Multi-channel differentially encoded phase shift keyed receivers

• US 20070216988A1
• Filed: 03/08/2007
• Published: 09/20/2007
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Caplan, David
• Granted Patent: US 7,411,726 B2
• Time in Patent Office: Days
• US Class Current: 359/325
• CPC Class Codes: H04B 10/677 for differentially modulated signal, e.g. DPSK signals
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems

Abstract

An optical, multi-channel, Differential Phase Shift Keying (DPSK) receiver demodulates multiple Wavelength Division Multiplexed (WDM) channels using at least one interferometer. This distributes expense of the interferometer(s) over all channels of an optical signal, allowing for deployment of cost-effective, scalable, wideband, WDM DPSK systems. For example, for an 80 channel WDM link, the receiver uses a single interferometer instead of eighty interferometers and associated stabilization hardware, dramatically reducing size, weight, power, and cost. The receiver is architecturally compatible with existing interferometer technologies so previous development and qualification efforts can be leveraged. This allows for expedited technology insertion into existing optical communications networks, including terrestrial and space-based optical networks.

Claims

1. An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising:

at least one delay line interferometer to (i) delay at least one channel in an optical signal by multiple bits, (ii) demodulate the optical signal from having DPSK channels to an optical signal having channels modulated in intensity and (iii) output the demodulated optical signal onto at least one main output optical path; and

channel selectors in the at least one main output optical path to direct channels onto tributary optical paths.

2. The apparatus according to claim 1 further including optoelectronic converters in the tributary optical paths to convert the demodulated optical signal into respective, corresponding, electrical signals.

3. The apparatus according to claim 1 wherein the at least one delay line interferometer delays at least one channel by at least one bit.

4. The apparatus according to claim 1 wherein the optical signal includes at least one of the following:

BDPSK, DQPSK, and/or 8-DPSK WDM optical signals.

5. The apparatus according to claim 1 wherein the delay line interferometer is selectably adjustable to interfere optical signal pulses offset by a selectable number.

6. The apparatus according to claim 1 wherein the interferometer includes an electronically tunable phase shifter to receive incoming wavelengths.

7. The apparatus according to claim 1 wherein wavelength spacing between carrier wavelengths defining the channels is an integer multiple of a channel rate of the optical signal.

8. The apparatus according to claim 1 wherein wavelength spacing between carrier wavelengths defining the channels is evenly divisible by an odd number of half channel rates of the optical signal.

9. The apparatus according to claim 8 further including a polarity corrector to correct polarity of the channels.

10. The apparatus according to claim 9 wherein the polarity corrector is configured to correct polarity of electrical signals corresponding to the channels.

11. The apparatus according to claim 9 wherein the polarity corrector is configured to optically correct polarity of the channels.

12. The apparatus according to claim 1 wherein channel rates are integer multiples of interferometer delay.

13. The apparatus according to claim 1 further including a feedback processor to generate signal(s) transmitted to a transmitter(s) of the optical signal(s) to cause the transmitter to tune carrier wavelengths defining the channels for adjusting wavelength position or channel separation.

14. The apparatus according to claim 1 further including a low noise optical amplifier to receive the optical signal and outputting the received amplified optical signal to the interferometer.

15. The apparatus according to claim 1 wherein the channel selectors include optical filters.

16. The apparatus according to claim 1 wherein the interferometer is configured to receive at least one pilot signal to allow for stabilization and control of the interferometer and wavelength alignment of the incoming optical signal(s).

17. The apparatus according to claim 1 used in an optical regenerator.

18. The apparatus according to claim 1 used in a free space optic communications network.

19. The apparatus according to claim 1 used in a fiber optic communications network.

20. The apparatus according to claim 1 wherein the optical signal includes multiple-rate WDM signals.

21. The apparatus according to claim 1 wherein two delay line interferometers are orthogonally phased

22. The apparatus according to claim 21 wherein the optical signals are WDM optical signals that are spaced by odd multiples of the interferometer FSR/4.

23. The apparatus according to claim 1 wherein two interferometers have different delays.

24. A method of demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising:

delaying at least one first series of differentially encoded optical signal pulses in respective DPSK channels of the at least one first series of optical signals by a multiple bit duration to align the at least one first series optical signal pulses with at least one respective second series of differentially encoded optical signal pulses also in the respective DPSK channels;

respectively interfering the at least one first and second series of optical signal pulses in an aligned state to demodulate the optical signals from having DPSK channels to at least one optical signal having channels modulated in intensity;

outputting the demodulated optical signal onto respective main output optical paths; and

directing channels in the respective main output optical paths onto tributary optical paths.

25. The method according to claim 24 further including converting the demodulated optical signal on the tributary optical paths into respective, corresponding, electrical signals.

26. The method according to claim 24 wherein demodulating the optical signal includes interfering adjacent optical signal pulses.

27. The method according to claim 24 wherein demodulating the optical signal includes interfering non-adjacent optical signal pulses.

28. The method according to claim 24 wherein demodulating the optical signal includes interfering optical signal pulses offset by a selectable number.

29. The method according to claim 24 wherein demodulating the optical signal includes tuning at least one interferometer for receiving incoming wavelengths.

30. The method according to claim 24 wherein wavelength spacing between carrier wavelengths defining the channels is an integer multiple of a channel rate of the optical signal.

31. The method according to claim 24 wherein delaying the at least one first series of optical signal pulses further comprises delaying each optical signal of the at least one first set a different amount.

32. The method according to claim 29 wherein the at least one delay line interferometer is controlled using a pilot signal.

33. The method according to claim 24 wherein wavelength spacing between carrier wavelengths defining the channels is evenly divisible by an odd number of half channel rates of the optical signal.

34. The method according to claim 24 wherein the delay is achieved with two orthogonally phased delay line interferometers.

35. The method according to claim 34 wherein wavelength spacing between carrier wavelengths defining the channels is an odd multiple of the delay line interferometer FSR/4.

36. The method according to claim 33 further including correcting polarity of the channels.

37. The method according to claim 33 wherein correcting the polarity of the channels includes correcting polarity of electrical signals corresponding to the channels.

38. The method according to claim 36 wherein correcting the polarity of the channels includes optically correcting polarity of the channels.

39. The method according to claim 24 wherein channel rate bit durations are integer multiples of demodulating delay.

40. The method according to claim 24 further including feeding back signal(s) to transmitter(s) of the optical signal(s) to cause the transmitter to tune carrier wavelengths defining the channels for adjusting wavelength position or channel separation.

41. The method according to claim 24 further including optically amplifying the optical signals prior to demodulating the optical signal.

42. The method according to claim 24 wherein directing the channels onto the tributary optical paths includes filtering the phase demodulated optical signals.

43. The method according to claim 24 further including controlling at least one demodulating interferometer based on at least one pilot signal.

44. The method according to claim 24 used in an optical regenerator.

45. The method according to claim 24 used in a free space optic communications network.

46. The method according to claim 24 used in a fiber optic communications network.

47. An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising:

means for delaying at least one first series of differentially encoded optical signal pulses in at least one respective DPSK channel of the optical signal by a multiple bit duration to align the at least one series of first optical signal pulses with at least one second series of differentially encoded optical signal pulses also in the at least one respective DPSK channel;

means for interfering the at least one first and second series differentially encoded optical signal pulses in an aligned state to demodulate the optical signal from having DPSK channels to a respective optical signal having channels modulated in intensity;

means for outputting the respective demodulated optical signal onto at least one respective main output optical path; and

means for directing channels in the at least one respective main output optical path onto tributary optical paths.

48. A method for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the method comprising:

feeding back a signal to constrain wavelength spacing of DPSK channels in an optical signal; and

interfering offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated.

49. The method according to claim 48 further including directing channels in the demodulated optical signal from at least one main optical path onto tributary optical paths.

50. A system for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the system comprising:

means for feeding back a signal to constrain wavelength spacing of DPSK channels in an optical signal; and

means for interfering offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated.

51. The method according to claim 50 further including means for directing channels in the demodulated optical signal from at least one main optical path onto tributary optical paths.

52. An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising:

a processor to feed back a signal to constrain wavelength spacing of DPSK channels in an optical signal; and

at least one interferometer that interferes offset optical signal pulses in the optical signal to demodulate the optical signal from being DPSK modulated to being intensity modulated.

53. The apparatus according to claim 52 wherein the at least one interferometer directs channels in the demodulated optical signal from at least one main optical path onto tributary optical paths.

54. An apparatus for demodulating an optical signal having Differentially Encoded Phase Shift Keying (DPSK) channels, the apparatus comprising:

a least one delay line interferometer to (i) demodulate an optical signal from having DPSK channels to an optical signal having channels modulated in intensity (ii) output the demodulated optical signal onto at least one main output optical path, and (iii) receive at least one pilot signal to allow for stabilization and control of the at least one interferometer and wavelength alignment of the incoming optical signal(s); and

channel selectors in the at least one main output optical path to direct channels onto tributary optical paths.