PRIVILEGED AND CONFIDENTIAL — ATTORNEY-CLIENT COMMUNICATION / ATTORNEY WORK PRODUCT
FREEDOM-TO-OPERATE ANALYSIS
Optiwave Semiconductor Corp. Commercial Silicon-Photonic Mach-Zehnder Modulator Products vs. Pinnacle Optics, Inc. Patent Family
(U.S. Patent Nos. 10,823,417 and 11,105,662)
Prepared by:
CALDERWOOD & HARKNESS LLP 555 California Street, 42nd Floor San Francisco, CA 94104
Authors: Catherine Bloom, Partner Intellectual Property Group USPTO Reg. No. 58,412
Christy Bauer, Associate Intellectual Property Group USPTO Reg. No. 74,329
Date: October 14, 2022
C&H Matter No.: 1014-00005
ADDRESSEES:
Marcus Whitfield, Esq. General Counsel Optiwave Semiconductor Corp. 4710 Ridgeview Parkway, Suite 300 Santa Clara, CA 95054
Sandra Koh, Esq. IP Manager / In-House Patent Counsel Optiwave Semiconductor Corp. 4710 Ridgeview Parkway, Suite 300 Santa Clara, CA 95054
This memorandum constitutes a privileged and confidential attorney-client communication and attorney work product prepared by Calderwood & Harkness LLP for the exclusive use of Optiwave Semiconductor Corp. It is protected from disclosure by the attorney-client privilege and the work-product doctrine. This document should not be disclosed to any third party without the prior written consent of both Optiwave Semiconductor Corp. and Calderwood & Harkness LLP.
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I. EXECUTIVE SUMMARY
At the request of Marcus Whitfield, General Counsel, and Sandra Koh, IP Manager and In-House Patent Counsel, of Optiwave Semiconductor Corp. ("OWS" or the "Company"), Calderwood & Harkness LLP ("C&H") has conducted a comprehensive freedom-to-operate ("FTO") analysis evaluating whether OWS's current and planned commercial silicon-photonic Mach-Zehnder modulator products designed for 800G and 1.6T data-center optical transceiver applications may infringe any valid claim of the patent family held by Pinnacle Optics, Inc. ("Pinnacle"), a primary competitor in the silicon-photonics modulator space.
This analysis was commissioned as part of C&H's broader patent prosecution strategy mandate for OWS, with the objective of informing claim drafting, continuation strategy, and product development decisions relating to the pending patent application family derived from Provisional Application No. 63/297,841. The analysis is also intended to support OWS's internal decision-making regarding the allocation of engineering resources to design-around efforts and to inform discussions with the Company's majority equity holder, Harborview Partners ("Veltrano"), and its senior secured lender, Meridian National Bank, N.A. ("Meridian"), regarding the strategic importance of the Company's intellectual property portfolio.
Scope of Analysis. This FTO analysis is focused on two issued U.S. utility patents assigned to Pinnacle Optics, Inc., a Delaware corporation headquartered at 7200 Gateway Boulevard, Newark, CA 94560:
• U.S. Patent No. 10,823,417 ("the '417 patent"), titled "Silicon-Photonic Mach-Zehnder Modulator with Segmented Traveling-Wave Electrode Architecture and Impedance-Matched Multi-Channel Configuration," issued November 3, 2020; and
• U.S. Patent No. 11,105,662 ("the '662 patent"), titled "Method and Apparatus for Fabricating Segmented Traveling-Wave Electrodes on Silicon-Photonic Substrates for High-Bandwidth Optical Modulation," issued August 31, 2021.
Both patents are assigned to Pinnacle Optics, Inc. and share a common specification disclosure. The analysis is limited to U.S. patent rights and does not address foreign counterparts, pending Pinnacle applications (except as noted in the competitive landscape discussion), trade secret claims, or other forms of intellectual property.
Summary Conclusion. Based on our detailed element-by-element claim analysis, which is set forth in full below, it is our assessment that OWS's commercial products as currently designed and manufactured present a "moderate-to-high" risk of infringement of Pinnacle's '417 patent, and a somewhat lesser but still meaningful "moderate" risk of infringement of the '662 patent. The primary source of risk is the substantial overlap between OWS's current segmented traveling-wave electrode geometry and the corresponding structural and impedance-related claim elements of the '417 patent's independent claims. Without modification to OWS's current electrode design, the Company faces meaningful exposure to an infringement assertion by Pinnacle.
The infringement risk analysis changes materially, however, when applied to the next-generation modulator architecture currently under development by OWS's engineering team, led by Dr. Lena Strickland (VP Engineering) and Dr. Feng-Yi Chen (Principal Engineer). That architecture incorporates a "tapered impedance-matching" design feature in the traveling-wave electrode structure that, in our assessment, falls outside the scope of the Pinnacle patent claims as properly construed. With the tapered impedance-matching design-around fully implemented in OWS's commercial products, the risk of literal infringement is substantially reduced to "low," and the risk under the doctrine of equivalents is assessed as "low-to-moderate."
Key Recommendation. C&H strongly recommends the aggressive prosecution of OWS's pending patent application family, consisting of twelve (12) applications across three sub-families (A, B, and C) derived from Provisional Application No. 63/297,841, filed January 10, 2022. The applications in Sub-Family A, in particular Application A1 (U.S. Application No. 17/672,204) and Application A3 (U.S. Application No. 17/672,489, a continuation-in-part), are of critical strategic importance because they specifically claim the tapered impedance-matching design-around architecture. If these applications mature into issued patents, OWS will secure a defensive patent position that both (i) demonstrates that the tapered impedance-matching design constitutes a distinct and separately patentable invention, thereby supporting non-infringement arguments against Pinnacle, and (ii) provides meaningful leverage in any future cross-licensing negotiation with Pinnacle. The abandonment of Application A1 would result in the irrevocable loss of the ability to obtain claims covering the tapered impedance-matching design-around, leaving OWS exposed to Pinnacle's infringement assertions without any defensive patent shield.
Note on Privilege. This memorandum constitutes a privileged attorney-client communication and attorney work product within the meaning of the attorney-client privilege and the work-product doctrine as recognized under federal and California law. It is prepared solely for the use of OWS and its authorized representatives. This memorandum should not be disclosed to any third party — including Veltrano Capital, Meridian National Bank, Graystone Valuation Advisors, or any other entity — without prior consultation with C&H regarding the potential implications of such disclosure for the preservation of privilege.
II. SCOPE AND LIMITATIONS
A. Scope of Analysis
Products Analyzed. This FTO analysis evaluates OWS's multi-channel silicon-photonic Mach-Zehnder modulator products designed for 800G and 1.6T data-center optical transceiver applications. The analysis encompasses both (i) OWS's currently shipping product lines, including the OWS-800G-MZM Series (comprising the OWS-800G-MZM-4 four-channel modulator and the OWS-800G-MZM-8 eight-channel modulator) and the OWS-1.6T-MZM Series (currently in qualification stage), and (ii) the next-generation designs incorporating the tapered impedance-matching architecture that are in active development. The analysis addresses these products as designed, manufactured, sold, offered for sale, and used within the United States.
Patents Analyzed. This analysis is limited to the following two issued U.S. utility patents:
• U.S. Patent No. 10,823,417, issued November 3, 2020, assigned to Pinnacle Optics, Inc.
• U.S. Patent No. 11,105,662, issued August 31, 2021, assigned to Pinnacle Optics, Inc.
The analysis is confined to U.S. patent rights under 35 U.S.C. § 271. No analysis has been conducted with respect to foreign counterpart patents or applications in any jurisdiction, including without limitation European Patent Office, Japan Patent Office, Korean intellectual Property Office, or China National intellectual Property Administration filings. Similarly, this analysis does not address pending Pinnacle patent applications (whether published or unpublished), except to the extent discussed in Section IX.A below regarding competitive monitoring. No analysis of trade secrets, copyrights, trademarks, or any other form of intellectual property right has been conducted.
Basis of Product Information. Our analysis of OWS's products and technology is based upon the following materials and information sources, which were made available to C&H during August and September 2022:
(a) Technical specifications and product data sheets for the OWS-800G-MZM-4, OWS-800G-MZM-8, and OWS-1.6T-MZM product families, as provided by Dr. Lena Strickland, VP Engineering;
(b) Engineering drawings and CAD files for the segmented traveling-wave electrode architecture, including both the current-generation design and the next-generation tapered impedance-matching design, as provided by Dr. Feng-Yi Chen, Principal Engineer;
(c) Fabrication process documentation, including process design kits (PDKs), photomask layouts, and fabrication process flow documents, as provided by Dr. Chen;
(d) Design review materials from internal engineering design reviews conducted in June, July, and August 2022, as provided by Dr. Strickland;
(e) Discussions and technical interviews conducted with Dr. Rajan Menon (CEO and named inventor on the pending OWS application family), Dr. Lena Strickland, Dr. Feng-Yi Chen, and Dr. Arjun Dasgupta (Senior Design Engineer and named inventor), during meetings held at OWS's Santa Clara headquarters on August 8, 2022, August 22, 2022, and September 12, 2022; and
(f) Provisional Application No. 63/297,841 and the specifications of the twelve pending non-provisional and PCT applications in the OWS family.
We have relied upon the accuracy and completeness of the materials and information provided by OWS. C&H has not independently verified the technical specifications or fabrication details of OWS's products and has assumed that the materials provided accurately reflect the products as designed, manufactured, and sold.
B. Limitations and Caveats
Standard FTO Limitations. This freedom-to-operate analysis is subject to the following standard limitations, which apply to all patent infringement risk assessments:
(a) Claim construction. The claim constructions adopted in this analysis represent C&H's best assessment of the proper construction of the relevant patent claims under the governing legal standards. No court or tribunal has construed the claims of the '417 or '662 patents, and a court or the Patent Trial and Appeal Board ("PTAB") may adopt different constructions that could broaden or narrow the scope of the claims. In particular, claim construction is inherently fact-intensive and may be influenced by evidence not available to C&H, including expert testimony, deposition testimony of the named inventors, and other extrinsic evidence.
(b) Presumption of validity. Under 35 U.S.C. § 282, issued patents are presumed valid. While we have identified certain prior art references and potential invalidity arguments (discussed in Section VIII below), these do not alter the fundamental infringement risk assessment. An invalidity defense requires proof by clear and convincing evidence, which is a demanding standard.
(c) Current claim scope. This analysis reflects the scope of the '417 and '662 patents as currently issued and does not account for potential changes resulting from continuation prosecution, reissue proceedings, ex parte reexamination, or inter partes review proceedings that Pinnacle may initiate or that may otherwise affect the scope of these patents in the future.
(d) Undisclosed pending applications. As of the date of this analysis, Pinnacle may have pending patent applications that have not yet been published under 35 U.S.C. § 122(b). Claims in such unpublished applications cannot be assessed until publication or issuance.
No Opinion on Willfulness. This analysis does not constitute an opinion of counsel for purposes of establishing or negating willful infringement under 35 U.S.C. § 284 or Halo Electronics, Inc. v. Pulse Electronics, Inc., 579 U.S. 93 (2016). Although a competent FTO analysis obtained prior to undertaking potentially infringing activity may be relevant to a willfulness inquiry, the legal standards for willfulness opinions differ from those applicable to this FTO analysis. If OWS desires a formal opinion of counsel regarding willfulness, C&H can prepare such an opinion as a separate engagement.
Pinnacle Prosecution Activity. C&H is aware that Pinnacle's outside patent counsel, Cavanaugh Holt & Sayer LLP (1300 I Street NW, Suite 900, Washington, DC 20005; lead partner Grant Sayer, USPTO Reg. No. 46,715), is actively prosecuting continuation applications from the same patent family as the '417 and '662 patents. While C&H has reviewed published prosecution files available through the USPTO's Public PAIR and Patent Center systems as of the date of this analysis, we cannot assure that all pending applications have been identified, particularly any applications filed within the eighteen-month pre-publication window. New claims issuing from continuation applications may materially alter the infringement risk analysis set forth herein. OWS should continue to monitor Pinnacle's prosecution docket on a regular basis. Pinnacle's VP of intellectual Property, Howard Raines, has been identified as the primary decision-maker within Pinnacle regarding patent prosecution strategy and enforcement, and his known aggressive posture in these matters warrants heightened vigilance.
Temporal Limitation. This analysis is current as of October 14, 2022. Any changes in the facts — including modifications to OWS's product designs, new Pinnacle patent issuances, claim construction developments in related litigation, or changes in controlling case law — may affect the conclusions reached herein. C&H recommends periodic updating of this analysis, and we are prepared to provide supplemental opinions as circumstances warrant.
III. BACKGROUND
A. Optiwave Semiconductor Corp. — Company Overview
Optiwave Semiconductor Corp. ("OWS" or the "Company") is a Delaware corporation, Delaware Secretary of State File No. 7284931, incorporated on April 12, 2017. The Company is registered to do business in the State of California, California Secretary of State Entity No. C4195872, and holds Employer Identification Number 83-2947105. OWS is headquartered at 4710 Ridgeview Parkway, Suite 300, Santa Clara, CA 95054.
OWS is a fabless semiconductor company specializing in high-speed photonic integrated circuit ("PIC") technology for data-center interconnects. The Company's core product line consists of silicon-photonic Mach-Zehnder modulator chips designed for integration into 800G and 1.6T optical transceiver modules used in hyperscale and enterprise data-center environments. As a fabless company, OWS designs and develops its modulator products in-house but outsources fabrication to third-party foundries with silicon-photonics process capabilities. The Company currently employs approximately 185 full-time employees, with the majority concentrated in engineering, product development, and applications engineering roles at its Santa Clara headquarters.
For the fiscal year ended December 31, 2022, OWS reported revenue of approximately $68.1 million. The vast majority of this revenue — approximately 87% — is attributable to sales of the Company's silicon-photonic modulator product families, underscoring the Company's dependence on the modulator product line that is the subject of this FTO analysis.
Existing IP Portfolio. As of the date of this analysis, OWS holds a portfolio of thirty-one (31) issued U.S. utility patents. These patents were prosecuted by OWS's prior outside patent counsel, Kessler & Morin LLP ("K&M"), of McLean, Virginia (lead partner Dr. Helen Kessler, USPTO Reg. No. 41,806). K&M handled OWS's patent prosecution from the Company's inception in 2017 through 2021. The issued patents cover various aspects of silicon-photonic modulator design, electrode architecture, fabrication processes, and transceiver integration.
In addition to the issued portfolio, OWS has twelve (12) pending U.S. and international patent applications, which are currently prosecuted by C&H and which form the subject of the prosecution strategy discussion in this analysis. The Company also has four (4) PCT international applications currently pending, likewise prosecuted by C&H. The pending application family is derived from Provisional Application No. 63/297,841, filed January 10, 2022 by K&M shortly before the transition of prosecution responsibilities to C&H.
Ownership Structure. OWS is majority-owned by Harborview Partners, a Delaware limited partnership with offices at 200 Lexington Avenue, 38th Floor, New York, NY 10016. Veltrano acquired its 72% equity stake in OWS in 2019 through a leveraged recapitalization valued at approximately $310 million enterprise value. The remaining equity is held by OWS's founders and management team, including Dr. Rajan Menon (CEO), Dr. Lena Strickland (VP Engineering), and other senior employees, primarily through vested and unvested equity awards under OWS's 2017 Equity Incentive Plan. Veltrano's investment thesis centered on OWS's proprietary silicon-photonic modulator technology and the anticipated growth of the 800G/1.6T optical transceiver market in hyperscale data centers.
B. Pinnacle Optics, Inc. — Competitor Overview
Pinnacle Optics, Inc. ("Pinnacle") is a Delaware corporation headquartered at 7200 Gateway Boulevard, Newark, CA 94560. Pinnacle is OWS's primary competitor in the silicon-photonics modulator space, and the two companies compete directly for design wins at major optical transceiver module manufacturers and hyperscale data-center operators.
Pinnacle holds a substantial patent portfolio in the silicon-photonics domain, including the two patents that are the subject of this FTO analysis. The '417 and '662 patents form part of a broader patent family that Pinnacle has been building through systematic prosecution efforts. Pinnacle's VP of intellectual Property, Howard Raines, is known within the industry for maintaining an aggressive patent prosecution and enforcement posture. Pinnacle's outside patent counsel, Cavanaugh Holt & Sayer LLP (1300 I Street NW, Suite 900, Washington, DC 20005; lead partner Grant Sayer), is a well-regarded patent prosecution and litigation firm with significant experience in the semiconductor and photonics sectors.
Pinnacle's enforcement posture is of particular concern to OWS. While Pinnacle has not, as of the date of this analysis, initiated any demand, licensing overture, or litigation against OWS, Pinnacle has been involved in patent enforcement actions against other participants in the silicon-photonics industry, and the competitive overlap between Pinnacle and OWS in the 800G/1.6T modulator market makes a future assertion reasonably foreseeable.
C. OWS Commercial Products Under Analysis
The OWS products under analysis in this FTO are the Company's multi-channel silicon-photonic Mach-Zehnder modulator integrated circuits, which serve as the core active photonic component in 800G and 1.6T optical transceiver modules for data-center interconnect applications.
Architecture Overview. OWS's modulator products employ a Mach-Zehnder interferometer ("MZI") architecture fabricated on a silicon-on-insulator ("SOI") photonic platform. In this architecture, an input optical signal is split into two waveguide arms, one or both of which are modulated by an applied electrical signal that changes the refractive index of the waveguide material through the plasma dispersion effect. The modulated optical signals are then recombined at the output, and constructive or destructive interference between the two arms produces amplitude modulation of the output optical signal. This basic MZI modulation architecture is the foundation of high-speed optical data transmission in modern data-center environments.
Key Technical Features. The distinguishing technical features of OWS's modulator products, which are most relevant to this FTO analysis, include the following:
(a) Segmented traveling-wave electrode design. Rather than employing a single continuous electrode to drive the phase modulation in each MZI arm, OWS's current-generation products use a segmented traveling-wave electrode architecture in which the electrode is divided into a plurality of discrete segments, each driven by a separate electrical driver signal. This segmented design enables higher modulation bandwidth and improved electro-optic efficiency compared to continuous electrode designs, but it also implicates the claim coverage of the Pinnacle '417 patent.
(b) Multi-channel integration. OWS's products integrate multiple modulator channels (four channels for the OWS-800G-MZM-4 product and eight channels for the OWS-800G-MZM-8 product) on a single silicon-photonic chip, enabling compact, high-density transceiver designs. The multi-channel integration is a key product differentiator for OWS, but it also corresponds to a claimed feature in the Pinnacle patents.
(c) High-bandwidth modulation. OWS's products are designed to support modulation rates sufficient for 800G and 1.6T data rates using advanced modulation formats such as PAM-4 (pulse amplitude modulation, four-level). Achieving these data rates requires modulation bandwidths in excess of 50 GHz per channel, which drives the need for the segmented traveling-wave electrode architecture.
Current Product Generation and Pinnacle Overlap. The critical observation underlying this FTO analysis is that OWS's current-generation electrode segmentation geometry — specifically, the number, dimensions, and impedance characteristics of the electrode segments — exhibits substantial overlap with the structural features claimed in Pinnacle's '417 patent. As described in detail in Section VI below, each independent claim element of the '417 patent appears to be met by OWS's current product design.
Next-Generation Design-Around. Recognizing the infringement risk posed by the Pinnacle patent family, OWS's engineering team, under the direction of Dr. Rajan Menon (CEO), has developed a next-generation modulator architecture incorporating a "tapered impedance-matching" feature in the traveling-wave electrode design. This design-around, which was conceived and developed by Dr. Lena Strickland, Dr. Feng-Yi Chen, and Dr. Arjun Dasgupta, replaces the uniform (constant) impedance profile across electrode segments — a hallmark of both the Pinnacle architecture and OWS's current design — with a graduated, tapered impedance profile that varies along the length of the electrode. The tapered design offers both technical performance advantages (improved impedance matching with the driver circuitry over a broader frequency range) and, critically, structural differentiation from the Pinnacle claimed architecture. The design-around is the subject of the pending patent applications in Sub-Family A and is analyzed in detail in Section VII below.
D. Engagement Context
C&H's engagement by OWS was initiated in early 2022 in connection with the transition of the Company's patent prosecution activities from Kessler & Morin LLP. The engagement letter was executed on February 10, 2022 and countersigned by Marcus Whitfield, General Counsel. The engagement was formally opened on February 14, 2022, under C&H Matter No. 1014-00005.
The transition from K&M to C&H was driven by OWS's desire to consolidate its patent prosecution and IP strategy work with a single firm having both deep prosecution expertise in the semiconductor and photonics arts and the litigation capabilities necessary to address the growing competitive threat from Pinnacle's patent portfolio. K&M had ably handled OWS's patent prosecution from the Company's founding in 2017 through 2021 and was responsible for obtaining all thirty-one issued U.S. utility patents in OWS's portfolio.
Shortly before the transition, K&M filed Provisional Application No. 63/297,841 on January 10, 2022, titled "Multi-Channel Silicon-Photonic Mach-Zehnder Modulator with Segmented Traveling-Wave Electrode Architecture." This provisional application disclosed the tapered impedance-matching design-around and forms the priority basis for the twelve-application family now under C&H's prosecution. C&H assumed responsibility for all non-provisional and PCT filings derived from the provisional.
This FTO analysis was commissioned as part of C&H's broader patent prosecution strategy mandate for OWS. The analysis is intended to serve several interrelated purposes: (i) to inform the claim drafting and continuation strategy for the pending application family, ensuring that OWS's claims are drafted to maximize differentiation from the Pinnacle patents while securing the broadest available coverage for the tapered impedance-matching design; (ii) to assess the infringement risk posed by OWS's current commercial products, enabling informed product development and engineering resource allocation decisions; and (iii) to support OWS's discussions with its stakeholders regarding the strategic importance of the Company's IP portfolio and the necessity of continued investment in patent prosecution.
IV. PATENTS UNDER ANALYSIS
A. U.S. Patent No. 10,823,417
1. Bibliographic Data
Title: Silicon-Photonic Mach-Zehnder Modulator with Segmented Traveling-Wave Electrode Architecture and Impedance-Matched Multi-Channel Configuration
Patent Number: 10,823,417
Issue Date: November 3, 2020
Filing Date: March 22, 2018 (non-provisional); claims priority to Provisional Application No. 62/475,218, filed March 23, 2017
Assignee: Pinnacle Optics, Inc.
Named Inventors: Dr. Raymond K. Ishida, Dr. Nadia L. Volkov, Dr. Tomohiro Sato, and Dr. Priya Ranganathan
Number of Claims: 22 total claims, of which 3 are independent (Claims 1, 12, and 19)
U.S. Classification: H04B 10/50 (Transmitters); G02F 1/225 (Electro-optic modulators)
References Cited: 47 references (28 U.S. patents, 8 foreign patents, 11 non-patent literature references)
Examiner: Michael J. Radigan, Art Unit 2872
2. Summary of Disclosed Technology
The '417 patent discloses a silicon-photonic Mach-Zehnder modulator employing a segmented traveling-wave electrode architecture designed for high-speed optical modulation in data-center optical transceiver applications. The specification describes the modulator as fabricated on a silicon-on-insulator (SOI) photonic platform, with the Mach-Zehnder interferometer structure formed in the silicon waveguide layer and the traveling-wave electrodes formed in overlying metal layers.
The core innovation disclosed in the '417 patent is the segmented traveling-wave electrode design, in which the electrode is divided into a plurality of discrete segments arranged along the optical waveguide. According to the specification, each electrode segment is characterized by a substantially uniform impedance value, and the segments are arranged such that the impedance is matched across the multi-segment electrode to maintain signal integrity and minimize reflections at high modulation frequencies. The specification describes the impedance matching as being achieved through uniform segment geometry, including substantially equal segment lengths, widths, and spacings, such that the characteristic impedance of each segment is within a specified tolerance range (e.g., 45-55 ohms) of a target impedance value (e.g., 50 ohms).
The specification further discloses a multi-channel modulator configuration in which a plurality of Mach-Zehnder modulator channels are integrated on a single silicon-photonic chip, each channel having its own segmented traveling-wave electrode structure. The multi-channel arrangement enables high-aggregate-bandwidth modulation for 400G, 800G, and higher data rates using wavelength-division multiplexing (WDM) or parallel lane architectures.
The specification includes detailed descriptions of electrode segment dimensions (lengths ranging from 200 micrometers to 2 millimeters, widths from 3 to 30 micrometers), impedance values (target 50 ohms with 10% tolerance), and performance parameters (modulation bandwidths exceeding 50 GHz per channel). The specification also describes fabrication methods, including standard CMOS-compatible photolithographic patterning and metal deposition techniques.
3. Independent Claim Analysis
The '417 patent includes three independent claims: Claims 1, 12, and 19. Each is reproduced below with key elements identified.
Claim 1 (apparatus claim directed to the modulator structure):
A silicon-photonic Mach-Zehnder modulator comprising:
(a) a silicon-on-insulator substrate comprising a silicon device layer, a buried oxide layer, and a silicon handle layer;
(b) a Mach-Zehnder interferometer structure formed in the silicon device layer, the Mach-Zehnder interferometer structure comprising an input optical splitter, a first waveguide arm, a second waveguide arm, and an output optical combiner;
(c) a segmented traveling-wave electrode disposed along at least one of the first waveguide arm and the second waveguide arm, the segmented traveling-wave electrode comprising a plurality of electrode segments arranged in series along a direction of optical propagation, wherein each electrode segment has a characteristic impedance within a range of 45 ohms to 55 ohms and adjacent electrode segments are separated by inter-segment gaps having a gap length of between 5 micrometers and 50 micrometers;
(d) an impedance-matching network associated with the segmented traveling-wave electrode, wherein the impedance-matching network is configured to maintain a substantially uniform impedance profile across the plurality of electrode segments such that the variation in characteristic impedance among the plurality of electrode segments is no greater than 10% of a target impedance value; and
(e) a multi-channel arrangement comprising at least four Mach-Zehnder modulator channels integrated on the silicon-on-insulator substrate, each channel comprising a respective Mach-Zehnder interferometer structure and a respective segmented traveling-wave electrode.
The key elements of Claim 1, for purposes of this FTO analysis, are:
• Element (a): Silicon-on-insulator substrate — This is a platform-level limitation that is met by substantially all silicon-photonic modulators fabricated on SOI wafers.
• Element (b): Mach-Zehnder interferometer structure — This is a standard MZI configuration that is likewise met by the basic architecture of OWS's products.
• Element (c): Segmented traveling-wave electrode — This element defines the core structural feature of the Pinnacle invention, specifying segmented electrodes with per-segment impedance within a 45-55 ohm range and inter-segment gap lengths of 5-50 micrometers. This is the element of greatest concern for OWS.
• Element (d): Impedance-matching network with substantially uniform impedance profile — This element specifies that the impedance profile across the electrode segments must be "substantially uniform," with no more than 10% variation. This is the element that the tapered impedance-matching design-around is intended to address.
• Element (e): Multi-channel arrangement with at least four channels — This element requires integration of at least four modulator channels on a single chip, which OWS's products satisfy.
Claim 12 (apparatus claim directed to the electrode structure in greater detail):
A multi-channel optical modulator device for high-speed data-center optical interconnect applications, the device comprising:
(a) a photonic integrated circuit fabricated on a silicon-on-insulator wafer;
(b) a plurality of Mach-Zehnder modulator channels, each channel comprising a pair of optical waveguide arms formed in a silicon device layer of the silicon-on-insulator wafer;
(c) for each of the plurality of Mach-Zehnder modulator channels, a segmented traveling-wave electrode structure comprising at least six electrode segments arranged in series along a respective optical waveguide arm, each electrode segment having a length in the range of 200 micrometers to 2 millimeters and a width in the range of 3 micrometers to 30 micrometers;
(d) a uniform impedance-matching configuration for each segmented traveling-wave electrode structure, wherein each electrode segment has a characteristic impedance of approximately 50 ohms with a tolerance of no greater than plus or minus 5 ohms; and
(e) electrical interconnections coupling each electrode segment to a respective driver circuit output, the electrical interconnections configured to minimize parasitic inductance and capacitance.
Claim 12 is narrower than Claim 1 in several respects. It specifies at least six electrode segments (versus the open-ended "plurality" in Claim 1), defines specific dimensional ranges for segment length and width, and requires individual driver circuit outputs for each electrode segment. The "uniform impedance-matching configuration" limitation in element (d) of Claim 12 parallels the "substantially uniform impedance profile" limitation in element (d) of Claim 1, further emphasizing the uniformity requirement in the Pinnacle claims.
Claim 19 (method claim directed to operation of the modulator):
A method of modulating an optical signal for high-speed data transmission, the method comprising:
(a) providing a silicon-photonic Mach-Zehnder modulator having a segmented traveling-wave electrode comprising a plurality of electrode segments disposed along a waveguide arm of a Mach-Zehnder interferometer structure, the plurality of electrode segments having a substantially uniform impedance profile;
(b) applying a plurality of electrical drive signals to the plurality of electrode segments, each electrical drive signal being applied to a respective electrode segment with a predetermined time delay corresponding to the propagation velocity of an optical signal in the waveguide arm;
(c) modulating the optical signal propagating through the waveguide arm by the plasma dispersion effect induced by the plurality of electrical drive signals; and
(d) combining the modulated optical signal with a reference optical signal from a second waveguide arm of the Mach-Zehnder interferometer structure to produce an amplitude-modulated output optical signal.
Claim 19 is a method claim that recites the operational use of a modulator having the claimed segmented electrode structure with a "substantially uniform impedance profile." To the extent OWS's products are designed to be operated in the manner described in this claim — which is their intended and ordinary use — this method claim presents an independent basis for infringement liability under 35 U.S.C. § 271(a) (direct infringement by OWS's customers) and potentially § 271(b) or (c) (induced or contributory infringement by OWS).
4. Dependent Claim Analysis
The nineteen dependent claims of the '417 patent (Claims 2-11, 13-18, and 20-22) further narrow the independent claims by specifying additional structural, dimensional, material, fabrication, and performance limitations. Key dependent claims include:
• Claim 2 (dependent on Claim 1): Specifies that the plurality of electrode segments comprises between 6 and 24 segments.
• Claim 3 (dependent on Claim 1): Specifies that each electrode segment has a length of approximately 500 micrometers.
• Claim 5 (dependent on Claim 1): Specifies that the electrodes are formed of aluminum, copper, or gold.
• Claim 7 (dependent on Claim 1): Specifies a modulation bandwidth of at least 50 GHz per channel.
• Claim 9 (dependent on Claim 1): Specifies that the multi-channel arrangement comprises eight channels.
• Claim 14 (dependent on Claim 12): Specifies that the electrical interconnections comprise wire bonds or flip-chip bump bonds.
• Claim 16 (dependent on Claim 12): Specifies a specific driver circuit topology (distributed driver architecture).
• Claim 20 (dependent on Claim 19): Specifies that the modulation format is PAM-4.
• Claim 22 (dependent on Claim 19): Specifies a data rate of at least 100 Gbps per channel.
Several of these dependent claims correspond to features present in OWS's products. In particular, Claim 9 (eight-channel configuration), Claim 7 (50 GHz bandwidth), and Claim 20 (PAM-4 modulation) each describe features that OWS's OWS-800G-MZM-8 product employs. However, for purposes of this analysis, the infringement risk is driven primarily by the independent claims, and the dependent claims serve to define the scope of potential narrower infringement allegations.
B. U.S. Patent No. 11,105,662
1. Bibliographic Data
Title: Method and Apparatus for Fabricating Segmented Traveling-Wave Electrodes on Silicon-Photonic Substrates for High-Bandwidth Optical Modulation
Patent Number: 11,105,662
Issue Date: August 31, 2021
Filing Date: September 14, 2020 (non-provisional); claims priority as a continuation of U.S. Application No. 15/933,147 (now U.S. Patent No. 10,823,417) and to Provisional Application No. 62/475,218, filed March 23, 2017
Assignee: Pinnacle Optics, Inc.
Named Inventors: Dr. Raymond K. Ishida, Dr. Nadia L. Volkov, Dr. Tomohiro Sato, and Dr. Priya Ranganathan
Number of Claims: 18 total claims, of which 2 are independent (Claims 1 and 10)
U.S. Classification: H04B 10/50; G02F 1/225; H01L 21/768
References Cited: 52 references (31 U.S. patents, 9 foreign patents, 12 non-patent literature references)
Examiner: Michael J. Radigan, Art Unit 2872
2. Summary of Disclosed Technology
The '662 patent is a continuation of the '417 patent and shares the same specification disclosure. However, the claims of the '662 patent are directed to a different aspect of the technology: specifically, the method of fabricating segmented traveling-wave electrodes on silicon-photonic substrates and the resulting electrode structure as defined by specific fabrication process parameters. While the '417 patent focuses on the structural arrangement and impedance characteristics of the segmented electrode architecture, the '662 patent focuses on the fabrication process steps and process-defined structural features.
The '662 patent claims recite specific fabrication steps, including photolithographic patterning of electrode segments on a silicon-photonic wafer, metal deposition parameters (deposition thickness, material composition), and post-fabrication impedance tuning steps. The claims also recite specific fabrication tolerances and process control parameters that define the resulting electrode structure.
3. Independent Claim Analysis
Claim 1 (method claim directed to fabrication process):
A method of fabricating a segmented traveling-wave electrode on a silicon-photonic substrate, the method comprising:
(a) providing a silicon-on-insulator wafer having a Mach-Zehnder interferometer structure formed in a silicon device layer thereof;
(b) depositing a first metal layer on the silicon-on-insulator wafer by a physical vapor deposition process, the first metal layer having a thickness in the range of 0.5 micrometers to 5 micrometers;
(c) patterning the first metal layer by photolithographic processing to define a plurality of electrode segments arranged in series along a waveguide arm of the Mach-Zehnder interferometer structure, the plurality of electrode segments being separated by inter-segment gaps;
(d) depositing a second metal layer over the patterned first metal layer to increase the total electrode thickness to a range of 2 micrometers to 10 micrometers;
(e) performing an impedance-tuning step comprising measuring the characteristic impedance of each electrode segment and adjusting the electrode segment geometry by selective etching to achieve a target impedance value of approximately 50 ohms for each electrode segment with a tolerance of no greater than plus or minus 5 ohms; and
(f) repeating steps (a) through (e) for each of a plurality of Mach-Zehnder modulator channels on the silicon-on-insulator wafer.
Claim 10 (apparatus claim defined by fabrication-process features):
A silicon-photonic modulator device fabricated by a process comprising:
(a) forming a Mach-Zehnder interferometer structure in a silicon device layer of a silicon-on-insulator wafer;
(b) forming a segmented traveling-wave electrode along a waveguide arm of the Mach-Zehnder interferometer structure by sequential metal deposition and photolithographic patterning steps, the segmented traveling-wave electrode comprising at least six electrode segments, each having a characteristic impedance tuned to approximately 50 ohms by a post-deposition impedance-tuning process comprising selective etching;
(c) forming electrical interconnections to each electrode segment; and
(d) forming at least four Mach-Zehnder modulator channels on the silicon-on-insulator wafer, each channel having a respective segmented traveling-wave electrode formed by steps (b) and (c).
The '662 patent claims are significant because they introduce fabrication process limitations that may or may not be met by OWS's manufacturing process. In particular, element (e) of Claim 1 recites a specific "impedance-tuning step" involving measurement and selective etching, and Claim 10 recites a "post-deposition impedance-tuning process comprising selective etching." Whether OWS's fabrication process includes such a post-deposition impedance-tuning step using selective etching is a factual question that affects the infringement analysis.
4. Dependent Claim Analysis
The sixteen dependent claims of the '662 patent (Claims 2-9 and 11-18) further narrow the independent claims by specifying additional fabrication process details, including:
• Claim 3 (dependent on Claim 1): Specifies that the physical vapor deposition process is electron-beam evaporation or sputtering.
• Claim 5 (dependent on Claim 1): Specifies that the first metal layer comprises aluminum or an aluminum-copper alloy.
• Claim 7 (dependent on Claim 1): Specifies that the selective etching comprises reactive ion etching or wet chemical etching.
• Claim 12 (dependent on Claim 10): Specifies that the at least four channels comprise eight channels.
• Claim 15 (dependent on Claim 10): Specifies a modulation bandwidth of at least 50 GHz per channel after impedance tuning.
These dependent claims introduce additional specificity regarding fabrication process parameters, which may provide avenues for non-infringement arguments if OWS's fabrication process differs in material respects from the recited process steps.
V. CLAIM CONSTRUCTION
A. Methodology
The claim constructions set forth in this section were developed in accordance with the framework established by the Federal Circuit in Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc). Under Phillips, claim terms are generally given their ordinary and customary meaning as understood by a person of ordinary skill in the art at the time of the invention, in view of the intrinsic evidence: the claims themselves, the specification (including the written description and any drawings), and the prosecution history. Extrinsic evidence — including expert testimony, dictionaries, and learned treatises — may also be considered, but it is generally less reliable than intrinsic evidence and may not be used to contradict the intrinsic record. Id. at 1317-19.
It is important to note that no court or the PTAB has construed the claims of either the '417 or the '662 patent. The constructions adopted herein represent C&H's best assessment of the proper construction of the relevant claim terms and may differ from constructions that a court or the PTAB would ultimately adopt. In particular, claim construction is often the pivotal issue in patent litigation, and reasonable minds may differ as to the proper construction of key terms. OWS should be aware that Pinnacle may advocate for broader constructions of its claim terms than those adopted here, particularly with respect to the "substantially uniform impedance profile" limitation, which is critical to the design-around analysis.
B. Key Claim Terms — '417 Patent
"Segmented traveling-wave electrode"
This term appears in all three independent claims of the '417 patent (Claims 1, 12, and 19). Based on the specification and the prosecution history, we construe this term to mean: a traveling-wave electrode that is physically divided into a plurality of discrete, individually addressable electrode segments arranged in series along a direction of optical propagation in a waveguide, as distinguished from a continuous (non-segmented) traveling-wave electrode.
The specification clearly distinguishes the claimed segmented electrode design from prior art continuous electrode designs. At column 2, lines 34-48, the specification states: "Unlike conventional continuous traveling-wave electrodes, which suffer from velocity mismatch between the electrical and optical signals at high modulation frequencies, the segmented traveling-wave electrode of the present invention divides the electrode into a plurality of discrete segments, each of which is individually driven by a separate electrical driver signal." This language confirms that "segmented" requires physical division into discrete segments, each with its own driver connection.
This construction is significant because OWS's current products unquestionably employ a segmented traveling-wave electrode design, as does the next-generation tapered impedance-matching design. The segmentation itself is not the basis for the design-around; rather, the design-around is directed to the impedance profile across the segments (as discussed below).
"Impedance matching" / "substantially uniform impedance profile"
These related terms appear in the independent claims of the '417 patent and are central to the FTO analysis. Claim 1, element (d), recites "an impedance-matching network . . . configured to maintain a substantially uniform impedance profile across the plurality of electrode segments such that the variation in characteristic impedance among the plurality of electrode segments is no greater than 10% of a target impedance value." Claim 12, element (d), similarly recites "a uniform impedance-matching configuration . . . wherein each electrode segment has a characteristic impedance of approximately 50 ohms with a tolerance of no greater than plus or minus 5 ohms."
Based on the specification and prosecution history, we construe "substantially uniform impedance profile" to mean: an impedance profile in which the characteristic impedance of each electrode segment is intentionally designed and manufactured to be approximately equal to a single target impedance value (e.g., 50 ohms), with permissible manufacturing tolerances, such that the impedance does not systematically vary along the length of the electrode.
This construction is supported by the specification's repeated emphasis on impedance uniformity as a design objective. At column 4, lines 12-28, the specification states: "The impedance-matching network of the present invention is designed to maintain a substantially uniform impedance across all electrode segments. By ensuring that each segment presents the same characteristic impedance to the electrical drive signal, the segmented electrode achieves optimal velocity matching and minimal signal reflection over its entire length." At column 5, lines 45-52, the specification further states: "In preferred embodiments, the impedance variation among segments is minimized to no greater than 10% of the target impedance value, and ideally to no greater than 5%."
The prosecution history provides additional support for this construction. During examination of the '417 patent, the examiner rejected the original claims over a prior art reference (Patel, U.S. Patent No. 9,612,458) that disclosed a segmented electrode with varying impedance values along its length. In response to this rejection, Pinnacle's counsel at Cavanaugh Holt & Sayer LLP amended the claims to add the "substantially uniform impedance profile" and "no greater than 10% variation" limitations and argued that the claimed invention was distinguishable from Patel because Patel's electrode segments had intentionally different impedance values, whereas the present invention required a "substantially uniform" impedance profile. This prosecution history argument is significant for two reasons: first, it confirms that the "substantially uniform" limitation was added to overcome prior art, and second, it may give rise to prosecution history estoppel that limits Pinnacle's ability to assert equivalents against designs that employ a non-uniform, tapered impedance profile.
This construction is favorable to OWS's design-around strategy. OWS's tapered impedance-matching design intentionally employs a graduated impedance profile in which the characteristic impedance of the electrode segments systematically varies along the length of the electrode — for example, tapering from a higher impedance value at the input end to a lower impedance value at the output end. Under the construction adopted above, such a tapered design would fall outside the scope of the "substantially uniform impedance profile" limitation because the impedance variation is systematic and intentional, not merely within manufacturing tolerances.
"Silicon-photonic Mach-Zehnder modulator"
This term is construed broadly to encompass any Mach-Zehnder interferometric modulator fabricated on a silicon-photonic platform, including silicon-on-insulator platforms. The specification does not limit this term to any particular SOI process node, waveguide geometry, or doping configuration. This construction is consistent with the ordinary meaning of the term in the art. OWS's products clearly fall within this construction.
"Multi-channel arrangement" / "at least four Mach-Zehnder modulator channels"
Claim 1, element (e), requires "at least four Mach-Zehnder modulator channels integrated on the silicon-on-insulator substrate." This term is construed according to its plain meaning. OWS's four-channel (OWS-800G-MZM-4) and eight-channel (OWS-800G-MZM-8) products each satisfy this limitation.
"Inter-segment gaps having a gap length of between 5 micrometers and 50 micrometers"
Claim 1, element (c), specifies this dimensional range for the gaps between adjacent electrode segments. Based on the specification and claim language, this is construed as a definite numerical limitation requiring the gap length to fall within the specified range. OWS's current products employ inter-segment gaps with lengths that fall within this range, as confirmed by the fabrication process documentation reviewed by C&H.
C. Key Claim Terms — '662 Patent
"Impedance-tuning step" / "post-deposition impedance-tuning process comprising selective etching"
Claim 1, element (e), of the '662 patent recites a specific fabrication step: "performing an impedance-tuning step comprising measuring the characteristic impedance of each electrode segment and adjusting the electrode segment geometry by selective etching to achieve a target impedance value." Claim 10, element (b), similarly recites "a characteristic impedance tuned to approximately 50 ohms by a post-deposition impedance-tuning process comprising selective etching."
We construe these terms to require a specific post-deposition fabrication step in which the impedance of each electrode segment is measured (i.e., electrically characterized) and then the electrode geometry is physically modified by an etching process (e.g., reactive ion etching, wet chemical etching, or another subtractive process) to bring the impedance to the target value. This is a narrow construction that requires both the measurement step and the etching-based adjustment step. Alternative impedance-tuning approaches — such as tuning by additive metal deposition, by laser trimming, or by design-stage optimization without post-fabrication adjustment — would not satisfy this limitation.