# US 12,003,317 B2 · Bidirectional single-fiber coherent transmission system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,003,317 B2 - Document ID: US12003317B2 - Status: Granted - Kind: B2 - Application number: 17/781,513 - Filed: 2020-12-07 - Published: 2023-01-05 - Granted: 2024-06-04 - Earliest claimed: 2019-12-05 - Assignees: Lumentum Operations LLC - Applicants: Lumentum Operations LLC - Inventors: George BuAbbud - Web page: https://patentgrep.com/patent/US12003317B2 ## CPC - H04B 10/40: Transceivers - H04J 14/0227: {Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation} - H04B 10/2589: {Bidirectional transmission} - H04J 14/0241: {Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths} - H04B: TRANSMISSION - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) ## Abstract The Bi-Di coherent transmission system is configured with at least one pair of modules coupled to one another via a single fiber. The modules each are configured with a pair of laser outputting two reference signals at respective different wavelengths λ1o and λ2o, photonic transceiver and a wavelength division multiplexer (WDM) coupler. The photonic transceivers each have transmitter and receiver branches integrated in a photonic circuit and receiving the reference signals. The transmitter is configured to modulate the received reference signals λ1oT and λ2oT which are further coupled into the WDM coupler. The WDM couplers each sort out one of the modulated signals and transmit the other modulated signal such that the transmitted modulated signal at different wavelengths λ1oT and λ2oT are coupled into respective opposite ends of the fiber and propagate towards one another in opposite directions. The transmitted modulated signals are coupled into respective branches through the WDM couplers with each transmitted modulated signal interfering with the reference signals at wavelengths λ1o and λ2o. The photodiodes of respective receiving branches are configured to detect a beat frequency of the interfering signals at the same wavelength. ## Claims ### Claim 1 A bidirectional (BiDi) coherent transmission system comprising: at least one pair of spaced modules each configured with: two lasers outputting respective reference signals at different wavelengths λ1o and λ2o, a photonic transceiver including transmitting and receiving branches which both receive the reference signals, the transmitting branches of respective transceivers each being configured to output respective modulated signals λ1oT and λ2oT, a Bi-Di wavelength division multiplexer (WDM) coupler receiving modulated signals λ1oT and λ2oT and sorting out one of them, so that only modulated signals at respective different wavelengths λ1oT and λ2oT are transmitted by respective WDMs, and a single fiber guiding transmitted modulated signals λ1oT and λ2oT in respective directions opposite to one another towards respective receiving branches which each have a photodiode (PD), the transmitted modulated signals each interfering with the reference signals at respective wavelengths λ1o and λ2o such that each PD detects a beat frequency of the reference and transmitted modulated signals at the same wavelength but is not responsive to a beat frequency of the reference and transmitted modulated signals at respective different wavelengths. ### Claim 2 (depends on 1) The Bi-Di coherent transmission system of claim 1, wherein the transceivers each are integrated in a photonic integrated circuit (PIC). ### Claim 3 (depends on 2) The Bi-Di coherent transmission system of claim 2, wherein the lasers each are integrated in respective PICs or are pigtailed. ### Claim 4 (depends on 3) The Bi-Di coherent transmission system of claim 3, wherein the lasers each are a single frequency diode laser or single frequency fiber laser. ### Claim 5 (depends on 3) The Bi-Di coherent transmission system of claim 3 further comprising a pair of couplers each located between the pigtailed lasers and transceiver and configured to split an output of the lasers between the transmitting and receiving branches of each PIC. ### Claim 6 (depends on 2) The Bi-Di coherent transmission system of claim 2, wherein the transmitting branches each are configured with one or more phase modulators integrated in the PIC. ### Claim 7 (depends on 2) The Bi-Di coherent transmission system of claim 2, wherein the WDM couplers each are integrated in the PIC or pigtailed. ### Claim 8 (depends on 1) The Bi-Di coherent transmission system of claim 1, wherein the fiber is a single transverse mode fiber. ### Claim 9 (depends on 1) The Bi-Di coherent transmission system of claim 1, further comprising a plurality of additional modules grouped in one and other clusters such that each module of one cluster is paired with a corresponding module of the other cluster to form a plurality of pairs of modules. ### Claim 10 (depends on 9) The Bi-Di coherent transmission system of claim 9, wherein the modules of the other cluster are located in a hub and optically coupled to the WDM which is common to the modules of the hub, the modules of the one cluster having respective WDMs which are optically coupled to an output WDM, the output WDM and WDM common to the modules of the other cluster being coupled to respective opposite ends of the single fiber. ### Claim 11 (depends on 10) The Bi-Di coherent transmission system of claim 10, wherein the lasers of each pair of the modules output different reference signals at respective wavelengths which differ from wavelengths of respective reference signals of all other pairs. ### Claim 12 (depends on 9) The Bi-Di coherent transmission system of claim 9, wherein the output WDM and WDM of the other cluster each have a multichannel configuration. ### Claim 13 A bidirectional (BiDi) coherent transmission module comprising: two lasers outputting respective reference signals at different wavelengths λ1o and λ2o; a photonic transceiver including a transmitting branch and a receiving branch, wherein both the transmitting branch and the receiving branch are configured to receive the reference signals, wherein the receiving branch comprises a photodiode (PD), and wherein the transmitting branch is configured to output the modulated reference signals, including modulated signal λ1oT and modulated signal λ2oT; a Bi-Di wavelength division multiplexer (WDM) coupler configured to receive the modulated reference signals and filter the modulated reference signals so that only one of the modulated reference signals, modulated signal λ1oT or modulated signal λ2oT, is transmitted by the WDM; and a single fiber configured to guide a transmitted modulated signal from the WDM in a direction opposite to another transmitted modulated signal, such that the other transmitted modulated signal interferes with the reference signals at wavelengths λ1o or λ2o, wherein the PD is configured to detect a beat frequency of the reference signal and the other transmitted modulated signal at a same wavelength but is not responsive to a beat frequency of the reference signal and the other transmitted modulated signal at different wavelengths. ### Claim 14 (depends on 13) The Bi-Di coherent transmission module of claim 13, wherein the transceiver is integrated in a photonic integrated circuit (PIC). ### Claim 15 (depends on 14) The Bi-Di coherent transmission module of claim 14, wherein the lasers are integrated in the PIC or are pigtailed. ### Claim 16 (depends on 15) The Bi-Di coherent transmission module of claim 15, wherein the lasers are single frequency diode lasers or single frequency fiber lasers. ### Claim 17 (depends on 15) The Bi-Di coherent transmission module of claim 15, further comprising a coupler located between the pigtailed lasers and the transceiver and configured to split an output of the lasers between the transmitting branch and the receiving branch. ### Claim 18 (depends on 14) The Bi-Di coherent transmission module of claim 14, wherein the transmitting branch is configured with one or more phase modulators integrated in the PIC. ### Claim 19 (depends on 14) The Bi-Di coherent transmission module of claim 14, wherein the WDM coupler is integrated in the PIC or pigtailed. ### Claim 20 (depends on 13) The Bi-Di coherent transmission module of claim 13, wherein the fiber is a single transverse mode fiber.