Method and apparatus for phase shift keyed optical communications

• US 9,264,147 B2
• Filed: 03/24/2011
• Issued: 02/16/2016
• Est. Priority Date: 03/24/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Caplan, David O., Spellmeyer, Neal W., Robinson, Bryan S., Hamilton, Scott A., Boroson, Don M., Rao, Hemonth G., Norvig, Marc C.
• Primary Examiner(s): DOBSON, DANIEL G
• Application Number:
  US13/071,460
• Publication Number:
  US 20110274429A1
• Time in Patent Office: 1,790 Days
• Field of Search: 398/140, 398/162
• US Class Current: 1/1
• CPC Class Codes: E21B 47/002 by visual inspection
• CPC Class Codes: E21B 47/007 Measuring stresses in a pipe string or casing for locating blocked portions of pipes E21B47/09
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
• CPC Class Codes: E21B 49/006 Measuring wall stresses in the borehole
• CPC Class Codes: E21B 49/06 using side-wall drilling tools pressing or scrapers
• CPC Class Codes: G01V 1/40 specially adapted for well-logging
• CPC Class Codes: H04B 10/5561 Digital phase modulation
• CPC Class Codes: H04B 10/677 for differentially modulated signal, e.g. DPSK signals
• CPC Class Codes: H04B 7/18508 with satellite system used as relay, i.e. aeronautical mobile satellite service
• CPC Class Codes: H04B 7/18521 Systems of inter linked satellites, i.e. inter satellite service for optical links between satellites H04B10/118
• CPC Class Codes: H04L 27/2075 in which the data are represented by the change in carrier phase
• CPC Class Codes: H04L 27/2096 Arrangements for directly or externally modulating an optical carrier optical modulation H04B10/503
• CPC Class Codes: H04L 27/223 Demodulation in the optical domain optical demodulation H04B10/676
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A burst-mode phase shift keying (PSK) communications system according to an embodiment of the present invention enables practical, power-efficient, multi-rate communications between an optical transmitter and receiver. Embodiments may operate on differential PSK (DPSK) signals. An embodiment of the system utilizes a single interferometer in the receiver with a relative path delay that is matched to the DPSK symbol rate of the link. DPSK symbols are transmitted in bursts, and the data rate may be varied by changing the ratio of the burst-on time to the burst-off time. This approach offers a number of advantages over conventional DPSK implementations, including near-optimum photon efficiency over a wide range of data rates, simplified multi-rate transceiver implementation, and relaxed transmit laser line-width requirements at low data rates.

Claims

1. An optical communications system, comprising:

an optical transmitter/receiver pair configured, or operable to be configured, to communicate via a dedicated communications path extending an entire distance between a transmitter and a receiver of the optical transmitter/receiver pair in a given direction along the dedicated communications path, the transmitter/receiver pair being further configured, or operable to be configured, to operate at a selectable data rate with data transmitted in bursts, the data rate being a function of a burst-on duty cycle, and the transmitter being average power limited.

2. The system according to claim 1 wherein the data transmitted in bursts is accompanied by a periodic header.

3. The system according to claim 1, wherein the transmitter/receiver pair are configured to operate based on differentially encoded phase-shift keying and wherein the receiver is configured to use a fixed interferometric demodulator.

4. The system according to claim 1 wherein the data rate is adjusted depending on channel conditions to accommodate transmission rate, throughput, security at the receiver, or signal-to-noise ratio.

5. The system according to claim 4 wherein the receiver or an external manager sends data via a return link or supervisory channel to change the rate at which the transmitter transmits data.

6. The system according to claim 1 wherein the transmitter includes an interleaver configured to spread out data bits in time and wherein the receiver includes a de-interleaver configured to perform a complementary function.

7. The system according to claim 1 wherein the burst-on length is selectable.

8. The system according to claim 1 wherein a burst-off time is less than or equal to 100 microseconds.

9. The system according to claim 1 wherein optical signals carrying the data transmitted in bursts have a transmission extinction ratio greater than the burst mode duty cycle plus 3 dB.

10. The system according to claim 1 wherein a penalty is less than 2 dB for a range of duty cycles of greater than 25 dB.

11. The system according to claim 1 wherein the transmitter and receiver include substantially matched filters and wherein the receiver further includes a high gain preamplifier.

12. The system according to claim 11 wherein the receiver includes a polarization filtering element.

13. The system according to claim 1 wherein the receiver is configured to learn error rate from a header or forward error correction data independent of the transmitter and is further configured to use the error rate internally or notify the transmitter of the error rate.

14. The system according to claim 1 wherein the receiver is an interferometric receiver and is pilot tone stabilized.

15. The system according to claim 1 wherein the receiver is a phase sensitive or a coherent receiver.

16. The system according to claim 15 wherein the coherent receiver is configured to receive a signal with a modulation selected from a group consisting of:

M-Phase Shift Keying (M-PSK), M-Quadrature Amplitude Modulation (M-QAM), polarization modulation, Orthogonal Frequency Division Multiplexing (OFDM) or polarization multiplexing or combination thereof.

17. The system according to claim 1 wherein the transmitter/receiver pair is configured to use forward error correction coding and interleaving.

18. The system according to claim 1 wherein the transmitter and receiver are configured to communicate via a free space medium.

19. The system according to claim 1 wherein the transmitter and receiver are configured to communicate via a guided wave channel.

20. The system according to claim 19 wherein the guided wave channel is a multi-mode guided wave channel.

21. The system according to claim 1 wherein the transmitter/receiver pair are configured to communicate up to a maximum rate equal to a free spectral range of an interferometric-based receiver demodulator, and wherein the transmitter/receiver pair are still further configured to communicate at lower rates than the maximum rate equal to the free spectral range by fractions equal to the burst-on duty cycle.

22. The system according to claim 1 wherein the duty cycle is 100 percent and wherein the optical transmitter/receiver pair are further configured to operate at an increased data rate through non-adjacent Differential Phase Shift Keying (DPSK) signaling.

23. The system according to claim 1 wherein the transmitter uses a linewidth of a transmitter laser that is greater than or equal to 0.1% of the data rate.

24. The system according to claim 3 wherein misalignment of the interferometric demodulator and incoming wavelength is less than 5% of the free spectral range.

25. The system according to claim 24 wherein misalignment of the interferometric demodulator and incoming wavelength is greater than 1% of the selected data rate.

26. The system according to claim 1 wherein the transmitter includes a single modulator configured to perform pulse carving, data modulating, and window modulating, or combination of at least two thereof.

27. The system according to claim 1 wherein the receiver includes a preamplifier with adjustable gain to enable preamplification without saturation.

28. The system according to claim 27 wherein the preamplifier is configured to avoid saturation penalties and extend dynamic range as a function of the duty cycle.

29. The system according to claim 1 wherein the transmitter/receiver pair are components in a bi-directional system of transceiver pairs.

30. The system according to claim 1 wherein the transmitter/receiver pair is configured to communicate using at least one of the following modulation formats:

Wavelength Division Multiplexing (WDM), Differential Phase Shift Keying (DPSK), Pulse Position Modulation (PPM), or Pulse Code Modulation (PCM).

31. The system according to claim 1, wherein the dedicated communications path is a first dedicated communications path and further comprising an additional transmitter/receiver pair configured to communicate via a second dedicated communications path, coincidental with the first dedicated communications path, in a direction along the second communications path opposite the given direction.

32. The system according to claim 1 wherein the transmitter/receiver pair are configured to communicate up to a maximum rate, and wherein the transmitter/receiver pair are still further configured to communicate at lower rates than the maximum rate by fractions equal to the burst-on duty cycle.

33. The system of claim 1, wherein at least one of the transmitter and receiver is mountable on a mobile platform and configured to communicate via the dedicated communications path in a given direction along the dedicated communications path while in motion.

34. A method of communicating in an optical communications system, the method comprising:

transmitting, by an optical transmitter, via a dedicated communications path in a given direction along the dedicated communications path, transmitting being at a selectable data rate with data transmitted in bursts using average power limited waveforms, the data rate being a function of a burst-on duty cycle; and

receiving, by an optical receiver, the data at the selectable data rate via the dedicated communications path, the dedicated communications path extending an entire distance between the optical transmitter and optical receiver.

35. The method of claim 34, wherein the dedicated communications path is a first dedicated communications path and further comprising transmitting via a second dedicated communications path, coincidental with the first dedicated communications path, in a direction along the second dedicated communications path opposite the given direction, the method further comprising receiving via the second dedicated communications path.

36. The method of claim 34, transmitting at the selectable data rate includes transmitting at up to a maximum rate or at lower rates than the maximum rate by fractions equal to the burst-on duty cycle.

37. The method of claim 34, wherein at least one of transmitting via the dedicated communications path and receiving via the dedicated communications path includes, respectively, transmitting from or receiving at a position changing with time.

38. The method according to claim 34 further comprising transmitting a periodic header with the data transmitted in bursts and receiving the periodic header.

39. The method according to claim 34 further comprising transmitting the data using differentially encoded phase-shift keying and wherein receiving the data includes using fixed interferometric demodulation.

40. The method according to claim 34 further comprising adjusting the data rate depending on channel conditions to accommodate transmission rate, throughput, security at the receiver, or signal-to-noise ratio.

41. The method according to claim 40 further comprising sending data via a return link or supervisory channel to change the rate of the transmitting.

42. The method according to claim 34 wherein the transmitting includes interleaving to spread out data bits in time and wherein the receiving includes de-interleaving configured to perform a complementary function.

43. The method according to claim 34 wherein the burst-on length is selectable.

44. The method according to claim 34 wherein a burst-off time is less than or equal to 100 microseconds.

45. The method according to claim 34 wherein optical signals carrying the data transmitted in bursts have a transmission extinction ratio greater than the burst mode duty cycle plus 3 dB.

46. The method according to claim 34 wherein a penalty is less than 2 dB for a range of duty cycles of greater than 25 dB.

47. The method according to claim 34 wherein the transmitting and receiving include substantially matched filtering and wherein the receiving further includes high gain preamplifying.

48. The method according to claim 47 wherein the receiving further includes polarization filtering.

49. The method according to claim 34 wherein the receiving includes learning error rate from a header or forward error correction data independent of the transmitting and wherein the receiving further uses the error rate internally or causes and adjustment to a transmitter transmitting the error rate.

50. The method according to claim 34 wherein the receiving includes interferometric receiving and is pilot tone stabilized.

51. The method according to claim 34 wherein the receiving is phase sensitive or coherent.

52. method according to claim 51 wherein coherent receiving is configured to receive a signal with a modulation selected from a group consisting of:

M-Phase Shift Keying (M-PSK), M-Quadrature Amplitude Modulation (M-QAM), polarization modulation, Orthogonal Frequency Divisional Multiplexing (OFDM), polarization multiplexing, or combination thereof.

53. The method according to claim 34 further comprising using forward error correction coding and interleaving.

54. The method according to claim 34 wherein the transmitting and receiving are performed via a free space medium.

55. The method according to claim 34 wherein the transmitting and receiving are performed via a guided wave channel.

56. The method according to claim 55 wherein the guided wave channel is a multi-mode guided wave channel.

57. The method according to claim 56 wherein the transmitting and receiving enable communicating up to a maximum rate equal to a free spectral range of an interferometric-based receiver demodulator, and wherein the transmitting and receiving are still further configured to enable communicating at lower rates than the maximum rate by fractions equal to the burst-on duty cycle.

58. The method according to claim 34 wherein the duty cycle is 100 percent and further including increasing the data rate using non-adjacent Differential Phase Shift Keying (DPSK) signaling.

59. The method according to claim 34 wherein the transmitting includes using a linewidth of a transmitter laser that is greater than or equal to 0.1% of the data rate.

60. The method according to claim 39 wherein misalignment of the fixed interferomtric demodulation and incoming wavelength is less than 5% of the free spectral range.

61. The method according to claim 60 wherein misalignment of the fixed interferomtric demodulation and incoming wavelength is greater than 1% of the selected data rate.

62. The method according to claim 34 wherein the transmitting includes pulse carving, data modulating, and window modulating, or combination of at least two thereof.

63. The method according to claim 34 wherein the receiving includes preamplifying with adjustable gain to enable preamplification without saturation.

64. The method according to claim 63 wherein the preamplifying is configured to avoid saturation penalties and extend dynamic range as a function of the duty cycle.

65. The method according to claim 34 wherein the transmitting and receiving occur bi-directionally.

66. The method according to claim 34 wherein the transmitting and receiving are configured to enable communicating using at least one of the following modulation formats:

Wavelength Division Multiplexing (WDM), Differential Phase Shift Keying (DPSK), Pulse Position Modulation (PPM), or Pulse Code Modulation (PCM).

67. An optical communications system, comprising:

means for optically transmitting data via a dedicated communications path in a given direction along the dedicated communications path in bursts at a selectable data rate using average power limited waveforms, the data rate being a function of a burst-on duty cycle; and

means for optically receiving, via the communications path, the data at the selectable data rate, the means for transmitting and the means for receiving being configured to operate as a pair, the dedicated communications path extending an entire distance between the means for optically transmitting and means for optically receiving.