DCT

8:20-cv-01468

Core Optical Tech LLC v. Cisco Systems Inc

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 8:20-cv-01468, C.D. Cal., 05/07/2021
  • Venue Allegations: Venue is alleged to be proper based on Defendant having regular and established places of business in the district and committing acts of alleged infringement within the district.
  • Core Dispute: Plaintiff alleges that Defendant’s optical transport platforms and related modules, which enable high-speed data transmission using polarization-division multiplexing, infringe a patent related to methods for mitigating cross-polarization interference in fiber optic signals.
  • Technical Context: The technology concerns coherent optical receivers designed to increase data capacity on fiber optic networks by transmitting two independent data streams on orthogonal polarizations in the same frequency band and then separating them at the receiver.
  • Key Procedural History: The complaint notes that the patent-in-suit has survived three separate inter partes review (IPR) petitions at the PTAB, all of which were denied institution. The complaint also alleges Defendant had pre-suit knowledge of the patent through multiple channels, including prior litigation involving its customer (Fujitsu) and competitors (Ciena, Infinera), and through the prosecution of Defendant’s own patent, where the patent-in-suit was cited as prior art by the USPTO examiner.

Case Timeline

Date Event
1998-11-05 '211' Patent Priority Date (Provisional App. 60/107,123)
2004-08-24 '211 Patent Issue Date
2012-10-29 Core files suit against Ciena asserting the '211 patent
2015-10-22 USPTO Examiner cites '211 patent during prosecution of Cisco's '745 patent
2016-07-07 Cisco allegedly becomes aware of '211 patent via its customer Fujitsu
2017-03-24 Core files suit against Infinera asserting the '211 patent
2021-05-07 Complaint Filing Date

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

U.S. Patent No. 6,782,211 - Cross Polarization Interface [sic] Canceler

  • Issued: August 24, 2004

The Invention Explained

  • Problem Addressed: The patent addresses the problem of increasing data transmission rates over fiber optic networks (’211 Patent, col. 1:12-20). A key challenge is that when two independent signals are sent on orthogonal polarizations over the same fiber to double the bandwidth, the signals interfere with each other ("cross polarization interference" or XPI) due to effects during propagation, making it difficult to recover the original information (’211 Patent, col. 2:40-51).
  • The Patented Solution: The patent describes a "cross polarization interference canceler" (XPIC) implemented in a receiver (’211 Patent, Abstract). The XPIC is a form of coherent signal processing that takes the mixed signal, separates it into its polarized components, and applies a series of complex filters or coefficients (as shown in Fig. 4A/4B) to mathematically reverse the interference and reconstruct the two original, independent data streams (’211 Patent, col. 4:18-36).
  • Technical Importance: This technology allows for a significant increase in the bandwidth efficiency of a single optical fiber, reducing the need for additional network hardware like regenerative repeaters that would otherwise be required to combat signal degradation over long distances (’211 Patent, col. 2:52-65).

Key Claims at a Glance

  • The complaint asserts independent method claim 33 (Compl. ¶18).
  • Independent Claim 33 requires:
    • receiving an optical signal over a single fiber optic transmission medium,
    • the optical signal being at least two polarized field components independently modulated with independent information bearing waveforms; and
    • mitigating cross polarization interference associated with the at least two modulated polarized field components to reconstruct the information bearing waveforms
    • by using a plurality of matrix coefficients being complex values to apply both amplitude scaling and phase shifting to the at least two modulated polarized field components.
  • The complaint also asserts dependent claims 30, 32, 35, and 37 (Compl. ¶5).

III. The Accused Instrumentality

Product Identification

The accused instrumentalities are a wide range of Cisco's optical networking products, collectively termed "Fiber Optic XPIC Devices" (Compl. ¶5). This includes the Network Convergence System (NCS) 1000, 2000, 4000, and 5500 Series Platforms; the ASR 9000 Series Platform; the ONS 15454 Platform; CRS-series Platforms; and numerous associated modules, line cards, transponders, and software (Compl. ¶¶19-20).

Functionality and Market Context

The accused products are described as high-capacity platforms and modules for optical transport networks that provide services like Dense Wavelength-Division Multiplexing (DWDM) (Compl. ¶24). Their accused functionality involves performing "dual-polarization communication," also referred to as Polarization-Division Multiplexed (PDM) optical communication, which is a technique to increase data rates (Compl. ¶¶1, 28). This is achieved using coherent optical receivers that perform advanced signal processing to compensate for signal impairments that occur during transmission (Compl. ¶39).

IV. Analysis of Infringement Allegations

'211 Patent Infringement Allegations

Claim Element (from Independent Claim 33) Alleged Infringing Functionality Complaint Citation Patent Citation
receiving an optical signal over a single fiber optic transmission medium, The accused platforms and their line cards are configured to send and receive optical signals over fiber optic cables as part of their normal operation in an optical transport network. ¶¶23-26 col. 3:5-10
the optical signal being at least two polarized field components independently modulated with independent information bearing waveforms; and The accused devices are alleged to perform Polarization-Division Multiplexed (PDM) communication, using modulation formats like "coherent polarization-multiplexing differential quadrature phase shift keying (CP-DQPSK)," which inherently involves at least two independently modulated polarized signals. ¶¶27-37 col. 11:59-65
mitigating cross polarization interference associated with the at least two modulated polarized field components to reconstruct the information bearing waveforms The accused coherent optical receivers perform signal processing to address transmission impairments, including Polarization Mode Dispersion (PMD) mitigation. The complaint alleges this processing calculates an "Inverse Optical System Matrix" to recover the original signal polarization. ¶¶38-43 col. 4:20-24
using a plurality of matrix coefficients being complex values to apply both amplitude scaling and phase shifting to the at least two modulated polarized field components. The complaint alleges that to fully account for both amplitude and phase effects of the fiber medium, the "Inverse Optical System Matrix" computed by the accused devices must necessarily use complex coefficients, which inherently apply both amplitude scaling and phase shifting. ¶¶44-48 col. 22:29-34

A diagram from a Cisco presentation shows the structure of the coherent optical receivers in the accused devices, including a "Signal Processing" block alleged to perform the claimed mitigation (Compl. ¶39, p. 12).

  • Identified Points of Contention:
    • Scope Questions: A central dispute may concern the scope of "mitigating cross polarization interference." The complaint alleges that Cisco's systems, which perform general signal processing to address impairments like chromatic dispersion and PMD, meet this limitation (Compl. ¶39). A question for the court is whether this claim language requires a specific structure or algorithm aimed explicitly at XPI, as opposed to a more general-purpose impairment compensation system.
    • Technical Questions: The infringement theory for the "matrix coefficients" element appears to rest on an inference: because the accused systems successfully recover the signals, they must be using complex matrix coefficients to do so (Compl. ¶46). A key technical question will be what evidence demonstrates that the accused "Signal Processing" block actually operates by calculating and applying a plurality of complex matrix coefficients, as opposed to using a different, non-infringing technique to achieve a similar result.

V. Key Claim Terms for Construction

  • The Term: "mitigating cross polarization interference"

  • Context and Importance: This term defines the core function of the claimed method. Its construction will be critical to determining if the general-purpose signal processing performed by Cisco's devices, which addresses multiple types of signal degradation (Compl. ¶39), falls within the scope of the claim. Practitioners may focus on this term because the accused functionality is described as "PMD [polarization mode dispersion] mitigation," and the relationship between mitigating PMD and mitigating XPI will be a central technical and legal issue.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: The claim uses broad functional language ("mitigating... to reconstruct"), which may support an interpretation covering any process that achieves the stated result of reducing XPI and reconstructing the waveforms. The patent also states the XPIC may be directed to mitigate the effects of chromatic and/or polarization mode dispersion (’211 Patent, col. 4:6-9).
    • Evidence for a Narrower Interpretation: The specification's embodiments show specific "XPIC" filter structures (e.g., the "butterfly" configuration of Fig. 4A) designed to operate on separated polarization components (’211 Patent, col. 13:17-30). This could support an argument that "mitigating" implies using such a specific structure, rather than any generic signal processing.

  • The Term: "matrix coefficients"

  • Context and Importance: This term specifies the mathematical mechanism for the mitigation step. The complaint alleges Cisco's "Inverse Optical System Matrix" embodies these coefficients (Compl. ¶¶45-47). The dispute will likely turn on whether Cisco's system actually uses a structure that can be characterized as "matrix coefficients" or if it employs a different computational approach.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: The patent describes the coefficients in functional terms as applying "amplitude scaling and phase shifting," which could be argued to cover a variety of mathematical operations that achieve that effect (’211 Patent, col. 22:32-34).
    • Evidence for a Narrower Interpretation: The patent consistently depicts the coefficients as discrete elements in a 2x2 matrix structure (e.g., W11, W12, W21, W22 in Fig. 4B) that perform a specific matrix multiplication (’211 Patent, col. 13:17-21). This could support a narrower definition tied to this explicit structure.

VI. Other Allegations

  • Indirect Infringement: The complaint alleges inducement by asserting that Defendant sells the accused products with the specific intent for its customers to use them in an infringing manner. This intent is allegedly evidenced by product documentation, configuration guides, datasheets, and technical support that instruct users on how to enable the infringing dual-polarization functionality (Compl. ¶¶60-69). Contributory infringement is alleged on the basis that the components for performing the mitigation are not staple articles of commerce and are especially adapted for an infringing use (Compl. ¶¶97-101).
  • Willful Infringement: The complaint makes extensive allegations of willful infringement based on alleged pre-suit knowledge from multiple sources: (1) Defendant was allegedly informed of the patent and a lawsuit against its customer Fujitsu on July 7, 2016 (Compl. ¶72); (2) Defendant allegedly learned of the patent through industry monitoring of suits against its competitors Ciena (filed 2012) and Infinera (filed 2017) (Compl. ¶83); and (3) the '211 patent was cited by the USPTO examiner as "pertinent prior art" during the prosecution of Defendant's own U.S. Patent No. 9,515,745 on October 22, 2015 (Compl. ¶¶90-91). The complaint includes a diagram from Cisco's '745 patent to show its similarity to the technology of the patent-in-suit (Compl. ¶88, p. 24).

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

  • A core issue will be one of claim construction and scope: can the term "mitigating cross polarization interference," as used in the patent, be construed to cover the accused products' more general-purpose signal processing systems that are described as performing "PMD mitigation," or is the claim limited to a specific structure or algorithm explicitly designed for XPI cancellation?
  • A key evidentiary question will be one of technical proof: the complaint infers that the accused devices must use "complex matrix coefficients" to function. The case may turn on what direct evidence, if any, emerges from the accused systems' source code or hardware design to prove that they operate in the specific manner required by the claim language.
  • A third central issue will be willfulness and damages: given the multiple, documented instances of alleged pre-suit notice—particularly the examiner's citation of the '211 patent during the prosecution of Cisco's own related patent—a significant focus will be on Cisco's state of mind and whether its continued sales after these events rise to the level of willful infringement, which could expose it to enhanced damages.