Fujitsu Ltd. v. Tellabs Operations, Inc. (821 F. Supp. 2d 1009, 2011)

MEMORANDUM OPINION AND ORDER

JAMES F. HOLDERMAN, Chief Judge.

On January 29, 2008, Fujitsu Limited filed a complaint against Tellabs, Inc. and Tellabs Operations, Inc. in the United States District Court for the Eastern District of Texas (“Texas Action”) alleging infringement of U.S. Patent Nos. 5,526,163 (“'163 Patent”); 5,521,737 (“'737 Patent”); 5,386,418 (“'418 Patent”); and 6,487,686 (“'686 Patent”). (Case No. 09-4530, Dkt. No. 1, Fujitsu’s Compl. ¶¶ 1, 12-35.) Tel-labs Operations, Inc. then filed suit against Fujitsu Limited and Fujitsu Network Communications, Inc. (collectively “Fujitsu”) in the United States District Court for the Northern District of Illinois (“Illinois Action”) on June 11, 2008, alleging infringement of U.S. Patent No. 7,369,772 (“'772 Patent”). (Case No. 08-3379, Dkt. No. 1, Tellabs’s Compl. ¶ 1.) Both Fujitsu Limited and Fujitsu Network Communications, Inc. filed their amended answers, affirmative defenses, and counterclaims in the Illinois Action on April 1, 2009. (Dkt. Nos.119, 120.) In its counterclaims, Fujitsu Limited alleged that Tellabs Operations, Inc., Tellabs, Inc., and Tellabs North America (collectively “Tellabs”) infringed two additional patents assigned to Fujitsu Limited: U.S. Patent Nos. 7,227,681 (“'681 Patent”) and 5,533,006 (“'006 Patent”). (Dkt. No. 119.)

On May 13, 2009, this court issued its preliminary claim constructions of certain disputed claim terms in the '772, '681, and '006 Patents. (Case No. 08-3370, Dkt. No. 145 (“Prelim.Constr.Op.”).) The Texas Action subsequently was transferred to the Northern District of Illinois on July 29, 2009, and the two cases were consolidated before this court for purposes of discovery. (Case No. 08-3379, Dkt. No. 202.) After the cases were consolidated, this court held a three-day technology tutorial related to the general technology underlying the six patents-in-suit.

The parties then identified additional claim terms for the court to construe and filed briefs related to those proposed constructions. Tellabs also filed two motions for summary judgment: Tellabs’s “Motion for Summary Judgment of Invalidity Based on Indefiniteness of All Asserted Claims (1 and 6-9) of U.S. Patent No. 5,386,418” (Case No. 09-4530, Dkt. No. 165) and its “Motion for Summary Judgment of Invalidity Based on Indefiniteness of All Claims of U.S. Patent 5,533,006” (Case No. 08-3379, Dkt. No. 305). Fujitsu then filed its “Motion for Summary Judgment for Judicial Correction of ‘And’ to ‘A’ in Claim 1 of U.S. Patent 5,386,418” (Case No. 09-4530, Dkt. No. 202 (“Fujitsu’s Mot.”)). On November 30 and December 1, 2, 3, and 7, 2010, the court held a Markman hearing, during which the parties’ counsel addressed the respective claim construction positions as well as parties’ motions for summary judgment. The parties have presented the court with over 900 pages of demonstrative slides, nearly 400 pages of briefing, and a multitude of exhibits, addressing their respective claim construction positions.

On March 31, 2011, 2011 WL 1303358, this court issued its Memorandum Opinion an Order denying Tellabs’s “Motion for Summary Judgment of Invalidity Based on Indefiniteness of All Asserted Claims (1 and 6-9) of U.S. Patent No. 5,386,418” and granting Fujitsu’s “Motion for Summary Judgment for Judicial Correction of ‘And’ to ‘A’ in Claim 1 of U.S. Patent 5,386,418.” (Case No. 09-4530, Dkt. No. 305). That same day, the court issued its Memorandum Opinion and Order granting Tellabs’s “Motion for Summary Judgment of Invalidity Based on Indefiniteness of All Claims of U.S. Patent 5,533,006.” (Case No. OS-3379, Dkt. No. 369.)

The court now sets forth its constructions of the nineteen remaining disputed claim terms in the '418, '163, '737, '681, and '772 Patents.

LEGAL STANDARDS

Claim construction is a matter of law for the court. Markman v. Westview Instruments, Inc., 517 U.S. 370, 390-91, 116 S.Ct. 1384, 134 L.Ed.2d 577 (1996). “It is a ‘bedrock principle’ of patent law that ‘the claims of a patent define the invention to which the patentee is entitled the right to exclude.’ ” Phillips v. AWH Corp., 415 F.3d 1303, 1312 (Fed.Cir.2005) (quoting Innova/Pure Water, Inc. v. Safari Water Filtration Sys., Inc., 381 F.3d 1111, 1115 (Fed.Cir.2004)). In construing a patent’s claims, the court gives claim terms their “ordinary and customary meaning,” which is “the meaning that the term would have to a person of ordinary skill in the art in question at the time of the invention.” Id. at 1312-13. The ordinary and customary meaning of a claim term is determined in light of the entire intrinsic evidence, i.e., the claims, the specification, and the prosecution history. Id. at 1313-17. Usually, the specification “is the single best guide to the meaning of a disputed term.” Id. at 1315 (citation omitted). However, “[t]here is a fine line between construing the claims in light of the specification and improperly importing a limitation from the specification into the claims,” Retractable Techs., Inc. v. Becton, 653 F.3d 1296, 1305 (Fed.Cir.2011), and “[generally, a claim is not limited to the embodiments described in the specification unless the patentee has demonstrated a ‘clear intention’ to limit the claim’s scope with ‘words or expressions of manifest exclusion or restriction.’ ” i4i Ltd. P’ship v. Microsoft Corp., 598 F.3d 831, 843 (Fed.Cir.2010) (quoting Liebeh-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 906 (Fed.Cir.2004)).

The prosecution history also “provides evidence of how the PTO [U.S. Patent and Trademark Office] and the inventor understood the patent” and “can often inform the meaning of the claim language by demonstrating ... whether the inventor limited the invention in the course of prosecution.” Phillips, 415 F.3d at 1317. Nevertheless, “because the prosecution history represents an ongoing negotiation between the PTO and the applicant, rather than the final product of that negotiation, it often lacks the clarity of the specification and thus is less useful for claim construction purposes.” Id.

Finally, the court can rely on extrinsic evidence such as “expert and inventor testimony, dictionaries, and learned treatises” in construing a patent’s claims. Id. (citation omitted). Such extrinsic evidence “can shed useful light on the relevant art” but is “less significant than the intrinsic record in determining the legally operative meaning of claim language.” Id. (citations omitted).

ANALYSIS

I. '418 Patent

A. Background

The '418 Patent is titled “Method for Synchronizing Synchronous Data Communication Network and Communication Device Used in the Synchronous Data Communication Network.” It issued on January 31, 1995, and is assigned to Fujitsu Limited. The '418 Patent relates to synchronous data communication networks, including networks using fiber optics to transmit high-speed digital signals, such as those used in cable television transmissions.

The acronym “SONET” is one of the known high-speed networks that transmits large capacities of information and stands for “Synchronous Optical Network.” (2/23/10 Tech. Tutorial Tr. 327:13-15; '418 Patent, col.l 11.32-34.) The SONET system is comprised of various stations or nodes connected via lines for transmitting and receiving information. In a SONET system, information is transmitted in frames, and each frame is organized into bytes. The frame structure is two-dimensionally depicted in graphic form as a matrix containing three main areas: (1) section overhead, (2) line overhead, and (3) synchronous payload envelop, which includes the transmitted customer data and a path overhead. (See 08-3379, Dkt. No. 263 (“Fujitsu’s '006 and '418 Patent Tutorial”) 15; 2/23/10 Tech. Tutorial Tr. 330:11-331:9; '418 Patent, Fig. 1 (depicting a frame matrix).) In the SONET system, a frame is transmitted row by row, one byte at a time, moving from the upper left corner of the frame to the lower right corner. (Fujitsu’s '006 and '418 Patent Tutorial 16; 2/23/10 Tech. Tutorial Tr. 331:10-18.)

The rate of delivery for transmitting the frames is driven by a clock source, i.e. an oscillator, which could come from an external timing source, a clock from the incoming bit stream (i.e., line timing), or the station’s own internal clock (i.e., internal timing). (Fujitsu’s '006 and '418 Patent Tutorial 23; 2/23/10 Tech. Tutorial Tr. 335:15-24.) During the operation of the system, the availability of a clock source may change. (2/23/10 Tech. Tutorial Tr. 342:17.) The '418 Patent discloses the sending of a “flag bit data” between the stations in the SONET system to indicate whether a clock source is available. (Id. at 342:7-11.) In a SONET system, the flag bit data — also referred to in SONET as a “synchronous status message” or “SSM”— is carried in the frame line overhead, which includes the information used by the network that is invisible to the network’s customers. (2/23/10 Tech. Tutorial Tr. 343:9-23; Fujitsu’s '006 and '418 Tutorial 17, 27.)

According to the '418 Patent, an object of the invention

is to provide a synchronizing method of a synchronous data communication network in which a plurality of synchronizing signal sources are provided in a data communication network and data communication is maintained upon an occurrence of a failure by efficiently switching among the synchronizing signal sources in response to the failure that occurred, as well as to provide a communication apparatus used in such a synchronous data communication network.

'418 Patent, col. 2 ll.45-54.

Independent claim 1 of the '418 Patent recites:

A method of switching from one synchronizing signal source to another in a synchronous data communication network including a plurality of stations with at least one child station and at least one parent station connected to each other via lines, and a plurality of synchronizing signal sources provided for said stations, the method comprising, in combination, steps of:

(a) setting, in a signal transmitted via said lines and including synchronizing information related to one of said plurality of synchronized signal sources, a flag bit data indicative of whether or not timing of said one of the plurality of synchronizing signal sources related to said synchronizing information transmitted via said lines can be used as a synchronizing signal source on each station which receives said information transmitted via said lines;

(b) referring each station, from among said plurality of stations on the basis of said flag bit data, to a table provided in each said station for specifying an order of priority for selection of a synchronizing signal source, upon occurrence of a predetermined event in any of said plurality of synchronizing signal sources, and for selecting a synchronizing signal source; and

(c) switching each station from the currently selected synchronizing signal source to the synchronizing signal source selected in said step (b).

Id. at col. 18 1. 51-col. 19 1.9 (emphasis added). Step (a) in claim 1 originally read “setting ... and flag bit data,” but was corrected by a PTO issued Certificate of Correction to instead read “setting .... a flag bit data.” This court performed the same correction in its March 31, 2011 Order. (Case No. 09-4530, Dkt. No. 305.)

B. Person of Ordinary Skill in the Art

Based on the parties’ proposals, the court finds that a person of ordinary skill in the art with respect to the '418 Patent had (1) at least four years of experience in synchronization techniques for synchronous optical networks, or (2) a Bachelor’s degree in systems engineering or electrical engineering with at least two years of experience either in synchronization techniques for synchronous optical networks or in researching and designing components for synchronous optical networks.

C. Claim Constructions

The parties have identified the following three claim terms in the '418 Patent for the court’s construction: “flag bit data” (claims 1, 6-9); “switching each station” (claim 1); and “table” (claim l).

1. “flag bit data” (claims 1 & 6-9)

The term “flag bit data” appears in claims 1, 6-9 of the '418 Patent. Fujitsu’s proposed construction of “flag bit data” is “a predetermined code occupying a fixed position in each frame and is provided in a predetermined position of the overhead (i.e., not the payload).” (Case No. 09-4530, Dkt. No. 195 (“Fujitsu’s Resp.”) 47.) Tellabs, on the other hand, relies on the uncorrected phrase “and flag bit data” in claim 1 to contend that the term “flag bit data” is indefinite. (Case No. 09-4530, Dkt. No. 164 (“Tellabs’s Op. Br.”) 43.) As stated above, in its March 31, 2011 Order, this court corrected the phrase “and flag bit data” in claim 1 of the '418 Patent to read “a flag bit data.” (See Case No. 09-4530, Dkt. No. 305.) As a result, the court finds that the term “flag bit data” is not indefinite. For the following reasons, this court adopts Fujitsu’s proposed construction of the term “flag bit data” with minor alteration and construes “flag bit data” to mean “a predetermined code that occupies a fixed position in each frame and is provided in a predetermined position of the overhead (i.e. not the payload).”

The specification provides an express definition of “flag bit data” which is consistent with Fujitsu’s proposed construction:

The flag bit data is defined such that it occupies a fixed position in each frame (for example, the aforementioned reserved bit Zl). Accordingly, each station separates the frame multiplexed line signal into frames so as to detect the flag bit data. Moreover, the flag bit data contains a predetermined code consisting, for example, of only “l’s” or of only “0’s.”

'418 Patent, col.17 ll.52-58 (emphasis added).

The specification additionally explains that the “Zl” bit referenced in the above excerpt is located in a defined position in the overhead of a frame:

A synchronizing bit data for transmitting the synchronizing signal and a flag bit data indicating availability/non-availability of the synchronizing signal are provided in a predetermined position of the overhead of the signal transmitted through the stations in the digital communication network of the present invention. For example, the aforementioned reserved byte Z1 may be used.

Id. at col.6 ll.11-18 (emphasis added).

Tellabs has not presented any arguments challenging Fujitsu’s proposed construction, other than to argue that the term cannot be construed. The court finds that Fujitsu’s construction is consistent with the intrinsic evidence, particularly the '418 Patent’s specification. Consequently, the court construes the term “flag bit data” to mean “a predetermined code which occupies a fixed position in each frame and is provided in a predetermined position of the overhead (i.e. not the payload).”

2. “switching each station” (claim 1)

The claim term “switching each station” appears in step (c) of claim 1 of the '418 Patent: “(c) switching each station from the currently selected synchronizing signal source to the synchronizing signal source selected in said step (b).” Id. at col. 19 ll.7-9. According to Fujitsu, “switching each station” means “switching each station which receives said information transmitted via said lines (as recited in step (a) of claim 1).” (Fujitsu’s Resp. 38.) Tellabs, however, contends that the proper construction is “switching every station of the plurality of stations.” (Tel-labs’s Op. Br. 41.) The parties’ primary dispute as to this claim term centers around whether every station must switch its synchronizing signal source. As explained below, the court agrees with Fujitsu and construes the claim term “switching each station” to mean “switching each station which receives said information transmitted via said lines (as recited in step (a) of claim 1).”

Looking first to the claim language, the network described in claim 1 includes “a plurality of stations with at least one child station and at least one parent station.” '418 Patent, col.18 11.53-54. The claim term “each station” appears in steps (a), (b), and (c) of claim 1:

(a) setting ... a flag bit data indicative of whether or not a timing of said one of the plurality of synchronizing signal sources related to said synchronizing information transmitted via said lines can be used as a synchronizing signal source on each station which receives said information transmitted via said lines;

(b) referring each station from among said plurality of stations on the basis of said flag bit data, to a table ...; and

(c) switching each station from the currently selected synchronizing signal source selected in said step (b).

Id. at col.18 1.58-col.2 1.9 (emphasis added).

Fujitsu argues that “each station” in step (c) refers to “each station” recited in step (a). Tellabs, however, contends that the “each station” in step (c) refers to the “plurality of stations” recited in the preamble of claim 1 and thus requires the switching of “every station of the plurality of stations.” The court agrees with Fujitsu’s interpretation of claim 1 because the term “each station” appearing in step (c) clearly refers to “each station which receives said information transmitted via said lines” recited in step (a) of claim 1. In other words, not every station in the network must switch its synchronizing signal source as Tellabs contends. Only the station or stations receiving the transmitted synchronizing information must switch because the term “switching each station” in step (c) refers only to those stations which receive the transmitted synchronizing information.

This interpretation of “switching each station” comports with the teachings of the specification. Although the specification does disclose embodiments where all the stations ultimately do switch their signal sources, see '418 Patent, Figs. 3-14 (disclosing first embodiment); Figs. 37-42 (disclosing fifth embodiment), the court finds that rather than limiting the claims, these embodiments instead merely illustrate the various ways in which the stations in a network system respond to the unavailability of different signal sources. Switching depends on which signal source becomes unavailable and where the available signal source is located in the system as well as the configuration of nodes in the system. For example, the unavailability of the parent station’s external clock will affect the system differently than the unavailability of a signal source between two child stations. See id. at Figs. 4-19, 22-42.

Additionally, the specification draws a distinction between the station sending the flag bit data and the stations receiving that data:

The present invention allows the parent station A to send, during normal operation, a flag bit data S, indicating that the synchronizing signal thereof is available, to all of its neighboring stations, and to send, when there is a failure in the synchronizing signal source, a flag bit data *S indicating that the same signal is not available.

Id. at col.5 11.21-27. After receiving the signal indicating the availability of the synchronizing signal source, “the child stations B, C, D selects [sic], from among the neighboring stations having their flag bit data indicating that their synchronizing signal is available, a station to receive the synchronizing signal from, the selection being based on the order of priority specified in the table.” Id. at col.5 11.29-34. The specification, therefore, distinguishes between the station sending the information (e.g., the parent station) and the stations receiving the information (e.g., the child stations), which are the stations that switch their synchronizing signal source if the flag bit data indicates that the current source is unavailable. In other words, not every station in the network receives the transmitted synchronizing information as recited in step (a) of claim 1, and consequently step (c) of claim 1 does not require every station to switch its synchronizing signal source. Based on the specification, the court finds that a person of ordinary skill would not understand that “switching each station,” as recited in step (c) of claim 1 requires every station in the network to switch.

The parties have not identified anything in the prosecution history that supports their respective constructions. Yet, the court has considered Tellabs’s additional arguments for requiring that every station of the plurality of stations switch its synchronizing signal source and finds that those arguments similarly lack merit. Consequently, based on the intrinsic evidence, the court finds that Fujitsu’s proposed construction is consistent with the plain language of the claims and is confirmed by the teachings of the specification. To require that “every station” switch its signal source, as Tellabs proposes, would improperly import a limitation into the claims. The court, therefore, construes “switching each station” to mean “switching each station which receives said information transmitted via said lines (as recited in step (a) of claim 1).”

3. “table” (claim 1)

The claim term “table” appears in claim 1 of the '418 Patent. Fujitsu proposes that the court construe “table” to mean “a list of data stored in memory.” (Fujitsu’s Resp. 28.) Tellabs, however, contends that “table” is “a data structure containing stored data elements and corresponding labels or indices.” (Tellabs’s Op. Br. 38.) The parties’ dispute on this term centers around whether the table must include labels or indices or could instead be a single column, such as a list. As explained below, the court construes “table” to mean “a list of data stored in memory.”

Step (b) in claim 1 recites:

[Referring each station, from among said plurality of stations on the basis of said flag bit data, to a table provided in each said station for specifying an order of priority for selection of a synchronizing signal source, upon occurrence of a predetermined event in any of said plurality of synchronizing signal sources, and for selecting a synchronizing signal source.

'418 patent, col. 18 1.67-col. 19 1.6 (emphasis added). Based on the claim language, the stations rely on the table for “specifying an order of priority for selection of a synchronizing signal source” and “selecting a synchronizing signal source.” Fujitsu argues that a list of data would fulfill these requirements. Tellabs, on the other hand, argues that a list alone “does not provide an order of priority.” (Case No. 09-4530, Dkt. No. 220 (“Tellabs’s Reply”) 45.) Instead, accordingly to Tellabs, labels or indices are also necessary to prioritize the signal sources. (Id.) Tellabs further contends that the table must include “usage and availability labels” indicating whether a signal source is available to specify the order of priority for selection of a synchronizing source. (Id. at 46.) In other words, without labels identify the usage and availability of the signal source, the table does not assist in the selection of a synchronizing source.

The plain language of claim 1 explains that the “table” is used for “specifying an order of priority for selection of a synchronizing signal source” and “for selecting a synchronizing signal source.” The claim does not expressly require that the “table” provide information regarding the availability and usage of the signal source and therefore does not support Tellabs’s position that the “table” must include such labels or indices indicating the source’s availability and usage. Moreover, the court agrees with Fujitsu that a single list without labels or indices specifies an order of priority, e.g., highest to lowest or first to last, as required by claim 1.

The specification similarly does not warrant a narrower construction of “table.” First, the specification discloses embodiments where the selecting station references the table only to ascertain the order of priority — not the availability or usage of the synchronizing signal source — and then independently determines whether the signal is available:

FIG. 5 illustrates the second stage of a failure that follows the stage shown in FIG. 4. The station B, which has received the flag bit data *S from the adjacent station A to the E direction, refers to the order of priority specified in the table T-B and checks the station C to the W direction. Since, however, the flag bit data *S is detected again, the station B selects the internal synchronizing signal source INT and changes the flag bit data supplied to the station C, from S to *S.

'418 Patent, col.7 11.3-11. In this embodiment, station B does not rely on the table to determine the availability or usage of the signal source but rather “checks the station C to the W direction” to detect the flag bit data which indicates the availability of the source. Thus, one of ordinary skill, having reviewed the specification for the '418 Patent, would understand that the “table” need not include information identifying the availability and usage of the signal source.

Second, the specification depicts tables where the order of priority is identified by a list of synchronizing signal sources without corresponding labels or indices specifying the priority of those sources. For example, Figures 3-19 of the '418 Patent disclose tables where the order of priority of the signal source is conveyed simply by arranging the sources from top to bottom in the table. Although Tellabs is correct that these tables additionally include a first column that refers to the usage and availability of the signal source, as discussed above, the specification does not require that the table include such information.

The court has also considered that parties’ proffered dictionary definitions to assist in determining the ordinary and customary meaning of “table” to a person of ordinary skill. “Dictionaries or comparable sources are often useful to assist in understanding the commonly understood meaning of words .... ” Phillips, 415 F.3d at 1322. In this case, the court finds that the dictionary definitions provided by the parties further confirm that Tellabs’s proposed construction of “table” is overly narrow.

For example, the McGraw-Hill Dictionary of Scientific and Technical Terms (4th ed. 1989), cited by Tellabs, defines a table as “[a] set of continuous, related items, each uniquely identified either by its relative position in the set or by some label.” Id. (attached as Ex. 10 to Tellabs’s Op. Br.). Similarly, The New IEEE Standard Dictionary of Electrical and Electronic Terms (5th ed. 1993), also cited by Tellabs, defines “table” as “[a] collection of data in which each item is uniquely identified by a label, by its position relative to other items, or by some other means.” Id. (attached as Ex. 11 to Tellabs’s Op. Br.). Neither of these definitions indicates that a table necessarily includes labels. Instead, based on these definitions, labels are one of multiple possibilities for organizing data in a table. In addition to labels, the data may be identified “by its position relative to other items” or “by its relative position in the set,” both of which support Fujitsu’s contention that the “table” could consist of a single column. Lastly, The Harper Collins Dictionary of Computer Terms (1991), cited by Fujitsu, defines “table” as “a list of data stored in memory.” Id. at 236 (attached as Ex. B-3 to Fujitsu’s Resp.).

Based on the above evidence, the court finds that it can ascertain the meaning of “table” to a person of ordinary skill without considering the additional extrinsic evidence presented by the parties. To a person of ordinary skill in the art at the time of the invention disclosed in the '418 Patent, the term “table,” as used in the '418 Patent, is data stored in memory in the form of either one or multiple columns and does not necessarily include labels or indices. Consequently, the court adopts Fujitsu’s proposed construction and construes “table” to mean “a list of data stored in memory.”

II. '772 Patent

A. Background

The '772 patent was issued to Tellabs Operations, Inc. on May 6, 2008, and is titled “Optical Line Terminal Arrangement, Apparatus and Methods.” Ornan A. Gerstel and Rajiv Ramaswami are the named inventors. The '772 Patent claims priority to non-provisional application 09/293,775, filed on April 19, 1999, and to provisional application 60/112,510, filed on December 14,1998.

The '772 Patent is directed to various configurations of a wavelength division multiplexing (“WDM”) optical add/drop multiplexing system that adds, drops, or passes through optical signals at corresponding wavelengths and to the related methods for adding, dropping, and passing through WDM optical signals. In a typical optical communication system, a number of stations or nodes transmit data to and receive data from adjacent nodes in the system using optical signals. (9/23/09 Tech. Tutorial Tr. 46:25-47:5.) According to the '772 Patent, the prior art WDM systems required all wavelengths “to pass through from a source optical node to a predetermined sink optical node.” '772 Patent, col.l 11.38-40. The invention disclosed in the '772 Patent purports to advance the prior art by “selectively pass[ing]-through” individual wavelengths or “add[ing] or drop[ing] individual wavelengths at selected optical nodes.” Id. at col. 1 11.41-43 (emphasis added). At a basic level, in a WDM system like the one disclosed in the '772 Patent, multiple optical signals are generated, multiplexed (i.e., combined) to form an optical signal comprised of the individual optical signal channel wavelengths, transmitted, and then demultiplexed (i.e., separated) into individual channel wavelengths. (See Case No. 08-3379, Dkt. No. 204 (“Willner Tutorial”) 24-26.) The demultiplexed wavelengths can be added to or dropped from the node or passed through the node depending on their ultimate destination in the network. (See id.)

The Abstract for the '772 Patent provides the following description of the invention:

A wavelength division multiplexed optical communication system including a first optical line interface optically coupled to a first transponder and an optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder. The system also includes a second optical line interface and at least one switch. The switch is operable to optically couple the second optical line interface to (a) the first optical line interface through at least the optical demultiplexer, and alternatively (b) the second transponder. A method for an optical add/drop multiplexing system also is provided.

'772 Patent, Abstract.

Independent claim 1 of the '772 Patent is representative of the asserted apparatus claims:

A wavelength division multiplexed optical communication system comprising: a first optical line interface optically coupled to a first transponder; a first local port optically coupled to the first transponder;

an optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder;

a second optical line interface; a second local port optically coupled to a second transponder; and at least one switch operable to optically couple the second optical line interface to (a) the first optical line interface through at least the optical demultiplexer, and alternatively (b) the second transponder.

Id. at col.711.1-17 (emphasis added). Independent claim 17 of the '772 Patent is representative of the asserted method claims:

A method for an optical add/drop multiplexing system in a wavelength division multiplexed (WDM) optical network environment, comprising the steps of: establishing at least a first optical path extending from a first optical line interface of the system to a local transponder;

establishing at least a second optical path that in a first state of the system extends from a local transponder to a second optical line interface of the system and is established by at least an optical switch, and in a second state of the system the second optical path alternatively extends from the first optical line interface to the second optical line interface and is established by at least both the optical switch and an optical demultiplexer through which the first optical path does not extend; in the first state of the system, communicating a wavelength along the second optical path to add the wavelength to a WDM signal the system transmits to a WDM network from the second optical line interface; and

in the second state of the system, alternatively communicating along the second optical path a wavelength of a WDM signal received from a WDM network at the first optical line interface to optically pass the wavelength to a WDM signal the system transmits to a WDM network from the second optical line interface.

Id. at col. 9 1.58-col. 10 1.17.

B. Status of Reexamination Proceedings

Fujitsu filed a Request for Inter Partes Reexamination of the '772 Patent with the PTO on July 2, 2009, and the PTO granted that request. (Case No. 08-3379, Dkt. No. 322 (“Tellabs’s Resp.”) 1.) During the inter partes reexamination proceedings, Tellabs cancelled claims 1 and 3-5, and on June 24, 2010, the PTO issued an Action Closing Prosecution which confirmed the patentability of claims 2 and 6-24 without amendment. (Id. at 2.) Fujitsu has appealed that decision to the PTO Board of Patent Appeals and Interferences, and the appeal remains pending. (Case No. 08-3379, Dkt. No. 423 (“Tellabs’s Reexam Status”) at 2.)

Fujitsu also filed a Request for Ex Parte Reexamination of the '772 Patent on December 9, 2009, which the PTO ultimately granted in part with respect to claims 14-16 of the '772 Patent. (Case No. 09-4530, Dkt. No. 298 (“Fujitsu’s Reexam Status”) 2-3.) The PTO issued an Ex Parte Reexamination Certificate dated May 27, 2011, reflecting Tellabs’s cancellation of claims 14-16 of the '772 Patent during reexamination. (See Tellabs’s Reexam Status 2.) To date, claims 2, 6-13, and 17-24 of the '772 Patent remain pending before this court. In the court’s discussion below, the court must refer to now-cancelled independent claim 1 because claim 2, which Tel-labs still asserts against Fujitsu, depends from claim 1.

C. Person of Ordinary Skill in the Art

After extensively reviewing the record, the court has been unable to locate any proposed definition of a person of ordinary skill in the art of the '772 Patent proposed by Fujitsu. The court accordingly adopts Tellabs’s proposed definition, which provides that one of ordinary skill “had at least a Master’s degree in electrical engineering, or the equivalent, and two to five years of experience researching or designing optical communication systems and the components” for such systems. (Tellabs’s Resp. 3.)

D. Claim Constructions

The parties have identified the following eight claim terms in the '772 Patent for the court’s construction: “optical demultiplexer” (claims 2, 6-13 & 17-24); “optical line interface” (claims 2, 6-13 & 17-24); “optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder” (claim 2 & 6-13) and “optical demultiplexer through which the first optical path does not extend” (claims 17-24); “transponder” (claims 2, 6-13 & 17-24); “local port” (claim 2); “modular card” (claims 11-13, 22 & 24); and “office/reside in the same office (claims 8 & 21).”

1. “optical demultiplexer” (claims 2, 6-13 & 17-24)

The claim term “optical demultiplexer” appears in claims 2, 6-13, and 17-24 of the '772 Patent. In its preliminary construction, this court construed the claim term “optical demultiplexer” to mean “a device that receives a plurality of wavelengths multiplexed together as an optical signal and outputs each of the plurality of wavelengths as at least one of the following: (a) individual wavelengths, (b) bands of wavelengths or (c) a combination of bands and individual wavelengths.” (Prelim. Constr. Op. 10.)

Fujitsu argues that the court should modify its previous construction to require that the optical demultiplexer receives its input on a single optical waveguide and that the optical signal input be comprised of N optical wavelength channels. Fujitsu accordingly proposed the following construction of “optical demultiplexer”: “a device that receives a single optical waveguide carrying an optical signal having N optical wavelength channels and outputs the N wavelength channels on individual optical waveguides, where the device outputs each of the N wavelengths as at least one of the following: (a) individual wavelengths, (b) bands of wavelengths or (c) a combination of bands and individual wavelengths.” (Case No. 08-3379, Dkt. No. 335 (“Fujitsu’s Reply”) 33 & n.65.) This amendment to the court’s preliminary construction, Fujitsu contends, reflects the ordinary and customary meaning of “optical demultiplexer” and to prevents the optical demultiplexer from reading on an optical multiplexer or a router, which are devices having multiple inputs. (Case No. OS-3379, Dkt. No. 298 (“Fujitsu’s Op. Br.”) 38-42.)

Tellabs, however, argues that these limitations in Fujitsu’s construction are not supported by either the intrinsic or extrinsic evidence and improperly impose structural limitations on the term. (Tellabs’s Resp. 21-22.) Tellabs instead submits that the court should maintain its preliminary construction with minor amendment: “a device that receives a plurality of wavelengths multiplexed together as an optical signal and outputs each ■ of separates the plurality of wavelengths as into at least one of the following: (a) individual wavelengths, (b) bands of wavelengths or (c) a combination of bands and individual wavelengths.” (Tellabs’s Resp. 19.) According to Tellabs, with this minor modification, its proposed construction differentiates a “optical demultiplexer,” which separates the wavelengths, from an optical multiplexer which combines the wavelengths. Having reviewed the parties’ respective positions, the court modifies its construction of the term “optical demultiplexer” to mean:

A device that receives a single optical waveguide carrying an optical signal having N optical wavelength channels and outputs the N wavelength channels on individual optical waveguides, where the device outputs each of the N wavelengths as at least one of the following: (a) individual wavelengths, (b) bands of wavelengths or (c) a combination of bands and individual wavelengths.

The court’s construction of “optical demultiplexer” requires the resolution of two primary issues: first, whether the optical demultiplexer has a single input; and second, whether that input must be a waveguide. First addressing the claims, the plain language of the claims does not reference the optical demultiplexer’s input. The specification, however, illustrates that a person of ordinary skill would understand the “optical demultiplexer” to have a single waveguide input.

In the “Background of Invention” section, the '772 Patent explains that “[i]n a WDM system optical signal channels are generated, multiplexed to form an optical signal comprised of the individual optical signal channels, transmitted over a single wavegidde, and demultiplexed such that each channel wavelength is individually routed to a designated receiver.” '772 Patent, col. 1 11.29-34 (emphasis added). The specification also discloses that optical demultiplexer receiving the optical signals over a “single optical fiber,” which is a type of waveguide. (See 12/3/10 Markman Tr. 490:3-6 (recognizing that “waveguides” is broader than “optical fibers”).) The following embodiment, for example, includes optical wavelengths on “a single optical fiber” being demultiplexed:

The OLT 2 has an input/output line interface 4 which is connected to an external fiber facility and transmits/receives an optical signal having N optical wavelengths, for example 32 wavelengths, on a single optical fiber which is multiplexed/demultiplexed by a multiplexer/demultiplexer 6, which outputs demultiplexed wavelengths Xl-XN on individual optical fibers.

'772 Patent, col.2 11.38-46; see also id. at col.3 11.61-63; col.4 11.16-20. Tellabs has not directed the court to any evidence in the specification that identifies a non-waveguide input for the demultiplexer.

This interpretation of the customary meaning of optical demultiplexer to a person of ordinary skill is also consistent with Optical Networks, a cited prior art reference that was co-authored by Dr. Rajiv Ramaswami, one of the named inventors of the '772 Patent. The parties agree that Optical Networks reflects the understanding of a person of ordinary skill at the time of the invention. (See Fujitsu’s Op. Br. 39; Tellabs’s Resp. 25.) Optical Networks explains that “[a] multiplexer combines signals at different wavelengths on its input ports onto a common output port, and a demultiplexer performs the opposite function.” Optical Networks 90 (1st ed. 1998) (attached as Ex. A-5 to Fujitsu’s Op. Br). Optical Networks also explains that the demultiplexer receives the multiple wavelengths on a single fiber in describing Figure 3.6: “A multiplexer, which combines multiple wavelengths into a single fiber. In the reverse direction, the same device acts as a demultiplexer to separate the different wavelengths.” Optical Networks 116 (2d ed. 2002) (attached as Ex. B-13 to Fujitsu’s Op. Br.). Additionally, as Tellabs admits, Optical Networks “clearly discloses at least one embodiment of an optical demultiplexer that employs waveguides, not optical fibers, for coupling optical signals to and from the optical demultiplexer.” (Tellabs’s Resp. 25 (emphasis added).)

The requirement that the demultiplexer include a single input on a waveguide is further supported by the Fiber Optics Standard Dictionary (1997), which was cited by the PTO during the reexamination of the '772 Patent. (Tellabs’s Resp. 19 n. 86.) The Fiber Optics Standard Dictionary defines “demultiplex” as “[t]he inverse of multiplex, i.e., to separate two or more signals, such as optical pulses, that previously were combined, i.e., were multiplexed, by a compatible multiplexer and transmitted over a single channel, such as a fiber optical channel, for subsequent demultiplexing.” Fiber Optics Standard Dictionary 209 (3d ed. 1997) (emphasis added) (attached as Ex. 17 to Tellabs’s Resp.). A “demultiplexer,” the Fiber Optics Standard Dictionary further explains, is “[a] device that performs demultiplexing.” Id.

Based on this evidence, the court disagrees with Tellabs’s position that “the means for coupling optical signals to and from an optical demultiplexer is separate and distinct from the optical demultiplexer itself.” (Tellabs’s Resp. 27.) Instead, the above evidence demonstrates that the physical structure of the input is an integral part of an “optical demultiplexer” as that term is commonly understood to a person of ordinary skill in the art.

The court notes that Tellabs has presented certain extrinsic evidence suggesting that the optical signal could be input into the optical demultiplexer through the air rather than through a single waveguide. {See Case No. 09-4530, Dkt. No. 261 (“Tellabs’s '772 Patent Presentation”) 48.) Based on the disclosures of the '772 Patent coupled with the additional intrinsic evidence and dictionary definitions addressed above by the court, the court disagrees that one of ordinary skill in the art of the '772 Patent would understand that an ordinary optical demultiplexer would have such an input. The evidence discussed above repeatedly refers to an input over a physical medium, with that medium being either broadly described as a waveguide or more specifically referred to as a single optical fiber or a fiber optical channel. Thus, although inputting the optical signal into optical demultiplexer via air may be possible, one of ordinary skill in the art of the '772 Patent would not understand that the “optical demultiplexer” for the WDM system disclosed in the '772 Patent could receive such an input.

The parties have presented additional extrinsic evidence in support of their respective positions as to whether an optical demultiplexer must receive its optical signal input on a single input waveguide, but the court finds that it need not consider this evidence to ascertain the meaning of this term to a person of ordinary skill. From the intrinsic evidence and the proffered dictionary definitions, the court finds that “optical demultiplexer,” as that term appears in the '772 Patent, “receives a single optical waveguide carrying an optical signal,” as proposed by Fujitsu. The court has considered Tellabs’s additional arguments in support of its proposed construction and finds that they also do not support a broader interpretation of “optical demultiplexer.”

Lastly, the court agrees with Fujitsu that the “optical demultiplexer” is not used to perform the function of a “filter,” which discards at least one of the constituent wavelengths input to the filter. As the specification explains, “an optical signal having N optical wavelengths .. [is] multiplexed/demultiplexed by a multiplexer/demultiplexer 6, which outputs demultiplexed wavelengths X.1-XN on individual optical fibers.” '772 Patent, col.2 11.42 — 46. In other words, all the wavelengths input into the demultiplexer are subsequently output after being demultiplexed. Thus, for clarity and to distinguish the optical demultiplexer from a filter, the court construes the claim term “optical demultiplexer” to mean:

A device that receives N optical wavelengths multiplexed together as an optical signal on a single optical waveguide and outputs the N wavelength channels on individual optical waveguides, where the device outputs each of the N wavelengths as at least one of the following: (a) individual wavelengths, (b) bands of wavelengths or (c) a combination of bands and individual wavelengths.

2. “optical line interface” (claims 2, 6-13 & 17-24)

The term “optical line interface” appears in claims 2, 6-13, and 17-24 of the '772 Patent. In its preliminary construction, this court construed the claim term “optical line interface” to mean “an interface that can carry a plurality of wavelengths multiplexed together as an optical signal.” (Prelim. Constr. Op. 13.) Tellabs agrees with the court’s preliminary construction. Fujitsu, however, argues that the court should revise this construction to read: “An interface adapted for transmitting/receiving wavelength division multiplexed optical communication signals on a single optical fiber (where ‘transmitting/receiving’ means ‘transmitting and receiving’).” For the following reasons, the court adopts Fujitsu’s proposed construction and construes “optical line interface” in claims 2, 6-13, and 17-24 of the '772 Patent to mean “an interface adapted for transmitting/receiving wavelength division multiplexed optical communication signals on a single optical fiber (where ‘transmitting/receiving’ means ‘transmitting and receiving’).” The parties agree that an “optical line interface” can send or receive a plurality of wavelengths multiplexed together. The dispute centers on (1) whether the “optical line interface” must be bidirectional and (2) whether the signals must travel over a single optical fiber.

First, the term “optical line interface” does not appear to have a customary meaning to a person of ordinary skill. Tellabs admits that the term “optical line interface” is an “uncommon term” (Case No. 09-4530, Dkt. No. 261, Tellabs’s '772 Patent Presentation 117; 12/3/10 Mark-man Tr. Vol. 4, 433:6-10), and the inventor testimony presented by Fujitsu further confirms that this term lacks an ordinary meaning. Specifically, Dr. Ramaswami acknowledged that “optical line interface” was not “commonly used” (Ramaswami Dep. -149:15-21 (attached as Ex. B-5 to Fujitsu’s Op. Br.)), and Dr. Gerstel similarly stated that the term is “somewhat generic” (Gerstel Dep. 97:3-4 (attached as Ex. B-2 to Fujitsu’s Op. Br.)). “Without a customary meaning of a term within the art, the specification usually supplies the best context for deciphering claim meaning.” Honeywell Int’l Inc. v. Universal Avionics Sys. Corp., 488 F.3d 982, 991 (Fed.Cir.2007).

Here, the specification repeatedly and uniformly discloses that the “optical line interface” is bidirectional and transmits the signals over a single optical fiber. The Detailed Description of the Invention section instructs that

FIG. 1 is a block diagram of an optical line terminal (OLT) 2 which is the basic element of the present embodiment. The OLT 2 has an input/owtput line interface 4 which is connected to an external fiber facility and transmits/receives an optical signal having N optical wavelengths, for example 32 wavelengths, on a single optical fiber which is multiplexed/demultiplexed by a multiplexer/demultiplexer 6, which outputs demultiplexed wavelengths Xl-XN on individual optical fibers.

'772 Patent, col.2 11.39-46 (emphasis added). Figure 1 confirms that the phase “transmits/receives” in the above excerpt refers to both transmitting and receiving. In Figure 1, signals are traveling both left to right and right to left and either enter or exit the multiplexer/demultiplexer 6 through the input/output line interface 4.

Similarly, in Figure 3, “[t]he OLT terminal 200 has input/output line interface 202 which is connected to an external fiber facility and receives on a single optical fiber N ... wavelengths which are demultiplexed by a multiplexer/demultiplexer 204.” Id. at col.4 11.16-20. Finally, in describing Figure 4 of the '772 Patent, the specification states:

FIG. 4 is a simplified schematic diagram representative of the OLT 2 shown in FIG. 1 or the OLT 200 of FIG. 3.... The OLT 300 interfaces and operates in a bidirectional manner as discussed in detail with respect to FIGS. 1 and 3. The line interface 302 is adapted for wavelength division multiplexed (WDM) optical communication signals of the highest relative order ... corresponding to the N optical wavelengths on a single optical fiber which are applied to input/output line interfaces 4 and 202 of OLT 2 (FIG. 1) and OLT 200 (FIG. 3), respectively.

Id. at col.411.53-54.

The '772 Patent’s embodiments disclosed in the specification consistently require that the “optical line interface” is a single, bidirectional optical fiber, and Tel-labs has not identified any evidence in the specification suggesting that “optical line interface” could have a broader meaning to a person of ordinary skill.

Tellabs, however, argues that the language of the claims does not support limiting requiring that the “optical line interface” be bidirectional. The court disagrees. Claim 6 recites, inter alia, “a first optical line interface operable to receive from a WDM network an optical signal” and “a second optical line interface operable to transmit to a WDM network an optical signal.” Id. at col.7 11.39-40, 51-52. According to Tellabs, because claim 6 only requires that the optical line interface “receive” or “transmit” the optical signal, the optical line interface need not be bidirectional. This interpretation is not persuasive. Instead, the court agrees with Fujitsu that claim 6 refers to a first optical line interface that receives a signal from a first WDM network and a second optical line interface that transmits the signal to a second, different WDM network. Moreover, to the extent that claim 6 could be interpreted as implying that the “optical line interface” is unidirectional, that interpretation is inconsistent with the teachings of the specification.

In Retractable Technologies, Inc. v. Becton, 653 F.3d 1296 (Fed.Cir.2011), the Federal Circuit held that the district court erred in broadly construing the claim term “body” as not being limited to a “one-piece structure.” The patent in Retractable Technologies recited a “body” in an independent claim and a “one-piece body” in a dependent claim, but none of the claims “expressly recite[d] a body that contains multiple pieces.” Id. at 1305. As a result, the court concluded that “while the claims [could] be read to imply that a ‘body’ [was] not limited to a one-piece structure, that implication [was] not a strong one.” Id. Emphasizing that the “[c]laim language must always be read in view of the written description,” the court ultimately found that the specification limited the claimed “body” to a one-piece structure. Id. at 1304-06.

Similarly here, the specification uniformly discloses that the optical line interface both transmits and receives signals bidirectionally on a single fiber; it provides no examples of a unidirectional optical line interface. Additionally, the '681 Patent’s claims, like the claims in Retractable Technologies, do not “expressly recite” that the optical line interface need only transmit or receive signals unidirectionally. The court, therefore, disagrees with Tellabs that the language of claim 6 supports broadening the optical line interface beyond the disclosures of the specification.

Nor does Tellabs’s cited excerpt from Optical Networks (1st ed. 1998) suggest that one of ordinary skill would understand that the optical line interface disclosed in the '772 Patent could be unidirectional and on multiple fibers. Tellabs relies on the following statement from that text:

A unidirectional WDM system uses two fibers, one for each direction of traffic .... A bidirectional system, on the other hand, requires only one fiber, and typically uses half the wavelengths for transmitting data in one direction and the other half for transmitting data in the opposite direction on the same fiber. Both types of systems are being developed and have their pros and cons.

Optical Networks 505 (1st ed. 1998) (attached as Ex. 13 to Tellabs’s Resp.). This excerpt, however, does not refer to an “optical line interfaces” and thus provides little guidance as to how one of ordinary skill in the art would understand that claim term. Moreover, the '772 Patent’s specification uniformly discloses a bidirectional — not a unidirectional — system. That a person of ordinary skill would have been aware of unidirectional WDM systems does not change the express teachings of the specification or support broadening the claims. Tellabs is not entitled to a construction of “optical line interface” that is “divorced from what the specification conveys is the invention.” Retractable Techs., 653 F.3d at 1305. Consequently, for the reasons explained above, the court construes “optical line interface” to mean “an interface adapted for transmitting/receiving wavelength division multiplexed optical communication signals on a single optical fiber (where ‘transmitting/receiving’ means ‘transmitting and receiving’).”

3. “optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder” (claims 2 & 6-13) and “optical demultiplexer through which the first optical path does not extend” (claims 17-24)

The claim term “optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder” appears in claims 2 and 6-13 of the '772 Patent. The claim term “optical demultiplexer through which the first optical path does not extend” appears in claims 17-24 of the '772 Patent. Because these terms are so closely related, the parties refer to these phrases collectively as “optical demultiplexer through which .... ” The court, therefore, addresses them together.

In its prehminary construction, this court construed the claim term “optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder” to mean “the first optical line interface does not send optical information to the first transponder through the optical demultiplexer. Alternatively, the first optical line interface does not receive optical information from the first transponder through the optical demultiplexer.” (Preliminary Constr. Op. 12.) The court similarly construed the claim term “optical demultiplexer through which the first optical path does not extend” in claims 17-24 of the '772 Patent to mean “the first optical path does not pass through the optical demultiplexer.” (Id. at 26.)

Fujitsu argues that the court should revise its preliminary constructions of these terms because the claims of the '772 Patent are expressly directed to a two-stage optical demultiplexer arrangement. (Fujitsu’s Op. Br. 47.) Fujitsu also contends that Tellabs’s statements during the prosecution of the '772 Patent amounted to a disavowal of a single-stage demultiplexer system, thereby limiting the terms to two-stage optical demultiplexer arrangements. (Id. at 53-55.) Consequently, Fujitsu contends that the proper construction of these terms is “optical demultiplexer that receives a band of a predetermined number of wavelengths output from another demultiplexer, separates the band into its individual wavelengths and does not provide any of those individual wavelengths to the first transponder.” Id. at 47 (emphasis added). Tellabs, on the other hand, maintains that the claim language of the '772 Patent does not require a second-stage demultiplexer and that the court’s preliminary construction of these terms was correct. (Tellabs’s Resp. 28.) The central issue regarding these claim terms, therefore, is whether the “optical demultiplexer through which ...” must be a demultiplexer that receives a band of wavelengths from another demultiplexer, i.e., whether the claims are limited to a two-stage demultiplexing arrangement. After reviewing the parties’ respective arguments and the relevant evidence, the court agrees with Tellabs that the phrase “optical demultiplexer through which ...” does not require such a two-stage demultiplexing arrangement.

The claim terms “optical demultiplexer through which the first optical line interface is not optically coupled to the first transponder” and “optical demultiplexer through which the first optical path does not extend” were added by amendment during prosecution in the PTO in September 2007. The claims alone do not indicate that the “optical demultiplexer through which ...” phrases require a two-stage demultiplexer arrangement. Claim 1, for example, only refers to one optical demultiplexer, the “optical multiplexer through which the first optical line interface is not optically coupled to the first transponder.” That claim similarly does not reference both first- and second-stage demultiplexing. When the claims are intended to require the inclusion of multiple devices, however, the claims clearly recite such a limitation. Claim 1, for example, refers to a first and second optical line interface, a first and second local port, and a first and second transponder. A similar reference to a first and second optical demultiplexer is noticeably absent from the claim language, thereby suggesting that the “optical demultiplexer through which ...” phrases do not require the presence of both a first and second optical demultiplexer.

Turning to the specification, Fujitsu argues that the only support for the “optical demultiplexer through which ...” claim limitations is the two-stage demultiplexer arrangement disclosed in Figure 3 of the '772 Patent.

Figure 3 depicts a first-stage demultiplexer (204) that demultiplexes the input signal from line 320 into smaller parts (e.g. bands of wavelengths) and outputs those smaller parts on lines 206 and 214. Lines 206 and 214 are inputs for the second-stage demultiplexers (208, 216). Mapping a path between the first optical line interface (202) and the first transponder (here, the T connected to the lower second-stage demultiplexer (214)), demultiplexer (208) is the only demultiplexer “through which the first optical line interface is not optically coupled to the first transponder.” Although Tellabs has not identified any additional embodiments expressly disclosed in the specification supporting the “optical demultiplexer through which ...” limitation, the Federal Circuit has repeatedly ca