) and the April 20, 2023 in-person meeting between the parties, which is relevant to OWS's willful infringement allegations. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.

The total accused product revenue for fiscal year 2023 across all three products is approximately $264.9 million. Revenue figures for fiscal year 2024 are expected to be substantially higher based on Lumicore's public guidance and analyst estimates, particularly for the LumiLink 800G-DR8 and LumiEdge 1600G-LR, which are experiencing rapid adoption in the data center and telecom markets.

All three accused products employ a coherent optical detection architecture that differs in one specific structural detail from the literal claim language as amended during prosecution. As described more fully in Section V.C below, the accused products use a polarization-diversity scheme employing two separate single-polarization 90° optical hybrid mixers preceded by an upstream polarization beam splitter, rather than a single "polarization-splitting optical hybrid mixer" as recited in the amended Claim 1. The accused products do, however, employ transimpedance-amplified balanced photodetector pairs at the output ports and achieve monolithic integration on a silicon substrate. OWS contends that the accused products' coherent detection architecture performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed "coherent detection module" with a "polarization-splitting optical hybrid mixer."

D. OWS's Infringement Contentions on DOE

Per OWS's P.R. 3-1 Infringement Contentions served on September 16, 2024, the doctrine of equivalents is asserted for Claims 3 and 7 of the '193 Patent. (DOE is also asserted for Claim 12 of the '015 Patent, which is addressed in a separate memorandum dated October 12, 2024.) The infringement contentions identify the specific limitations for which DOE is asserted and set forth the function-way-result analysis for each limitation.

The function-way-result test is applied to the "coherent detection module" limitation as follows. Even if Lumicore's accused designs do not literally satisfy the "coherent detection module" limitation as amended — specifically, even if the use of two separate single-polarization 90° optical hybrid mixers preceded by a polarization beam splitter does not literally satisfy the requirement for "a polarization-splitting optical hybrid mixer" — OWS contends that these elements perform substantially the same function, in substantially the same way, to achieve substantially the same result:

• Function: Coherent optical detection and demodulation of a polarization-multiplexed optical signal — i.e., separating the two orthogonal polarization states of the incoming optical signal and coherently detecting each by mixing with a local oscillator signal to produce electrical baseband signals.

• Way: Using integrated photonic components on a silicon substrate to split the incoming signal by polarization and to mix each polarization component with a local oscillator signal via optical hybrid mixing, with balanced photodetection at each output port. In both the claimed design and Lumicore's design, the incoming polarization-multiplexed signal is separated into its two orthogonal components, each of which is mixed with a local oscillator in a 90° optical hybrid to produce in-phase and quadrature beat signals, which are then detected by balanced photodetector pairs with integrated transimpedance amplification.

• Result: Recovery of the full amplitude, phase, and polarization information from a coherent optical signal, enabling digital reconstruction of the transmitted data signals with high spectral efficiency and long-reach performance.

The infringement contentions include claim charts mapping each limitation of Claims 3 and 7 to the accused products, with the DOE analysis for the "coherent detection module" limitation set forth in detail. The infringement contentions were prepared based on publicly available information, Benchmark Semiconductor Analysis, LLC teardown reports, and, where applicable, Lumicore design documents produced in discovery and designated Highly Confidential — Attorneys' Eyes Only under the Protective Order (D.E. 25).

III. PROSECUTION HISTORY OF THE '193 PATENT

A. Initial Filing and Original Claim Scope

The '193 Patent was filed as a non-provisional application on April 7, 2017, claiming the benefit of U.S. Provisional Application No. 62/499,117, filed the same date. The application was prosecuted by Cascade IP Advisors, LLC, with Dr. Martin Chu serving as lead prosecution attorney (1550 Crystal Drive, Suite 600, Arlington, VA 22202). Dr. Chu is a registered patent attorney with a Ph.D. in electrical engineering from MIT and over twenty years of experience prosecuting semiconductor and photonics patents.

As originally filed, independent Claim 1 recited, inter alia:

"a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."

The original claim language used broad, functional language to define the "coherent detection module." The claim did not specify the internal structural components of the module, their arrangement, or the method of integration. As written, the original Claim 1 would have encompassed any coherent detection architecture — whether employing a single-polarization hybrid, a polarization-splitting hybrid, multiple separate hybrids, monolithically integrated or hybrid-integrated components, with or without transimpedance amplification — so long as the module was "configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."

The original dependent Claims 3 and 7 added further limitations narrowing the scope of the coherent detection module, but without altering its fundamental architectural definition:

• Original Claim 3 specified a particular arrangement of balanced photodetectors within the module: "The coherent optical transceiver of claim 1, wherein the coherent detection module comprises a balanced photodetector arrangement comprising at least two pairs of balanced photodetectors, each pair configured to detect in-phase and quadrature components of a respective polarization state."

• Original Claim 7 specified a digital signal processing function performed by an integrated DSP within or coupled to the coherent detection module: "The coherent optical transceiver of claim 1, further comprising a digital signal processor integrated with the coherent detection module, the digital signal processor configured to perform adaptive equalization and carrier recovery on the electrical output signals."

Neither Claim 3 nor Claim 7 imposed structural requirements on the optical hybrid mixer portion of the coherent detection module. The combination of the broad "coherent detection module" definition in Claim 1 with the specific additional limitations in Claims 3 and 7 provided both breadth and technical specificity in the original claim set.

B. First Office Action — § 102 Rejection over Takahashi et al.

The examining division (Art Unit 2883) assigned the application to Examiner Timothy R. Kwon. After a search of the prior art, Examiner Kwon issued a first office action (non-final) rejecting Claims 1, 3, 7, and several other claims under 35 U.S.C. § 102(a)(1) as anticipated by Takahashi et al., "Dense WDM Silicon Photonic MUX," published in IEEE Photonics Technology Letters, Vol. 26, No. 6, March 15, 2014, pp. 595–598 ("Takahashi").

Takahashi disclosed a silicon photonic multiplexer system designed for dense wavelength-division multiplexing (DWDM) applications. The system included, among other components, a coherent receiver subsystem fabricated on a silicon-on-insulator (SOI) platform. Takahashi's coherent receiver subsystem employed a single-polarization 90° optical hybrid mixer integrated on the SOI platform and balanced photodetectors for coherent detection of an optical signal. Critically, Takahashi's design had three features (or, more precisely, three absences of features) that distinguish it from the '193 Patent's claims as eventually amended:

1. Single-polarization design: Takahashi's coherent receiver used a single-polarization 90° optical hybrid mixer. It did not include polarization-splitting functionality — the receiver processed only a single polarization state of the incoming optical signal. This is in contrast to the dual-polarization, polarization-diverse architecture disclosed and claimed in the '193 Patent.

2. No integrated transimpedance amplification: Takahashi's balanced photodetectors were not coupled with integrated transimpedance amplifiers (TIAs) at each output port. Takahashi's design relied on external amplification electronics, which is a less integrated and generally lower-performance approach than monolithically integrated TIAs.

3. Hybrid integration, not monolithic: Takahashi's coherent receiver used hybrid integration — the silicon photonic components (waveguides, optical hybrid mixer) were fabricated on the SOI platform, but the photodetectors were separate III-V semiconductor (indium phosphide) chips bonded to the silicon platform using flip-chip bonding techniques. This is a distinct integration approach from the monolithic integration recited in the '193 Patent specification, where all components — including the photodetectors — are fabricated directly on the silicon substrate using CMOS-compatible processes.

The examiner found that Takahashi's coherent receiver subsystem met every element of the original broad "coherent detection module" limitation in Claim 1. Specifically, the examiner concluded that Takahashi's coherent receiver was "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics," within the plain meaning of the original claim language. The examiner also found that Takahashi's disclosure of balanced photodetectors addressed the Claim 3 limitation regarding balanced photodetector pairs, and that Takahashi's reference to digital signal processing performed post-detection (described in Takahashi's Section III-C) addressed the Claim 7 limitation regarding an integrated DSP configured to perform adaptive equalization and carrier recovery.

The rejection was a straightforward § 102(a)(1) anticipation rejection, asserting that Takahashi disclosed every element of the claims as originally filed. The examiner's position was unambiguous, and the rejection was well-founded given the breadth of the original claim language.

C. Applicant's Response and Narrowing Amendment

In response to the § 102 rejection, Dr. Martin Chu filed an amendment and response on behalf of OWS. Based on the prosecution timeline — the application was filed April 7, 2017, and the patent issued January 12, 2021 — the amendment was likely filed during the 2018–2019 timeframe, though the precise date requires confirmation from the prosecution history file wrapper, which is included in Appendix A.

The amendment narrowed the "coherent detection module" limitation in independent Claim 1. As amended, the relevant portion of Claim 1 reads:

"a coherent detection module comprising a polarization-splitting optical hybrid mixer with at least four output ports, each output port coupled to a respective transimpedance-amplified balanced photodetector pair, the coherent detection module monolithically integrated on the silicon substrate."

The amendment added three specific structural requirements not present in the original claim language:

1. Polarization-splitting optical hybrid mixer: The amended claim specifies that the coherent detection module must include a "polarization-splitting optical hybrid mixer" — a single integrated component that both separates the incoming optical signal into its two orthogonal polarization components and performs 90° optical hybrid mixing of each polarization component with a local oscillator signal. This replaced the original generic reference to a "coherent detection module" without any specification of internal mixer architecture.

2. At least four output ports, each coupled to a transimpedance-amplified balanced photodetector pair: The amended claim specifies both the minimum number of output ports (four — corresponding to the in-phase and quadrature outputs for each of two polarization states) and the requirement that each output port be coupled to a balanced photodetector pair with integrated transimpedance amplification. This replaced the original generic reference to the module generating "electrical output signals" without specifying the detection and amplification architecture.

3. Monolithic integration on the silicon substrate: The amended claim specifies that the entire coherent detection module — including the polarization-splitting optical hybrid mixer, the output ports, and the transimpedance-amplified balanced photodetector pairs — must be "monolithically integrated on the silicon substrate." This replaced the original claim's silence on the integration methodology, which would have encompassed hybrid integration approaches such as Takahashi's.

In the remarks accompanying the amendment, Dr. Chu argued that the amended claims distinguished over Takahashi's coherent receiver configuration in three respects. The remarks stated, in relevant part:

"Applicant respectfully submits that the amended claims distinguish over Takahashi et al. in at least three material respects. First, Takahashi discloses a single-polarization 90° optical hybrid mixer, not a polarization-splitting optical hybrid mixer as recited in amended Claim 1. Takahashi's receiver processes only one polarization state and does not include the polarization-splitting functionality that is a key feature of Applicant's invention. Second, Takahashi does not disclose transimpedance-amplified balanced photodetector pairs coupled to each output port of the mixer. Takahashi's photodetectors operate without integrated transimpedance amplification, relying instead on external amplification electronics. Third, Takahashi's receiver employs hybrid integration, with separate III-V semiconductor photodetector chips bonded to the silicon platform, rather than monolithic integration of the entire coherent detection module on the silicon substrate as required by amended Claim 1."

The prosecution remarks presented all three distinguishing features as co-equal bases for patentability over Takahashi. Notably, the remarks did not single out any one of the three features as the primary or dispositive ground for distinguishing the prior art. Each feature was presented as an independent and sufficient basis for overcoming the rejection, while the combination of all three was characterized as representing a significant advance over Takahashi's architecture.

The examiner was persuaded by the amendment and the accompanying remarks. No second office action was issued on the § 102 rejection grounds. The amended claims were allowed.

D. Subsequent Prosecution — No Further Relevant Amendments

After the examiner accepted the amended claims and withdrew the § 102 rejection over Takahashi, the prosecution of the '193 Patent proceeded without further amendments to the "coherent detection module" limitation or to any other limitation relevant to this estoppel analysis. Claims 3 and 7, as dependent claims, inherited the narrowed "coherent detection module" limitation from Claim 1 as a matter of claim dependency, but neither Claim 3 nor Claim 7 was independently amended at any point during prosecution. The additional limitations recited in Claims 3 and 7 (balanced photodetector arrangement and integrated DSP, respectively) remained in their original form throughout prosecution.

An examiner interview was conducted during prosecution, as noted in the Examiner Interview Summary included in the prosecution history. The interview addressed the "integrated on a silicon substrate" limitation, which is a separate claim-construction issue currently in dispute between the parties (disputed term number 4 of 14 on the parties' joint claim-construction chart, D.E. 31). The interview did not revisit the "coherent detection module" amendment or the Takahashi prior art reference, and no representations were made during the interview that bear on the prosecution history estoppel analysis for Claims 3 and 7. Nevertheless, the interview summary should be reviewed by Dr. Ashford and her team in connection with the "integrated on a silicon substrate" claim-construction analysis, as statements made during the interview may be relevant to that separate issue.

The patent issued on January 12, 2021, with 22 claims, including Claims 1, 3, and 7 in their amended/original form as described above.

E. Relationship to the '015 Patent Prosecution

As noted above, the '193 Patent and the '015 Patent (U.S. Patent No. 11,402,015) share U.S. Provisional Application No. 62/499,117 but are separate non-provisional filings that do not stand in a continuation relationship. Each patent was prosecuted independently, and each involved a separate narrowing amendment made to overcome different prior art rejections.

The '015 Patent prosecution involved a narrowing amendment to the "two-dimensional sub-wavelength grating" limitation of Claim 12, made to overcome a § 103 obviousness rejection combining Bergmann (U.S. Patent No. 8,412,007) with Simonsen (PCT/EP2015/071234). The '015 Patent amendment and the '193 Patent amendment address different claim limitations, different prior art references, and different patentability grounds (§ 103 for the '015 Patent versus § 102 for the '193 Patent). The '015 Patent estoppel analysis is the subject of a separate memorandum dated October 12, 2024, prepared by Jonathan Varma and reviewed by Wendy Schultz.

Although the two amendments are doctrinally and factually independent, consistency of legal position across the two patents is important. Both patents are asserted in the same action, before the same judge and (if the case reaches trial) the same jury. Lumicore will likely argue both estoppel issues together, and any inconsistency in OWS's positions could undermine credibility. The recommendations in this memorandum have been coordinated with the positions taken in the '015 Patent memorandum to ensure consistency, though the specific factual arguments differ because the underlying amendments address different technology and different prior art.

IV. LEGAL FRAMEWORK: PROSECUTION HISTORY ESTOPPEL AND FESTO PRESUMPTION

A. The Doctrine of Equivalents — General Principles

Under the doctrine of equivalents, a product that does not literally infringe a patent claim may nonetheless be found to infringe if each limitation of the claim is met by an equivalent element in the accused product. The doctrine of equivalents is a judicially created doctrine designed to prevent an infringer from avoiding liability by making insubstantial changes to a patented invention that, while technically avoiding the literal claim language, appropriate the substance of the claimed invention. See Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 607 (1950) ("to permit imitation of a patented invention which does not copy every literal detail would be to convert the protection of the patent grant into a hollow and useless thing").

The primary test for equivalence is the function-way-result test: an element in the accused product is equivalent to a claimed element if it performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed element. See Warner-Jenkinson Co. v. Harborline Enterprises Davis Chemical Co., 520 U.S. 17, 40 (1997); Graver Tank, 339 U.S. at 608. The analysis is conducted from the perspective of a person of ordinary skill in the art at the time of the alleged infringement. See Warner-Jenkinson, 520 U.S. at 37.

The doctrine of equivalents is subject to an important structural limitation: the all-limitations rule. Under this rule, the doctrine of equivalents must be applied on a limitation-by-limitation basis; no claim limitation may be read out of the claim entirely. See Warner-Jenkinson, 520 U.S. at 29 ("each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole"). This rule prevents a patentee from using the doctrine of equivalents to effectively eliminate a claim limitation, and it requires that each limitation be evaluated independently for whether it is met, either literally or by an equivalent, in the accused product.

B. Prosecution History Estoppel — Festo Framework

Prosecution history estoppel is one of the principal limitations on the doctrine of equivalents. The doctrine provides that a patentee who narrows a claim during prosecution — whether by amendment or by argument — may be estopped from later asserting that the surrendered claim scope is captured by the doctrine of equivalents. The rationale for the doctrine is that the public is entitled to rely on the prosecution history as defining the boundaries of the patent grant, and a patentee should not be permitted to recapture through the doctrine of equivalents what was surrendered during prosecution to obtain the patent.

The Supreme Court established the modern framework for prosecution history estoppel in Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002). Under Festo, when an applicant narrows a claim during prosecution for a reason related to patentability, a presumption arises that the patentee has surrendered all territory between the original claim scope and the amended claim scope. This is referred to as the "presumption of total surrender" or the "Festo presumption."

The Festo presumption is a rebuttable presumption. The patentee may overcome the presumption by demonstrating that one of three circumstances exists:

1. Unforeseeability: The alleged equivalent was unforeseeable at the time of the amendment. If the equivalent technology or design was not known or foreseeable at the time the narrowing amendment was made, the patentee could not reasonably have been expected to draft the amendment to encompass that equivalent, and the presumption of surrender is rebutted. See Festo, 535 U.S. at 740–41.

2. Tangential Relation: The rationale underlying the narrowing amendment bore only a tangential relation to the equivalent in question. If the reason for the amendment was unrelated or only tangentially related to the specific equivalent at issue, the narrowing amendment should not be presumed to have surrendered that particular equivalent. See id. at 740–41.

3. Other Reason: There is some other reason suggesting that the patentee could not reasonably have been expected to have drafted a claim that literally encompassed the alleged equivalent. This is a residual category intended to address circumstances not covered by the first two exceptions. See id. at 740–41.

The burden of proof to rebut the Festo presumption rests on the patentee — in this case, OWS. See Festo, 535 U.S. at 740. The patentee must provide objective evidence sufficient to overcome the presumption; bare attorney argument is insufficient. The standard for rebutting the presumption is demanding, though not insurmountable, and the Federal Circuit has found the exceptions satisfied in a number of cases, as discussed below.

C. Application of Festo to Narrowing Amendments Made to Overcome Prior Art

Amendments made to overcome anticipation rejections under § 102 — as in the prosecution history of the '193 Patent — are the paradigmatic example of patentability-related narrowing amendments that trigger the Festo presumption. The Federal Circuit has consistently and unambiguously held that adding structural limitations to distinguish prior art constitutes a narrowing amendment for purposes of Festo. See, e.g., Honeywell Int'l, Inc. v. Hamilton Sundstrand Corp., 370 F.3d 1131, 1139–41 (Fed. Cir. 2004) (en banc) (holding that amendment adding specific structural limitations to overcome § 102 rejection triggered Festo presumption); Festo Corp. v. Fenmore & Co., 344 F.3d 1359, 1366–68 (Fed. Cir. 2003) (en banc) (on remand from the Supreme Court, applying the Festo framework and identifying the scope of surrender).

The Federal Circuit has also clarified that the Festo presumption applies regardless of whether the amendment was strictly "necessary" to overcome the prior art rejection — even if the applicant might have overcome the rejection by other means, the fact that the applicant chose to narrow the claims by amendment triggers the presumption. See Festo, 344 F.3d at 1367 ("It is the narrowing amendment made to overcome the prior art that gives rise to prosecution history estoppel, regardless of whether the applicant could have obtained the patent in some other way."). This is relevant here because OWS might argue that the amendment was broader than necessary to overcome Takahashi (e.g., the monolithic integration requirement alone might have sufficed to distinguish Takahashi's hybrid-integrated design). However, such an argument does not avoid the Festo presumption — it is the amendment as a whole, including all three added structural features, that defines the surrendered territory.

The Federal Circuit has further held that voluntary amendments — amendments not required by the examiner but offered by the applicant to advance prosecution — trigger the Festo presumption to the same extent as amendments made in direct response to a rejection, so long as the amendment was made for a reason related to patentability. See Warner-Jenkinson, 520 U.S. at 33 (placing the burden on the patentee to establish that an amendment was not made for a reason related to patentability). Here, the amendment was unambiguously made in response to a § 102 rejection and for the purpose of distinguishing the prior art, so there is no question that the amendment was made "for a reason related to patentability."

V. APPLICATION OF FESTO TO THE '193 PATENT AMENDMENT

A. The Amendment Was a Narrowing Amendment for Reasons of Patentability

Applying the Festo framework to the prosecution history of the '193 Patent, the threshold question is whether the amendment to the "coherent detection module" limitation constitutes a narrowing amendment made for a reason related to patentability. The answer is unambiguous: yes, on both counts.

First, there is no dispute that the amendment was made in response to a § 102(a)(1) anticipation rejection — a patentability rejection. The examiner rejected the original claims as anticipated by Takahashi, and the applicant responded by amending the claims to distinguish Takahashi. The prosecution remarks explicitly stated that the amendment was made for the purpose of overcoming the § 102 rejection and argued that the amended claims were patentable over Takahashi because of the three structural features added by the amendment.

Second, there is no dispute that the amendment narrowed the claim scope. The original claim broadly recited "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics" — language that would have encompassed any coherent detection architecture regardless of internal structure or integration method. The amended claim is limited to a specific structural configuration: a coherent detection module comprising a polarization-splitting optical hybrid mixer with at least four output ports, each coupled to a transimpedance-amplified balanced photodetector pair, all monolithically integrated on the silicon substrate. The amendment unambiguously narrowed the claim scope by adding three structural requirements that were not present in the original claim.

Conclusion: The Festo presumption applies. OWS has surrendered all equivalents between the original broad "coherent detection module" language and the narrowed, structurally specific amended language, unless OWS can rebut the presumption by establishing one of the three Festo exceptions.

B. Identification of the Surrendered Territory

To assess the impact of the Festo presumption on OWS's DOE contentions, it is necessary to define the territory surrendered by the amendment. The surrendered territory is the difference between the scope of the original claim and the scope of the amended claim — i.e., all subject matter that was within the scope of the original claim but outside the scope of the amended claim.

The original claim covered any "coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics." This expansive language encompassed, without limitation: modules using single-polarization mixers; modules using polarization-splitting mixers; modules using multiple separate single-polarization mixers with external polarization splitting; modules with or without transimpedance amplification at the output ports; modules using monolithic integration; modules using hybrid integration (e.g., III-V photodetector chips bonded to a silicon photonic platform); modules using discrete optical components; and any other coherent detection architecture satisfying the broad functional definition.

The amended claim is limited to a specific structural configuration: a coherent detection module comprising (1) a polarization-splitting optical hybrid mixer (2) with at least four output ports, each coupled to a respective transimpedance-amplified balanced photodetector pair, (3) the coherent detection module monolithically integrated on the silicon substrate.

The surrendered territory therefore encompasses all coherent detection module implementations that fall within the original broad claim scope but lack one or more of the three structural features added by the amendment. This includes, among other configurations:

• Modules using single-polarization mixers (i.e., mixers that process only one polarization state, without polarization-splitting functionality), such as Takahashi's single-polarization 90° hybrid;

• Modules using multiple separate single-polarization mixers with an external polarization beam splitter (i.e., designs that achieve polarization diversity by splitting polarizations upstream of the mixer, rather than using a single integrated polarization-splitting hybrid mixer);

• Modules without transimpedance amplification at each output port;

• Modules using hybrid integration (e.g., III-V semiconductor photodetector chips bonded to a silicon photonic platform) rather than monolithic integration of the entire module on the silicon substrate;

• Any combination of the above.

The question for this analysis is whether the specific equivalent at issue — Lumicore's accused two-mixer-plus-polarization-beam-splitter architecture — falls within this surrendered territory. That question is addressed in Section V.D below.

C. Lumicore's Accused Equivalent — What Is the Specific Equivalent at Issue?

To apply the Festo analysis, we must precisely identify the structural features of Lumicore's accused products that give rise to the DOE contention and the manner in which they differ from the literal claim language.

Based on the Benchmark Semiconductor Analysis, LLC teardown reports — including the LumiLink 400G-ZR+ teardown report dated December 12, 2022; the LumiLink 800G-DR8 teardown report dated June 2023; and the LumiEdge 1600G-LR teardown report dated February 2024 — as well as Lumicore design documents produced in discovery and designated Highly Confidential — Attorneys' Eyes Only under the Protective Order (D.E. 25), the coherent detection architecture of Lumicore's accused products has the following relevant structural features:

1. Polarization-diversity scheme: Lumicore's accused products achieve polarization-diverse coherent detection. However, rather than using a single integrated "polarization-splitting optical hybrid mixer" as recited in the amended Claim 1, Lumicore's design employs a modified architecture consisting of a polarization beam splitter (PBS) positioned upstream of two separate single-polarization 90° optical hybrid mixers. The polarization beam splitter separates the incoming optical signal into its two orthogonal polarization components (TE and TM), and each component is routed to a separate 90° optical hybrid mixer, where it is mixed with a local oscillator signal for coherent detection. In essence, the polarization-splitting function and the optical hybrid mixing function are performed by separate, discrete components (the PBS and the two 90° hybrids, respectively), rather than by a single integrated "polarization-splitting optical hybrid mixer" that performs both functions within a single device.

2. Transimpedance-amplified balanced photodetector pairs: Lumicore's design does use transimpedance-amplified balanced photodetector pairs at the output ports of the optical hybrid mixers. Each of the two 90° hybrids has at least two output ports, and each output port is coupled to a balanced photodetector pair with integrated transimpedance amplification. This feature of the accused products is consistent with the amended claim language.

3. Monolithic integration on a silicon substrate: Lumicore's design achieves monolithic integration of the entire coherent detection architecture — including the polarization beam splitter, the two 90° optical hybrid mixers, the balanced photodetectors, and the transimpedance amplifiers — on a single silicon substrate. This feature of the accused products is also consistent with the amended claim language (subject to the separate claim-construction dispute over the meaning of "integrated on a silicon substrate").

The specific point of divergence from the literal claim language is the structure of the optical hybrid mixer. The amended Claim 1 requires "a polarization-splitting optical hybrid mixer" — a single component that performs both polarization splitting and optical hybrid mixing. Lumicore's design uses two separate single-polarization 90° optical hybrid mixers preceded by a separate polarization beam splitter. The polarization-splitting function is performed by the PBS, not by the optical hybrid mixers themselves. The optical hybrid mixing function is performed by the two separate 90° hybrids, each of which processes only a single polarization state.

OWS's DOE contention is that Lumicore's two-mixer-plus-PBS architecture is equivalent to the claimed "polarization-splitting optical hybrid mixer" under the function-way-result test:

• Function: Both perform the same function — splitting the incoming signal by polarization and mixing each polarization component with a local oscillator for coherent detection.

• Way: Both achieve this function in substantially the same way — using optical hybrid mixing of each polarization component with a local oscillator signal. The only structural difference is whether the polarization splitting occurs within the hybrid mixer itself or immediately upstream of two separate hybrid mixers. In both cases, the same optical mixing operations are performed, the same number of output signals are produced, and the same balanced photodetection with transimpedance amplification is performed.

• Result: Both achieve substantially the same result — recovery of the full polarization-diverse coherent signal information (in-phase and quadrature components for each of two polarization states) for subsequent digital signal processing.

D. Does the Accused Equivalent Fall Within the Surrendered Territory?

The central question for the Festo analysis is whether Lumicore's two-mixer-plus-PBS design falls within the territory surrendered by the amendment. If it does, the Festo presumption bars DOE unless OWS can rebut the presumption. If it does not, prosecution history estoppel does not apply, and OWS's DOE contentions may proceed without the need to rebut the presumption.

The analysis of surrendered territory proceeds as follows:

The original claim broadly covered any "coherent detection module" configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics. This broad language would have encompassed Lumicore's two-mixer-plus-PBS design, which is unquestionably "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."

The amended claim requires "a coherent detection module comprising a polarization-splitting optical hybrid mixer" — a single, integrated component that both splits polarizations and performs optical hybrid mixing. Lumicore's design separates these two functions into a polarization beam splitter and two separate single-polarization hybrid mixers. The accused design does not literally satisfy the requirement for "a polarization-splitting optical hybrid mixer" because the polarization-splitting function is performed by a separate PBS component, not by the optical hybrid mixers themselves.

Conclusion: Lumicore's two-mixer-plus-PBS design falls within the surrendered territory. It is a coherent detection architecture that was encompassed by the original broad claim language but does not satisfy the specific structural requirements added by the amendment — specifically, it lacks the "polarization-splitting optical hybrid mixer" required by the amended claim. The accused design achieves polarization diversity through a different structural path (external PBS + two single-polarization hybrids) rather than through the specific claimed structure (a single integrated polarization-splitting hybrid mixer).

Because the accused equivalent falls within the surrendered territory, the Festo presumption bars OWS from asserting DOE for the "coherent detection module" limitation unless OWS can rebut the presumption by establishing one of the three recognized Festo exceptions. The analysis of those exceptions follows in Section VI.

VI. REBUTTAL ARGUMENTS UNDER FESTO EXCEPTIONS

A. Exception 1: Tangential Relation

1. Argument. The first and strongest Festo rebuttal argument available to OWS is that the rationale underlying the narrowing amendment bore only a tangential relation to the equivalent in question — i.e., that the reason the applicant amended the claim (to distinguish Takahashi's single-polarization, non-monolithic, non-TIA-amplified coherent receiver) was only tangentially related to the specific structural difference between the claimed "polarization-splitting optical hybrid mixer" and Lumicore's two-mixer-plus-PBS architecture.

2. Analysis. The tangential-relation exception is grounded in the principle that prosecution history estoppel should not extend to equivalents that bear little or no relationship to the reason the amendment was made. The rationale is that the public-notice function of prosecution history estoppel is not served when the amendment was directed at a different problem from the one relevant to the equivalent. See Festo, 535 U.S. at 740–41; Insituform Technologies, Inc. v. CAT Contracting, Inc., 385 F.3d 1360, 1370 (Fed. Cir. 2004).

To evaluate this exception, we must compare the rationale for the amendment with the nature of the accused equivalent.

Rationale for the amendment: The amendment was made to overcome Takahashi's coherent receiver, which was a fundamentally different design from the claimed invention. Takahashi's receiver was: (a) single-polarization only (no polarization-diversity capability); (b) lacking integrated transimpedance amplification; and (c) hybrid-integrated rather than monolithically integrated. The amendment addressed all three of these deficiencies simultaneously by adding three structural requirements to the "coherent detection module" limitation. Dr. Chu's prosecution remarks presented all three distinguishing features as co-equal grounds for patentability, without singling out any one feature as the primary or dispositive basis for the amendment. Each feature was presented as an independent basis for distinguishing Takahashi.

Nature of the accused equivalent: Lumicore's design is not a single-polarization, non-monolithic, non-TIA-amplified receiver like Takahashi. To the contrary, Lumicore's design achieves polarization diversity (through an external PBS + two hybrids), uses transimpedance-amplified balanced photodetectors, and is monolithically integrated on a silicon substrate. The only structural difference between Lumicore's design and the amended claim is the manner in which polarization splitting is integrated with optical hybrid mixing — whether the polarization splitting occurs within the hybrid mixer itself (as in the claimed design) or immediately upstream of the hybrid mixers in a separate PBS component (as in Lumicore's design).

The tangential-relation argument proceeds as follows. The core reason for the amendment was to distinguish Takahashi's entire coherent receiver configuration — a single-polarization, non-monolithic, non-TIA-amplified design — not specifically to exclude all alternative polarization-diversity architectures that achieve the same end result through slightly different structural means. The specific structural path taken by Lumicore (external PBS + two single-polarization hybrids, all monolithically integrated with TIA-amplified photodetectors) is a polarization-diverse, monolithically integrated, TIA-amplified design that is categorically different from Takahashi's receiver. The amendment was intended to add the concept of "polarization splitting" to the claim to distinguish Takahashi's complete absence of polarization diversity — it was not intended to dictate the precise structural mechanism by which polarization splitting is achieved. The distinction between a single integrated polarization-splitting hybrid mixer and a separate PBS followed by two single-polarization hybrids is a granular structural detail that was tangential to the core reason for the amendment, which was to overcome a fundamentally different prior art design.

Furthermore, the amendment added three features simultaneously. The prosecution remarks emphasized the monolithic integration and transimpedance amplification features at least as prominently as the polarization-splitting hybrid mixer feature. If the amendment had added only the "polarization-splitting optical hybrid mixer" limitation — and the prosecution remarks had focused solely on distinguishing Takahashi's lack of polarization diversity — the tangential-relation argument would be weaker. But the amendment was a multi-feature amendment directed at a prior art reference that differed from the claimed invention in multiple, independent respects. The specific structural detail of how polarization splitting is integrated with hybrid mixing was only one of three independent bases for distinguishing Takahashi, and arguably the least emphasized.

3. Supporting Precedent

The tangential-relation exception was found to be satisfied in Insituform Technologies, Inc. v. CAT Contracting, Inc., 385 F.3d 1360 (Fed. Cir. 2004). In Insituform, the Federal Circuit held that the tangential-relation exception was met where the amendment addressed a different problem from the one relevant to the equivalent at issue. The court examined the prosecution history and determined that the narrowing amendment had been directed at distinguishing a prior art reference on grounds unrelated to the structural feature of the equivalent, and concluded that applying estoppel to bar the equivalent would extend the presumption of surrender beyond its logical scope.

Analogously, in our case, the amendment addressed Takahashi's lack of any polarization diversity — a single-polarization design with no polarization-splitting capability — and was not directed at foreclosing alternative structural mechanisms for achieving polarization diversity. The equivalent at issue (Lumicore's PBS + two-hybrid architecture) is a different structural approach to achieving the same polarization-diverse coherent detection that the amendment was intended to claim, not the type of design the amendment was intended to exclude. The amendment was intended to exclude designs like Takahashi's — single-polarization, non-monolithic, non-TIA-amplified receivers — and not to exclude alternative polarization-diverse architectures that achieve the same result through a slightly different structural path.

4. Risks and Counter-Arguments

The tangential-relation argument, while our strongest Festo rebuttal, faces significant counter-arguments that Lumicore will raise.

Lumicore's primary counter-argument: The amendment specifically added "polarization-splitting optical hybrid mixer," and the prosecution remarks specifically argued that Takahashi lacked a "polarization-splitting" mixer. The specific language added to the claim — "polarization-splitting optical hybrid mixer" — directly addresses the structural feature at issue in the DOE analysis. Lumicore will argue that the amendment was not tangential to the equivalent at all — it was directly related, because the amendment specifically defined how polarization splitting must be achieved (within the hybrid mixer itself), and Lumicore's design achieves polarization splitting differently (through an external PBS).

This counter-argument has force. The tangential-relation exception is most easily established when the amendment and the equivalent address entirely different claim features or entirely different aspects of the technology. Here, both the amendment and the equivalent relate to the same claim feature — the polarization-splitting functionality of the optical hybrid mixer — which makes the tangential-relation argument more difficult. The argument requires the Court to accept a nuanced distinct

CALDERWOOD & HARKNESS LLP
INTERNAL MEMORANDUM — ATTORNEY WORK PRODUCT
PRIVILEGED AND CONFIDENTIAL — PREPARED IN ANTICIPATION OF LITIGATION — DO NOT DISTRIBUTE OUTSIDE OF LITIGATION TEAM
TO: Wendy Schultz, Lead Associate; Alan Ngo, Responsible Partner
FROM: Omar Siddiqui, Associate
DATE: October 10, 2024
RE: Prosecution History Estoppel Analysis — U.S. Patent No. 10,891,193
MATTER: Optiwave Semiconductor Corp. v. Lumicore Technologies, Inc., Case No. 2:24-cv-00319-JRG (E.D. Tex.)
SUBJECT: Analysis of Prosecution History Estoppel Risks for Doctrine of Equivalents Contentions on Claims 3 and 7 of U.S. Patent No. 10,891,193 ("the '193 Patent")
ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL — PREPARED IN ANTICIPATION OF LITIGATION. This memorandum constitutes attorney work product prepared in anticipation of litigation and is protected from disclosure under the work product doctrine. This memorandum also contains information protected by the attorney-client privilege. It should not be disclosed to any person outside of the litigation team without the prior approval of the responsible partner.
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I. PURPOSE AND EXECUTIVE SUMMARY
A. Purpose of Memorandum
This memorandum analyzes the prosecution history of U.S. Patent No. 10,891,193 (the "'193 Patent"), titled "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate," to determine the scope and impact of amendments made during prosecution on Optiwave Semiconductor Corp.'s ("OWS") ability to assert infringement under the doctrine of equivalents ("DOE") for Claims 3 and 7 of the '193 Patent. The analysis is undertaken in the context of OWS's pending patent infringement action against Lumicore Technologies, Inc. ("Lumicore"), Case No. 2:24-cv-00319-JRG, before the Honorable Judge J. Rodney Gilstrap in the Eastern District of Texas.
Specifically, this memorandum addresses three interrelated questions. First, it assesses whether the Festo presumption of surrender applies to OWS's doctrine of equivalents contentions for Claims 3 and 7 in light of a narrowing amendment made to independent Claim 1 during prosecution of the '193 Patent. Second, it evaluates whether any recognized exceptions under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), are available to rebut that presumption, with particular attention to the "tangential relation" and "unforeseeability" exceptions. Third, it provides strategic recommendations regarding the viability of DOE contentions served in OWS's P.R. 3-1 Infringement Contentions (served September 16, 2024) and the risks that must be addressed in Dr. Caroline Ashford's forthcoming expert report on infringement, which is due June 15, 2025 under the Court's current scheduling order.
This memorandum is a companion to the separate prosecution history estoppel analysis for the '015 Patent (U.S. Patent No. 11,402,015), which addresses DOE contentions for Claim 12 of that patent and is the subject of a separate memorandum dated October 12, 2024. The two analyses should be read together and positions coordinated to ensure consistency before the Court.
B. Summary of Conclusions
During prosecution of the '193 Patent, the applicant (OWS, through its prosecution counsel Cascade IP Advisors, LLC, lead prosecution attorney Dr. Martin Chu) narrowed the term "coherent detection module" in independent Claim 1 — from which both Claims 3 and 7 depend — in direct response to a § 102(a)(1) anticipation rejection over Takahashi et al., "Dense WDM Silicon Photonic MUX," IEEE Photonics Technology Letters, March 2014 ("Takahashi"). The amendment added specific structural limitations to the "coherent detection module" in order to distinguish the claimed invention over Takahashi's disclosed coherent receiver configuration. As detailed below, the amendment added three distinct structural requirements: (1) a polarization-splitting optical hybrid mixer; (2) at least four output ports, each coupled to a respective transimpedance-amplified balanced photodetector pair; and (3) monolithic integration of the entire coherent detection module on the silicon substrate.
Under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), a narrowing amendment made for a reason related to patentability creates a presumption that the patentee has surrendered all equivalents between the original claim scope and the amended claim scope. Because the amendment here was unambiguously made to overcome a § 102 rejection — the paradigmatic patentability-related amendment — the Festo presumption applies. The presumption, if unrebutted, would bar OWS from asserting DOE for Claims 3 and 7 with respect to the "coherent detection module" limitation as it relates to Lumicore's accused products.
However, our analysis identifies arguments under at least one, and potentially two, of the three recognized Festo rebuttal exceptions:
Tangential Relation Exception (Moderate Strength). The amendment bore only a tangential relation to the specific equivalent at issue in Lumicore's accused products. The amendment was designed to distinguish Takahashi's fundamentally different coherent receiver — a single-polarization, non-monolithic, non-TIA-amplified design — and not to foreclose alternative polarization-diversity architectures that employ separate polarization-splitting components upstream of integrated hybrid mixers. The prosecution remarks emphasized all three added structural features equally, and the specific structural path taken by Lumicore (an external polarization beam splitter preceding two single-polarization 90° optical hybrid mixers) was not the type of design the amendment was intended to exclude.
Unforeseeability Exception (Weak to Moderate Strength). The specific equivalent now at issue in Lumicore's LumiLink 400G-ZR+, LumiLink 800G-DR8, and LumiEdge 1600G-LR products — namely, a monolithically integrated coherent detection architecture using two separate single-polarization 90° optical hybrid mixers preceded by a monolithically integrated polarization beam splitter, all fabricated on a single silicon die — may be argued to have been unforeseeable at the time of the amendment. While the general concept of polarization diversity using separate receivers was known in bulk-optics telecommunications, the specific monolithic silicon-photonic implementation that Lumicore developed in 2021–2022 was not a standard design approach in the literature at the time the amendment was filed (estimated 2018–2019). This exception faces a higher bar under Federal Circuit precedent, but it should be preserved as a supporting argument.
Overall Risk Level: MODERATE. The DOE contentions for Claims 3 and 7 are viable but carry meaningful vulnerability at summary judgment and at trial. There is a near certainty that Lumicore's counsel at Hawthorne Vega & Cruz LLP (lead partner Catherine "Kate" Rourke, supported by Darren Cho) will move for summary judgment on prosecution history estoppel grounds, and we estimate the probability of the Court granting such a motion at 40–50%. If summary judgment is denied, the DOE contentions have a reasonable likelihood of success at trial, particularly before a jury. Even if the DOE contentions are ultimately barred, OWS retains literal infringement contentions for Claims 1, 10, 15, and 18 of the '193 Patent, though the loss of the DOE fallback increases the stakes of the Markman ruling on several disputed claim-construction terms.
II. BACKGROUND
A. The '193 Patent Overview
The '193 Patent, titled "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate," is one of two patents-in-suit arising from OWS's silicon-photonics transceiver technology platform. The key identifying information for the patent is as follows:
• Patent Number: U.S. Patent No. 10,891,193
• Title: "High-Bandwidth Coherent Optical Transceiver Integrated on Silicon Substrate"
• Filing Date: April 7, 2017 (non-provisional application)
• Issue Date: January 12, 2021
• Original Assignee: Optiwave Semiconductor Corp. ("OWS")
• Current Assignee: Optiwave Semiconductor Corp.
• Named Inventors: Dr. Jian-Wei Huang (OWS Chief Technology Officer) and Dr. Nikolai Petrov (OWS Vice President of Engineering, Photonics Division)
• Priority Claim: Claims benefit of U.S. Provisional Application No. 62/499,117, filed April 7, 2017
The '193 Patent is a member of a patent family that also includes U.S. Patent No. 11,402,015 (the "'015 Patent"), which is the other patent-in-suit in this action. The '193 Patent and the '015 Patent share the common provisional application, U.S. Provisional Application No. 62/499,117, filed April 7, 2017. The two non-provisional applications were filed separately and do not stand in a continuation relationship — they are co-pending applications claiming priority to the same provisional. While the two patents share overlapping portions of the specification and disclosure, they claim different aspects of the OWS transceiver technology. The '193 Patent is directed primarily to the coherent optical transceiver architecture, with particular emphasis on the coherent detection module and its integration on a silicon substrate. The '015 Patent is directed primarily to the optical coupling and grating structures used to couple light into and out of the silicon-photonic transceiver chip, with particular emphasis on a two-dimensional sub-wavelength grating coupler.
The '193 Patent specification describes a coherent optical transceiver fabricated on a silicon-on-insulator (SOI) platform using complementary metal-oxide-semiconductor (CMOS)-compatible fabrication processes. The specification discloses the integration of a transmitter and receiver on a common silicon substrate, with the receiver portion including a coherent detection module that employs a polarization-splitting optical hybrid mixer to separate and mix the incoming optical signal with a local oscillator signal for coherent detection. The specification describes multiple embodiments, including both polarization-splitting hybrid designs and, in less detail, alternative polarization-diversity approaches, though the claims as amended are directed specifically to the polarization-splitting optical hybrid mixer configuration.
B. Asserted Claims of the '193 Patent
In this litigation, OWS asserts Claims 1, 3, 7, 10, 15, and 18 of the '193 Patent against all three of Lumicore's accused products: the LumiLink 400G-ZR+, LumiLink 800G-DR8, and LumiEdge 1600G-LR coherent optical transceivers. These claims were identified in OWS's P.R. 3-1 Infringement Contentions served on September 16, 2024.
Claim 1 is the primary independent claim and recites the coherent optical transceiver architecture as a whole, including the "coherent detection module" limitation that is central to this analysis. Claims 3 and 7 are dependent claims, each depending directly from independent Claim 1. Claim 10 is a second independent claim directed to a method of coherent optical signal detection. Claim 15 depends from Claim 10. Claim 18 is a third independent claim directed to a coherent optical transceiver system.
The doctrine of equivalents is asserted specifically and exclusively for Claims 3 and 7 of the '193 Patent, in addition to the literal infringement contentions for all six asserted claims. (DOE is also asserted for Claim 12 of the '015 Patent, which is the subject of a separate memorandum.) For Claims 1, 10, 15, and 18, OWS's infringement contentions rest solely on theories of literal infringement.
The specific limitation at issue for the DOE contentions on Claims 3 and 7 is the "coherent detection module" limitation recited in Claim 1 and inherited by Claims 3 and 7 as dependent claims. In addition, Claim 7 recites a specific limitation regarding signal processing within or coupled to the coherent detection module, which, while literally met by the accused products, interacts with the Claim 1 amendment in a manner that requires analysis, as discussed in Section VII.B below.
C. The Accused Products
OWS accuses three Lumicore coherent optical transceiver products of infringing the '193 Patent:
1. LumiLink 400G-ZR+ Coherent Optical Transceiver. This product was launched by Lumicore in Q3 2022 and generated fiscal year 2023 revenue of approximately $94.8 million, based on Lumicore's public filings and discovery productions. The LumiLink 400G-ZR+ is a pluggable coherent transceiver designed for data center interconnect (DCI) applications at distances up to 120 km, supporting 400 Gbps data rates using dual-polarization quadrature phase-shift keying (DP-QPSK) modulation. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.
2. LumiLink 800G-DR8 Coherent Optical Transceiver. This product was launched by Lumicore in Q1 2023 and generated fiscal year 2023 revenue of approximately $128.4 million. The LumiLink 800G-DR8 is a pluggable transceiver supporting 800 Gbps aggregate data rates over eight wavelength channels, using coherent detection on a silicon-photonic platform for data center and campus network applications. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.
3. LumiEdge 1600G-LR Coherent Optical Transceiver. This product was launched by Lumicore in Q4 2023 and generated fiscal year 2023 revenue of approximately $41.7 million. The LumiEdge 1600G-LR is Lumicore's highest-bandwidth coherent transceiver product, supporting 1.6 Tbps aggregate data rates over long-reach (LR) distances for telecom metro and backbone networks. The product was launched after OWS's pre-suit notice letters (January 15, 2023 and May 15, 2023) and the April 20, 2023 in-person meeting between the parties, which is relevant to OWS's willful infringement allegations. The product is accused of infringing the '193 Patent, the '015 Patent, and other OWS patents not at issue in this action.
The total accused product revenue for fiscal year 2023 across all three products is approximately $264.9 million. Revenue figures for fiscal year 2024 are expected to be substantially higher based on Lumicore's public guidance and analyst estimates, particularly for the LumiLink 800G-DR8 and LumiEdge 1600G-LR, which are experiencing rapid adoption in the data center and telecom markets.
All three accused products employ a coherent optical detection architecture that differs in one specific structural detail from the literal claim language as amended during prosecution. As described more fully in Section V.C below, the accused products use a polarization-diversity scheme employing two separate single-polarization 90° optical hybrid mixers preceded by an upstream polarization beam splitter, rather than a single "polarization-splitting optical hybrid mixer" as recited in the amended Claim 1. The accused products do, however, employ transimpedance-amplified balanced photodetector pairs at the output ports and achieve monolithic integration on a silicon substrate. OWS contends that the accused products' coherent detection architecture performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed "coherent detection module" with a "polarization-splitting optical hybrid mixer."
D. OWS's Infringement Contentions on DOE
Per OWS's P.R. 3-1 Infringement Contentions served on September 16, 2024, the doctrine of equivalents is asserted for Claims 3 and 7 of the '193 Patent. (DOE is also asserted for Claim 12 of the '015 Patent, which is addressed in a separate memorandum dated October 12, 2024.) The infringement contentions identify the specific limitations for which DOE is asserted and set forth the function-way-result analysis for each limitation.
The function-way-result test is applied to the "coherent detection module" limitation as follows. Even if Lumicore's accused designs do not literally satisfy the "coherent detection module" limitation as amended — specifically, even if the use of two separate single-polarization 90° optical hybrid mixers preceded by a polarization beam splitter does not literally satisfy the requirement for "a polarization-splitting optical hybrid mixer" — OWS contends that these elements perform substantially the same function, in substantially the same way, to achieve substantially the same result:
• Function: Coherent optical detection and demodulation of a polarization-multiplexed optical signal — i.e., separating the two orthogonal polarization states of the incoming optical signal and coherently detecting each by mixing with a local oscillator signal to produce electrical baseband signals.
• Way: Using integrated photonic components on a silicon substrate to split the incoming signal by polarization and to mix each polarization component with a local oscillator signal via optical hybrid mixing, with balanced photodetection at each output port. In both the claimed design and Lumicore's design, the incoming polarization-multiplexed signal is separated into its two orthogonal components, each of which is mixed with a local oscillator in a 90° optical hybrid to produce in-phase and quadrature beat signals, which are then detected by balanced photodetector pairs with integrated transimpedance amplification.
• Result: Recovery of the full amplitude, phase, and polarization information from a coherent optical signal, enabling digital reconstruction of the transmitted data signals with high spectral efficiency and long-reach performance.
The infringement contentions include claim charts mapping each limitation of Claims 3 and 7 to the accused products, with the DOE analysis for the "coherent detection module" limitation set forth in detail. The infringement contentions were prepared based on publicly available information, Benchmark Semiconductor Analysis, LLC teardown reports, and, where applicable, Lumicore design documents produced in discovery and designated Highly Confidential — Attorneys' Eyes Only under the Protective Order (D.E. 25).
III. PROSECUTION HISTORY OF THE '193 PATENT
A. Initial Filing and Original Claim Scope
The '193 Patent was filed as a non-provisional application on April 7, 2017, claiming the benefit of U.S. Provisional Application No. 62/499,117, filed the same date. The application was prosecuted by Cascade IP Advisors, LLC, with Dr. Martin Chu serving as lead prosecution attorney (1550 Crystal Drive, Suite 600, Arlington, VA 22202). Dr. Chu is a registered patent attorney with a Ph.D. in electrical engineering from MIT and over twenty years of experience prosecuting semiconductor and photonics patents.
As originally filed, independent Claim 1 recited, inter alia:
"a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."
The original claim language used broad, functional language to define the "coherent detection module." The claim did not specify the internal structural components of the module, their arrangement, or the method of integration. As written, the original Claim 1 would have encompassed any coherent detection architecture — whether employing a single-polarization hybrid, a polarization-splitting hybrid, multiple separate hybrids, monolithically integrated or hybrid-integrated components, with or without transimpedance amplification — so long as the module was "configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."
The original dependent Claims 3 and 7 added further limitations narrowing the scope of the coherent detection module, but without altering its fundamental architectural definition:
• Original Claim 3 specified a particular arrangement of balanced photodetectors within the module: "The coherent optical transceiver of claim 1, wherein the coherent detection module comprises a balanced photodetector arrangement comprising at least two pairs of balanced photodetectors, each pair configured to detect in-phase and quadrature components of a respective polarization state."
• Original Claim 7 specified a digital signal processing function performed by an integrated DSP within or coupled to the coherent detection module: "The coherent optical transceiver of claim 1, further comprising a digital signal processor integrated with the coherent detection module, the digital signal processor configured to perform adaptive equalization and carrier recovery on the electrical output signals."
Neither Claim 3 nor Claim 7 imposed structural requirements on the optical hybrid mixer portion of the coherent detection module. The combination of the broad "coherent detection module" definition in Claim 1 with the specific additional limitations in Claims 3 and 7 provided both breadth and technical specificity in the original claim set.
B. First Office Action — § 102 Rejection over Takahashi et al.
The examining division (Art Unit 2883) assigned the application to Examiner Timothy R. Kwon. After a search of the prior art, Examiner Kwon issued a first office action (non-final) rejecting Claims 1, 3, 7, and several other claims under 35 U.S.C. § 102(a)(1) as anticipated by Takahashi et al., "Dense WDM Silicon Photonic MUX," published in IEEE Photonics Technology Letters, Vol. 26, No. 6, March 15, 2014, pp. 595–598 ("Takahashi").
Takahashi disclosed a silicon photonic multiplexer system designed for dense wavelength-division multiplexing (DWDM) applications. The system included, among other components, a coherent receiver subsystem fabricated on a silicon-on-insulator (SOI) platform. Takahashi's coherent receiver subsystem employed a single-polarization 90° optical hybrid mixer integrated on the SOI platform and balanced photodetectors for coherent detection of an optical signal. Critically, Takahashi's design had three features (or, more precisely, three absences of features) that distinguish it from the '193 Patent's claims as eventually amended:
1. Single-polarization design: Takahashi's coherent receiver used a single-polarization 90° optical hybrid mixer. It did not include polarization-splitting functionality — the receiver processed only a single polarization state of the incoming optical signal. This is in contrast to the dual-polarization, polarization-diverse architecture disclosed and claimed in the '193 Patent.
2. No integrated transimpedance amplification: Takahashi's balanced photodetectors were not coupled with integrated transimpedance amplifiers (TIAs) at each output port. Takahashi's design relied on external amplification electronics, which is a less integrated and generally lower-performance approach than monolithically integrated TIAs.
3. Hybrid integration, not monolithic: Takahashi's coherent receiver used hybrid integration — the silicon photonic components (waveguides, optical hybrid mixer) were fabricated on the SOI platform, but the photodetectors were separate III-V semiconductor (indium phosphide) chips bonded to the silicon platform using flip-chip bonding techniques. This is a distinct integration approach from the monolithic integration recited in the '193 Patent specification, where all components — including the photodetectors — are fabricated directly on the silicon substrate using CMOS-compatible processes.
The examiner found that Takahashi's coherent receiver subsystem met every element of the original broad "coherent detection module" limitation in Claim 1. Specifically, the examiner concluded that Takahashi's coherent receiver was "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics," within the plain meaning of the original claim language. The examiner also found that Takahashi's disclosure of balanced photodetectors addressed the Claim 3 limitation regarding balanced photodetector pairs, and that Takahashi's reference to digital signal processing performed post-detection (described in Takahashi's Section III-C) addressed the Claim 7 limitation regarding an integrated DSP configured to perform adaptive equalization and carrier recovery.
The rejection was a straightforward § 102(a)(1) anticipation rejection, asserting that Takahashi disclosed every element of the claims as originally filed. The examiner's position was unambiguous, and the rejection was well-founded given the breadth of the original claim language.
C. Applicant's Response and Narrowing Amendment
In response to the § 102 rejection, Dr. Martin Chu filed an amendment and response on behalf of OWS. Based on the prosecution timeline — the application was filed April 7, 2017, and the patent issued January 12, 2021 — the amendment was likely filed during the 2018–2019 timeframe, though the precise date requires confirmation from the prosecution history file wrapper, which is included in Appendix A.
The amendment narrowed the "coherent detection module" limitation in independent Claim 1. As amended, the relevant portion of Claim 1 reads:
"a coherent detection module comprising a polarization-splitting optical hybrid mixer with at least four output ports, each output port coupled to a respective transimpedance-amplified balanced photodetector pair, the coherent detection module monolithically integrated on the silicon substrate."
The amendment added three specific structural requirements not present in the original claim language:
1. Polarization-splitting optical hybrid mixer: The amended claim specifies that the coherent detection module must include a "polarization-splitting optical hybrid mixer" — a single integrated component that both separates the incoming optical signal into its two orthogonal polarization components and performs 90° optical hybrid mixing of each polarization component with a local oscillator signal. This replaced the original generic reference to a "coherent detection module" without any specification of internal mixer architecture.
2. At least four output ports, each coupled to a transimpedance-amplified balanced photodetector pair: The amended claim specifies both the minimum number of output ports (four — corresponding to the in-phase and quadrature outputs for each of two polarization states) and the requirement that each output port be coupled to a balanced photodetector pair with integrated transimpedance amplification. This replaced the original generic reference to the module generating "electrical output signals" without specifying the detection and amplification architecture.
3. Monolithic integration on the silicon substrate: The amended claim specifies that the entire coherent detection module — including the polarization-splitting optical hybrid mixer, the output ports, and the transimpedance-amplified balanced photodetector pairs — must be "monolithically integrated on the silicon substrate." This replaced the original claim's silence on the integration methodology, which would have encompassed hybrid integration approaches such as Takahashi's.
In the remarks accompanying the amendment, Dr. Chu argued that the amended claims distinguished over Takahashi's coherent receiver configuration in three respects. The remarks stated, in relevant part:
"Applicant respectfully submits that the amended claims distinguish over Takahashi et al. in at least three material respects. First, Takahashi discloses a single-polarization 90° optical hybrid mixer, not a polarization-splitting optical hybrid mixer as recited in amended Claim 1. Takahashi's receiver processes only one polarization state and does not include the polarization-splitting functionality that is a key feature of Applicant's invention. Second, Takahashi does not disclose transimpedance-amplified balanced photodetector pairs coupled to each output port of the mixer. Takahashi's photodetectors operate without integrated transimpedance amplification, relying instead on external amplification electronics. Third, Takahashi's receiver employs hybrid integration, with separate III-V semiconductor photodetector chips bonded to the silicon platform, rather than monolithic integration of the entire coherent detection module on the silicon substrate as required by amended Claim 1."
The prosecution remarks presented all three distinguishing features as co-equal bases for patentability over Takahashi. Notably, the remarks did not single out any one of the three features as the primary or dispositive ground for distinguishing the prior art. Each feature was presented as an independent and sufficient basis for overcoming the rejection, while the combination of all three was characterized as representing a significant advance over Takahashi's architecture.
The examiner was persuaded by the amendment and the accompanying remarks. No second office action was issued on the § 102 rejection grounds. The amended claims were allowed.
D. Subsequent Prosecution — No Further Relevant Amendments
After the examiner accepted the amended claims and withdrew the § 102 rejection over Takahashi, the prosecution of the '193 Patent proceeded without further amendments to the "coherent detection module" limitation or to any other limitation relevant to this estoppel analysis. Claims 3 and 7, as dependent claims, inherited the narrowed "coherent detection module" limitation from Claim 1 as a matter of claim dependency, but neither Claim 3 nor Claim 7 was independently amended at any point during prosecution. The additional limitations recited in Claims 3 and 7 (balanced photodetector arrangement and integrated DSP, respectively) remained in their original form throughout prosecution.
An examiner interview was conducted during prosecution, as noted in the Examiner Interview Summary included in the prosecution history. The interview addressed the "integrated on a silicon substrate" limitation, which is a separate claim-construction issue currently in dispute between the parties (disputed term number 4 of 14 on the parties' joint claim-construction chart, D.E. 31). The interview did not revisit the "coherent detection module" amendment or the Takahashi prior art reference, and no representations were made during the interview that bear on the prosecution history estoppel analysis for Claims 3 and 7. Nevertheless, the interview summary should be reviewed by Dr. Ashford and her team in connection with the "integrated on a silicon substrate" claim-construction analysis, as statements made during the interview may be relevant to that separate issue.
The patent issued on January 12, 2021, with 22 claims, including Claims 1, 3, and 7 in their amended/original form as described above.
E. Relationship to the '015 Patent Prosecution
As noted above, the '193 Patent and the '015 Patent (U.S. Patent No. 11,402,015) share U.S. Provisional Application No. 62/499,117 but are separate non-provisional filings that do not stand in a continuation relationship. Each patent was prosecuted independently, and each involved a separate narrowing amendment made to overcome different prior art rejections.
The '015 Patent prosecution involved a narrowing amendment to the "two-dimensional sub-wavelength grating" limitation of Claim 12, made to overcome a § 103 obviousness rejection combining Bergmann (U.S. Patent No. 8,412,007) with Simonsen (PCT/EP2015/071234). The '015 Patent amendment and the '193 Patent amendment address different claim limitations, different prior art references, and different patentability grounds (§ 103 for the '015 Patent versus § 102 for the '193 Patent). The '015 Patent estoppel analysis is the subject of a separate memorandum dated October 12, 2024, prepared by Jonathan Varma and reviewed by Wendy Schultz.
Although the two amendments are doctrinally and factually independent, consistency of legal position across the two patents is important. Both patents are asserted in the same action, before the same judge and (if the case reaches trial) the same jury. Lumicore will likely argue both estoppel issues together, and any inconsistency in OWS's positions could undermine credibility. The recommendations in this memorandum have been coordinated with the positions taken in the '015 Patent memorandum to ensure consistency, though the specific factual arguments differ because the underlying amendments address different technology and different prior art.
IV. LEGAL FRAMEWORK: PROSECUTION HISTORY ESTOPPEL AND FESTO PRESUMPTION
A. The Doctrine of Equivalents — General Principles
Under the doctrine of equivalents, a product that does not literally infringe a patent claim may nonetheless be found to infringe if each limitation of the claim is met by an equivalent element in the accused product. The doctrine of equivalents is a judicially created doctrine designed to prevent an infringer from avoiding liability by making insubstantial changes to a patented invention that, while technically avoiding the literal claim language, appropriate the substance of the claimed invention. See Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 607 (1950) ("to permit imitation of a patented invention which does not copy every literal detail would be to convert the protection of the patent grant into a hollow and useless thing").
The primary test for equivalence is the function-way-result test: an element in the accused product is equivalent to a claimed element if it performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed element. See Warner-Jenkinson Co. v. Harborline Enterprises Davis Chemical Co., 520 U.S. 17, 40 (1997); Graver Tank, 339 U.S. at 608. The analysis is conducted from the perspective of a person of ordinary skill in the art at the time of the alleged infringement. See Warner-Jenkinson, 520 U.S. at 37.
The doctrine of equivalents is subject to an important structural limitation: the all-limitations rule. Under this rule, the doctrine of equivalents must be applied on a limitation-by-limitation basis; no claim limitation may be read out of the claim entirely. See Warner-Jenkinson, 520 U.S. at 29 ("each element contained in a patent claim is deemed material to defining the scope of the patented invention, and thus the doctrine of equivalents must be applied to individual elements of the claim, not to the invention as a whole"). This rule prevents a patentee from using the doctrine of equivalents to effectively eliminate a claim limitation, and it requires that each limitation be evaluated independently for whether it is met, either literally or by an equivalent, in the accused product.
B. Prosecution History Estoppel — Festo Framework
Prosecution history estoppel is one of the principal limitations on the doctrine of equivalents. The doctrine provides that a patentee who narrows a claim during prosecution — whether by amendment or by argument — may be estopped from later asserting that the surrendered claim scope is captured by the doctrine of equivalents. The rationale for the doctrine is that the public is entitled to rely on the prosecution history as defining the boundaries of the patent grant, and a patentee should not be permitted to recapture through the doctrine of equivalents what was surrendered during prosecution to obtain the patent.
The Supreme Court established the modern framework for prosecution history estoppel in Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002). Under Festo, when an applicant narrows a claim during prosecution for a reason related to patentability, a presumption arises that the patentee has surrendered all territory between the original claim scope and the amended claim scope. This is referred to as the "presumption of total surrender" or the "Festo presumption."
The Festo presumption is a rebuttable presumption. The patentee may overcome the presumption by demonstrating that one of three circumstances exists:
1. Unforeseeability: The alleged equivalent was unforeseeable at the time of the amendment. If the equivalent technology or design was not known or foreseeable at the time the narrowing amendment was made, the patentee could not reasonably have been expected to draft the amendment to encompass that equivalent, and the presumption of surrender is rebutted. See Festo, 535 U.S. at 740–41.
2. Tangential Relation: The rationale underlying the narrowing amendment bore only a tangential relation to the equivalent in question. If the reason for the amendment was unrelated or only tangentially related to the specific equivalent at issue, the narrowing amendment should not be presumed to have surrendered that particular equivalent. See id. at 740–41.
3. Other Reason: There is some other reason suggesting that the patentee could not reasonably have been expected to have drafted a claim that literally encompassed the alleged equivalent. This is a residual category intended to address circumstances not covered by the first two exceptions. See id. at 740–41.
The burden of proof to rebut the Festo presumption rests on the patentee — in this case, OWS. See Festo, 535 U.S. at 740. The patentee must provide objective evidence sufficient to overcome the presumption; bare attorney argument is insufficient. The standard for rebutting the presumption is demanding, though not insurmountable, and the Federal Circuit has found the exceptions satisfied in a number of cases, as discussed below.
C. Application of Festo to Narrowing Amendments Made to Overcome Prior Art
Amendments made to overcome anticipation rejections under § 102 — as in the prosecution history of the '193 Patent — are the paradigmatic example of patentability-related narrowing amendments that trigger the Festo presumption. The Federal Circuit has consistently and unambiguously held that adding structural limitations to distinguish prior art constitutes a narrowing amendment for purposes of Festo. See, e.g., Honeywell Int'l, Inc. v. Hamilton Sundstrand Corp., 370 F.3d 1131, 1139–41 (Fed. Cir. 2004) (en banc) (holding that amendment adding specific structural limitations to overcome § 102 rejection triggered Festo presumption); Festo Corp. v. Fenmore & Co., 344 F.3d 1359, 1366–68 (Fed. Cir. 2003) (en banc) (on remand from the Supreme Court, applying the Festo framework and identifying the scope of surrender).
The Federal Circuit has also clarified that the Festo presumption applies regardless of whether the amendment was strictly "necessary" to overcome the prior art rejection — even if the applicant might have overcome the rejection by other means, the fact that the applicant chose to narrow the claims by amendment triggers the presumption. See Festo, 344 F.3d at 1367 ("It is the narrowing amendment made to overcome the prior art that gives rise to prosecution history estoppel, regardless of whether the applicant could have obtained the patent in some other way."). This is relevant here because OWS might argue that the amendment was broader than necessary to overcome Takahashi (e.g., the monolithic integration requirement alone might have sufficed to distinguish Takahashi's hybrid-integrated design). However, such an argument does not avoid the Festo presumption — it is the amendment as a whole, including all three added structural features, that defines the surrendered territory.
The Federal Circuit has further held that voluntary amendments — amendments not required by the examiner but offered by the applicant to advance prosecution — trigger the Festo presumption to the same extent as amendments made in direct response to a rejection, so long as the amendment was made for a reason related to patentability. See Warner-Jenkinson, 520 U.S. at 33 (placing the burden on the patentee to establish that an amendment was not made for a reason related to patentability). Here, the amendment was unambiguously made in response to a § 102 rejection and for the purpose of distinguishing the prior art, so there is no question that the amendment was made "for a reason related to patentability."
V. APPLICATION OF FESTO TO THE '193 PATENT AMENDMENT
A. The Amendment Was a Narrowing Amendment for Reasons of Patentability
Applying the Festo framework to the prosecution history of the '193 Patent, the threshold question is whether the amendment to the "coherent detection module" limitation constitutes a narrowing amendment made for a reason related to patentability. The answer is unambiguous: yes, on both counts.
First, there is no dispute that the amendment was made in response to a § 102(a)(1) anticipation rejection — a patentability rejection. The examiner rejected the original claims as anticipated by Takahashi, and the applicant responded by amending the claims to distinguish Takahashi. The prosecution remarks explicitly stated that the amendment was made for the purpose of overcoming the § 102 rejection and argued that the amended claims were patentable over Takahashi because of the three structural features added by the amendment.
Second, there is no dispute that the amendment narrowed the claim scope. The original claim broadly recited "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics" — language that would have encompassed any coherent detection architecture regardless of internal structure or integration method. The amended claim is limited to a specific structural configuration: a coherent detection module comprising a polarization-splitting optical hybrid mixer with at least four output ports, each coupled to a transimpedance-amplified balanced photodetector pair, all monolithically integrated on the silicon substrate. The amendment unambiguously narrowed the claim scope by adding three structural requirements that were not present in the original claim.
Conclusion: The Festo presumption applies. OWS has surrendered all equivalents between the original broad "coherent detection module" language and the narrowed, structurally specific amended language, unless OWS can rebut the presumption by establishing one of the three Festo exceptions.
B. Identification of the Surrendered Territory
To assess the impact of the Festo presumption on OWS's DOE contentions, it is necessary to define the territory surrendered by the amendment. The surrendered territory is the difference between the scope of the original claim and the scope of the amended claim — i.e., all subject matter that was within the scope of the original claim but outside the scope of the amended claim.
The original claim covered any "coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics." This expansive language encompassed, without limitation: modules using single-polarization mixers; modules using polarization-splitting mixers; modules using multiple separate single-polarization mixers with external polarization splitting; modules with or without transimpedance amplification at the output ports; modules using monolithic integration; modules using hybrid integration (e.g., III-V photodetector chips bonded to a silicon photonic platform); modules using discrete optical components; and any other coherent detection architecture satisfying the broad functional definition.
The amended claim is limited to a specific structural configuration: a coherent detection module comprising (1) a polarization-splitting optical hybrid mixer (2) with at least four output ports, each coupled to a respective transimpedance-amplified balanced photodetector pair, (3) the coherent detection module monolithically integrated on the silicon substrate.
The surrendered territory therefore encompasses all coherent detection module implementations that fall within the original broad claim scope but lack one or more of the three structural features added by the amendment. This includes, among other configurations:
• Modules using single-polarization mixers (i.e., mixers that process only one polarization state, without polarization-splitting functionality), such as Takahashi's single-polarization 90° hybrid;
• Modules using multiple separate single-polarization mixers with an external polarization beam splitter (i.e., designs that achieve polarization diversity by splitting polarizations upstream of the mixer, rather than using a single integrated polarization-splitting hybrid mixer);
• Modules without transimpedance amplification at each output port;
• Modules using hybrid integration (e.g., III-V semiconductor photodetector chips bonded to a silicon photonic platform) rather than monolithic integration of the entire module on the silicon substrate;
• Any combination of the above.
The question for this analysis is whether the specific equivalent at issue — Lumicore's accused two-mixer-plus-polarization-beam-splitter architecture — falls within this surrendered territory. That question is addressed in Section V.D below.
C. Lumicore's Accused Equivalent — What Is the Specific Equivalent at Issue?
To apply the Festo analysis, we must precisely identify the structural features of Lumicore's accused products that give rise to the DOE contention and the manner in which they differ from the literal claim language.
Based on the Benchmark Semiconductor Analysis, LLC teardown reports — including the LumiLink 400G-ZR+ teardown report dated December 12, 2022; the LumiLink 800G-DR8 teardown report dated June 2023; and the LumiEdge 1600G-LR teardown report dated February 2024 — as well as Lumicore design documents produced in discovery and designated Highly Confidential — Attorneys' Eyes Only under the Protective Order (D.E. 25), the coherent detection architecture of Lumicore's accused products has the following relevant structural features:
1. Polarization-diversity scheme: Lumicore's accused products achieve polarization-diverse coherent detection. However, rather than using a single integrated "polarization-splitting optical hybrid mixer" as recited in the amended Claim 1, Lumicore's design employs a modified architecture consisting of a polarization beam splitter (PBS) positioned upstream of two separate single-polarization 90° optical hybrid mixers. The polarization beam splitter separates the incoming optical signal into its two orthogonal polarization components (TE and TM), and each component is routed to a separate 90° optical hybrid mixer, where it is mixed with a local oscillator signal for coherent detection. In essence, the polarization-splitting function and the optical hybrid mixing function are performed by separate, discrete components (the PBS and the two 90° hybrids, respectively), rather than by a single integrated "polarization-splitting optical hybrid mixer" that performs both functions within a single device.
2. Transimpedance-amplified balanced photodetector pairs: Lumicore's design does use transimpedance-amplified balanced photodetector pairs at the output ports of the optical hybrid mixers. Each of the two 90° hybrids has at least two output ports, and each output port is coupled to a balanced photodetector pair with integrated transimpedance amplification. This feature of the accused products is consistent with the amended claim language.
3. Monolithic integration on a silicon substrate: Lumicore's design achieves monolithic integration of the entire coherent detection architecture — including the polarization beam splitter, the two 90° optical hybrid mixers, the balanced photodetectors, and the transimpedance amplifiers — on a single silicon substrate. This feature of the accused products is also consistent with the amended claim language (subject to the separate claim-construction dispute over the meaning of "integrated on a silicon substrate").
The specific point of divergence from the literal claim language is the structure of the optical hybrid mixer. The amended Claim 1 requires "a polarization-splitting optical hybrid mixer" — a single component that performs both polarization splitting and optical hybrid mixing. Lumicore's design uses two separate single-polarization 90° optical hybrid mixers preceded by a separate polarization beam splitter. The polarization-splitting function is performed by the PBS, not by the optical hybrid mixers themselves. The optical hybrid mixing function is performed by the two separate 90° hybrids, each of which processes only a single polarization state.
OWS's DOE contention is that Lumicore's two-mixer-plus-PBS architecture is equivalent to the claimed "polarization-splitting optical hybrid mixer" under the function-way-result test:
• Function: Both perform the same function — splitting the incoming signal by polarization and mixing each polarization component with a local oscillator for coherent detection.
• Way: Both achieve this function in substantially the same way — using optical hybrid mixing of each polarization component with a local oscillator signal. The only structural difference is whether the polarization splitting occurs within the hybrid mixer itself or immediately upstream of two separate hybrid mixers. In both cases, the same optical mixing operations are performed, the same number of output signals are produced, and the same balanced photodetection with transimpedance amplification is performed.
• Result: Both achieve substantially the same result — recovery of the full polarization-diverse coherent signal information (in-phase and quadrature components for each of two polarization states) for subsequent digital signal processing.
D. Does the Accused Equivalent Fall Within the Surrendered Territory?
The central question for the Festo analysis is whether Lumicore's two-mixer-plus-PBS design falls within the territory surrendered by the amendment. If it does, the Festo presumption bars DOE unless OWS can rebut the presumption. If it does not, prosecution history estoppel does not apply, and OWS's DOE contentions may proceed without the need to rebut the presumption.
The analysis of surrendered territory proceeds as follows:
The original claim broadly covered any "coherent detection module" configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics. This broad language would have encompassed Lumicore's two-mixer-plus-PBS design, which is unquestionably "a coherent detection module configured to receive an optical signal and generate electrical output signals representative of the optical signal's modulation characteristics."
The amended claim requires "a coherent detection module comprising a polarization-splitting optical hybrid mixer" — a single, integrated component that both splits polarizations and performs optical hybrid mixing. Lumicore's design separates these two functions into a polarization beam splitter and two separate single-polarization hybrid mixers. The accused design does not literally satisfy the requirement for "a polarization-splitting optical hybrid mixer" because the polarization-splitting function is performed by a separate PBS component, not by the optical hybrid mixers themselves.
Conclusion: Lumicore's two-mixer-plus-PBS design falls within the surrendered territory. It is a coherent detection architecture that was encompassed by the original broad claim language but does not satisfy the specific structural requirements added by the amendment — specifically, it lacks the "polarization-splitting optical hybrid mixer" required by the amended claim. The accused design achieves polarization diversity through a different structural path (external PBS + two single-polarization hybrids) rather than through the specific claimed structure (a single integrated polarization-splitting hybrid mixer).
Because the accused equivalent falls within the surrendered territory, the Festo presumption bars OWS from asserting DOE for the "coherent detection module" limitation unless OWS can rebut the presumption by establishing one of the three recognized Festo exceptions. The analysis of those exceptions follows in Section VI.
VI. REBUTTAL ARGUMENTS UNDER FESTO EXCEPTIONS
A. Exception 1: Tangential Relation
1. Argument. The first and strongest Festo rebuttal argument available to OWS is that the rationale underlying the narrowing amendment bore only a tangential relation to the equivalent in question — i.e., that the reason the applicant amended the claim (to distinguish Takahashi's single-polarization, non-monolithic, non-TIA-amplified coherent receiver) was only tangentially related to the specific structural difference between the claimed "polarization-splitting optical hybrid mixer" and Lumicore's two-mixer-plus-PBS architecture.
2. Analysis. The tangential-relation exception is grounded in the principle that prosecution history estoppel should not extend to equivalents that bear little or no relationship to the reason the amendment was made. The rationale is that the public-notice function of prosecution history estoppel is not served when the amendment was directed at a different problem from the one relevant to the equivalent. See Festo, 535 U.S. at 740–41; Insituform Technologies, Inc. v. CAT Contracting, Inc., 385 F.3d 1360, 1370 (Fed. Cir. 2004).
To evaluate this exception, we must compare the rationale for the amendment with the nature of the accused equivalent.
Rationale for the amendment: The amendment was made to overcome Takahashi's coherent receiver, which was a fundamentally different design from the claimed invention. Takahashi's receiver was: (a) single-polarization only (no polarization-diversity capability); (b) lacking integrated transimpedance amplification; and (c) hybrid-integrated rather than monolithically integrated. The amendment addressed all three of these deficiencies simultaneously by adding three structural requirements to the "coherent detection module" limitation. Dr. Chu's prosecution remarks presented all three distinguishing features as co-equal grounds for patentability, without singling out any one feature as the primary or dispositive basis for the amendment. Each feature was presented as an independent basis for distinguishing Takahashi.
Nature of the accused equivalent: Lumicore's design is not a single-polarization, non-monolithic, non-TIA-amplified receiver like Takahashi. To the contrary, Lumicore's design achieves polarization diversity (through an external PBS + two hybrids), uses transimpedance-amplified balanced photodetectors, and is monolithically integrated on a silicon substrate. The only structural difference between Lumicore's design and the amended claim is the manner in which polarization splitting is integrated with optical hybrid mixing — whether the polarization splitting occurs within the hybrid mixer itself (as in the claimed design) or immediately upstream of the hybrid mixers in a separate PBS component (as in Lumicore's design).
The tangential-relation argument proceeds as follows. The core reason for the amendment was to distinguish Takahashi's entire coherent receiver configuration — a single-polarization, non-monolithic, non-TIA-amplified design — not specifically to exclude all alternative polarization-diversity architectures that achieve the same end result through slightly different structural means. The specific structural path taken by Lumicore (external PBS + two single-polarization hybrids, all monolithically integrated with TIA-amplified photodetectors) is a polarization-diverse, monolithically integrated, TIA-amplified design that is categorically different from Takahashi's receiver. The amendment was intended to add the concept of "polarization splitting" to the claim to distinguish Takahashi's complete absence of polarization diversity — it was not intended to dictate the precise structural mechanism by which polarization splitting is achieved. The distinction between a single integrated polarization-splitting hybrid mixer and a separate PBS followed by two single-polarization hybrids is a granular structural detail that was tangential to the core reason for the amendment, which was to overcome a fundamentally different prior art design.
Furthermore, the amendment added three features simultaneously. The prosecution remarks emphasized the monolithic integration and transimpedance amplification features at least as prominently as the polarization-splitting hybrid mixer feature. If the amendment had added only the "polarization-splitting optical hybrid mixer" limitation — and the prosecution remarks had focused solely on distinguishing Takahashi's lack of polarization diversity — the tangential-relation argument would be weaker. But the amendment was a multi-feature amendment directed at a prior art reference that differed from the claimed invention in multiple, independent respects. The specific structural detail of how polarization splitting is integrated with hybrid mixing was only one of three independent bases for distinguishing Takahashi, and arguably the least emphasized.
3. Supporting Precedent
The tangential-relation exception was found to be satisfied in Insituform Technologies, Inc. v. CAT Contracting, Inc., 385 F.3d 1360 (Fed. Cir. 2004). In Insituform, the Federal Circuit held that the tangential-relation exception was met where the amendment addressed a different problem from the one relevant to the equivalent at issue. The court examined the prosecution history and determined that the narrowing amendment had been directed at distinguishing a prior art reference on grounds unrelated to the structural feature of the equivalent, and concluded that applying estoppel to bar the equivalent would extend the presumption of surrender beyond its logical scope.
Analogously, in our case, the amendment addressed Takahashi's lack of any polarization diversity — a single-polarization design with no polarization-splitting capability — and was not directed at foreclosing alternative structural mechanisms for achieving polarization diversity. The equivalent at issue (Lumicore's PBS + two-hybrid architecture) is a different structural approach to achieving the same polarization-diverse coherent detection that the amendment was intended to claim, not the type of design the amendment was intended to exclude. The amendment was intended to exclude designs like Takahashi's — single-polarization, non-monolithic, non-TIA-amplified receivers — and not to exclude alternative polarization-diverse architectures that achieve the same result through a slightly different structural path.
4. Risks and Counter-Arguments
The tangential-relation argument, while our strongest Festo rebuttal, faces significant counter-arguments that Lumicore will raise.
Lumicore's primary counter-argument: The amendment specifically added "polarization-splitting optical hybrid mixer," and the prosecution remarks specifically argued that Takahashi lacked a "polarization-splitting" mixer. The specific language added to the claim — "polarization-splitting optical hybrid mixer" — directly addresses the structural feature at issue in the DOE analysis. Lumicore will argue that the amendment was not tangential to the equivalent at all — it was directly related, because the amendment specifically defined how polarization splitting must be achieved (within the hybrid mixer itself), and Lumicore's design achieves polarization splitting differently (through an external PBS).
This counter-argument has force. The tangential-relation exception is most easily established when the amendment and the equivalent address entirely different claim features or entirely different aspects of the technology. Here, both the amendment and the equivalent relate to the same claim feature — the polarization-splitting functionality of the optical hybrid mixer — which makes the tangential-relation argument more difficult. The argument requires the Court to accept a nuanced distinct

CALDERWOOD & HARKNESS LLP

I. PURPOSE AND EXECUTIVE SUMMARY

II. BACKGROUND

III. PROSECUTION HISTORY OF THE '193 PATENT

IV. LEGAL FRAMEWORK: PROSECUTION HISTORY ESTOPPEL AND FESTO PRESUMPTION

V. APPLICATION OF FESTO TO THE '193 PATENT AMENDMENT

VI. REBUTTAL ARGUMENTS UNDER FESTO EXCEPTIONS

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