Optical ring networks using circulating optical probe in protection switching with automatic reversion

• US 20070086332A1
• Filed: 10/13/2006
• Published: 04/19/2007
• Est. Priority Date: 10/13/2005
• Status: Active Grant

• Current Assignee: Snell Holdings, LLC (Treq Labs, Inc.)
• Original Assignee: Vello Systems Incorporated
• Inventors: Way, Winston, Lam, Cedric
• Granted Patent: US 8,139,476 B2
• Time in Patent Office: Days
• US Class Current: 370/223
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/0227 Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
• CPC Class Codes: H04J 14/0232 for downstream transmission
• CPC Class Codes: H04J 14/0235 for upstream transmission
• CPC Class Codes: H04J 14/0283 WDM ring architectures
• CPC Class Codes: H04J 14/0295 Shared protection at the optical channel (1:1, n:m)
• CPC Class Codes: H04J 3/14 Monitoring arrangements for SDH/SONET rings H04J3/085

Abstract

Techniques and apparatus for optical communication networks including fiber ring networks with protection switching to maintain optical communications when an optical failure occurs and to automatically revert to normal operation when the optical failure is corrected. Implementations include use of a circulating optical probe signal at an optical probe wavelength within the gain spectral range of optical amplifiers used in a fiber ring network to detect an optical failure.

Claims

1. An optical communication method, comprising:

in an optical ring network carrying optical WDM signals and comprising optical amplifiers operable to amplify light in a gain spectral range covering optical wavelengths of the optical WDM signals,

coupling to the optical ring network at least one optical probe signal at a probe wavelength which is inside or near one end of the gain spectral range to obtain a sufficient optical gain from the optical amplifiers to sustain a detectable signal level;

monitoring the optical probe signal to detect an optical failure in the optical ring network; and

controlling a protection switch mechanism in the optical ring network, in response to a status of the monitored optical probe signal, to sustain communications in the optical ring network outside a location of the optical failure and to restore communications in the optical ring network after the optical failure is repaired.

2. The method as in claim 1, wherein the probe wavelength is greater or smaller than any wavelength of the optical WDM signals and at one end of the gain spectral range.

3. The method as in claim 1, wherein the probe wavelength is greater than at least one of the optical WDM signals and is less than at least another-one of the optical WDM signals.

4. The method as in claim 1, further comprising:

configuring one of the ring nodes in the optical ring network as a central node which controls the protection switch mechanism and couples the optical probe signal to the optical ring network;

monitoring the optical probe signal in each ring node;

communicating monitored status of the optical probe signal from each ring node to the central node;

operating the central node to process received status information on the optical probe signal at different ring nodes and to determine a location of the optical failure; and

operating the central node to control the ring nodes to effectuate the protection switch mechanism.

5. The method as in claim 4, further comprising:

using a node-to-node optical communication signal at a wavelength different from the optical probe wavelength to communicate the monitored status of the optical probe signal from each ring node to the central node.

6. The method as in claim 4, further comprising:

modulating the optical probe signal at each ring node to carry information on the monitored status of the optical probe signal from each ring node; and

using the modulated optical probe signal to communicate to the central node the monitored status of the optical probe signal from each ring node.

7. The method as in claim 6, further comprising:

using a variable optical attenuator in each ring node to modulate the optical probe signal.

8. The method as in claim 1, further comprising:

configuring one of the ring nodes in the optical ring network as a central node which provides a default optical break point in the optical ring network when there is no optical failure in the optical ring network, and which couples the optical probe signal to the optical ring network;

closing the default optical break point in the central node when the optical probe signal is not detected in the central node;

in a ring node that is not the central node, detecting a total optical power of light received in the ring node, without separately monitoring the optical probe signal; and

creating a protective optical break point in a ring node when the detected total optical power is below a power threshold, without relying on a command from the central node.

9. The method as in claim 8, further comprising:

controlling ring nodes in the optical ring network to provide optical traffic in first and second opposite directions;

communicating information on detected total optical power of light received in each ring node to the central node;

processing the information on detected total optical power of light from different ring nodes in the ring network to determine a location of the optical failure;

using the central node to command a first ring node adjacent to the location of optical failure to create a first protective optical break point upstream from the location of the optical failure in the first direction, and to command a second ring node, which is adjacent to the first ring node and the location of the optical failure, to create a second protective optical break point upstream from the location of the optical failure in the second direction;

using the central node to control the first and the second ring nodes to simultaneously close the first and the second optical break points after the detected total optical power levels at both the first and the second ring nodes are above the power threshold; and

creating a default optical break point in each of the first and second directions the central node when the optical probe signal is detected in the central node in both the first and the second directions.

10. The method as in claim 9, further comprising:

using a node-to-node optical communication signal at a wavelength different from the optical probe wavelength to communicate the information on detected total optical power of light received in each ring node to the central node.

11. The method as in claim 9, further comprising:

modulating the optical probe signal at each ring node to carry information on the information on detected total optical power of light received in each ring node; and

using the modulated optical probe signal to communicate to the central node the information on detected total optical power of light received in each ring node.

12. The method as in claim 11, further comprising:

using a variable optical attenuator in each ring node to modulate the optical probe signal.

13. An optical communication method, comprising:

connecting a plurality of optical ring nodes to form a optical ring network carrying optical WDM signals in first and second, opposite directions, each ring node comprising at least one optical amplifier operable to amplify light in a gain spectral range covering at least optical wavelengths of optical WDM signals in the optical ring network, each ring node operable to transmit a first portion of light in the gain spectral range, including the optical WDM signals, and to drop a second portion of the light in the gain spectral range;

coupling to the optical ring network a first optical probe signal to circulate in the optical ring network in the first direction and a second optical probe signal to circulate in the optical ring network in the second direction, each of the first and second optical probe signals being at a probe wavelength that is within the gain spectral range of each optical amplifier in each ring node; and

monitoring the first and the second optical probe signals to detect a failure that causes a break in the optical ring network.

14. The method of claim 13, wherein the probe wavelength is less or greater than any optical wavelength used or reserved for an optical WDM signal in the optical ring network.

15. The method of claim 14, wherein the probe wavelength is located at one end of the gain spectral range of each optical amplifier in each ring node where a total optical gain in the optical ring network at the probe wavelength is sufficient to sustain each of the first and second optical probe signals to be above a detectable level in each ring node.

16. The method as in claim 13, wherein the probe wavelength is greater than at a wavelength of least one of the optical WDM signals and is less than a wavelength of at least another one of the optical WDM signals.

17. The method of claim 13, further comprising:

operating a selected ring node to create a default break point for each circulating optical signal in the optical ring network when there is no break point, other than the default break point, in the optical ring network for each circulating optical signal and to close the default break point when there is a break point between two other ring nodes in the optical ring network for each circulating optical signal.

18. The method of claim 17, further comprising:

using an optical switch in the selected ring node to create or close the default break point.

19. The method of claim 17, further comprising:

using an optical amplifier in the selected ring node to create the default break point by turning off the optical amplifier and to close the default break point by turning on the optical amplifier.

20. The method of claim 17, further comprising:

using a variable optical attenuator in the selected ring node to create the default break point by controlling an optical attenuation of the variable optical attenuator at a high level and to close the default break point by controlling the optical attenuation at a low level.

21. The method of claim 17, further comprising:

using the selected ring node as a central node to control operations of other ring nodes;

providing communications between the central node and each ring node to send information of each ring node to the central and to use the central node to control protection switching in each ring node;

within each ring node, selectively dropping a portion of each of the first and the second optical probe signals while allowing a remainder of each of the first and the second optical probe signals to continue on in the optical ring network;

within each ring node, monitoring the dropped portion to detect whether the first and the second optical probe signals are present; and

operating the central node to receive information from other ring nodes and to control other ring nodes in response to the received information.

22. The method of claim 21, further comprising:

using the monitoring in each ring node to detect a break point other than the default break point in the optical ring network;

when the break point between two ring nodes is detected, operating the central protection switch mechanism to close the default break point, and causing a protective optical break point in each of the two ring nodes to cut off light in both the first and the second directions; and

after the break point is repaired to allow for transmission of light, operating the central protection switch mechanism to restore the default break point and closing the protective optical break point in each of the two ring nodes to restore transmission of light through the two ring nodes in both the first and the second directions.

23. The method of claim 22, further comprising:

turning on and off an optical amplifier in one of the two ring nodes to create and close a protective optical break point, respectively.

24. The method of claim 22, further comprising:

controlling an optical attenuation in a variable optical attenuator in one of the two ring nodes at a high level and a low level to create and close the protective optical break point, respectively.

25. The method of claim 22, further comprising:

opening and closing an optical switch in one of the two ring nodes to create and close the protective optical break point, respectively.

26. The method of claim 21, further comprising:

using the central node to couple the first and the second optical probe signals to the optical ring network.

27. The method of claim 21, further comprising:

using an optical switch inside the central node to create or close the default break point.

28. The method of claim 21, further comprising:

using an optical amplifier inside the central node to create the default break point by turning off the optical amplifier and to close the default break point by turning on the optical amplifier.

29. The method of claim 21, further comprising:

using a variable optical attenuator inside the central node to create the default break point by controlling an optical attenuation of the variable optical attenuator at a high level and to close the default break point by controlling the optical attenuation at a low level.

30. The method of claim 21, wherein two adjacent ring nodes are connected by a first fiber to carry light in the first direction and a second fiber to carry light in the second direction.

31. The method of claim 21, wherein two adjacent ring nodes are connected by a single fiber to carry light in both the first and the second directions.

32. The method as in claim 21, further comprising:

processing the received information in the central node from other ring nodes to construct a map of status of detected optical probes at the other ring nodes to determine a location of an optical failure; and

using the central node to command two ring nodes near the location of the optical failure to create an optical break point downstream from the location of the optical failure in each of the first and the second directions.

33. The method of claim 17, further comprising:

coupling the first and the second optical probe signals to the optical ring network within the selected ring node;

operating the selected ring node to selectively drop a portion of each of the first and the second optical probe signals while allowing a remainder of each of the first and the second optical probe signals to continue on in the optical ring network, and to monitor presence or absence of the first and the second optical probe signals to decide whether there is a break point elsewhere in the optical ring network;

when at least one of the first and the second optical probe signals is absent in the selected ring node, operating the selected ring node to close the default break point, without relying on information from other ring nodes; and

when both of the first and the second optical probe signals are absent in the selected ring node, operating the selected ring node to open the default break point; and

wherein the method further comprises;

operating a ring node, that is not the selected ring node, to control optical transmission in each ring node, without relying on a control command from the selected ring node, to

monitor a total amount of optical power in each of the first and the second directions in the optical ring network, without monitoring each of the first and the second optical probe signals alone,

create a local break point in each of the first and the second directions within the ring node when the total amount of optical power in one of the first and the second directions is detected to be below a power threshold, thus leading to shutting down optical transmission of a neighboring ring node, and

after creating the local break point in each of the first and the second directions, subsequently close one local break point in one direction.

34. The method of claim 33, further comprising:

communicating information on the monitored total optical power at each ring node to the selected ring node; and

using the selected ring node to control closing of a local break point at a ring node based on the monitored total optical power in the ring node.

35. The method of claim 34, further comprising:

using the selected ring node to synchronize closing of two local break points in two different ring nodes adjacent to a location of an optical failure.

36. The method of claim 34, further comprising

using an optical supervision channel signal at a wavelength different from the optical probe wavelength to communicate the information on the monitored total optical power at each ring node to the selected ring node.

37. The method of claim 34, further comprising

Modulating the optical probe signal to carry and to communicate the information on the monitored total optical power at each ring node to the selected ring node.

38. The method of claim 33, further comprising:

operating a ring node next to the central node that does not receive the optical WDM signals from the central node when there is no break point, other than the default break point, in the optical ring network for each circulating optical signal to detect an optical monitor signal from the central node, wherein the optical monitor signal indicates whether there is a break point between the central node and the ring node next to the central node;

operating the ring node next to the central node to transmit light in both the first and the second directions when the optical monitor signal indicates there is no break point between the central node and the ring node next to the central node; and

operating the ring node next to the central node to block light in both the first and the second directions when the optical monitor signal indicates there is a break point between the central node and the ring node next to the central node.

39. The method as in claim 38, wherein the optical monitor signal is an optical supervision channel signal between the central node and the ring node next to the central node.

40. An optical communication system, comprising:

a plurality of optical ring nodes connected to form an optical ring network which carries optical WDM signals, the optical ring network comprising optical amplifiers operable to amplify light in a gain spectral range covering optical wavelengths of the optical WDM signals;

an optical probe transmitter coupled to the optical ring network to supply to the optical ring network an optical probe signal at a probe wavelength which is inside or near one end of the gain spectral range to obtain a sufficient optical gain from the optical amplifiers to sustain a detectable signal level;

a probe monitor in at least one optical ring node to split a portion of the optical probe signal and to monitor the optical probe signal to detect an optical failure in the optical ring network; and

a protection switch in the optical ring network to create a default optical break point when the probe monitor indicates that there is no optical failure in the optical ring network and to close the default optical break point when the probe monitor indicates that there is an optical failure,

wherein the optical ring network is responsive to a status of the monitored optical probe signal to control the protection switch and the optical ring nodes to sustain communications in the optical ring network outside a location of the optical failure and to restore communications in the optical ring network after the optical failure is repaired.

41. The system as in claim 40, wherein each ring node comprises:

an optical drop coupler to split a portion of light in the optical ring network for dropping one or more of the optical WDM signals to the ring node;

an optical add coupler coupled to the optical ring network downstream from the optical drop coupler, the optical add coupler operable to add one or more add optical WDM signal to the optical ring network; and

a wavelength-selective optical blocker, which allows optical transmission of light at the probe wavelength, optically connected between the optical drop coupler and the optical add coupler to block light of the one or more of the optical WDM signals that are dropped from reaching the optical add coupler.

42. The system as in claim 40, wherein the protection switch comprises:

a first optical terminal to receive an input signal;

a second optical terminal to output an output signal;

a first optical path comprising first and second optical switches connected in series; and

a second optical path comprising third and fourth optical switches connected in series;

wherein the first optical terminal is coupled to join a first end of the first optical path and a first end of the second optical path to split the input signal between the first and the second optical paths, and

wherein the second optical terminal to join a second end of the first optical path and a second end of the second optical path to combine light from the first and the second optical paths to produce the output signal.

43. The system as in claim 40, wherein

the optical ring nodes comprise a central ring node in which the optical probe transmitter and the protection switch are located, and

the protection switch includes a first switch coupled in the first optical ring path and a second switch coupled in the second optical ring path;

and

the system further comprises;

a first optical ring path connecting the optical ring nodes to carry the optical WDM signals in a first ring direction;

a second optical ring path connecting the optical ring nodes to carry a replica of the optical WDM signals in a second, opposite ring direction;

a first optical probe coupler inside the central node and coupled to the first optical ring path downstream from the first switch in the first ring direction to couple the optical probe signal into the first optical ring path in the first ring direction; and

a second optical probe coupler inside the central node and coupled to the second optical ring path downstream from the second switch in the second ring direction to couple the optical probe signal into the second optical ring path in the second ring direction.

44. The system as in claim 43, further comprising:

a first add coupler inside the central node and coupled to the first ring path on a first side of the first switch to add one or more optical add signals to the first ring path along the first ring direction;

a first drop coupler inside the central node and coupled to the first ring path on the first side of the first switch to drop optical signals from the first ring path along the first ring direction;

a second add coupler inside the central node and coupled to the second ring path on the first side of the second switch to add the one or more optical add signals to the second ring path along the second ring direction; and

a second drop coupler inside the central node and coupled to the second ring path on the first side of the second switch to drop the optical signals from the second ring path along the second ring direction.

45. The system as in claim 44, further comprising:

a first optical amplifier in the central ring node and coupled in the first ring path upstream from the first add and drop couplers in the first ring direction;

a first probe monitor coupler in the central ring node and coupled in the first ring path upstream from the first optical amplifier to split a fraction of light from the first ring path;

a first optical probe filter in the central ring node to filter light from the first probe monitor coupler to selectively transmit light at the probe wavelength;

a first probe photodetector to receive transmitted light from the first optical probe filter;

a second probe monitor coupler in the central ring node and coupled in the second ring path upstream from the second switch to split a fraction of light from the second ring path;

a second optical probe filter in the central ring node to filter light from the second probe monitor coupler to selectively transmit light at the probe wavelength; and

a second probe photodetector in the central ring node to receive transmitted light from the first optical probe filter.

46. The system as in claim 45, wherein the second switch is a second optical amplifier.

47. The system as in claim 45, wherein a ring node that is not the central ring node comprises:

a first optical amplifier in the first optical path at an entrance of the ring node;

a first variable optical attenuator in the first optical path downstream from the first optical amplifier at an output of the ring node;

a first add coupler coupled to the first ring path between the first optical amplifier and the first variable optical attenuator to add one or more optical add signals to the first ring path along the first ring direction;

a first drop coupler coupled to the first ring path between the first optical amplifier and the first variable optical attenuator to drop optical signals from the first ring path along the first ring direction;

a second optical amplifier in the second optical path at an entrance of the ring node;

a second variable optical attenuator in the second optical path downstream from the second optical amplifier at an output of the ring node;

a second add coupler coupled to the second ring path between the second optical amplifier and the second variable optical attenuator to add one or more optical add signals to the second ring path along the second ring direction;

a second drop coupler coupled to the second ring path between the second optical amplifier and the second variable optical attenuator to drop optical signals from the second ring path along the second ring direction

48. The system as in claim 47, wherein the ring node that is not the central ring node further comprises

a first probe monitor coupler coupled in the first ring path upstream from the first optical amplifier to split a fraction of light from the first ring path;

a first optical probe filter to filter light from the first probe monitor coupler to selectively transmit light at the probe wavelength;

a first probe photodetector to receive transmitted light from the first optical probe filter;

a second probe monitor coupler coupled in the second ring path upstream from the second optical amplifier to split a fraction of light from the second ring path;

a second optical probe filter to filter light from the second probe monitor coupler to selectively transmit light at the probe wavelength; and

a second probe photodetector to receive transmitted light from the first optical probe filter.

49. An optical communication system, comprising:

a plurality of optical ring nodes connected to form an optical ring network which carries optical WDM signals; and

a protection switch in the optical ring network to create a default optical break point when there is no optical failure in the optical ring network and to close the default optical break point when there is an optical failure,

wherein the protection switch comprises;

a first optical terminal to receive an input signal;

a second optical terminal to output an output signal;

a first optical path comprising first and second optical switches connected in series; and

a second optical path comprising third and fourth optical switches connected in series;

wherein the first optical terminal is coupled to join a first end of the first optical path and a first end of the second optical path to split the input signal between the first and the second optical paths, and

wherein the second optical terminal to join a second end of the first optical path and a second end of the second optical path to combine light from the first and the second optical paths to produce the output signal.