System and method for adaptively selecting a signal threshold of an optical link

• US 6,915,076 B1
• Filed: 05/14/2001
• Issued: 07/05/2005
• Est. Priority Date: 05/14/2001
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Kennedy, Chris, Mittal, Rohit
• Primary Examiner(s): Pascal, Leslie
• Assistant Examiner(s): Nguyen, Chau M.
• Application Number:
  US09/855,319
• Time in Patent Office: 1,513 Days
• Field of Search: 398/37, 398/38, 398/27, 398/210, 375/317, 375/318, 375/346
• US Class Current: 398/38
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04B 10/0799 Monitoring line transmitter or line receiver equipment
• CPC Class Codes: H04B 10/695 Arrangements for optimizing the decision element in the receiver, e.g. by using automatic threshold control

Abstract

An apparatus and method for detecting a signal in an optical data network is disclosed. A peak power level and an average power level are measured for an optical input to an optical detector. A threshold power level is associated with each average power level that is sufficient to distinguish a data signal form optical noise at the average power level. A signal is detected if the measured peak power level exceeds the threshold power level appropriate for the average power level. In one embodiment, a threshold value of a ratio of the peak power level to the average power level is calculated and a signal is detected if the ratio of the measured peak power level to the average power exceeds the threshold value.

Claims

1. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier generating optical noise adapted to amplify an optical data stream, and an optical path link coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical attenuation with a range of attenuation between a minimum attenuation and a maximum attenuation, a method of selecting a signal detection threshold for an optical input received by the optical detection circuit appropriate for the optical attenuation of the optical path link, the method comprising:

receiving a first signal indicative of an average power level of the optical input;

receiving a second signal indicative of a peak power level of the optical input; and

selecting the signal detection threshold to distinguish an optical signal condition from a loss of signal condition appropriate for the optical attenuation of the optical path link, the signal detection threshold selected to have an associated threshold power level that is greater than a peak power level for an optical input composed of optical noise having the average power level and less than a peak power level for an optical input composed of optical data pulses having the average power level;

the signal detection circuit operable for the range of attenuation of the optical path link being sufficiently large that the threshold power level is adjusted at least once over the range of attenuation.

2. The method of claim 1, further comprising:

generating an output signal having a first value responsive to the peak power level of the optical input being greater than the threshold power level and a second value responsive to the peak power level of the optical input being less than the threshold power level.

3. The method of claim 2, further comprising:

characterizing an average power level and a peak power level of simulated optical noise over the range of attenuation; and

characterizing an average power level and a peak power level of test optical data pulses over the range of attenuation.

4. The method of claim 3, wherein the peak power level of the optical noise at the minimum attenuation is at least as large as the peak power level of the optical data pulses at the maximum attenuation.

5. The method of claim 1, wherein the peak power level of the optical noise at the minimum attenuation is at least as great as the peak power level of the optical data pulses at the maximum attenuation.

6. The method of claim 1, further comprising:

in a test mode, coupling an optical test amplifier and an optical attenuator having an adjustable attenuation between the optical detection circuit and an optical test transmitter;

in the test mode, characterizing a peak power level and an average power level of optical test pulses received by the optical detection circuit over the range of attenuation;

in the test mode, characterizing a peak power level and the average power level of optical noise received by the optical detection circuit from the optical test amplifier over the range of attenuation; and

in an operational mode, selecting the threshold power level for each average power level using characterization data collected during the test mode.

7. The method of claim 1, further comprising:

responsive to the peak power level of the optical input being greater than the threshold power level, outputting a first signal indicative of a signal detect condition; and

responsive to the peak power level of the optical input being less than the threshold power level, outputting a second signal indicative of a loss-of-signal condition.

8. The method of claim 1, wherein the signal detection threshold is a threshold ratio of the peak power level to the average power level, the method further comprising:

calculating a ratio of the peak power level to the average power level; and

generating an output signal having a first value responsive to the ratio being greater than the signal detection threshold and a second value responsive to the ratio being less than the signal detection threshold.

9. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier adapted to amplify an optical data stream, and an optical path link coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical attenuation within a range of attenuation between a minimum attenuation and a maximum attenuation, a method of adjusting a signal detection threshold for an optical input received by the optical detection circuit, the method comprising:

receiving a signal indicative of an average power level of the optical input; and

selecting a threshold power level appropriate for the optical attenuation of optical path link, the threshold power level being greater than a peak power level of optical noise for a loss-of-signal condition at the average power level and the threshold power level being less than a peak power level for an optical signal condition at the average power level;

the signal detection circuit operable for the range of attenuation of the optical path link being sufficiently large that the threshold power level is adjusted at least once over the range of attenuation.

10. The method of claim 9, further comprising:

receiving a second signal indicative of a peak power level of the optical input; and

generating an output signal having a first value responsive to the peak power level of the optical input being greater than the threshold power level and a second value responsive to the peak power level of the optical input being less than the threshold power level.

11. The method of claim 9, further comprising:

characterizing an average power level and a peak power level of optical noise over the range of attenuation; and

characterizing an average power level and a peak power level of simulated optical data pulses over the range of attenuation.

12. The method of claim 11 wherein the peak power level of optical noise at the minimum attenuation is at least as large as the peak power level of optical data pulses at the maximum attenuation.

13. The method of claim 9 wherein the peak power level of optical noise at the minimum attenuation is at least as large as the peak power level of optical data pulses at the maximum attenuation.

14. The method of claim 9, further comprising:

in a test mode, coupling a variable attenuator between the optical detection circuit and an optical test transmitter with at least one optical amplifier disposed between the optical detection circuit and the optical test transmitter;

in the test mode, measuring a peak power level and an average power level of optical pulses received by the optical detection circuit over a range of optical attenuation that may be encountered in the optical network;

in the test mode, measuring a peak power level and an average power level of optical noise received by the optical detection circuit over the range of optical attenuation with the optical test transmitter in a quiescent state; and

selecting the threshold power level for each average power level using data collected during the test mode.

18. The method of claim 14, further comprising:

characterizing the average power level and the peak power level of optical noise over the range of attenuation; and

characterizing the average power level and the peak power level of simulated optical data pulses over the range of attenuation.

19. The method of claim 18, wherein the peak power level of optical noise at the minimum attenuation is at least as large as the peak power level of optical data pulses at the maximum attenuation.

20. The method of claim 19, wherein the data pulses are encoded with a forward error correction code.

15. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier arranged to amplify an optical data stream, and an optical path link coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical attenuation having a range of attenuation between a minimum attenuation and a maximum attenuation, a method of detecting a data signal, the method comprising:

for each average power level over a range of average power levels, selecting a threshold power level greater than a peak power level of optical noise at the average power level and less than a peak optical power level of optical data pulses at the average power level;

receiving a signal indicative of a measured average power level of an optical input received by the optical detection circuit;

receiving a signal indicative of a measured peak power level of the optical input;

determining the threshold power level appropriate for the measured average power level;

responsive to the measured peak power level being greater than the threshold power level, outputting a first signal having a value indicative of a signal detect condition; and

responsive to the peak power level being less than the threshold power level, outputting a second signal having a value indicative of a loss-of-signal condition;

the signal detection circuit operable for the range of attenuation of the optical path link being sufficiently large that the threshold power level is adjusted at least once over the range of attenuation.

16. The method of claim 15, wherein the peak power level of optical noise at the minm attenuation is at least as large as the peak power level of optical data pulses at the maximum attenuation.

17. The method of claim 16, wherein the optical data pulses are encoded with a forward error correction code.

21. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier arranged to amplify an optical data stream, and an optical path link coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical attenuation within a range of attenuation between a minimum attenuation and a maximum attenuation, a method of adjust a threshold level for detecting a signal, the method comprising:

characterizing a peak power level and an average power level of optical data pulses received by the optical detection circuit over the range of attenuation;

characterizing a peak power level and an average power level of optical noise received by the optical detection circuit for a loss of signal condition over the range of attenuation;

measuring an average power level of an optical input to the optical detection circuit;

measuring a peak power level of the optical input; and

selecting a signal detection threshold sufficient to distinguish a data signal from optical noise for the optical attenuation of the optical path link associated with the measured average power level;

the range of attenuation being sufficiently large that the peak power level of optical noise at the minimum attenuation is at least as great as optical data pulses at the maximum attenuation.

22. The method of claim 21, wherein the signal detection threshold is a threshold peak power level, the method further comprising:

generating an output signal having a first value responsive to the measured peak power level of the optical input being greater than signal detection threshold and a second value responsive to the measured peak power level being less than the signal detection threshold.

23. The method of claim 22, wherein the signal detection threshold is a threshold ratio of the peak power level to the average power level, the method further comprising:

calculating a ratio of the measured peak power level to the measured average power level; and

generating an output signal having a first value responsive to the ratio being greater than the signal detection threshold and a second value responsive to the ratio being less than the signal detection threshold.

24. In an optical network with an optical detection circuit residing on a first optical node, a second optical node having an optical amplifier arranged to amplify an optical data stream, and an optical path link coupling the nodes having an optical attenuation having a range of attenuation between a minimum attenuation and a maximum attenuation, a method of adapting a signal detect threshold to maintain the signal detect threshold above the power level of the optical noise over the range of attenuation, the method comprising:

characterizing a peak power level and an average power level of the optical noise over the range of attenuation;

detecting a signal indicative of a measured peak optical power level of an optical input to the optical detector;

detecting a signal indicative of a measured average optical power level of the optical input; and

selecting a signal detection threshold corresponding to a threshold peak optical power level being greater than the peak power level of the optical noise at the measured average power level;

the signal detection circuit operable for the range of attenuation of the optical path link being sufficiently large that the threshold peak optical power level is adjusted at least once over the range of attenuation.

25. The method of claim 24, further comprising:

responsive to the measured peak power level being greater than the signal detection threshold, outputting a first signal indicative of a signal detect condition; and

responsive to the measured peak power level being less than the threshold level, outputting a second signal indicative of a loss-of-signal condition.

26. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier arranged to amplify an optical data stream, and an optical path link coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical attenuation within a range of attenuation between a minimum attenuation and a maximum attenuation, a method of detecting a data signal for an optical input received by the optical detection circuit, the method comprising:

receiving a first signal indicative of an average power level of the optical input;

receiving a second signal indicative of a peak power level of the optical input;

calculating a ratio of the peak power level to the average power level; and

generating an output signal having a first value responsive to the ratio being greater than a threshold value and a second value responsive to the ratio being less than the threshold value;

the threshold value selected to be greater than a ratio of a peak power level to an average power level for optical noise and less than the ratio of a peak power level to an average power level for optical data pulses.

27. The method of claim 26, further comprising:

characterizing an average power level and a peak power level of optical noise over the range of attenuation; and

characterizing an average power level and a peak power level of test optical data pulses over the range of attenuation.

28. The method of claim 27, wherein the peak power level of optical noise at the minimum attenuation is at least as large as the peak power level of optical data pulses at the maximum attenuation.

29. The method of claim 28, wherein the data pulses are encoded with a forward error correction code.

30. The method of claim 26, further comprising:

in a test mode, coupling a variable attenuator between the optical detection circuit and an optical test transmitter with at least one optical amplifier disposed between the optical detection circuit and the optical test transmitter;

in the test mode, characterizing a peak power level and an average power level of optical test pulses received by the optical detection circuit over the range of attenuation;

in the test mode, characterizing the peak power level and the average power level of optical noise received by the optical detection circuit over the range of attenuation; and

selecting the threshold value using characterization data collected during the test mode.

31. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier adapted to receive an optical data stream and output an amplified data stream, and an optical path link having an optical fiber coupling the optical detection circuit in the first node and an output of the optical amplifier of the second node, a method of signal detection, the method comprising:

selecting a range of optical attenuation for the optical path link between a minimum attenuation and a maximum attenuation;

characterizing a peak power level and an average power level of optical data pulses over the range of attenuation;

characterizing a peak power level and an average power level of optical noise over the range of attenuation; and

selecting a threshold value of a ratio of peak power level to average power level sufficient to distinguish the optical data pulses from the optical noise over the range of attenuation;

wherein the peak power level of optical noise at the minimum attenuation is at least as great as optical data pulses at the maximum attenuation.

32. The method of claim 31, further comprising:

in an operational mode of the optical network, measuring the peak power level and the average power level of an optical input;

calculating a ratio of the measured peak power level to the average power level; and

generating an output signal having a first value responsive to the ratio being than the threshold value and a second value responsive to the ratio being less than the threshold value.

33. In an optical network, a method of selecting a signal detection threshold for an optical input received by an optical detection circuit residing on a receiving node, the method comprising:

selecting an optical path from a transmitter on a first node to the optical detection circuit of the receiving node, the optical path including an optical amplifier residing on a node upstream of the receiving node coupled to the optical detection circuit of the receiving node by an optical path link having an optical fiber;

receiving a first signal indicative of an average power level of an optical input to the optical detection circuit;

receiving a second signal indicative of a peak power level of the optical input; and

selecting a signal detection threshold to distinguish an optical signal condition from a loss of signal condition appropriate for the optical attenuation of the optical path link, the signal detection threshold selected to have an associated threshold power level that is greater than a peak power level for an optical input composed of optical noise having the average power level and less than a peak power level for an optical input composed of optical data pulses having the average power level;

the signal detection circuit operable for a range of attenuation of the optical path link being sufficiently large that the threshold power level is adjusted at least once over the range of attenuation.

34. The method of claim 33, further comprising:

generating an output signal having a first value responsive to the peak power level of the optical input being greater than the threshold power level and a second value responsive to the peak power level of the optical input being less than the threshold power level.

35. The method of claim 34, further comprising:

characterizing an average power level and a peak power level of simulated optical noise over the range of attenuation; and

characterizing an average power level and a peak power level of test optical data pulses over the range of attenuation.

36. The method of claim 35, wherein the peak power level of the optical noise at the minimum attenuation is at least as large as the peak power level of the optical data pulses at the maximum attenuation.

37. The method of claim 33, wherein the peak power level of the optical noise at the minimum attenuation is at least as great as the peak power level of the optical data pulses at the maximum attenuation.

38. The method of claim 33, further comprising:

in a test mode, coupling an optical test amplifier and an optical attenuator having an adjustable attenuation between the optical detection circuit and an optical test transmitter;

in the test mode, characterizing a peak power level and an average power level of optical test pulses received by the optical detection circuit over the range of attenuation;

in the test mode, characterizing a peak power level and the average power level of optical noise received by the optical detection circuit from the optical test amplifier over the range of attenuation; and

in an operational mode, selecting the threshold power level for each average power level using characterization data collected during the test mode.

39. The method of claim 33, further comprising:

responsive to the peak power level of the optical input being greater than the threshold power level, outputting a first signal indicative of a signal detect condition; and

responsive to the peak power level of the optical input being less than the threshold power level, outputting a second signal indicative of a loss-of-signal condition.

40. The method of claim 33, wherein the signal detection threshold is a threshold ratio of the peak power level to the average power level, the method further comprising:

calculating a ratio of the peak power level to the average power level; and

generating an output signal having a first value responsive to the ratio being greater than the signal detection threshold and a second value responsive to the ratio being less than the signal detection threshold.

41. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier generating optical noise adapted to amplify an optical data stream, and an optical path link including an optical fiber coupling an output of the optical amplifier of the second node to an optical input of the optical detection circuit in the first node, a method of detecting a signal, the method comprising:

selecting a range of optical attenuation of the optical path link between a minimum attenuation and a maximum attenuation, the optical attenuation decreasing the optical input received by the optical detector, the range of attenuation being sufficiently great that a peak power level of the optical input at the minimum attenuation for a loss-of-signal condition is at least as great as a peak power level of the optical input for an optical signal condition at the maximum attenuation;

characterizing optical power characteristics of the optical input over the range of attenuation for the optical signal condition;

characterizing optical power characteristics of the optical input over the range of attenuation for the loss-of-signal condition;

selecting an optical power characteristic of the optical input sufficient to distinguish a time domain behavior associated with optical noise for the loss-of-signal condition from a time domain behavior associated with optical data pulses for the signal condition;

measuring the optical power characteristic; and

responsive to a measured value of the optical characteristic being greater than the threshold value, detecting a signal; and

responsive to the measured value of the optical power characteristic being less than the threshold value, detecting a loss-of-signal.

42. The method of claim 41, wherein the optical power characteristic is a ratio of a peak power level to an average power level.

43. The method of claim 41, wherein the optical characteristics is a ratio of a peak-detect voltage to a photocurrent.

44. In an optical network with an optical detection circuit residing on a first optical node, a second upstream optical node having an optical amplifier generating optical noise adapted to amplify an optical data stream, and an optical path link including an optical fiber coupling an optical input of the optical detection circuit in the first node and an output of the optical amplifier of the second node, the optical path link having an optical, a method of detecting a signal, the method comprising:

determining a relationship between a peak power level and an average power of the optical input sufficient to distinguish an optical signal condition from a loss-of-signal condition over a range of attenuation of the optical path link between a minimum attenuation and a maximum attenuation;

receiving a first signal indicative of the peak power level of the optical input;

receiving a second signal indicative of the average power level of the optical input;

detecting a signal responsive to the peak power level and the average power level having values relative to each other indicative of a signal condition; and

detecting a loss-of-signal responsive to the peak power level and average power having values relative to each other indicative of a loss-of-signal condition.

45. An optical detection circuit for a node of an optical network receiving an optical signal from an optical amplifier of an upstream optical node coupled to the node by an optical path link, the optical detection circuit comprising:

an optical detector generating at least one electrical output responsive to an optical input received by the optical detector;

an electrical circuit coupled to the at least one electrical output of the optical detector configured to provide a first signal indicative of a peak optical power level of the optical input and a second signal indicative of an average optical power level of the optical input; and

a signal detector receiving the signals of the electrical circuit configured to select a a signal detection threshold having a threshold peak optical power level sufficient to distinguish an optical signal input from an optical amplifier noise input at the average power level, the signal detector adapted to adjust the threshold peak optical power level at least once over a range of optical attenuation of the optical path link that includes a minimum attenuation and a maximum attenuation.

46. The optical detection circuit of claim 45, wherein the peak power level of optical noise at the minimum attenuation is at least as great as the peak power level of an optical data signal at the maximum attenuation.

47. The optical detection circuit of claim 45, wherein the signal detector outputs a first value responsive to the peak power level being greater than the threshold power level and a second value responsive to the peak power level being less than the threshold power level.

48. The optical detection circuit of claim 45, wherein the optical detector includes a microprocessor controller and a memory coupled to the microprocessor controller.

49. The optical detection circuit of claim 48, wherein the signal detector is configured to record characterization data in the memory of peak power level and average power level of optical noise and peak power level and average power level of optical data pulses over the range of attenuation.

50. The optical detection circuit of claim 45, wherein the signal detector calculates a threshold ratio of peak power level to average power level sufficient to distinguish an optical signal input from an optical amplifier noise input.

51. The optical detection circuit of claim 50, wherein the signal detector calculates a ratio of peak power level to average power level and outputs a first value responsive to the ratio being greater than the threshold ratio and a second value responsive to the ratio being less than the threshold ratio.

52. An optical network, comprising:

a first node having an optical amplifier for amplifying an optical data stream of optical data pulses;

a second node;

an optical path link coupling the first node to the second node having at least one optical fiber; and

and an optical detection circuit coupled to the second node, the optical detection circuit including;

an optical detector generating at least one electrical output responsive to an optical input received by the optical detector;

an electrical amplifier circuit coupled to the at least one electrical output of the optical detector configured to measure a peak optical power level and an average optical power level of the optical input; and

a signal detector receiving the signals of the electrical circuit configured to select a signal detection threshold having a threshold peak optical power level sufficient to distinguish an optical signal input from an optical amplifier noise input at the average power level, the signal detector adapted to adjust the threshold peak optical power level at least once over a range of optical attenuation of the optical path link that includes a minimum attenuation and a maximum attenuation.

53. The optical detection circuit of claim 52, wherein the peak power level of optical noise at the minimum attenuation is at least as great as the peak power level of an optical data signal at the maximum attenuation.

54. The optical network of claim 52, wherein the signal detector outputs a first value responsive to the peak power level being greater than the threshold power level and a second value responsive to the peak power level being less than the threshold power level.

55. The optical network of claim 52, wherein the optical detector includes a microprocessor controller and a memory coupled to the microprocessor controller.

56. The optical network of claim 55, wherein the signal detector is configured to record characterization data in the memory of peak power level and average power level of optical noise and peak power level and average power level of optical data pulses over the range of attenuation.

57. The optical detection circuit of claim 52, wherein the signal detector calculates a threshold ratio of peak power level to average power level sufficient to distinguish an optical signal input from an optical amplifier noise input.

58. The optical detection circuit of claim 57, wherein the signal detector calculates a ratio of peak power level to average power level and outputs a first value responsive to the ratio being greater than the threshold ratio and a second value responsive to the ratio being less than the threshold ratio.

59. An optical network, comprising:

a first node having an optical amplifier receiving an optical data stream and having an output coupled to an output port of the optical amplifier;

a second node having an input port;

an optical fiber coupling the output port of the first node to the input port of the second node, the optical fiber having an optical attenuation that depends upon the length of the optical fiber; and

an optical detection circuit residing in the second node receiving an optical input coupled by the input port of the second node, the optical detection circuit including;

an optical detector coupled to an electrical circuit adapted to measure signals indicative of a peak optical power level and an average optical power level of the optical input; and

a signal detector receiving the signals of the electrical circuit configured to select a signal detection threshold having a threshold peak optical power level sufficient to distinguish an optical signal input from an optical amplifier noise input at the average power level;

the signal detector adapted to adjust the threshold peak optical power level at least once over a range of length of the optical fiber having a minimum attenuation at a minimum length and a maximum attenuation at a maximum length with the peak power level of the optical amplifier noise input at the minimum attenuation being at least as great as the peak power level of the optical signal input at the maximum attenuation.

60. An optical detection circuit for an optical node coupled to an output of an optical amplifier in an upstream optical node by an optical path link including an optical fiber, the optical path link having an optical attenuation, comprising:

optical detector means for receiving an input optical signal from the upstream optical amplifier and outputting a first signal indicative of an average optical power level and a second signal indicative of a peak optical power level; and

signal detector means receiving the first and second signals and selecting a signal detection threshold corresponding to a threshold peak power level at the average power level sufficient to distinguish an optical data signal from optical noise for the optical attenuation of the optical path link over a range of attenuation in which the threshold peak power level is adjusted at least once.