# US 8,787,767 B2 · High-speed low-jitter communication system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,767 B2 - Document ID: US8787767B2 - Status: Granted - Kind: B2 - Application number: 13/469,650 - Filed: 2012-05-11 - Published: 2013-08-08 - Granted: 2014-07-22 - Earliest claimed: 2012-02-03 - Assignees: Raytheon Company - Applicants: Steven R. Wilkinson; Gabriel N. Price - Inventors: Steven R. Wilkinson; Gabriel N. Price - Web page: https://patentgrep.com/patent/US8787767B2 ## CPC - H04B 10/516: Details of coding or modulation - H04B 10/548: Phase or frequency modulation - H04B 10/61: Coherent receivers - H04B 10/65: {Intradyne, i.e. coherent receivers with a free running local oscillator having a frequency close but not phase-locked to the carrier signal} - H04L 27/2096: {Arrangements for directly or externally modulating an optical carrier (optical modulation H04B10/503)} - H04L 27/2697: {in combination with other modulation techniques} - H04L 27/3818: {using coherent demodulation, i.e. using one or more nominally phase synchronous carriers (H04L27/227 and H04L27/389 take precedence)} - H04J 14/0298: {with sub-carrier multiplexing [SCM]} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - 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 Communication apparatus and techniques, such as for optical communication, can include providing a reference frequency derived from an atomic energy level transition or a molecular energy level transition, generating at least two specified optical carrier signals at least in part using the reference frequency, coherently modulating the specified optical carrier signals using respective baseband information signals to provide respective coherently-modulated optical subcarriers. A combined optical information signal comprising the optical subcarriers can be transmitted to a receiver, such as via a fiber optic cable. In an example, a received optical information signal can be optically Fourier transformed to provide respective coherent outputs, which can be coherently downconverted. ## Claims ### Claim 1 A communication system, comprising: a local optical oscillator configured to provide a reference frequency derived from an atomic energy level transition or a molecular energy level transition; an optical carrier generator configured to generate at least two specified optical carrier signals at least in part using the reference frequency provided by the local optical oscillator; a complex modulator coupled to the optical carrier generator and configured to coherently modulate the at least two specified optical carrier signals using respective baseband information signals to provide at least two respective coherently-modulated optical subcarriers; a optical combiner coupled to the complex modulator and configured to combine the at least two respective modulated optical subcarriers to provide a combined optical information signal. ### Claim 2 (depends on 1) The communication system of claim 1, wherein the local optical oscillator is stabilized using a cavity mode supported by an optical cavity, and using one or more of an atomic or a molecular energy level transition. ### Claim 3 (depends on 1) The communication system of claim 1, wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers. ### Claim 4 (depends on 3) The communication system of claim 3, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap. ### Claim 5 (depends on 1) The communication system of claim 1, wherein the optical carrier generator comprises an optical frequency comb generator configured to provide an optical frequency comb comprising at least two specified frequency peaks, the at least two specified frequency peaks are separated by a specified frequency offset. ### Claim 6 (depends on 1) The communication system of claim 1, comprising an electrical coupling between the local optical oscillator and the optical carrier generator; and wherein the optical carrier generator is configured to receive the reference frequency via the electrical coupling. ### Claim 7 (depends on 1) The communication system of claim 1, comprising a complex modulator driver configured to provide the respective complex baseband information signals to the complex modulator, including respective in-phase and quadrature signals; and an electrical coupling between the local optical oscillator and the complex modulator driver; and wherein the complex modulator driver is configured to receive the reference frequency via the electrical coupling. ### Claim 8 (depends on 1) The communication system of claim 1, wherein the local optical oscillator is configured to provide a reference frequency derived from an atomic energy level transition. ### Claim 9 (depends on 1) The communication system of claim 1, wherein local optical oscillator is configured to provide a reference frequency derived from a molecular energy level transition. ### Claim 10 A communication system, comprising: a local optical oscillator configured to provide a reference frequency derived from an atomic energy level transition or a molecular energy level transition; an optical Fourier transform module configured to receive an optical signal comprising at least two coherently-modulated optical subcarriers and configured to provide at least two coherent outputs respectively corresponding to the at least two coherently-modulated optical subcarriers, at least in part using the reference frequency; and an optical mixer coupled to the optical Fourier transform module and configured to coherently downconvert the at least two coherent outputs corresponding to the at least two coherently-modulated optical subcarriers to provide at least two respective coherently-downconverted signals, at least in part using the reference frequency. ### Claim 11 (depends on 10) The communication system of claim 10, wherein the local optical oscillator is stabilized using a cavity mode supported by an optical cavity, and using one or more of an atomic or a molecular energy level transition. ### Claim 12 (depends on 10) The communication system of claim 10, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap. ### Claim 13 (depends on 10) The communication system of claim 10, wherein the optical Fourier transform module comprises an optical discrete Fourier transform module. ### Claim 14 (depends on 10) The communication system of claim 10, comprising a balanced detector coupled to the optical mixer and configured to provide at least two respective electrical signals corresponding to at least two coherently-downconverted signals. ### Claim 15 (depends on 14) The communication system of claim 14, wherein the optical mixer and the balanced detector comprise a direct-conversion receiver configured to provide a respective in-phase electrical signal and a respective quadrature electrical signal for each of the at least two respective electrical signals. ### Claim 16 (depends on 14) The communication system of claim 14, comprising an electrical mixer coupled to the balanced detector and configured to provide a respective in-phase electrical signal and a respective quadrature electrical signal for each of the at least two respective electrical signals. ### Claim 17 (depends on 14) The communication system of claim 14, comprising a processor configured to receive information indicative of the at least two respective electrical signals and configured to reconstruct respective baseband information signals; wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers comprising the optical signal received by the optical Fourier transform module. ### Claim 18 (depends on 10) The communication system of claim 10, wherein the local optical oscillator is configured to provide a reference frequency derived from an atomic energy level transition. ### Claim 19 (depends on 10) The communication system of claim 10, wherein local optical oscillator is configured to provide a reference frequency derived from a molecular energy level transition. ### Claim 20 A method, comprising: providing a reference frequency derived from an atomic energy level transition or a molecular energy level transition; generating at least two specified optical carrier signals at least in part using the reference frequency; coherently modulating the at least two specified optical carrier signals using respective baseband information signals to provide at least two respective coherently-modulated optical subcarriers; and combining the at least two respective modulated optical subcarriers to provide the combined optical information signal. ### Claim 21 (depends on 20) The method of claim 20, wherein providing the reference frequency includes stabilizing a local optical oscillator using a cavity mode supported by an optical cavity, and using one or more of an atomic or molecular energy level transition. ### Claim 22 (depends on 20) The method of claim 20, wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers. ### Claim 23 (depends on 22) The method of claim 22, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap. ### Claim 24 (depends on 20) The method of claim 20, wherein generating at least two specified optical carrier signals includes generating an optical frequency comb comprising at least two specified frequency peaks, the at least two frequency peaks separated by a specified frequency offset. ### Claim 25 A method, comprising: providing a reference frequency derived from an atomic energy level transition or a molecular energy level transition; optically Fourier transforming a received optical signal comprising at least two coherently-modulated optical subcarriers to provide at least two coherent outputs respectively corresponding to the at least two coherently-modulated optical subcarriers, at least in part using the reference frequency; and coherently downconverting the at least two coherent outputs corresponding to the at least two coherently-modulated optical subcarriers to provide at least two respective coherently-downconverted signals, at least in part using the reference frequency. ### Claim 26 (depends on 25) The method of claim 25, wherein providing the reference frequency includes stabilizing a local optical oscillator using a cavity mode supported by an optical cavity, and using one or more of an atomic or molecular energy level transition. ### Claim 27 (depends on 25) The method of claim 25, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap. ### Claim 28 (depends on 25) The method of claim 25, wherein the optically Fourier transforming the received optical signal includes using a discrete optical Fourier transform. ### Claim 29 (depends on 25) The method of claim 25, comprising providing at least two respective electrical signals corresponding to at least two coherently-downconverted signals using a balanced detector. ### Claim 30 (depends on 25) The method of claim 25, comprising receiving information indicative of the at least two respective electrical signals; and reconstructing respective baseband information signals; wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers comprising the optically-Fourier-transformed optical signal. ### Claim 31 A system, comprising: a local optical oscillator configured to provide a reference frequency derived from an atomic energy level transition or a molecular energy level transition; a carrier generator configured to generate at least two specified carrier signals at least in part using the reference frequency provided by the local optical oscillator; a complex modulator coupled to the carrier generator and configured to coherently modulate the at least two specified carrier signals using respective baseband information signals to provide at least two respective coherently-modulated subcarriers; wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated subcarriers; and wherein respective spectra of adjacent coherently-modulated subcarriers overlap. ### Claim 32 A method, comprising: providing a reference frequency derived from an atomic energy level transition or a molecular energy level transition; generating at least two specified carrier signals at least in part using the reference frequency provided by the local optical oscillator; coherently modulating the at least two specified carrier signals using respective baseband information signals to provide at least two respective coherently-modulated subcarriers; wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated subcarriers; and wherein respective spectra of adjacent coherently-modulated subcarriers overlap. ### Claim 33 A system, comprising: a transmitter configured to generate a modulated information signal synchronized to a first reference frequency provided by a first local optical oscillator, the first local optical oscillator configured to provide the first reference frequency at least in part using an atomic energy level transition or a molecular energy level transition; and a receiver configured to receive the modulated information signal at least in part using a second reference frequency provided by a second local optical oscillator, the second local optical oscillator configured to provide the second reference frequency at least in part using an atomic energy level transition or a molecular energy level transition; wherein a frequency offset between the first reference frequency and the second reference frequency is specified to provide a symbol error rate of a received information signal below a specified threshold for a duration of at least one second of information transfer without requiring a resynchronization between the transmitter and the receiver. ### Claim 34 (depends on 33) The system of claim 33, wherein the transmitter is coupled to the receiver using at least one of a fiber optic link, a wireless link, or a conductive link. ### Claim 35 (depends on 34) The system of claim 34, wherein the transmitter is coupled to the receiver using a wireless link including a free-space optical link. ### Claim 36 A method, comprising: at a first location, generating a modulated information signal synchronized to a first reference frequency provided by a first local optical oscillator, the first local optical oscillator configured to provide the first reference frequency at least in part using an atomic energy level transition or a molecular energy level transition; at a second location, receiving the modulated information signal at least in part using a second reference frequency provided by a second local optical oscillator, the second local optical oscillator configured to provide the second reference frequency at least in part using an atomic energy level transition or a molecular energy level transition; and wherein a frequency offset between the first reference frequency and the second reference frequency is specified to provide a symbol error rate of a received information signal below a specified threshold for a duration of at least one second of information transfer without requiring a frequency offset estimation between the first reference frequency and the second reference frequency. ### Claim 37 (depends on 36) The method of claim 36, wherein the receiving the information signal includes receiving the information signal via at least one of a fiber optic link, a wireless link, or a conductive link. ### Claim 38 (depends on 37) The method of claim 37, wherein the receiving the information signal includes receiving the information signal via a wireless link including a free-space optical link.