High-speed low-jitter communication system

• US 8,787,767 B2
• Filed: 05/11/2012
• Issued: 07/22/2014
• Est. Priority Date: 02/03/2012
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Wilkinson, Steven R., Price, Gabriel N.
• Primary Examiner(s): Bello, Agustin
• Application Number:
  US13/469,650
• Publication Number:
  US 20130202303A1
• Time in Patent Office: 802 Days
• Field of Search: 398/182, 398/183, 398/202, 398/203, 398/204, 398/140
• US Class Current: 398/140
• CPC Class Codes: H04B 10/516 Details of coding or modulation
• CPC Class Codes: H04B 10/548 Phase or frequency modulation
• CPC Class Codes: H04B 10/61 Coherent receivers
• CPC Class Codes: 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
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]
• CPC Class Codes: H04L 27/2096 Arrangements for directly or externally modulating an optical carrier optical modulation H04B10/503
• CPC Class Codes: H04L 27/2697 in combination with other modulation techniques
• CPC Class Codes: H04L 27/3818 using coherent demodulation, i.e. using one or more nominally phase synchronous carriers H04L27/227 and H04L27/389 take precedence

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

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.

2. 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.

3. The communication system of claim 1, wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers.

4. The communication system of claim 3, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap.

5. 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.

6. 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.

7. 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.

8. 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.

9. The communication system of claim 1, wherein local optical oscillator is configured to provide a reference frequency derived from a molecular energy level transition.

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.

11. 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.

12. The communication system of claim 10, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap.

13. The communication system of claim 10, wherein the optical Fourier transform module comprises an optical discrete Fourier transform module.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. The communication system of claim 10, wherein local optical oscillator is configured to provide a reference frequency derived from a molecular energy level transition.

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.

21. 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.

22. The method of claim 20, wherein the respective baseband signals are specified to provide orthogonality between the respective coherently-modulated optical subcarriers.

23. The method of claim 22, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap.

24. 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.

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.

26. 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.

27. The method of claim 25, wherein respective spectra of adjacent coherently-modulated optical subcarriers overlap.

28. The method of claim 25, wherein the optically Fourier transforming the received optical signal includes using a discrete optical Fourier transform.

29. 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.

30. 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.

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.

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.

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.

34. 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.

35. The system of claim 34, wherein the transmitter is coupled to the receiver using a wireless link including a free-space optical link.

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.

37. 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.

38. 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.