DCT

1:22-cv-00674

Cisco Systems Inc v. Ramot At Tel Aviv University Ltd

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 1:22-cv-00674, D. Del., 05/24/2022
  • Venue Allegations: Plaintiffs allege venue is proper in the District of Delaware, where Defendant Ramot has previously filed related patent infringement lawsuits and counterclaims, thereby consenting to personal jurisdiction.
  • Core Dispute: Plaintiffs seek a declaratory judgment that their optical transceiver modules and related networking equipment do not infringe Defendant’s patent related to methods for linearizing optical digital-to-analog modulators.
  • Technical Context: The technology concerns high-speed optical communications, specifically methods to correct for inherent non-linearities in optical modulators to improve the accuracy of converting digital data into modulated light signals for fiber-optic transmission.
  • Key Procedural History: This declaratory judgment action is the latest in a series of disputes between the parties over a family of patents dating back to 2014. The complaint details prior lawsuits filed by Ramot against Cisco and Acacia in Texas and Delaware, some of which were stayed pending ex parte reexaminations of the asserted patents. This history forms the basis for Plaintiffs' belief that Ramot will assert the newly-issued patent-in-suit against the same or similar products, creating an actual controversy sufficient for declaratory judgment jurisdiction.

Case Timeline

Date Event
2007-06-13 ’998 Patent Priority Date
2014-11-05 Ramot sues Cisco in E.D. Tex. on ancestor patents (2014 Action)
2019-06-12 Ramot sues Cisco in E.D. Tex. on related patents (2019 Texas Action)
2021-02-26 Ramot sues Acacia in D. Del. on related patents (Feb. 2021 Delaware Action)
2021-03-01 Cisco completes acquisition of Acacia
2021-09-28 Cisco/Acacia file DJ action in D. Del. on parent '872 patent
2022-02-07 Ramot counterclaims for infringement of the '872 patent in DJ action
2022-05-24 U.S. Patent No. 11,342,998 Issues
2022-05-24 Complaint for Declaratory Judgment Filed

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 11,342,998 - “Linearized Optical Digital-to-Analog Modulator”

  • Patent Identification: U.S. Patent No. 11,342,998, “Linearized Optical Digital-to-Analog Modulator,” issued May 24, 2022.

The Invention Explained

  • Problem Addressed: The patent addresses the inherent non-linear response of optical modulators, particularly Mach-Zehnder Interferometer (MZI) modulators. In these devices, a linear change in the applied voltage used to encode data results in a non-linear (specifically, cosine-shaped) change in the output optical signal's intensity, which distorts the signal and limits performance ('998 Patent, col. 1:58-2:4).
  • The Patented Solution: The invention proposes a system that uses a "digital-to-digital converter" (DDC) to linearize the output. Instead of a direct one-to-one mapping of input data bits to modulator electrodes, the DDC maps an N-bit input data word to a specific M-bit output pattern (where M is typically greater than or equal to N) that drives M actuating electrodes. This mapping is chosen specifically to counteract the modulator's non-linear response, producing an optical output that more closely approximates an ideal linear function of the original digital input ('998 Patent, Abstract; col. 2:42-56).
  • Technical Importance: This approach aims to enable high-performance, large-bandwidth digital-to-analog conversion directly in the optical domain, which is critical for increasing data rates in fiber-optic communication systems ('998 Patent, col. 1:38-44).

Key Claims at a Glance

  • The complaint identifies independent claims 1, 16, 32, 45, and 58 as the claims it seeks a declaration of non-infringement against (Compl. ¶73).
  • Independent Claim 1 (System Claim):
    • An input for a plurality of N digital input data bits.
    • A modulator for modulating an input optical signal responsively to the N digital input data bits.
    • A "digital-to-digital mapping" that maps the N digital input data bits to a set of M digital output data bits associated with a plurality of voltage values.
    • The input optical signal is modulated based on the plurality of voltage values.
    • The mapping comprises, for each possible digital input value, a corresponding set of digital output values.
    • The mapping includes specific relationships where, for certain subsets of successively increasing input values, the "deltas" (differences) between successive output values either decrease or increase.

III. The Accused Instrumentality

Product Identification

  • The complaint identifies a broad category of "Accused Products" which Plaintiffs seek a declaration of non-infringement for. These include Acacia's AC1200 and AC400 products, various pluggable optical transceiver modules (e.g., CIM8, CFP2, OSFP, QSFP-DD), their components such as Digital Signal Processing (DSP) ASICs and Silicon Photonic integrated circuits, and Cisco networking equipment that incorporates these components, such as line cards and routers (Compl. ¶¶37-38).

Functionality and Market Context

  • The complaint divides the Accused Products into two categories for its non-infringement analysis.
    1. "Analog-driven" products: These are alleged to use a DSP that has a digital-to-analog converter (DAC) at its output. The DAC generates a continuous analog voltage signal that drives the optical modulator (Compl. ¶72).
    2. "Digitally-driven" products: These are alleged to use coding changes, such as "gray coding with thermometer coding," which Plaintiffs contend are distinct from the claimed mapping technology (Compl. ¶¶79, 81).
  • These products are high-speed optical interconnects that form the backbone of modern data centers and telecommunications networks, enabling data transmission at rates of 100 Gbps, 400 Gbps, and higher (Compl. ¶¶38, 43, 46).

IV. Analysis of Infringement Allegations

This is a declaratory judgment action where Plaintiffs allege non-infringement. The following table summarizes Plaintiffs' primary non-infringement arguments with respect to Claim 1.

’998 Patent Non-Infringement Allegations (per Plaintiffs)

Claim Element (from Independent Claim 1) Alleged Non-Infringing Functionality Complaint Citation Patent Citation
a modulator for modulating the input optical signal responsively to the plurality of N digital input data bits... For "analog-driven" products, the modulator is allegedly responsive to a single analog drive voltage signal from a DAC, not directly to the N digital input data bits (Compl. ¶74.a). For "digitally-driven" products, this limitation is also alleged to be missing (Compl. ¶80). ¶¶74, 80 col. 17:25-34
wherein a digital-to-digital mapping maps the plurality of N digital input bits to a set of M digital output data bits... For "analog-driven" products, Plaintiffs allege the modulator is driven by an analog signal, not by M digital output data bits resulting from a mapping (Compl. ¶74.b). For "digitally-driven" products, Plaintiffs allege the use of "gray coding with thermometer coding" does not perform the claimed "digital-to-digital mapping" (Compl. ¶81). ¶¶74, 81 col. 17:36-39
wherein, within the digital-to-digital mapping... deltas between numerical values of successive digital outputs... decrease [or] increase Plaintiffs allege that "digitally-driven" products, which use gray and thermometer coding, do not meet these specific limitations relating to how the differences ("deltas") between successive output values must change (Compl. ¶82). ¶82 col. 17:42 - 18:2

No probative visual evidence provided in complaint.

  • Identified Points of Contention:
    • Architectural Questions: A central dispute will be whether an "analog-driven" architecture, where a DAC creates an intermediate analog signal, can infringe claims requiring a modulator to be responsive to "digital input data bits" and a "digital-to-digital mapping." This raises the question of how the claims treat the presence of a DAC between the digital processing and the optical modulator.
    • Scope Questions: The case will likely turn on whether the accused "gray coding and thermometer coding" falls within the scope of the patent's term "digital-to-digital mapping." The complaint suggests a fundamental technical difference, which Ramot would need to rebut.
    • Technical Questions: What evidence exists that the accused "digitally-driven" products' coding schemes actually perform the specific "delta" adjustments required by Claim 1? Plaintiffs' complaint asserts that they do not, creating a factual question for the court regarding the precise function of the accused coding algorithms (Compl. ¶82).

V. Key Claim Terms for Construction

  • The Term: "digital-to-digital mapping"

  • Context and Importance: This term is the core of the invention and appears in every independent claim (Compl. ¶¶23, 74-78, 81). Its construction will be dispositive, particularly for the "digitally-driven" products. The dispute will be whether this term is limited to the specific linearization techniques described in the patent or if it is broad enough to cover other data conversion schemes like gray coding.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: The claims define the mapping functionally, requiring it to map N input bits to M output bits and to comprise, for each input value, a corresponding output value ('998 Patent, col. 17:36-42). This functional language might be argued to encompass any process that achieves this input-output relationship.
    • Evidence for a Narrower Interpretation: The specification repeatedly describes the mapping in the context of selecting an "electrode actuation pattern which best approximates a desired ideal output" to correct for non-linearity ('998 Patent, col. 7:31-34). The detailed "delta" limitations in Claim 1 further specify the mathematical properties of the mapping, which may be argued to exclude conventional coding schemes that do not share these properties ('998 Patent, col. 17:42-18:2).

  • The Term: "responsively to the plurality of N digital input data bits"

  • Context and Importance: This term is critical for the "analog-driven" products. Plaintiffs argue their modulators are responsive to an analog signal from a DAC, not the digital bits that preceded the DAC (Compl. ¶74.a). The construction will determine if the claim requires direct digital control of the modulator or if indirect control via a DAC is sufficient.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: The patent's system-level description might support an interpretation where the modulator is ultimately responsive to the digital inputs, even with an intermediate DAC, as the analog signal is a direct consequence of those bits. The specification describes a "digital-to-analog converter" as the overall apparatus ('998 Patent, col. 4:42-44).
    • Evidence for a Narrower Interpretation: Claim 1 recites a "digital-to-digital mapping" that produces "M digital output data bits," and the modulation is based on "voltage values" associated with those M bits, suggesting a digital control architecture ('998 Patent, col. 17:36-41). The patent's emphasis on a "digital-to-digital converter" as a component within the system, distinct from a traditional DAC, could support a narrower reading that excludes architectures centered on a final-stage DAC ('998 Patent, col. 2:58-60).

VI. Other Allegations

  • Indirect Infringement: Plaintiffs seek a declaration of non-infringement of indirect infringement, arguing that their blog posts, datasheets, and other customer-facing materials do not encourage infringement or demonstrate the requisite specific intent to induce (Compl. ¶85). They further allege their products are staple articles of commerce capable of substantial non-infringing uses, precluding a claim of contributory infringement (Compl. ¶86).
  • Willful Infringement: The complaint does not allege willfulness but anticipates that Ramot would, based on the long litigation history between the parties (Compl. ¶¶61-63). The filing of the DJ action itself is a step to mitigate potential willfulness claims by seeking judicial clarity upon the patent's issuance.

VII. Analyst’s Conclusion: Key Questions for the Case

This declaratory judgment action will likely hinge on two primary technical questions and one procedural one:

  • A core issue will be one of architectural scope: Do the claims, which describe a "digital-to-digital mapping" and modulation "responsively to... digital input data bits," read on an "analog-driven" system that uses a traditional digital-to-analog converter to generate an analog waveform that drives the modulator?
  • A second key issue will be one of definitional equivalence: Can the term "digital-to-digital mapping," as defined and constrained by the patent's specific "delta" limitations, be construed broadly enough to cover the "gray coding and thermometer coding" algorithms allegedly used in Plaintiffs' "digitally-driven" products?
  • Finally, underlying the entire case is a jurisdictional question: Have Plaintiffs adequately demonstrated, through the extensive history of litigation over the same patent family and same accused product categories, a controversy of sufficient "immediacy and reality" to justify the court's exercise of declaratory judgment jurisdiction over the newly-issued '998 patent?