Method and apparatus for phase shift keyed optical communications

Patent metadata

Field	Value
Publication number	US-9264147-B2
Application number	US-201113071460-A
Country	US
Kind code	B2
Filing date	Mar 24, 2011
Priority date	Mar 24, 2010
Publication date	Feb 16, 2016
Grant date	Feb 16, 2016

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.

First claim

The invention claimed is:

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

Assignees

• Caplan David O
• Spellmeyer Neal W
• Robinson Bryan S
• Hamilton Scott A
• Boroson Don M
• Rao Hemonth G
• Norvig Marc C
• Massachusetts Inst Technology

Inventors

• Caplan David O
• Spellmeyer Neal W
• Robinson Bryan S
• Hamilton Scott A
• Boroson Don M
• Rao Hemonth G
• Norvig Marc C

Classifications

• E21B49/06

  using side-wall drilling tools {pressing} or scrapers · CPC title

• H04B10/5561

  Digital phase modulation · CPC title

• H04L27/223

  Demodulation in the optical domain (optical demodulation H04B10/676) · CPC title

• H04B7/18521

  Systems of inter linked satellites, i.e. inter satellite service (for optical links between satellites H04B10/118) · CPC title

• H04L27/2075 Primary

  in which the data are represented by the change in carrier phase · CPC title