# US 7,609,976 B2 · Method and system for ultra-high bit rate fiber-optic communications > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,976 B2 - Document ID: US7609976B2 - Status: Granted - Kind: B2 - Application number: 11/239,656 - Filed: 2005-09-29 - Published: 2007-03-29 - Granted: 2009-10-27 - Earliest claimed: 2005-09-29 - Assignees: Alcatel-Lucent USA Inc. - Inventors: Xiang Liu; Lothar Benedict Erhard Josef Moeller; Yikai Su; Chongjin Xie - Web page: https://patentgrep.com/patent/US7609976B2 ## CPC - H04B 10/5165: {Carrier suppressed; Single sideband; Double sideband or vestigial} - H04B 10/505: {using external modulation} - H04B 10/5162: {Return-to-zero modulation schemes} - H04B 10/5167: {Duo-binary; Alternative mark inversion; Phase shaped binary transmission} - H04L 7/0075: {with photonic or optical means} - H04L 7/027: extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method and system for ultra-high bit rate fiber-optic communications (e.g., 160 Gb/s) utilize a phase-correlated modulation format where phases of bits in adjacent four-bit groups in transmitted optical pulse trains are altered by π (or 180°). ## Claims ### Claim 1 A method of synchronizing a receiver in an ultra-high bit rate fiber-optic communications network, comprising: modulating a coherent continuous-wave (CW) laser to form a phase-correlated optical data stream comprising a sequence of four-bit groups, wherein adjacent four-bit groups have respective phase relationships offset by π; and transmitting the phase-correlated optical data stream, wherein the phase-correlated optical data stream is adapted to be filtered at the receiver using an optical band-pass filter to recover thereby a clock signal wherein the optical band-pass filter has a bandwidth of about ¼ of a bandwidth of the modulated optical signal of the CW laser. ### Claim 2 (depends on 1) The method of claim 1, further comprises: modulating a pump laser with a data pattern stream where a state of polarization of adjacent four-bit groups is altered. ### Claim 3 (depends on 2) The method of claim 2, further comprises: modulating the pump laser at a bit rate of about 160 Gb/s. ### Claim 4 (depends on 2) The method of claim 2, wherein the state of polarization of the adjacent four-bit groups is altered by π/2. ### Claim 5 (depends on 2) The method of claim 2, wherein the coherent CW laser is modulated using a fiber-based Kerr-effect shutter controlled by a modulated output signal of the pump laser. ### Claim 6 (depends on 1) The method of claim 1, wherein the method further comprises: using an electro-optical converter comprising a Mach-Zehnder modulator and a controlled polarizer for converting data to be transmitted. ### Claim 7 An apparatus for synchronizing a receiver in an ultra-high bit rate fiber-optic communications network, comprising: means for modulating a coherent continuous-wave (CW) laser to form a phase-correlated optical data stream comprising a sequence of four-bit groups, wherein adjacent four-bit groups have respective phase relationships offset by π; and means for transmitting the phase-correlated optical data stream, wherein the phase-correlated optical data stream is adapted to be filtered at the receiver using an optical band-pass filter to recover thereby a clock signal wherein the coherent CW laser is modulated using a fiber-based Kerr-effect shutter controlled by a modulated output signal of the pump laser. ### Claim 8 (depends on 7) The apparatus of claim 7, further comprises: means for modulating a pump laser with a data pattern stream where a state of polarization of adjacent four-bit groups is altered. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the pump laser is modulated at a bit rate of about 160 Gb/s. ### Claim 10 (depends on 8) The method of claim 8, wherein the state of polarization of the adjacent four-bit groups is altered by π/2. ### Claim 11 (depends on 9) The method of claim 9, wherein the transmitting means comprises: a Mach-Zehnder modulator and a controlled polarizer for converting data to be transmitted. ### Claim 12 A wavelength division multiplexing (WDM) system for ultra-high bit rate fiber-optic communications, comprising: a wavelength-matched transmitter at a first terminal comprises: a pump laser; an electro-optical converter for converting of data to be transmitted from the first terminal to a second terminal, the electro-optical converter including a modulator of a pump laser beam; a coherent continuous-wave (CW) laser; and a Kerr-effect shutter for producing, from the coherent beam of the CW laser, a phase-correlated optical data stream comprising a sequence of four-bit groups, whereby adjacent four-bit groups have respective phase relationships offset by π, wherein the shutter is controlled by a modulated signal of the pump laser; a fiber-optic span propagating the phase-correlated data stream between the wavelength-matched transmitter of the first terminal with a wavelength-matched receiver of a second terminal; and the wavelength-matched receiver for receiving the phase-correlated data stream comprises: an opto-electronic demodulator for demodulating the phase correlated data stream; and a synchronization circuit for recovering a clock signal. ### Claim 13 (depends on 12) The system of claim 12 wherein the modulator modulates the pump laser at an ultra-high bit rate. ### Claim 14 (depends on 12) The system of claim 12 wherein the CW laser is modulated to form a phase-correlated optical pulse train where phases of bits in adjacent four-bit groups are altered by π. ### Claim 15 (depends on 12) The system of claim 12 wherein the modulator uses on/off keying modulation scheme. ### Claim 16 (depends on 12) The system of claim 12 wherein the synchronization circuit further comprises an optical band-pass filter and an electrical band-pass filter, wherein a bandwidth of the optical band-pass filter is about ¼ of a bandwidth of the modulated optical signal of the CW laser. ### Claim 17 (depends on 16) The system of claim 16 wherein a Q-factor of the electrical band-pass filter is greater than or equal to 1000. ### Claim 18 (depends on 16) The system of claim 16 wherein a central frequency of the electrical band-pass filter is about ¼ of the ultra-high bit rate.