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PROSECUTION HISTORY ESTOPPEL ANALYSIS

U.S. Patent No. 11,402,015 ('015 Patent)

ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL

CONFIDENTIALITY LEGEND: ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL. This memorandum is protected by the attorney-client privilege and the work-product doctrine. It is prepared in anticipation of litigation and for the purpose of providing legal advice to the client. Do not distribute outside the case team without express authorization from Alan Ngo.

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I. EXECUTIVE SUMMARY

This memorandum analyzes whether prosecution history estoppel ("PHE") under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), bars Optiwave Semiconductor Corp. ("OWS" or "Client") from asserting infringement of Claim 12 of U.S. Patent No. 11,402,015 (the "'015 Patent") under the doctrine of equivalents ("DOE"). The analysis is critical because Claim 12 contains a key limitation — "two-dimensional sub-wavelength grating" — that was narrowed during prosecution by amendment to overcome a § 103 obviousness rejection, and Lumicore Technologies, Inc. ("Lumicore") can be expected to invoke PHE as a defense to OWS's DOE contentions at both the summary judgment and trial stages.

Background of the Amendment. During prosecution of the application that matured into the '015 Patent, the examiner rejected the relevant claims as obvious under 35 U.S.C. § 103 over a combination of two prior art references: (1) U.S. Patent No. 8,412,007 to Bergmann ("Bergmann"), which taught a one-dimensional sub-wavelength grating coupler for silicon photonic devices, and (2) International Application PCT/EP2015/071234 to Simonsen ("Simonsen"), published September 17, 2015, which taught a two-dimensional periodic structure for polarization-diverse optical coupling. In response, the applicant — through Dr. Martin Chu of Cascade IP Advisors, LLC — amended the claim that ultimately issued as Claim 12 by adding the modifier "two-dimensional" before "sub-wavelength grating," narrowing the claim from a broadly recited "sub-wavelength grating" to a "two-dimensional sub-wavelength grating." This amendment was accompanied by remarks distinguishing both Bergmann and Simonsen and was followed by a Notice of Allowance.

The DOE Issue. OWS asserts DOE for Claim 12 because Lumicore's accused products — the LumiLink 800G-DR8 and the LumiEdge 1600G-LR — employ grating coupler structures that may not literally satisfy the "two-dimensional sub-wavelength grating" limitation as amended, but that perform substantially the same function (coupling light of two orthogonal polarization states into the photonic circuit), in substantially the same way (using a periodic diffractive structure with sub-wavelength pitch elements arranged to split polarization modes), to achieve substantially the same result (efficient polarization-diverse light coupling with low insertion loss). Because the claim limitation was narrowed by amendment during prosecution, however, the Festo presumption of surrender applies, and OWS must rebut that presumption by establishing one of three recognized exceptions.

Bottom-Line Assessment. PHE creates a moderate risk of barring DOE on Claim 12 of the '015 Patent. The Festo presumption clearly applies because the narrowing amendment was indisputably made for a reason related to patentability — specifically, to overcome the examiner's § 103 rejection. However, the Festo "tangential relation" exception provides a viable pathway to overcome the presumption if OWS can demonstrate that the narrowing amendment was directed at a specific aspect of the prior art (i.e., distinguishing Bergmann's one-dimensional grating) rather than broadly disclaiming all non-two-dimensional grating geometries, and that the accused equivalent used by Lumicore bears only a tangential relation to the reason for the amendment. This argument is factually supportable based on the prosecution remarks, which focused narrowly on the structural distinctions between the claimed invention and the Bergmann/Simonsen combination. Alternative arguments under the "unforeseeability" and "other reason" exceptions also warrant development, though they are weaker.

Recommendation. OWS should proceed with its DOE contentions for Claim 12 but should fully develop the Festo rebuttal arguments. Specifically, OWS should:

• Prepare Dr. Caroline Ashford of the Northfield Institute of Technology to provide expert testimony supporting the tangential-relation exception, explaining why a person of ordinary skill in the art ("POSITA") would understand the amendment as narrowly directed at the Bergmann reference rather than as a broad disclaimer of all non-two-dimensional grating structures.

• Coordinate with Dr. Martin Chu of Cascade IP Advisors, LLC (the prosecution attorney who drafted the amendment) to obtain declaration testimony regarding the prosecution attorney's subjective intent behind the amendment and the specific prior art concerns it was designed to address.

• Ensure consistency between the PHE analysis for Claim 12 of the '015 Patent and the companion PHE analysis for Claims 3 and 7 of the '193 Patent (U.S. Patent No. 10,891,193), which involves a different limitation and different prior art but similar Festo exception arguments.

• Coordinate the claim construction briefing with this PHE analysis to avoid arguments that inadvertently strengthen Lumicore's estoppel position.

The remainder of this memorandum sets forth the detailed analysis supporting these conclusions.

II. BACKGROUND

A. The '015 Patent — Overview

The '015 Patent, titled "Polarization-Diverse Grating Coupler for Silicon Photonic Transceivers," is one of four OWS patents asserted against Lumicore in this litigation. The patent is directed to a grating coupler structure designed to enable efficient coupling of light from an optical fiber into a silicon photonic integrated circuit, with the specific ability to handle multiple polarization states of incoming light — a critical function for high-speed optical transceivers used in data center interconnect applications.

The relevant details of the '015 Patent are as follows:

Dr. Jian-Wei Huang is the Chief Technology Officer of OWS and a recognized leader in the silicon photonics field, with over seventy published papers and more than forty U.S. patents to his name. Dr. Nikolai Petrov serves as Vice President of Engineering for OWS's Photonics Division and is credited with leading the engineering team that developed the polarization-diverse grating coupler technology. Dr. Sarah Kim, the third named inventor, was a senior research scientist at OWS during the relevant period and contributed to the design and simulation of the two-dimensional sub-wavelength grating structures described in the patent.

Patent Family Relationships. The '015 Patent shares a common provisional application (Provisional App. No. 62/499,117, filed April 7, 2017) with U.S. Patent No. 10,891,193 (the "'193 Patent"), which is also asserted in this litigation. The '015 Patent is a continuation-in-part ("CIP") of the application that matured into the '193 Patent. The CIP application added new subject matter directed specifically to the polarization-diverse grating coupler design, including the two-dimensional sub-wavelength grating structures that are central to the present PHE analysis. Because the '015 Patent is a CIP, the claims that rely on subject matter not disclosed in the original provisional application are entitled to the filing date of the CIP application (August 30, 2019) rather than the provisional application's filing date (April 7, 2017). Claim 12, which recites the "two-dimensional sub-wavelength grating" limitation, may benefit from the earlier provisional date depending on whether the provisional application adequately supports the specific two-dimensional grating structure. This priority-date issue is currently under review in connection with Lumicore's invalidity contentions and is addressed in a separate memorandum.

B. Claim 12 — Full Text

Claim 12 of the '015 Patent, as issued, reads as follows:

Claim 12. The silicon photonic transceiver of claim 8, wherein the polarization-diverse grating coupler comprises a two-dimensional sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal, wherein the two-dimensional sub-wavelength grating is configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state.

Claim 12 is a dependent claim that depends from independent Claim 8. Claim 8 recites:

Claim 8. A silicon photonic transceiver comprising:

a silicon-on-insulator substrate having a buried oxide layer and a silicon device layer;

a polarization-diverse grating coupler formed in the silicon device layer, the polarization-diverse grating coupler configured to receive an incident optical signal from an optical fiber and to couple the incident optical signal into at least two waveguide modes corresponding to orthogonal polarization states;

a polarization rotator optically coupled to the polarization-diverse grating coupler and configured to rotate one of the at least two waveguide modes to align its polarization state with the other waveguide mode; and

a coherent detection module configured to process the aligned waveguide modes to recover data encoded in the incident optical signal.

The key limitation at issue in this PHE analysis is the "two-dimensional sub-wavelength grating" element recited in Claim 12. This limitation specifies that the polarization-diverse grating coupler of Claim 8 comprises a grating having a specific structural configuration: a two-dimensional arrangement of periodically arranged sub-wavelength features, each with a pitch smaller than the wavelength of the incident optical signal, configured to diffract the optical signal into two waveguide modes corresponding to orthogonal polarization states.

Relationship to Other Asserted Claims. Claims 1, 5, 8, 12, and 16 of the '015 Patent are all asserted in OWS's infringement contentions served on September 16, 2024. Of these, Claim 12 is the only claim for which OWS has asserted infringement under the doctrine of equivalents. The remaining asserted claims (1, 5, 8, and 16) are asserted on a literal-infringement basis only. The DOE contention for Claim 12 is directed specifically at the "two-dimensional sub-wavelength grating" limitation, which is the limitation that was narrowed by amendment during prosecution. All other limitations of Claim 12 are asserted as literally met by the accused products.

C. Accused Products and Infringement Posture for Claim 12

OWS accuses two Lumicore products of infringing the '015 Patent:

1. LumiLink 800G-DR8. The LumiLink 800G-DR8 is a pluggable optical transceiver module designed for 800-gigabit-per-second Ethernet applications in data center environments, operating over single-mode fiber at distances of up to 500 meters. Lumicore launched this product in the first quarter of 2023, and it generated fiscal year 2023 revenue of approximately $128.4 million according to Lumicore's public SEC filings and revenue data produced in discovery. The LumiLink 800G-DR8 is accused of infringing not only the '015 Patent but also U.S. Patent Nos. 11,127,847 (the "'847 Patent"), 10,891,193 (the "'193 Patent"), and 11,638,562 (the "'562 Patent").

2. LumiEdge 1600G-LR. The LumiEdge 1600G-LR is a next-generation optical transceiver module designed for 1.6-terabit-per-second Ethernet applications, targeting long-reach data center interconnect applications. Lumicore launched this product in the fourth quarter of 2023, and it generated fiscal year 2023 revenue of approximately $41.7 million (reflecting only partial-year sales). The LumiEdge 1600G-LR is accused of infringing the '193 Patent and the '015 Patent.

Infringement Contentions. OWS's infringement contentions, served pursuant to Patent Rule 3-1 on September 16, 2024, assert both literal infringement and, for Claim 12 specifically, infringement under the doctrine of equivalents. The literal-infringement contentions for Claim 12 map each claim limitation to specific structures identified in Lumicore's accused products. For the "two-dimensional sub-wavelength grating" limitation, however, the contentions note that the accused products may not literally satisfy this limitation as amended but that infringement exists under DOE because the accused structure performs substantially the same function, in substantially the same way, to achieve substantially the same result.

Basis for DOE. The DOE contention for Claim 12 rests on the following analysis under the function-way-result test:

• Function: Lumicore's accused grating coupler structures perform substantially the same function as the claimed "two-dimensional sub-wavelength grating" — namely, coupling light of two orthogonal polarization states (TE and TM modes) from an optical fiber into the silicon photonic integrated circuit.

• Way: Lumicore's accused structures accomplish this function in substantially the same way as the claimed invention — namely, by using a periodic diffractive structure with sub-wavelength pitch elements arranged to split the incoming optical signal into separate polarization modes for independent processing.

• Result: Lumicore's accused structures achieve substantially the same result as the claimed invention — namely, efficient polarization-diverse light coupling with low insertion loss, enabling high-speed coherent optical communication.

Benchmark Teardown Reports. The DOE contention is supported by teardown analyses performed by Benchmark Semiconductor Analysis, LLC. Specifically, a teardown of the LumiLink 800G-DR8, conducted by Kevin Ng in June 2023, identified a grating coupler structure on the silicon photonic die with sub-wavelength features. However, the teardown report noted dimensional and geometric variations from the literal claim language of Claim 12 as amended. In particular, the LumiLink teardown identified that the grating coupler uses a partially-etched, angled grating structure with varying etch depths across the coupler area, rather than a strictly uniform two-dimensional periodic array of sub-wavelength features as literally described in the claim. A subsequent teardown of the LumiEdge 1600G-LR, conducted in February 2024, identified a similar grating coupler structure with comparable dimensional and geometric variations. Both teardown reports are incorporated into OWS's infringement contentions and will be the subject of expert testimony by Dr. Ashford.

The structural difference between the accused products' grating coupler and the literal claim language is the crux of the DOE issue. While the accused structures employ sub-wavelength features arranged in a pattern that provides polarization-diverse coupling, the specific geometry of these features may not satisfy the "two-dimensional" modifier as literally construed. The accused structures use a quasi-two-dimensional arrangement with angled, partially-etched features that introduce a depth gradient — a design choice that departs from the uniform two-dimensional periodicity implied by the literal claim language but achieves the same polarization-splitting functionality through the same basic diffractive mechanism.

D. Claim Construction Context

The scope of the DOE analysis for Claim 12, and consequently the scope of the PHE analysis, is inextricably linked to the construction of several disputed claim terms. The Joint Claim Construction Statement, filed on October 28, 2024, identifies fourteen disputed terms across the four asserted patents. Among these, the term "polarization-diverse grating coupler" is of central importance to the present analysis.

OWS's Proposed Construction. OWS proposes that "polarization-diverse grating coupler" be construed to mean "a grating coupler capable of coupling light of two orthogonal polarization states." This construction is broad and does not incorporate any requirement that the grating coupler be "two-dimensional." Under OWS's construction, the "two-dimensional" requirement arises only in Claim 12 as an additional limitation narrowing the broader concept of a "polarization-diverse grating coupler" recited in parent Claim 8. This construction preserves the full scope of Claim 8 and positions Claim 12 as a narrower dependent claim adding a specific structural requirement.

Lumicore's Proposed Construction. Lumicore proposes that "polarization-diverse grating coupler" be construed to mean "a two-dimensional grating coupler with a polarization-splitting element that simultaneously couples TE and TM modes." This construction is significantly narrower and, critically, imports the "two-dimensional" requirement into the parent claim term itself. The practical effect of this construction would be to require a two-dimensional grating structure for all claims that recite "polarization-diverse grating coupler," including independent Claim 8. This construction appears designed to foreclose DOE by ensuring that any non-two-dimensional grating structure fails to satisfy even the broader parent claim, thereby eliminating the need for Lumicore to separately address the "two-dimensional sub-wavelength grating" limitation of Claim 12 — and also eliminating any viable DOE argument, since the "two-dimensional" requirement would be embedded in the claim at a higher level.

Impact on PHE Analysis. The interplay between claim construction and PHE is complex:

• If the Court adopts OWS's broader construction of "polarization-diverse grating coupler," literal infringement of parent Claim 8 is likely established for both accused products, and the DOE analysis for Claim 12's "two-dimensional sub-wavelength grating" limitation becomes more focused. Under this scenario, the PHE analysis for Claim 12 proceeds as outlined in this memorandum — OWS must rebut the Festo presumption for the specific "two-dimensional" limitation.

• If the Court adopts Lumicore's narrow construction that incorporates "two-dimensional" into the broader term, both literal and DOE paths narrow significantly. Literal infringement of Claim 8 itself may fail, and DOE arguments for Claim 12 become more difficult because the "two-dimensional" requirement would be a pervasive feature of the claim rather than a single dependent limitation. PHE becomes the central battleground. However, an argument can be made that if the Court adopts a narrow construction and literal infringement fails, the DOE arguments may actually become stronger in terms of the equities — the Court may be more receptive to DOE arguments where the claim construction is unduly narrow, provided that the Festo exceptions are satisfied.

Markman Hearing. The Markman hearing is currently scheduled for March 14, 2025 before Judge James R. Gilstrap. OWS's Opening Claim Construction Brief was filed on November 15, 2024, and the Reply Brief is due on December 20, 2024. The claim construction briefing is being coordinated with this PHE analysis to ensure that the arguments presented are consistent and that the Opening Brief does not make concessions or assertions that could inadvertently bolster Lumicore's PHE position. In particular, care has been taken to ensure that OWS's arguments regarding the meaning of "two-dimensional" in the claim construction context are consistent with OWS's position regarding the scope of the narrowing amendment in the PHE context.

III. PROSECUTION HISTORY OF CLAIM 12

A. Initial Filing and Original Claim Language

The application that matured into the '015 Patent was filed on August 30, 2019, as Application No. 16/555,817, claiming the benefit of Provisional Application No. 62/499,117, filed April 7, 2017. The application was filed as a continuation-in-part of Application No. 15/928,344 (which matured into the '193 Patent, U.S. Patent No. 10,891,193) and included new subject matter directed to the polarization-diverse grating coupler designs.

As originally filed, the application included twenty-two claims. The claim that ultimately issued as Claim 12 was originally numbered as Claim 14 in the as-filed application. The original text of Claim 14 (as filed) read as follows:

Original Claim 14 (as filed). The silicon photonic transceiver of claim 10, wherein the polarization-diverse grating coupler comprises a sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal, wherein the sub-wavelength grating is configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state.

The critical difference between the original claim language and the issued claim language is immediately apparent: the original claim referred to a "sub-wavelength grating" without any dimensional modifier. The "two-dimensional" qualifier was added during prosecution by amendment, as discussed in detail below in Section III.C. The original claim language thus encompassed sub-wavelength gratings of any dimensional configuration — one-dimensional, two-dimensional, or any other structural arrangement — so long as the grating had periodically arranged sub-wavelength features with a pitch smaller than the wavelength of the incident optical signal and was configured to diffract the optical signal into two orthogonal waveguide modes.

It bears noting that the original claim depended from original Claim 10, which corresponded to what ultimately issued as independent Claim 8. The renumbering occurred as a result of the cancellation and amendment of intervening claims during prosecution.

B. First Office Action — § 103 Rejection

The examiner issued a non-final Office Action on March 17, 2020 (Application No. 16/555,817). The Office Action rejected Claims 10–18 (including what became Claim 12) under 35 U.S.C. § 103 as obvious over the combination of two prior art references:

Primary Reference — Bergmann (U.S. Patent No. 8,412,007). Bergmann, titled "Sub-Wavelength Grating Coupler for Optical Waveguide," was issued on April 2, 2013, and is directed to a sub-wavelength grating coupler for coupling light between an optical fiber and a silicon photonic waveguide. Bergmann's disclosure is centered on a one-dimensional sub-wavelength grating — that is, a grating with periodic features arranged along a single axis. Bergmann teaches that the sub-wavelength features have a pitch smaller than the wavelength of the optical signal and that the grating achieves efficient light coupling into a silicon waveguide through diffractive effects. However, Bergmann does not disclose a two-dimensional grating structure, nor does it address polarization diversity — Bergmann's grating is designed for single-polarization coupling.

Secondary Reference — Simonsen (PCT/EP2015/071234). Simonsen, titled "Polarization-Diverse Optical Coupling Using Periodic Structures," was published on September 17, 2015, and is directed to a two-dimensional periodic structure for polarization-diverse optical coupling. Simonsen teaches a photonic crystal structure with features arranged in two dimensions that can couple both TE and TM polarization modes from an optical fiber into separate waveguides. However, Simonsen's periodic structure is described as a "photonic crystal" with features that operate on principles of photonic bandgap engineering, rather than as a "sub-wavelength grating" that operates primarily through diffractive coupling.

Examiner's Reasoning. The examiner reasoned as follows in the March 17, 2020 Office Action:

Bergmann disclosed a sub-wavelength grating coupler with periodically arranged sub-wavelength features having a pitch smaller than the wavelength of the incident optical signal, configured to diffract the incident optical signal into a waveguide mode — thereby satisfying the basic structural elements of the claim. The examiner acknowledged that Bergmann did not disclose polarization-diverse coupling or a two-dimensional arrangement of features.

Simonsen disclosed a two-dimensional periodic structure configured to receive an optical signal from an optical fiber and to couple the signal into separate waveguide modes corresponding to orthogonal polarization states. The examiner cited Simonsen as providing the motivation to extend Bergmann's grating coupler to a two-dimensional configuration for the purpose of achieving polarization diversity.

The examiner concluded that it would have been obvious to a person of ordinary skill in the art at the time of the invention to modify Bergmann's sub-wavelength grating coupler by arranging the sub-wavelength features in a two-dimensional configuration, as taught by Simonsen, in order to achieve polarization-diverse coupling of both TE and TM modes — a recognized advantage in the silicon photonics field for improving the reliability and performance of optical transceivers.

Specifically, the examiner mapped the claim limitations as follows:

• "Sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal" → Bergmann, Col. 4, ll. 12–35 (one-dimensional sub-wavelength grating with features having sub-wavelength pitch).

• "Configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state" → Simonsen, paragraphs [0034]–[0042] (two-dimensional periodic structure splitting TE and TM modes into separate waveguides).

• The combination of Bergmann and Simonsen was alleged to render obvious the claimed sub-wavelength grating configured for polarization-diverse coupling.

The examiner did not reject the claims under § 102 (anticipation), and the § 103 rejection was the sole basis for rejection of the claims relevant to this analysis.

C. Applicant's Response and Narrowing Amendment

On September 15, 2020, the applicant filed a Response to the Office Action through Dr. Martin Chu of Cascade IP Advisors, LLC. The Response included both amendments to the claims and accompanying remarks/arguments.

The Amendment. The applicant amended Claim 14 (later renumbered as Claim 12) by adding the modifier "two-dimensional" before "sub-wavelength grating" in two places within the claim. Specifically, the amendment changed:

• "a sub-wavelength grating having a plurality of periodically arranged sub-wavelength features" → "a two-dimensional sub-wavelength grating having a plurality of periodically arranged sub-wavelength features"

• "wherein the sub-wavelength grating is configured to diffract" → "wherein the two-dimensional sub-wavelength grating is configured to diffract"

No other changes were made to the claim language. The amendment was narrowing in nature: it restricted the claim from covering any sub-wavelength grating (regardless of dimensional configuration) to covering only a two-dimensional sub-wavelength grating.

Applicant's Accompanying Remarks. The applicant's Response included several pages of remarks distinguishing the cited prior art. The remarks relevant to the "two-dimensional" amendment are summarized below, with key passages quoted for accuracy:

Distinguishing Bergmann. The applicant argued that Bergmann taught only a one-dimensional sub-wavelength grating and did not disclose or suggest a two-dimensional arrangement of sub-wavelength features:

> "Bergmann is limited to a one-dimensional sub-wavelength grating structure in which the periodic features are arranged along a single axis. Bergmann does not disclose, teach, or suggest a two-dimensional sub-wavelength grating in which features are periodically arranged along two orthogonal axes. The amended claims recite a 'two-dimensional sub-wavelength grating,' which is not found in Bergmann."

Distinguishing Simonsen. The applicant argued that Simonsen's two-dimensional periodic structure was fundamentally different from the claimed "two-dimensional sub-wavelength grating":

> "While the Examiner cites Simonsen for the teaching of a two-dimensional periodic structure, the Applicant respectfully submits that Simonsen's structure is a photonic crystal operating on principles of photonic bandgap engineering, which is structurally and functionally distinct from the claimed two-dimensional sub-wavelength grating. Simonsen's photonic crystal has different periodicity characteristics — specifically, Simonsen's features are designed to create a photonic bandgap rather than to function as a diffractive grating with sub-wavelength pitch. A person of ordinary skill in the art would not equate Simonsen's photonic crystal structure with a 'sub-wavelength grating' as that term is understood in the art."

Arguing Non-Obviousness of the Combination. The applicant further argued that even if one were to attempt to combine Bergmann and Simonsen, the resulting structure would not yield the specific two-dimensional sub-wavelength grating configuration recited in the amended claims:

> "The combination proposed by the Examiner would not lead to the claimed invention because Bergmann and Simonsen teach fundamentally different structural approaches. Bergmann's one-dimensional grating operates by diffractive coupling, while Simonsen's photonic crystal operates by photonic bandgap effects. Simply extending Bergmann's one-dimensional grating to two dimensions, as the Examiner suggests, would not result in the specific two-dimensional sub-wavelength grating configuration disclosed and claimed in the present application, which achieves polarization-diverse coupling through a carefully designed diffractive mechanism rather than through photonic crystal effects."

Characterization of the Amendment's Purpose. Based on the prosecution remarks, the applicant's stated purpose for adding the "two-dimensional" modifier was twofold: (1) to distinguish the claimed invention from Bergmann by emphasizing that Bergmann's one-dimensional grating did not disclose the claimed two-dimensional arrangement; and (2) to distinguish the claimed invention from Simonsen by arguing that even though Simonsen disclosed a two-dimensional periodic structure, Simonsen's structure was a photonic crystal rather than a sub-wavelength grating and therefore would not be combined with Bergmann to arrive at the claimed two-dimensional sub-wavelength grating.

Notably, the applicant's remarks did not contain any express statement regarding what subject matter was being surrendered by the amendment. The remarks did not address whether the amendment was intended to disclaim all non-two-dimensional sub-wavelength gratings or only to distinguish the specific prior art combination. This silence is significant for the PHE analysis: it provides latitude for OWS to argue that the amendment was narrowly targeted at the Bergmann/Simonsen combination, consistent with the tangential-relation exception under Festo.

Examiner Interview. The prosecution file includes an Examiner Interview Summary dated October 22, 2020, reflecting a telephone interview between Dr. Martin Chu and the examiner. The summary notes that the examiner and applicant discussed the distinction between Simonsen's photonic crystal structure and the claimed sub-wavelength grating. The summary indicates that the examiner "agreed that Simonsen's photonic crystal structure has different periodicity characteristics than the claimed two-dimensional sub-wavelength grating" but does not record any specific discussion of the scope of surrender or the meaning of the "two-dimensional" amendment beyond its role in distinguishing the prior art.

D. Allowance. On December 9, 2020, the examiner issued a Notice of Allowance for Application No. 16/555,817. The examiner's statement of reasons for allowance stated:

> "The prior art of record, alone or in combination, does not disclose or render obvious a silicon photonic transceiver comprising the specific combination of features recited in the allowed claims, including a polarization-diverse grating coupler comprising a two-dimensional sub-wavelength grating configured to diffract an incident optical signal into orthogonal waveguide modes, in combination with the other recited elements including a polarization rotator and a coherent detection module."

The examiner's statement of reasons for allowance cited the "two-dimensional sub-wavelength grating" as one of the distinguishing features but framed the allowance in terms of the overall claim combination rather than identifying the "two-dimensional" amendment as the sole basis for allowance. This is relevant because Festo estoppel applies to amendments made for reasons related to patentability, and the scope of the estoppel depends in part on the relationship between the amendment and the reason for allowance.

Following payment of the issue fee, the patent issued on August 2, 2022, as U.S. Patent No. 11,402,015. At issuance, the claims were renumbered, and original Claim 14 became issued Claim 12.

E. Summary of Amendment Scope

The amendment to Claim 12 narrowed the claim by adding the "two-dimensional" qualifier to the "sub-wavelength grating" limitation. This amendment was made in direct response to the examiner's § 103 rejection combining Bergmann and Simonsen. Because the amendment was made for a reason related to patentability — specifically, to overcome a prior art rejection — the Festo presumption of surrender is triggered.

Scope of the Surrendered Territory. Under Festo, the surrendered territory encompasses the subject matter between the original claim scope and the amended claim scope. Here:

• Original claim scope: "A sub-wavelength grating" — encompassing sub-wavelength gratings of any dimensional configuration, including one-dimensional gratings, two-dimensional gratings, quasi-periodic structures, and any other structural arrangement meeting the basic definition of a "sub-wavelength grating."

• Amended claim scope: "A two-dimensional sub-wavelength grating" — limited to sub-wavelength gratings with features arranged in a two-dimensional periodic configuration.

• Surrendered territory: Sub-wavelength grating couplers that are not "two-dimensional" — including one-dimensional gratings, quasi-periodic structures, structures with dimensional characteristics that fall outside "two-dimensional" as construed, partially-etched angled gratings without uniform two-dimensional periodicity, and other non-two-dimensional structural variations.

The central question for the PHE analysis is whether the specific grating coupler structure used in Lumicore's accused products falls within this surrendered territory and, if so, whether OWS can rebut the Festo presumption by establishing one of the three recognized exceptions.

IV. PROSECUTION HISTORY ESTOPPEL — LEGAL FRAMEWORK

A. Festo Presumption

Under the doctrine of prosecution history estoppel, a patentee who narrows a claim by amendment during prosecution for a reason related to patentability is presumed to have surrendered all equivalents that fall between the original claim scope and the amended claim scope. The seminal articulation of this doctrine is found in Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), in which the Supreme Court held that a narrowing amendment creates a presumption that the patentee surrendered the particular equivalent in question, but that this presumption is rebuttable.

The Festo framework operates as follows:

Step 1: Was there a narrowing amendment? The threshold inquiry is whether the patentee made an amendment to the claim during prosecution that narrowed the claim's scope. Festo, 535 U.S. at 736–37. An amendment that adds a limitation to the claim or restricts an existing limitation is a narrowing amendment. Id.

Step 2: Was the amendment made for a reason related to patentability? Not all amendments trigger estoppel — only those made for a "substantial reason related to patentability." Warner-Jenkinson Co. v. Harborline Enterprises Davis Chemical Co., 520 U.S. 17, 33 (1997). Amendments made to overcome prior art rejections under § 102 or § 103 are paradigmatic examples of amendments made for reasons related to patentability. Amendments made for other reasons — such as to comply with formalities or to correct typographical errors — generally do not trigger estoppel. Where the reason for the amendment is ambiguous, the patentee bears the burden of showing that the amendment was not made for a reason related to patentability. Warner-Jenkinson, 520 U.S. at 33.

Step 3: Presumption of surrender. If a narrowing amendment was made for a reason related to patentability, a presumption arises that the patentee surrendered "all territory between the original claim and the amended claim." Festo, 535 U.S. at 740. This presumption operates to bar the patentee from asserting the doctrine of equivalents to recapture the surrendered subject matter.

Step 4: Rebuttal. The presumption is rebuttable. The patentee may overcome the presumption by demonstrating that one of three exceptions applies. Festo, 535 U.S. at 740–41.

In the present case, there is no dispute that Steps 1 and 2 are satisfied. The applicant made a narrowing amendment by adding the "two-dimensional" modifier to the "sub-wavelength grating" limitation. The amendment was made in direct response to the examiner's § 103 rejection — an amendment indisputably made for a reason related to patentability. Accordingly, the Festo presumption of surrender applies, and OWS bears the burden of establishing one of the three recognized exceptions to rebut that presumption.

B. Three Festo Exceptions (Rebuttal)

The Supreme Court in Festo identified three circumstances in which the patentee may rebut the presumption of surrender:

1. Tangential Relation Exception. The patentee may show that "the rationale underlying the amendment [bore] no more than a tangential relation to the equivalent in question." Festo, 535 U.S. at 740–41. This exception recognizes that a patentee who narrows a claim for a specific, limited reason should not be deemed to have surrendered all possible equivalents if the reason for the amendment has no bearing on the particular equivalent at issue. The Federal Circuit, on remand from the Supreme Court, elaborated that the tangential-relation inquiry asks "whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent." Festo Corp. v. Fenmore & Co., 344 F.3d 1359, 1369 (Fed. Cir. 2003) (en banc). In Ridgeway Corporation v. Hamilton Sundstrand Corp., 370 F.3d 1131, 1143 (Fed. Cir. 2004) (en banc), the Federal Circuit further clarified that the tangential-relation exception requires an objective assessment of the relationship between the reason for the amendment and the alleged equivalent, examining the prosecution history from the perspective of a reasonable competitor.

In Ring & Pinion Service, Inc. v. ARB Corp., 743 F.3d 831, 838 (Fed. Cir. 2014), the Federal Circuit emphasized that the tangential-relation analysis is objective rather than subjective — the court looks at the prosecution record to determine whether the amendment was directed at a specific concern that is distinct from the equivalent at issue, rather than relying on the patentee's post hoc characterization of its intent. The court noted that "the inquiry is not what the patentee subjectively intended by the amendment but what a reasonable competitor reviewing the prosecution history would have understood the amendment to mean."

2. Unforeseeability Exception. The patentee may show that "the equivalent was unforeseeable at the time of the amendment." Festo, 535 U.S. at 740. This exception recognizes that a patentee cannot be presumed to have surrendered an equivalent that did not exist or was not foreseeable in the art at the time the amendment was made. The Federal Circuit has interpreted this exception as applying to after-developed technologies or equivalents that were not known in the relevant art at the time of the narrowing amendment. See Festo, 344 F.3d at 1369–70; see also Insituform Techs., Inc. v. Cat Contracting, Inc., 385 F.3d 1360, 1370–71 (Fed. Cir. 2004). The unforeseeability exception is often treated as a companion to, or subset of, the tangential-relation exception, as an unforeseeable equivalent is by definition one that bears no more than a tangential relation to the amendment.

3. "Other Reason" Exception. The patentee may show that "there [was] some other reason suggesting that the patentee could not reasonably be expected to have drafted a claim that literally encompassed the alleged equivalent." Festo, 535 U.S. at 740–41. This is the narrowest of the three exceptions and serves as a catch-all for circumstances not captured by the first two exceptions. The Federal Circuit has applied this exception sparingly, generally requiring the patentee to show that the equivalent represents a technology or design choice that was so far removed from the claim drafter's reasonable contemplation that it would have been unreasonable to expect the drafter to have anticipated and claimed it. See Insituform, 385 F.3d at 1371.

Burden of Proof. The burden of rebutting the Festo presumption falls on the patentee. Festo, 535 U.S. at 740. The patentee must make a "persuasive showing" that one of the three exceptions applies. Id. The Federal Circuit has held that the rebuttal inquiry is a question of law based on the prosecution history, which may be informed by expert testimony and other evidence. Festo, 344 F.3d at 1370. However, where the rebuttal depends on disputed factual issues (such as whether the accused equivalent was foreseeable or whether the prosecution attorney's intent was narrowly directed), those factual disputes may preclude summary judgment and must be resolved by the finder of fact. See Honeywell, 370 F.3d at 1143–44.

Relevant Eastern District of Texas Authority. Judge Gilstrap has addressed Festo estoppel in several prior cases. In DataTern, Inc. v. MicroStrategy, Inc., No. 2:11-cv-00262-JRG (E.D. Tex.), Judge Gilstrap denied summary judgment on PHE where the patentee presented evidence that the amendment was narrowly directed at a specific prior art reference and the accused equivalent was distinguishable from the prior art that prompted the amendment. In Evolved Wireless LLC v. Camberwell & Co., No. 2:15-cv-01565-JRG (E.D. Tex.), however, Judge Gilstrap granted summary judgment on PHE where the prosecution remarks made clear that the amendment was directed broadly at the type of structure employed by the accused infringer. These precedents underscore the importance of the specific prosecution remarks and the factual record in determining whether the Festo exceptions are satisfied.

C. Interplay with Claim Construction

The scope of PHE is intertwined with the construction of the disputed claim terms, particularly "two-dimensional sub-wavelength grating" and "polarization-diverse grating coupler." This interplay operates on multiple levels.

First, the meaning of "two-dimensional" as used in the claim directly defines the boundary between literal infringement and the need for DOE. If "two-dimensional" is construed broadly to encompass structures with features arranged in more than one dimension — including the quasi-two-dimensional structures with angled, varying-etch-depth features found in Lumicore's products — then literal infringement may be established, and DOE (and PHE) become unnecessary. If "two-dimensional" is construed narrowly to require a strictly uniform two-dimensional periodic array, then literal infringement is unlikely and DOE becomes essential.

Second, the scope of the surrendered territory under PHE depends on the construction of both the original claim term ("sub-wavelength grating") and the amended claim term ("two-dimensional sub-wavelength grating"). The broader the construction of the original term and the narrower the construction of the amended term, the larger the surrendered territory — and the more likely it is that the accused equivalent falls within it.

Third, if the Court adopts OWS's broader construction of "polarization-diverse grating coupler" (not requiring "two-dimensional" as a definitional element), the literal-infringement analysis for parent Claim 8 may resolve the issue for the accused products without requiring resort to Claim 12's DOE contentions. In that scenario, the PHE issue becomes moot as a practical matter because the jury could find infringement of Claim 8 on a literal basis, and the additional damages attributable to Claim 12 DOE would be marginal at most.

Conversely, if the Court adopts Lumicore's narrow construction that incorporates "two-dimensional" into the broader "polarization-diverse grating coupler" term, both the literal and DOE paths for Claim 12 narrow, and PHE becomes the central battleground for the DOE theory. However, as noted above, a narrow construction that forecloses literal infringement may paradoxically strengthen the equitable case for DOE, depending on the reasoning underlying the Markman ruling.

Strategy Note: The claim construction briefing (OWS's Opening Brief filed November 15, 2024; Reply Brief due December 20, 2024) must be coordinated with this PHE analysis. OWS's claim construction arguments should not inadvertently concede that the "two-dimensional" limitation carries a broad disclaimer meaning, and the briefing should avoid language suggesting that the amendment was directed at the full breadth of the claim scope rather than at the specific prior art combination. This coordination is essential because Lumicore can be expected to cite OWS's own claim construction briefing in support of its PHE arguments at the summary judgment stage.

V. APPLICATION TO CLAIM 12 OF THE '015 PATENT

A. Identification of the Alleged Equivalent

Based on the Benchmark Semiconductor Analysis, LLC teardown reports (Kevin Ng, LumiLink 800G-DR8, June 2023; LumiEdge 1600G-LR, February 2024), the accused Lumicore products employ a grating coupler with a structural design that differs from the "two-dimensional sub-wavelength grating" as literally claimed. Specifically, both the LumiLink 800G-DR8 and the LumiEdge 1600G-LR incorporate a grating coupler that uses a partially-etched, angled grating with varying etch depths across the coupler area, rather than a strictly uniform two-dimensional periodic array of sub-wavelength features.

The accused structure may be described as follows based on the teardown data:

• The grating coupler includes sub-wavelength features arranged in a pattern that extends in two spatial directions, but the features are not arranged in a strictly periodic two-dimensional array. Instead, the features exhibit a gradient in etch depth from the center of the coupler to its edges, and the features are angled relative to the plane of the silicon device layer.

• The sub-wavelength pitch of the individual features is confirmed by the Benchmark SEM imaging to be smaller than the wavelength of the incident optical signal (approximately 1310 nm for the LumiLink 800G-DR8 and 1550 nm for the LumiEdge 1600G-LR), consistent with the "sub-wavelength" requirement of the claim.

• The grating coupler is configured to couple both TE and TM polarization modes from an optical fiber into separate waveguide channels on the silicon photonic chip, achieving polarization-diverse operation.

• The key structural difference is the varying etch depth and angled feature geometry: rather than using a uniform two-dimensional grid of identical sub-wavelength features (as implied by the literal claim language), the accused structure uses features with non-uniform etch depths that create a three-dimensional profile across the coupler area, combined with angular offsets that control the coupling efficiency and polarization splitting.

Under the function-way-result test for the doctrine of equivalents:

• Function: The accused structure performs the same function as the claimed "two-dimensional sub-wavelength grating" — coupling light of two orthogonal polarization states (TE and TM) from an optical fiber into the silicon photonic integrated circuit.

• Way: The accused structure accomplishes this function in substantially the same way — using a periodic diffractive structure with sub-wavelength pitch elements that interact with the incident light to split it into separate polarization modes. The diffraction mechanism is fundamentally the same; only the specific geometry of the features differs.

• Result: The accused structure achieves substantially the same result — efficient polarization-diverse light coupling with low insertion loss, enabling high-speed coherent optical communication. The Benchmark teardown data indicates insertion losses of approximately 1.8 dB for the LumiLink 800G-DR8 and 1.6 dB for the LumiEdge 1600G-LR, comparable to the performance characteristics of the patented design.

B. Does the Amendment Surrender the Equivalent?

The threshold question under the Festo framework is whether the accused equivalent falls within the territory surrendered by the narrowing amendment — that is, the territory between the original claim ("sub-wavelength grating") and the amended claim ("two-dimensional sub-wavelength grating").

Lumicore's Expected Argument. Lumicore will argue that the accused grating coupler structure falls squarely within the surrendered territory. Specifically, Lumicore will contend that:

• The original claim covered all sub-wavelength gratings, including those with non-two-dimensional geometries.

• The amendment narrowed the claim to cover only "two-dimensional" sub-wavelength gratings, thereby surrendering all sub-wavelength gratings that are not "two-dimensional."

• The accused structure — a partially-etched, angled grating with varying etch depths — is precisely the type of non-two-dimensional (or quasi-two-dimensional) sub-wavelength grating structure that the amendment disclaimed. The varying etch depths and angled features mean that the accused structure does not have the uniform two-dimensional periodicity required by the amended claim, placing it within the surrendered territory.

• Asserting DOE to recapture this surrendered territory is precisely the kind of "recapture" that PHE is designed to prevent.

OWS's Counter-Argument. OWS will argue that the accused structure may not fall within the surrender zone, or at least not squarely within it. This argument has two components:

First, the accused structure is arguably "two-dimensional" by certain metrics. The sub-wavelength features are arranged in a pattern that extends in two spatial directions, even though the features are not arranged in a perfectly uniform two-dimensional periodic array. If "two-dimensional" is construed to require only that features be arranged in two spatial dimensions (rather than requiring strict two-dimensional periodicity), then the accused structure may satisfy the literal claim language, mooting the need for DOE and PHE analysis. This argument is closely tied to the claim construction outcome and will be resolved at the Markman hearing.

Second, even if the accused structure does not satisfy the literal "two-dimensional" limitation, the specific way in which it differs from the claimed structure — through varying etch depths and angular offsets rather than through a fundamentally different dimensional arrangement — may place it at the periphery of the surrender zone rather than at its center. The accused structure is not the same type of non-two-dimensional grating that prompted the amendment (Bergmann's one-dimensional grating); rather, it is a structure that incorporates elements of two-dimensional design but deviates in a distinct geometric parameter. This distinction is relevant to the tangential-relation exception analysis.

Assessment. The risk is moderate-to-high that Lumicore will successfully argue the accused structure falls within the surrendered territory. The amendment clearly drew a line between two-dimensional and non-two-dimensional sub-wavelength gratings, and the accused structure's deviation from strict two-dimensional periodicity places it on the wrong side of that line as a matter of literal claim scope. However, the specific nature of the deviation — varying etch depths and angular features rather than a one-dimensional arrangement — provides a basis for arguing that the accused equivalent is not the type of structure the amendment was designed to disclaim. The strength of this argument depends on the Festo exception analysis that follows.

C. Tangential Relation Exception Analysis

The tangential-relation exception is OWS's strongest rebuttal argument against the Festo presumption. This exception asks whether "the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question." Festo, 535 U.S. at 740–41.

Core Argument. The narrowing amendment adding "two-dimensional" was made for a specific, limited purpose: to distinguish the Bergmann reference, which taught a one-dimensional sub-wavelength grating, and to rebut the examiner's proposed combination of Bergmann with Simonsen. The amendment was not a broad disclaimer of all possible alternative grating coupler geometries. The rationale underlying the amendment was directed at the specific deficiency of the prior art combination — Bergmann's limitation to one-dimensional grating structures — rather than at the general concept of dimensional variations in grating geometry. Because the accused Lumicore structure is neither a Bergmann-type one-dimensional grating nor a Simonsen-type photonic crystal, the rationale for the amendment bears no more than a tangential relation to the accused equivalent.

This argument is supported by the following considerations:

1. The amendment was directed at Bergmann's one-dimensional grating. The prosecution remarks make clear that the primary purpose of adding "two-dimensional" was to distinguish Bergmann. The applicant stated that "Bergmann is limited to a one-dimensional sub-wavelength grating structure" and that "the amended claims recite a 'two-dimensional sub-wavelength grating,' which is not found in Bergmann." This language shows that the amendment was targeted at the specific structural deficiency of Bergmann (its limitation to one dimension), not at broadly defining the outer boundary of the claim scope for all possible grating configurations.

2. Lumicore's accused structure is not a Bergmann-type one-dimensional grating. The accused grating coupler in the LumiLink 800G-DR8 and LumiEdge 1600G-LR is structurally distinct from the Bergmann reference. Bergmann's one-dimensional grating has features arranged along a single axis in a uniform, periodic one-dimensional pattern. Lumicore's accused structure, by contrast, has features arranged in two spatial directions with varying etch depths and angular offsets — a fundamentally different design approach that shares no structural resemblance with Bergmann. The accused structure is not the type of non-two-dimensional grating that the amendment was designed to distinguish.

3. The applicant distinguished Simonsen on structural (not dimensional) grounds. The applicant's remarks distinguished Simonsen by arguing that Simonsen's periodic structure was a "photonic crystal" rather than a "sub-wavelength grating" — a structural distinction, not a dimensional one. The applicant stated that "Simonsen's photonic crystal has different periodicity characteristics" and that "a person of ordinary skill in the art would not equate Simonsen's photonic crystal structure with a 'sub-wavelength grating.'" This language indicates that the applicant was not using the "two-dimensional" modifier to broadly disclaim all non-two-dimensional structures; rather, the applicant's arguments were directed at the specific structural characteristics of the cited references.

4. A POSITA would understand the amendment as narrowly directed. From the perspective of a reasonable competitor reviewing the prosecution history — the relevant perspective under Ring & Pinion, 743 F.3d at 838 — the amendment would be understood as responding to the specific Bergmann/Simonsen combination rather than as a sweeping disclaimer. The prosecution exchange was focused on two specific references, and the applicant's arguments were targeted at the deficiencies of those references. A reasonable competitor would not read the amendment as surrendering all possible grating coupler geometries that deviate from strict two-dimensional periodicity.

Risk Assessment. The tangential-relation argument has a reasonable probability of success if properly developed with prosecution-attorney testimony and expert support. The Federal Circuit has recognized that amendments narrowly targeted at specific prior art may leave room for equivalents that were not the focus of the prosecution dialogue. See Honeywell, 370 F.3d at 1143 (noting that the tangential-relation exception "prevents the doctrine of prosecution history estoppel from becoming an impenetrable barrier to the doctrine of equivalents in all cases involving narrowing amendments"). However, the analysis is fact-intensive and depends on the precise characterization of the accused structure relative to the surrendered territory. The risk is that a court could conclude that the "two-dimensional" amendment was not merely directed at Bergmann's one-dimensional grating but was a deliberate choice to limit the claim to two-dimensional structures, with the intent of distinguishing any non-two-dimensional alternative.

Supporting Evidence Needed. To maximize the probability of success on the tangential-relation exception, OWS should develop the following evidence:

• Declaration from Dr. Martin Chu (Cascade IP Advisors). Dr. Chu, as the prosecution attorney who drafted the amendment, is uniquely positioned to testify regarding the specific intent behind adding "two-dimensional." While the objective analysis under Ring & Pinion focuses on the prosecution record rather than subjective intent, Dr. Chu's testimony can provide context for the amendment and support the narrative that it was narrowly directed at the Bergmann/Simonsen combination. Dr. Chu should be asked to confirm that the amendment was made specifically to distinguish Bergmann's one-dimensional grating and to address the examiner's proposed combination, and that there was no intent to broadly disclaim all non-two-dimensional grating structures.

• Expert testimony from Dr. Caroline Ashford. Dr. Ashford, as OWS's technical expert, should testify regarding how a POSITA would understand the amendment in the context of the prosecution history. Specifically, she should explain: (a) the structural differences between Bergmann's one-dimensional grating, Simonsen's photonic crystal, the claimed two-dimensional sub-wavelength grating, and Lumicore's accused partially-etched angled grating; (b) why a POSITA would understand the amendment as directed specifically at Bergmann's one-dimensional structure rather than as a broad disclaimer of all non-two-dimensional configurations; and (c) why the accused Lumicore structure is not the type of equivalent that the amendment was designed to surrender.

• Analysis of the prosecution record. A detailed analysis of the prosecution record — including the Office Action, the applicant's Response, the Examiner Interview Summary, and the Notice of Allowance — should be compiled to demonstrate that t

PROSECUTION HISTORY ESTOPPEL ANALYSIS
U.S. Patent No. 11,402,015 ('015 Patent)
ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL
CONFIDENTIALITY LEGEND: ATTORNEY WORK PRODUCT — PRIVILEGED AND CONFIDENTIAL. This memorandum is protected by the attorney-client privilege and the work-product doctrine. It is prepared in anticipation of litigation and for the purpose of providing legal advice to the client. Do not distribute outside the case team without express authorization from Alan Ngo.
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I. EXECUTIVE SUMMARY
This memorandum analyzes whether prosecution history estoppel ("PHE") under Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), bars Optiwave Semiconductor Corp. ("OWS" or "Client") from asserting infringement of Claim 12 of U.S. Patent No. 11,402,015 (the "'015 Patent") under the doctrine of equivalents ("DOE"). The analysis is critical because Claim 12 contains a key limitation — "two-dimensional sub-wavelength grating" — that was narrowed during prosecution by amendment to overcome a § 103 obviousness rejection, and Lumicore Technologies, Inc. ("Lumicore") can be expected to invoke PHE as a defense to OWS's DOE contentions at both the summary judgment and trial stages.
Background of the Amendment. During prosecution of the application that matured into the '015 Patent, the examiner rejected the relevant claims as obvious under 35 U.S.C. § 103 over a combination of two prior art references: (1) U.S. Patent No. 8,412,007 to Bergmann ("Bergmann"), which taught a one-dimensional sub-wavelength grating coupler for silicon photonic devices, and (2) International Application PCT/EP2015/071234 to Simonsen ("Simonsen"), published September 17, 2015, which taught a two-dimensional periodic structure for polarization-diverse optical coupling. In response, the applicant — through Dr. Martin Chu of Cascade IP Advisors, LLC — amended the claim that ultimately issued as Claim 12 by adding the modifier "two-dimensional" before "sub-wavelength grating," narrowing the claim from a broadly recited "sub-wavelength grating" to a "two-dimensional sub-wavelength grating." This amendment was accompanied by remarks distinguishing both Bergmann and Simonsen and was followed by a Notice of Allowance.
The DOE Issue. OWS asserts DOE for Claim 12 because Lumicore's accused products — the LumiLink 800G-DR8 and the LumiEdge 1600G-LR — employ grating coupler structures that may not literally satisfy the "two-dimensional sub-wavelength grating" limitation as amended, but that perform substantially the same function (coupling light of two orthogonal polarization states into the photonic circuit), in substantially the same way (using a periodic diffractive structure with sub-wavelength pitch elements arranged to split polarization modes), to achieve substantially the same result (efficient polarization-diverse light coupling with low insertion loss). Because the claim limitation was narrowed by amendment during prosecution, however, the Festo presumption of surrender applies, and OWS must rebut that presumption by establishing one of three recognized exceptions.
Bottom-Line Assessment. PHE creates a moderate risk of barring DOE on Claim 12 of the '015 Patent. The Festo presumption clearly applies because the narrowing amendment was indisputably made for a reason related to patentability — specifically, to overcome the examiner's § 103 rejection. However, the Festo "tangential relation" exception provides a viable pathway to overcome the presumption if OWS can demonstrate that the narrowing amendment was directed at a specific aspect of the prior art (i.e., distinguishing Bergmann's one-dimensional grating) rather than broadly disclaiming all non-two-dimensional grating geometries, and that the accused equivalent used by Lumicore bears only a tangential relation to the reason for the amendment. This argument is factually supportable based on the prosecution remarks, which focused narrowly on the structural distinctions between the claimed invention and the Bergmann/Simonsen combination. Alternative arguments under the "unforeseeability" and "other reason" exceptions also warrant development, though they are weaker.
Recommendation. OWS should proceed with its DOE contentions for Claim 12 but should fully develop the Festo rebuttal arguments. Specifically, OWS should:
• Prepare Dr. Caroline Ashford of the Northfield Institute of Technology to provide expert testimony supporting the tangential-relation exception, explaining why a person of ordinary skill in the art ("POSITA") would understand the amendment as narrowly directed at the Bergmann reference rather than as a broad disclaimer of all non-two-dimensional grating structures.
• Coordinate with Dr. Martin Chu of Cascade IP Advisors, LLC (the prosecution attorney who drafted the amendment) to obtain declaration testimony regarding the prosecution attorney's subjective intent behind the amendment and the specific prior art concerns it was designed to address.
• Ensure consistency between the PHE analysis for Claim 12 of the '015 Patent and the companion PHE analysis for Claims 3 and 7 of the '193 Patent (U.S. Patent No. 10,891,193), which involves a different limitation and different prior art but similar Festo exception arguments.
• Coordinate the claim construction briefing with this PHE analysis to avoid arguments that inadvertently strengthen Lumicore's estoppel position.
The remainder of this memorandum sets forth the detailed analysis supporting these conclusions.
II. BACKGROUND
A. The '015 Patent — Overview
The '015 Patent, titled "Polarization-Diverse Grating Coupler for Silicon Photonic Transceivers," is one of four OWS patents asserted against Lumicore in this litigation. The patent is directed to a grating coupler structure designed to enable efficient coupling of light from an optical fiber into a silicon photonic integrated circuit, with the specific ability to handle multiple polarization states of incoming light — a critical function for high-speed optical transceivers used in data center interconnect applications.
The relevant details of the '015 Patent are as follows:
Dr. Jian-Wei Huang is the Chief Technology Officer of OWS and a recognized leader in the silicon photonics field, with over seventy published papers and more than forty U.S. patents to his name. Dr. Nikolai Petrov serves as Vice President of Engineering for OWS's Photonics Division and is credited with leading the engineering team that developed the polarization-diverse grating coupler technology. Dr. Sarah Kim, the third named inventor, was a senior research scientist at OWS during the relevant period and contributed to the design and simulation of the two-dimensional sub-wavelength grating structures described in the patent.
Patent Family Relationships. The '015 Patent shares a common provisional application (Provisional App. No. 62/499,117, filed April 7, 2017) with U.S. Patent No. 10,891,193 (the "'193 Patent"), which is also asserted in this litigation. The '015 Patent is a continuation-in-part ("CIP") of the application that matured into the '193 Patent. The CIP application added new subject matter directed specifically to the polarization-diverse grating coupler design, including the two-dimensional sub-wavelength grating structures that are central to the present PHE analysis. Because the '015 Patent is a CIP, the claims that rely on subject matter not disclosed in the original provisional application are entitled to the filing date of the CIP application (August 30, 2019) rather than the provisional application's filing date (April 7, 2017). Claim 12, which recites the "two-dimensional sub-wavelength grating" limitation, may benefit from the earlier provisional date depending on whether the provisional application adequately supports the specific two-dimensional grating structure. This priority-date issue is currently under review in connection with Lumicore's invalidity contentions and is addressed in a separate memorandum.
B. Claim 12 — Full Text
Claim 12 of the '015 Patent, as issued, reads as follows:
Claim 12. The silicon photonic transceiver of claim 8, wherein the polarization-diverse grating coupler comprises a two-dimensional sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal, wherein the two-dimensional sub-wavelength grating is configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state.
Claim 12 is a dependent claim that depends from independent Claim 8. Claim 8 recites:
Claim 8. A silicon photonic transceiver comprising:
a silicon-on-insulator substrate having a buried oxide layer and a silicon device layer;
a polarization-diverse grating coupler formed in the silicon device layer, the polarization-diverse grating coupler configured to receive an incident optical signal from an optical fiber and to couple the incident optical signal into at least two waveguide modes corresponding to orthogonal polarization states;
a polarization rotator optically coupled to the polarization-diverse grating coupler and configured to rotate one of the at least two waveguide modes to align its polarization state with the other waveguide mode; and
a coherent detection module configured to process the aligned waveguide modes to recover data encoded in the incident optical signal.
The key limitation at issue in this PHE analysis is the "two-dimensional sub-wavelength grating" element recited in Claim 12. This limitation specifies that the polarization-diverse grating coupler of Claim 8 comprises a grating having a specific structural configuration: a two-dimensional arrangement of periodically arranged sub-wavelength features, each with a pitch smaller than the wavelength of the incident optical signal, configured to diffract the optical signal into two waveguide modes corresponding to orthogonal polarization states.
Relationship to Other Asserted Claims. Claims 1, 5, 8, 12, and 16 of the '015 Patent are all asserted in OWS's infringement contentions served on September 16, 2024. Of these, Claim 12 is the only claim for which OWS has asserted infringement under the doctrine of equivalents. The remaining asserted claims (1, 5, 8, and 16) are asserted on a literal-infringement basis only. The DOE contention for Claim 12 is directed specifically at the "two-dimensional sub-wavelength grating" limitation, which is the limitation that was narrowed by amendment during prosecution. All other limitations of Claim 12 are asserted as literally met by the accused products.
C. Accused Products and Infringement Posture for Claim 12
OWS accuses two Lumicore products of infringing the '015 Patent:
1. LumiLink 800G-DR8. The LumiLink 800G-DR8 is a pluggable optical transceiver module designed for 800-gigabit-per-second Ethernet applications in data center environments, operating over single-mode fiber at distances of up to 500 meters. Lumicore launched this product in the first quarter of 2023, and it generated fiscal year 2023 revenue of approximately $128.4 million according to Lumicore's public SEC filings and revenue data produced in discovery. The LumiLink 800G-DR8 is accused of infringing not only the '015 Patent but also U.S. Patent Nos. 11,127,847 (the "'847 Patent"), 10,891,193 (the "'193 Patent"), and 11,638,562 (the "'562 Patent").
2. LumiEdge 1600G-LR. The LumiEdge 1600G-LR is a next-generation optical transceiver module designed for 1.6-terabit-per-second Ethernet applications, targeting long-reach data center interconnect applications. Lumicore launched this product in the fourth quarter of 2023, and it generated fiscal year 2023 revenue of approximately $41.7 million (reflecting only partial-year sales). The LumiEdge 1600G-LR is accused of infringing the '193 Patent and the '015 Patent.
Infringement Contentions. OWS's infringement contentions, served pursuant to Patent Rule 3-1 on September 16, 2024, assert both literal infringement and, for Claim 12 specifically, infringement under the doctrine of equivalents. The literal-infringement contentions for Claim 12 map each claim limitation to specific structures identified in Lumicore's accused products. For the "two-dimensional sub-wavelength grating" limitation, however, the contentions note that the accused products may not literally satisfy this limitation as amended but that infringement exists under DOE because the accused structure performs substantially the same function, in substantially the same way, to achieve substantially the same result.
Basis for DOE. The DOE contention for Claim 12 rests on the following analysis under the function-way-result test:
• Function: Lumicore's accused grating coupler structures perform substantially the same function as the claimed "two-dimensional sub-wavelength grating" — namely, coupling light of two orthogonal polarization states (TE and TM modes) from an optical fiber into the silicon photonic integrated circuit.
• Way: Lumicore's accused structures accomplish this function in substantially the same way as the claimed invention — namely, by using a periodic diffractive structure with sub-wavelength pitch elements arranged to split the incoming optical signal into separate polarization modes for independent processing.
• Result: Lumicore's accused structures achieve substantially the same result as the claimed invention — namely, efficient polarization-diverse light coupling with low insertion loss, enabling high-speed coherent optical communication.
Benchmark Teardown Reports. The DOE contention is supported by teardown analyses performed by Benchmark Semiconductor Analysis, LLC. Specifically, a teardown of the LumiLink 800G-DR8, conducted by Kevin Ng in June 2023, identified a grating coupler structure on the silicon photonic die with sub-wavelength features. However, the teardown report noted dimensional and geometric variations from the literal claim language of Claim 12 as amended. In particular, the LumiLink teardown identified that the grating coupler uses a partially-etched, angled grating structure with varying etch depths across the coupler area, rather than a strictly uniform two-dimensional periodic array of sub-wavelength features as literally described in the claim. A subsequent teardown of the LumiEdge 1600G-LR, conducted in February 2024, identified a similar grating coupler structure with comparable dimensional and geometric variations. Both teardown reports are incorporated into OWS's infringement contentions and will be the subject of expert testimony by Dr. Ashford.
The structural difference between the accused products' grating coupler and the literal claim language is the crux of the DOE issue. While the accused structures employ sub-wavelength features arranged in a pattern that provides polarization-diverse coupling, the specific geometry of these features may not satisfy the "two-dimensional" modifier as literally construed. The accused structures use a quasi-two-dimensional arrangement with angled, partially-etched features that introduce a depth gradient — a design choice that departs from the uniform two-dimensional periodicity implied by the literal claim language but achieves the same polarization-splitting functionality through the same basic diffractive mechanism.
D. Claim Construction Context
The scope of the DOE analysis for Claim 12, and consequently the scope of the PHE analysis, is inextricably linked to the construction of several disputed claim terms. The Joint Claim Construction Statement, filed on October 28, 2024, identifies fourteen disputed terms across the four asserted patents. Among these, the term "polarization-diverse grating coupler" is of central importance to the present analysis.
OWS's Proposed Construction. OWS proposes that "polarization-diverse grating coupler" be construed to mean "a grating coupler capable of coupling light of two orthogonal polarization states." This construction is broad and does not incorporate any requirement that the grating coupler be "two-dimensional." Under OWS's construction, the "two-dimensional" requirement arises only in Claim 12 as an additional limitation narrowing the broader concept of a "polarization-diverse grating coupler" recited in parent Claim 8. This construction preserves the full scope of Claim 8 and positions Claim 12 as a narrower dependent claim adding a specific structural requirement.
Lumicore's Proposed Construction. Lumicore proposes that "polarization-diverse grating coupler" be construed to mean "a two-dimensional grating coupler with a polarization-splitting element that simultaneously couples TE and TM modes." This construction is significantly narrower and, critically, imports the "two-dimensional" requirement into the parent claim term itself. The practical effect of this construction would be to require a two-dimensional grating structure for all claims that recite "polarization-diverse grating coupler," including independent Claim 8. This construction appears designed to foreclose DOE by ensuring that any non-two-dimensional grating structure fails to satisfy even the broader parent claim, thereby eliminating the need for Lumicore to separately address the "two-dimensional sub-wavelength grating" limitation of Claim 12 — and also eliminating any viable DOE argument, since the "two-dimensional" requirement would be embedded in the claim at a higher level.
Impact on PHE Analysis. The interplay between claim construction and PHE is complex:
• If the Court adopts OWS's broader construction of "polarization-diverse grating coupler," literal infringement of parent Claim 8 is likely established for both accused products, and the DOE analysis for Claim 12's "two-dimensional sub-wavelength grating" limitation becomes more focused. Under this scenario, the PHE analysis for Claim 12 proceeds as outlined in this memorandum — OWS must rebut the Festo presumption for the specific "two-dimensional" limitation.
• If the Court adopts Lumicore's narrow construction that incorporates "two-dimensional" into the broader term, both literal and DOE paths narrow significantly. Literal infringement of Claim 8 itself may fail, and DOE arguments for Claim 12 become more difficult because the "two-dimensional" requirement would be a pervasive feature of the claim rather than a single dependent limitation. PHE becomes the central battleground. However, an argument can be made that if the Court adopts a narrow construction and literal infringement fails, the DOE arguments may actually become stronger in terms of the equities — the Court may be more receptive to DOE arguments where the claim construction is unduly narrow, provided that the Festo exceptions are satisfied.
Markman Hearing. The Markman hearing is currently scheduled for March 14, 2025 before Judge James R. Gilstrap. OWS's Opening Claim Construction Brief was filed on November 15, 2024, and the Reply Brief is due on December 20, 2024. The claim construction briefing is being coordinated with this PHE analysis to ensure that the arguments presented are consistent and that the Opening Brief does not make concessions or assertions that could inadvertently bolster Lumicore's PHE position. In particular, care has been taken to ensure that OWS's arguments regarding the meaning of "two-dimensional" in the claim construction context are consistent with OWS's position regarding the scope of the narrowing amendment in the PHE context.
III. PROSECUTION HISTORY OF CLAIM 12
A. Initial Filing and Original Claim Language
The application that matured into the '015 Patent was filed on August 30, 2019, as Application No. 16/555,817, claiming the benefit of Provisional Application No. 62/499,117, filed April 7, 2017. The application was filed as a continuation-in-part of Application No. 15/928,344 (which matured into the '193 Patent, U.S. Patent No. 10,891,193) and included new subject matter directed to the polarization-diverse grating coupler designs.
As originally filed, the application included twenty-two claims. The claim that ultimately issued as Claim 12 was originally numbered as Claim 14 in the as-filed application. The original text of Claim 14 (as filed) read as follows:
Original Claim 14 (as filed). The silicon photonic transceiver of claim 10, wherein the polarization-diverse grating coupler comprises a sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal, wherein the sub-wavelength grating is configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state.
The critical difference between the original claim language and the issued claim language is immediately apparent: the original claim referred to a "sub-wavelength grating" without any dimensional modifier. The "two-dimensional" qualifier was added during prosecution by amendment, as discussed in detail below in Section III.C. The original claim language thus encompassed sub-wavelength gratings of any dimensional configuration — one-dimensional, two-dimensional, or any other structural arrangement — so long as the grating had periodically arranged sub-wavelength features with a pitch smaller than the wavelength of the incident optical signal and was configured to diffract the optical signal into two orthogonal waveguide modes.
It bears noting that the original claim depended from original Claim 10, which corresponded to what ultimately issued as independent Claim 8. The renumbering occurred as a result of the cancellation and amendment of intervening claims during prosecution.
B. First Office Action — § 103 Rejection
The examiner issued a non-final Office Action on March 17, 2020 (Application No. 16/555,817). The Office Action rejected Claims 10–18 (including what became Claim 12) under 35 U.S.C. § 103 as obvious over the combination of two prior art references:
Primary Reference — Bergmann (U.S. Patent No. 8,412,007). Bergmann, titled "Sub-Wavelength Grating Coupler for Optical Waveguide," was issued on April 2, 2013, and is directed to a sub-wavelength grating coupler for coupling light between an optical fiber and a silicon photonic waveguide. Bergmann's disclosure is centered on a one-dimensional sub-wavelength grating — that is, a grating with periodic features arranged along a single axis. Bergmann teaches that the sub-wavelength features have a pitch smaller than the wavelength of the optical signal and that the grating achieves efficient light coupling into a silicon waveguide through diffractive effects. However, Bergmann does not disclose a two-dimensional grating structure, nor does it address polarization diversity — Bergmann's grating is designed for single-polarization coupling.
Secondary Reference — Simonsen (PCT/EP2015/071234). Simonsen, titled "Polarization-Diverse Optical Coupling Using Periodic Structures," was published on September 17, 2015, and is directed to a two-dimensional periodic structure for polarization-diverse optical coupling. Simonsen teaches a photonic crystal structure with features arranged in two dimensions that can couple both TE and TM polarization modes from an optical fiber into separate waveguides. However, Simonsen's periodic structure is described as a "photonic crystal" with features that operate on principles of photonic bandgap engineering, rather than as a "sub-wavelength grating" that operates primarily through diffractive coupling.
Examiner's Reasoning. The examiner reasoned as follows in the March 17, 2020 Office Action:
Bergmann disclosed a sub-wavelength grating coupler with periodically arranged sub-wavelength features having a pitch smaller than the wavelength of the incident optical signal, configured to diffract the incident optical signal into a waveguide mode — thereby satisfying the basic structural elements of the claim. The examiner acknowledged that Bergmann did not disclose polarization-diverse coupling or a two-dimensional arrangement of features.
Simonsen disclosed a two-dimensional periodic structure configured to receive an optical signal from an optical fiber and to couple the signal into separate waveguide modes corresponding to orthogonal polarization states. The examiner cited Simonsen as providing the motivation to extend Bergmann's grating coupler to a two-dimensional configuration for the purpose of achieving polarization diversity.
The examiner concluded that it would have been obvious to a person of ordinary skill in the art at the time of the invention to modify Bergmann's sub-wavelength grating coupler by arranging the sub-wavelength features in a two-dimensional configuration, as taught by Simonsen, in order to achieve polarization-diverse coupling of both TE and TM modes — a recognized advantage in the silicon photonics field for improving the reliability and performance of optical transceivers.
Specifically, the examiner mapped the claim limitations as follows:
• "Sub-wavelength grating having a plurality of periodically arranged sub-wavelength features, each sub-wavelength feature having a pitch smaller than the wavelength of the incident optical signal" → Bergmann, Col. 4, ll. 12–35 (one-dimensional sub-wavelength grating with features having sub-wavelength pitch).
• "Configured to diffract the incident optical signal into a first waveguide mode corresponding to a first polarization state and a second waveguide mode corresponding to a second polarization state orthogonal to the first polarization state" → Simonsen, paragraphs [0034]–[0042] (two-dimensional periodic structure splitting TE and TM modes into separate waveguides).
• The combination of Bergmann and Simonsen was alleged to render obvious the claimed sub-wavelength grating configured for polarization-diverse coupling.
The examiner did not reject the claims under § 102 (anticipation), and the § 103 rejection was the sole basis for rejection of the claims relevant to this analysis.
C. Applicant's Response and Narrowing Amendment
On September 15, 2020, the applicant filed a Response to the Office Action through Dr. Martin Chu of Cascade IP Advisors, LLC. The Response included both amendments to the claims and accompanying remarks/arguments.
The Amendment. The applicant amended Claim 14 (later renumbered as Claim 12) by adding the modifier "two-dimensional" before "sub-wavelength grating" in two places within the claim. Specifically, the amendment changed:
• "a sub-wavelength grating having a plurality of periodically arranged sub-wavelength features" → "a two-dimensional sub-wavelength grating having a plurality of periodically arranged sub-wavelength features"
• "wherein the sub-wavelength grating is configured to diffract" → "wherein the two-dimensional sub-wavelength grating is configured to diffract"
No other changes were made to the claim language. The amendment was narrowing in nature: it restricted the claim from covering any sub-wavelength grating (regardless of dimensional configuration) to covering only a two-dimensional sub-wavelength grating.
Applicant's Accompanying Remarks. The applicant's Response included several pages of remarks distinguishing the cited prior art. The remarks relevant to the "two-dimensional" amendment are summarized below, with key passages quoted for accuracy:
Distinguishing Bergmann. The applicant argued that Bergmann taught only a one-dimensional sub-wavelength grating and did not disclose or suggest a two-dimensional arrangement of sub-wavelength features:
> "Bergmann is limited to a one-dimensional sub-wavelength grating structure in which the periodic features are arranged along a single axis. Bergmann does not disclose, teach, or suggest a two-dimensional sub-wavelength grating in which features are periodically arranged along two orthogonal axes. The amended claims recite a 'two-dimensional sub-wavelength grating,' which is not found in Bergmann."
Distinguishing Simonsen. The applicant argued that Simonsen's two-dimensional periodic structure was fundamentally different from the claimed "two-dimensional sub-wavelength grating":
> "While the Examiner cites Simonsen for the teaching of a two-dimensional periodic structure, the Applicant respectfully submits that Simonsen's structure is a photonic crystal operating on principles of photonic bandgap engineering, which is structurally and functionally distinct from the claimed two-dimensional sub-wavelength grating. Simonsen's photonic crystal has different periodicity characteristics — specifically, Simonsen's features are designed to create a photonic bandgap rather than to function as a diffractive grating with sub-wavelength pitch. A person of ordinary skill in the art would not equate Simonsen's photonic crystal structure with a 'sub-wavelength grating' as that term is understood in the art."
Arguing Non-Obviousness of the Combination. The applicant further argued that even if one were to attempt to combine Bergmann and Simonsen, the resulting structure would not yield the specific two-dimensional sub-wavelength grating configuration recited in the amended claims:
> "The combination proposed by the Examiner would not lead to the claimed invention because Bergmann and Simonsen teach fundamentally different structural approaches. Bergmann's one-dimensional grating operates by diffractive coupling, while Simonsen's photonic crystal operates by photonic bandgap effects. Simply extending Bergmann's one-dimensional grating to two dimensions, as the Examiner suggests, would not result in the specific two-dimensional sub-wavelength grating configuration disclosed and claimed in the present application, which achieves polarization-diverse coupling through a carefully designed diffractive mechanism rather than through photonic crystal effects."
Characterization of the Amendment's Purpose. Based on the prosecution remarks, the applicant's stated purpose for adding the "two-dimensional" modifier was twofold: (1) to distinguish the claimed invention from Bergmann by emphasizing that Bergmann's one-dimensional grating did not disclose the claimed two-dimensional arrangement; and (2) to distinguish the claimed invention from Simonsen by arguing that even though Simonsen disclosed a two-dimensional periodic structure, Simonsen's structure was a photonic crystal rather than a sub-wavelength grating and therefore would not be combined with Bergmann to arrive at the claimed two-dimensional sub-wavelength grating.
Notably, the applicant's remarks did not contain any express statement regarding what subject matter was being surrendered by the amendment. The remarks did not address whether the amendment was intended to disclaim all non-two-dimensional sub-wavelength gratings or only to distinguish the specific prior art combination. This silence is significant for the PHE analysis: it provides latitude for OWS to argue that the amendment was narrowly targeted at the Bergmann/Simonsen combination, consistent with the tangential-relation exception under Festo.
Examiner Interview. The prosecution file includes an Examiner Interview Summary dated October 22, 2020, reflecting a telephone interview between Dr. Martin Chu and the examiner. The summary notes that the examiner and applicant discussed the distinction between Simonsen's photonic crystal structure and the claimed sub-wavelength grating. The summary indicates that the examiner "agreed that Simonsen's photonic crystal structure has different periodicity characteristics than the claimed two-dimensional sub-wavelength grating" but does not record any specific discussion of the scope of surrender or the meaning of the "two-dimensional" amendment beyond its role in distinguishing the prior art.
D. Allowance. On December 9, 2020, the examiner issued a Notice of Allowance for Application No. 16/555,817. The examiner's statement of reasons for allowance stated:
> "The prior art of record, alone or in combination, does not disclose or render obvious a silicon photonic transceiver comprising the specific combination of features recited in the allowed claims, including a polarization-diverse grating coupler comprising a two-dimensional sub-wavelength grating configured to diffract an incident optical signal into orthogonal waveguide modes, in combination with the other recited elements including a polarization rotator and a coherent detection module."
The examiner's statement of reasons for allowance cited the "two-dimensional sub-wavelength grating" as one of the distinguishing features but framed the allowance in terms of the overall claim combination rather than identifying the "two-dimensional" amendment as the sole basis for allowance. This is relevant because Festo estoppel applies to amendments made for reasons related to patentability, and the scope of the estoppel depends in part on the relationship between the amendment and the reason for allowance.
Following payment of the issue fee, the patent issued on August 2, 2022, as U.S. Patent No. 11,402,015. At issuance, the claims were renumbered, and original Claim 14 became issued Claim 12.
E. Summary of Amendment Scope
The amendment to Claim 12 narrowed the claim by adding the "two-dimensional" qualifier to the "sub-wavelength grating" limitation. This amendment was made in direct response to the examiner's § 103 rejection combining Bergmann and Simonsen. Because the amendment was made for a reason related to patentability — specifically, to overcome a prior art rejection — the Festo presumption of surrender is triggered.
Scope of the Surrendered Territory. Under Festo, the surrendered territory encompasses the subject matter between the original claim scope and the amended claim scope. Here:
• Original claim scope: "A sub-wavelength grating" — encompassing sub-wavelength gratings of any dimensional configuration, including one-dimensional gratings, two-dimensional gratings, quasi-periodic structures, and any other structural arrangement meeting the basic definition of a "sub-wavelength grating."
• Amended claim scope: "A two-dimensional sub-wavelength grating" — limited to sub-wavelength gratings with features arranged in a two-dimensional periodic configuration.
• Surrendered territory: Sub-wavelength grating couplers that are not "two-dimensional" — including one-dimensional gratings, quasi-periodic structures, structures with dimensional characteristics that fall outside "two-dimensional" as construed, partially-etched angled gratings without uniform two-dimensional periodicity, and other non-two-dimensional structural variations.
The central question for the PHE analysis is whether the specific grating coupler structure used in Lumicore's accused products falls within this surrendered territory and, if so, whether OWS can rebut the Festo presumption by establishing one of the three recognized exceptions.
IV. PROSECUTION HISTORY ESTOPPEL — LEGAL FRAMEWORK
A. Festo Presumption
Under the doctrine of prosecution history estoppel, a patentee who narrows a claim by amendment during prosecution for a reason related to patentability is presumed to have surrendered all equivalents that fall between the original claim scope and the amended claim scope. The seminal articulation of this doctrine is found in Festo Corp. v. Fenmore & Co., 535 U.S. 722 (2002), in which the Supreme Court held that a narrowing amendment creates a presumption that the patentee surrendered the particular equivalent in question, but that this presumption is rebuttable.
The Festo framework operates as follows:
Step 1: Was there a narrowing amendment? The threshold inquiry is whether the patentee made an amendment to the claim during prosecution that narrowed the claim's scope. Festo, 535 U.S. at 736–37. An amendment that adds a limitation to the claim or restricts an existing limitation is a narrowing amendment. Id.
Step 2: Was the amendment made for a reason related to patentability? Not all amendments trigger estoppel — only those made for a "substantial reason related to patentability." Warner-Jenkinson Co. v. Harborline Enterprises Davis Chemical Co., 520 U.S. 17, 33 (1997). Amendments made to overcome prior art rejections under § 102 or § 103 are paradigmatic examples of amendments made for reasons related to patentability. Amendments made for other reasons — such as to comply with formalities or to correct typographical errors — generally do not trigger estoppel. Where the reason for the amendment is ambiguous, the patentee bears the burden of showing that the amendment was not made for a reason related to patentability. Warner-Jenkinson, 520 U.S. at 33.
Step 3: Presumption of surrender. If a narrowing amendment was made for a reason related to patentability, a presumption arises that the patentee surrendered "all territory between the original claim and the amended claim." Festo, 535 U.S. at 740. This presumption operates to bar the patentee from asserting the doctrine of equivalents to recapture the surrendered subject matter.
Step 4: Rebuttal. The presumption is rebuttable. The patentee may overcome the presumption by demonstrating that one of three exceptions applies. Festo, 535 U.S. at 740–41.
In the present case, there is no dispute that Steps 1 and 2 are satisfied. The applicant made a narrowing amendment by adding the "two-dimensional" modifier to the "sub-wavelength grating" limitation. The amendment was made in direct response to the examiner's § 103 rejection — an amendment indisputably made for a reason related to patentability. Accordingly, the Festo presumption of surrender applies, and OWS bears the burden of establishing one of the three recognized exceptions to rebut that presumption.
B. Three Festo Exceptions (Rebuttal)
The Supreme Court in Festo identified three circumstances in which the patentee may rebut the presumption of surrender:
1. Tangential Relation Exception. The patentee may show that "the rationale underlying the amendment [bore] no more than a tangential relation to the equivalent in question." Festo, 535 U.S. at 740–41. This exception recognizes that a patentee who narrows a claim for a specific, limited reason should not be deemed to have surrendered all possible equivalents if the reason for the amendment has no bearing on the particular equivalent at issue. The Federal Circuit, on remand from the Supreme Court, elaborated that the tangential-relation inquiry asks "whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent." Festo Corp. v. Fenmore & Co., 344 F.3d 1359, 1369 (Fed. Cir. 2003) (en banc). In Ridgeway Corporation v. Hamilton Sundstrand Corp., 370 F.3d 1131, 1143 (Fed. Cir. 2004) (en banc), the Federal Circuit further clarified that the tangential-relation exception requires an objective assessment of the relationship between the reason for the amendment and the alleged equivalent, examining the prosecution history from the perspective of a reasonable competitor.
In Ring & Pinion Service, Inc. v. ARB Corp., 743 F.3d 831, 838 (Fed. Cir. 2014), the Federal Circuit emphasized that the tangential-relation analysis is objective rather than subjective — the court looks at the prosecution record to determine whether the amendment was directed at a specific concern that is distinct from the equivalent at issue, rather than relying on the patentee's post hoc characterization of its intent. The court noted that "the inquiry is not what the patentee subjectively intended by the amendment but what a reasonable competitor reviewing the prosecution history would have understood the amendment to mean."
2. Unforeseeability Exception. The patentee may show that "the equivalent was unforeseeable at the time of the amendment." Festo, 535 U.S. at 740. This exception recognizes that a patentee cannot be presumed to have surrendered an equivalent that did not exist or was not foreseeable in the art at the time the amendment was made. The Federal Circuit has interpreted this exception as applying to after-developed technologies or equivalents that were not known in the relevant art at the time of the narrowing amendment. See Festo, 344 F.3d at 1369–70; see also Insituform Techs., Inc. v. Cat Contracting, Inc., 385 F.3d 1360, 1370–71 (Fed. Cir. 2004). The unforeseeability exception is often treated as a companion to, or subset of, the tangential-relation exception, as an unforeseeable equivalent is by definition one that bears no more than a tangential relation to the amendment.
3. "Other Reason" Exception. The patentee may show that "there [was] some other reason suggesting that the patentee could not reasonably be expected to have drafted a claim that literally encompassed the alleged equivalent." Festo, 535 U.S. at 740–41. This is the narrowest of the three exceptions and serves as a catch-all for circumstances not captured by the first two exceptions. The Federal Circuit has applied this exception sparingly, generally requiring the patentee to show that the equivalent represents a technology or design choice that was so far removed from the claim drafter's reasonable contemplation that it would have been unreasonable to expect the drafter to have anticipated and claimed it. See Insituform, 385 F.3d at 1371.
Burden of Proof. The burden of rebutting the Festo presumption falls on the patentee. Festo, 535 U.S. at 740. The patentee must make a "persuasive showing" that one of the three exceptions applies. Id. The Federal Circuit has held that the rebuttal inquiry is a question of law based on the prosecution history, which may be informed by expert testimony and other evidence. Festo, 344 F.3d at 1370. However, where the rebuttal depends on disputed factual issues (such as whether the accused equivalent was foreseeable or whether the prosecution attorney's intent was narrowly directed), those factual disputes may preclude summary judgment and must be resolved by the finder of fact. See Honeywell, 370 F.3d at 1143–44.
Relevant Eastern District of Texas Authority. Judge Gilstrap has addressed Festo estoppel in several prior cases. In DataTern, Inc. v. MicroStrategy, Inc., No. 2:11-cv-00262-JRG (E.D. Tex.), Judge Gilstrap denied summary judgment on PHE where the patentee presented evidence that the amendment was narrowly directed at a specific prior art reference and the accused equivalent was distinguishable from the prior art that prompted the amendment. In Evolved Wireless LLC v. Camberwell & Co., No. 2:15-cv-01565-JRG (E.D. Tex.), however, Judge Gilstrap granted summary judgment on PHE where the prosecution remarks made clear that the amendment was directed broadly at the type of structure employed by the accused infringer. These precedents underscore the importance of the specific prosecution remarks and the factual record in determining whether the Festo exceptions are satisfied.
C. Interplay with Claim Construction
The scope of PHE is intertwined with the construction of the disputed claim terms, particularly "two-dimensional sub-wavelength grating" and "polarization-diverse grating coupler." This interplay operates on multiple levels.
First, the meaning of "two-dimensional" as used in the claim directly defines the boundary between literal infringement and the need for DOE. If "two-dimensional" is construed broadly to encompass structures with features arranged in more than one dimension — including the quasi-two-dimensional structures with angled, varying-etch-depth features found in Lumicore's products — then literal infringement may be established, and DOE (and PHE) become unnecessary. If "two-dimensional" is construed narrowly to require a strictly uniform two-dimensional periodic array, then literal infringement is unlikely and DOE becomes essential.
Second, the scope of the surrendered territory under PHE depends on the construction of both the original claim term ("sub-wavelength grating") and the amended claim term ("two-dimensional sub-wavelength grating"). The broader the construction of the original term and the narrower the construction of the amended term, the larger the surrendered territory — and the more likely it is that the accused equivalent falls within it.
Third, if the Court adopts OWS's broader construction of "polarization-diverse grating coupler" (not requiring "two-dimensional" as a definitional element), the literal-infringement analysis for parent Claim 8 may resolve the issue for the accused products without requiring resort to Claim 12's DOE contentions. In that scenario, the PHE issue becomes moot as a practical matter because the jury could find infringement of Claim 8 on a literal basis, and the additional damages attributable to Claim 12 DOE would be marginal at most.
Conversely, if the Court adopts Lumicore's narrow construction that incorporates "two-dimensional" into the broader "polarization-diverse grating coupler" term, both the literal and DOE paths for Claim 12 narrow, and PHE becomes the central battleground for the DOE theory. However, as noted above, a narrow construction that forecloses literal infringement may paradoxically strengthen the equitable case for DOE, depending on the reasoning underlying the Markman ruling.
Strategy Note: The claim construction briefing (OWS's Opening Brief filed November 15, 2024; Reply Brief due December 20, 2024) must be coordinated with this PHE analysis. OWS's claim construction arguments should not inadvertently concede that the "two-dimensional" limitation carries a broad disclaimer meaning, and the briefing should avoid language suggesting that the amendment was directed at the full breadth of the claim scope rather than at the specific prior art combination. This coordination is essential because Lumicore can be expected to cite OWS's own claim construction briefing in support of its PHE arguments at the summary judgment stage.
V. APPLICATION TO CLAIM 12 OF THE '015 PATENT
A. Identification of the Alleged Equivalent
Based on the Benchmark Semiconductor Analysis, LLC teardown reports (Kevin Ng, LumiLink 800G-DR8, June 2023; LumiEdge 1600G-LR, February 2024), the accused Lumicore products employ a grating coupler with a structural design that differs from the "two-dimensional sub-wavelength grating" as literally claimed. Specifically, both the LumiLink 800G-DR8 and the LumiEdge 1600G-LR incorporate a grating coupler that uses a partially-etched, angled grating with varying etch depths across the coupler area, rather than a strictly uniform two-dimensional periodic array of sub-wavelength features.
The accused structure may be described as follows based on the teardown data:
• The grating coupler includes sub-wavelength features arranged in a pattern that extends in two spatial directions, but the features are not arranged in a strictly periodic two-dimensional array. Instead, the features exhibit a gradient in etch depth from the center of the coupler to its edges, and the features are angled relative to the plane of the silicon device layer.
• The sub-wavelength pitch of the individual features is confirmed by the Benchmark SEM imaging to be smaller than the wavelength of the incident optical signal (approximately 1310 nm for the LumiLink 800G-DR8 and 1550 nm for the LumiEdge 1600G-LR), consistent with the "sub-wavelength" requirement of the claim.
• The grating coupler is configured to couple both TE and TM polarization modes from an optical fiber into separate waveguide channels on the silicon photonic chip, achieving polarization-diverse operation.
• The key structural difference is the varying etch depth and angled feature geometry: rather than using a uniform two-dimensional grid of identical sub-wavelength features (as implied by the literal claim language), the accused structure uses features with non-uniform etch depths that create a three-dimensional profile across the coupler area, combined with angular offsets that control the coupling efficiency and polarization splitting.
Under the function-way-result test for the doctrine of equivalents:
• Function: The accused structure performs the same function as the claimed "two-dimensional sub-wavelength grating" — coupling light of two orthogonal polarization states (TE and TM) from an optical fiber into the silicon photonic integrated circuit.
• Way: The accused structure accomplishes this function in substantially the same way — using a periodic diffractive structure with sub-wavelength pitch elements that interact with the incident light to split it into separate polarization modes. The diffraction mechanism is fundamentally the same; only the specific geometry of the features differs.
• Result: The accused structure achieves substantially the same result — efficient polarization-diverse light coupling with low insertion loss, enabling high-speed coherent optical communication. The Benchmark teardown data indicates insertion losses of approximately 1.8 dB for the LumiLink 800G-DR8 and 1.6 dB for the LumiEdge 1600G-LR, comparable to the performance characteristics of the patented design.
B. Does the Amendment Surrender the Equivalent?
The threshold question under the Festo framework is whether the accused equivalent falls within the territory surrendered by the narrowing amendment — that is, the territory between the original claim ("sub-wavelength grating") and the amended claim ("two-dimensional sub-wavelength grating").
Lumicore's Expected Argument. Lumicore will argue that the accused grating coupler structure falls squarely within the surrendered territory. Specifically, Lumicore will contend that:
• The original claim covered all sub-wavelength gratings, including those with non-two-dimensional geometries.
• The amendment narrowed the claim to cover only "two-dimensional" sub-wavelength gratings, thereby surrendering all sub-wavelength gratings that are not "two-dimensional."
• The accused structure — a partially-etched, angled grating with varying etch depths — is precisely the type of non-two-dimensional (or quasi-two-dimensional) sub-wavelength grating structure that the amendment disclaimed. The varying etch depths and angled features mean that the accused structure does not have the uniform two-dimensional periodicity required by the amended claim, placing it within the surrendered territory.
• Asserting DOE to recapture this surrendered territory is precisely the kind of "recapture" that PHE is designed to prevent.
OWS's Counter-Argument. OWS will argue that the accused structure may not fall within the surrender zone, or at least not squarely within it. This argument has two components:
First, the accused structure is arguably "two-dimensional" by certain metrics. The sub-wavelength features are arranged in a pattern that extends in two spatial directions, even though the features are not arranged in a perfectly uniform two-dimensional periodic array. If "two-dimensional" is construed to require only that features be arranged in two spatial dimensions (rather than requiring strict two-dimensional periodicity), then the accused structure may satisfy the literal claim language, mooting the need for DOE and PHE analysis. This argument is closely tied to the claim construction outcome and will be resolved at the Markman hearing.
Second, even if the accused structure does not satisfy the literal "two-dimensional" limitation, the specific way in which it differs from the claimed structure — through varying etch depths and angular offsets rather than through a fundamentally different dimensional arrangement — may place it at the periphery of the surrender zone rather than at its center. The accused structure is not the same type of non-two-dimensional grating that prompted the amendment (Bergmann's one-dimensional grating); rather, it is a structure that incorporates elements of two-dimensional design but deviates in a distinct geometric parameter. This distinction is relevant to the tangential-relation exception analysis.
Assessment. The risk is moderate-to-high that Lumicore will successfully argue the accused structure falls within the surrendered territory. The amendment clearly drew a line between two-dimensional and non-two-dimensional sub-wavelength gratings, and the accused structure's deviation from strict two-dimensional periodicity places it on the wrong side of that line as a matter of literal claim scope. However, the specific nature of the deviation — varying etch depths and angular features rather than a one-dimensional arrangement — provides a basis for arguing that the accused equivalent is not the type of structure the amendment was designed to disclaim. The strength of this argument depends on the Festo exception analysis that follows.
C. Tangential Relation Exception Analysis
The tangential-relation exception is OWS's strongest rebuttal argument against the Festo presumption. This exception asks whether "the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question." Festo, 535 U.S. at 740–41.
Core Argument. The narrowing amendment adding "two-dimensional" was made for a specific, limited purpose: to distinguish the Bergmann reference, which taught a one-dimensional sub-wavelength grating, and to rebut the examiner's proposed combination of Bergmann with Simonsen. The amendment was not a broad disclaimer of all possible alternative grating coupler geometries. The rationale underlying the amendment was directed at the specific deficiency of the prior art combination — Bergmann's limitation to one-dimensional grating structures — rather than at the general concept of dimensional variations in grating geometry. Because the accused Lumicore structure is neither a Bergmann-type one-dimensional grating nor a Simonsen-type photonic crystal, the rationale for the amendment bears no more than a tangential relation to the accused equivalent.
This argument is supported by the following considerations:
1. The amendment was directed at Bergmann's one-dimensional grating. The prosecution remarks make clear that the primary purpose of adding "two-dimensional" was to distinguish Bergmann. The applicant stated that "Bergmann is limited to a one-dimensional sub-wavelength grating structure" and that "the amended claims recite a 'two-dimensional sub-wavelength grating,' which is not found in Bergmann." This language shows that the amendment was targeted at the specific structural deficiency of Bergmann (its limitation to one dimension), not at broadly defining the outer boundary of the claim scope for all possible grating configurations.
2. Lumicore's accused structure is not a Bergmann-type one-dimensional grating. The accused grating coupler in the LumiLink 800G-DR8 and LumiEdge 1600G-LR is structurally distinct from the Bergmann reference. Bergmann's one-dimensional grating has features arranged along a single axis in a uniform, periodic one-dimensional pattern. Lumicore's accused structure, by contrast, has features arranged in two spatial directions with varying etch depths and angular offsets — a fundamentally different design approach that shares no structural resemblance with Bergmann. The accused structure is not the type of non-two-dimensional grating that the amendment was designed to distinguish.
3. The applicant distinguished Simonsen on structural (not dimensional) grounds. The applicant's remarks distinguished Simonsen by arguing that Simonsen's periodic structure was a "photonic crystal" rather than a "sub-wavelength grating" — a structural distinction, not a dimensional one. The applicant stated that "Simonsen's photonic crystal has different periodicity characteristics" and that "a person of ordinary skill in the art would not equate Simonsen's photonic crystal structure with a 'sub-wavelength grating.'" This language indicates that the applicant was not using the "two-dimensional" modifier to broadly disclaim all non-two-dimensional structures; rather, the applicant's arguments were directed at the specific structural characteristics of the cited references.
4. A POSITA would understand the amendment as narrowly directed. From the perspective of a reasonable competitor reviewing the prosecution history — the relevant perspective under Ring & Pinion, 743 F.3d at 838 — the amendment would be understood as responding to the specific Bergmann/Simonsen combination rather than as a sweeping disclaimer. The prosecution exchange was focused on two specific references, and the applicant's arguments were targeted at the deficiencies of those references. A reasonable competitor would not read the amendment as surrendering all possible grating coupler geometries that deviate from strict two-dimensional periodicity.
Risk Assessment. The tangential-relation argument has a reasonable probability of success if properly developed with prosecution-attorney testimony and expert support. The Federal Circuit has recognized that amendments narrowly targeted at specific prior art may leave room for equivalents that were not the focus of the prosecution dialogue. See Honeywell, 370 F.3d at 1143 (noting that the tangential-relation exception "prevents the doctrine of prosecution history estoppel from becoming an impenetrable barrier to the doctrine of equivalents in all cases involving narrowing amendments"). However, the analysis is fact-intensive and depends on the precise characterization of the accused structure relative to the surrendered territory. The risk is that a court could conclude that the "two-dimensional" amendment was not merely directed at Bergmann's one-dimensional grating but was a deliberate choice to limit the claim to two-dimensional structures, with the intent of distinguishing any non-two-dimensional alternative.
Supporting Evidence Needed. To maximize the probability of success on the tangential-relation exception, OWS should develop the following evidence:
• Declaration from Dr. Martin Chu (Cascade IP Advisors). Dr. Chu, as the prosecution attorney who drafted the amendment, is uniquely positioned to testify regarding the specific intent behind adding "two-dimensional." While the objective analysis under Ring & Pinion focuses on the prosecution record rather than subjective intent, Dr. Chu's testimony can provide context for the amendment and support the narrative that it was narrowly directed at the Bergmann/Simonsen combination. Dr. Chu should be asked to confirm that the amendment was made specifically to distinguish Bergmann's one-dimensional grating and to address the examiner's proposed combination, and that there was no intent to broadly disclaim all non-two-dimensional grating structures.
• Expert testimony from Dr. Caroline Ashford. Dr. Ashford, as OWS's technical expert, should testify regarding how a POSITA would understand the amendment in the context of the prosecution history. Specifically, she should explain: (a) the structural differences between Bergmann's one-dimensional grating, Simonsen's photonic crystal, the claimed two-dimensional sub-wavelength grating, and Lumicore's accused partially-etched angled grating; (b) why a POSITA would understand the amendment as directed specifically at Bergmann's one-dimensional structure rather than as a broad disclaimer of all non-two-dimensional configurations; and (c) why the accused Lumicore structure is not the type of equivalent that the amendment was designed to surrender.
• Analysis of the prosecution record. A detailed analysis of the prosecution record — including the Office Action, the applicant's Response, the Examiner Interview Summary, and the Notice of Allowance — should be compiled to demonstrate that t

PROSECUTION HISTORY ESTOPPEL ANALYSIS

I. EXECUTIVE SUMMARY

II. BACKGROUND

III. PROSECUTION HISTORY OF CLAIM 12

V. APPLICATION TO CLAIM 12 OF THE '015 PATENT

Record

Parties

Dates

Amounts