System and method for training an optical cross-connect comprising steerable switching elements

• US 6,411,751 B1
• Filed: 10/06/2000
• Issued: 06/25/2002
• Est. Priority Date: 10/08/1999
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Guardian Corp. (Broadcom, Inc.), Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Gottlieb, Albert M, Neilson, David Thomas, Giles, Randy Clinton
• Primary Examiner(s): Healy, Brian
• Assistant Examiner(s): WOO, SARAH H
• Application Number:
  US09/680,753
• Time in Patent Office: 627 Days
• Field of Search: 385/16, 385/18, 324/97, 364/713
• US Class Current: 385/16
• CPC Class Codes: G02B 6/3512 the optical element being reflective, e.g. mirror
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/356 in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001
• CPC Class Codes: G02B 6/3586 Control or adjustment details, e.g. calibrating testing optical equipment G01M11/00
• CPC Class Codes: G02B 6/3588 of the processed beams, i.e. controlling during switching of orientation, alignment, or beam propagation properties such as intensity, size or shape

Abstract

Signal losses in an optical cross-connect having steerable switching elements for routing optical signals are substantially reduced by controllably and selectively training the steerable switching elements as a function of measured input and output power of a cross-connected optical signal. More specifically, adjustments to the alignment of one or more steerable switching elements associated with a particular cross-connection are performed in a non-intrusive manner to increase the optical signal power in an optical signal while maintaining an active cross-connection of the optical signal. In one illustrative embodiment, optical monitoring arrangements monitor the optical signal power of optical signals coupled to the cross-connect inputs and outputs. The cross-connect includes a switching fabric comprising a plurality of steerable MEMS mirror elements used as switching elements for controllably and selectively directing the light beams within the cross-connect. By comparing the measured optical signal power with a previously stored value representing the expected optical signal power for that cross-connection, small adjustments can then be made, as appropriate, to optimize the alignment of the mirrors associated with the cross-connection. For example, if the difference between the measured and expected optical signal power exceeds a prescribed threshold, then a dithering process is initiated whereby individual mirrors are “walked through” alternate tilt positions until the measured optical signal power has been optimized, e.g., increased.

Claims

1. A method of training an optical cross-connect having one or more steerable mirrors for routing optical signals, the method comprising:

measuring input signal power of an optical signal at an input of the cross-connect;

measuring output signal power of the optical signal at an output of the cross-connect, wherein the optical signal is routed from the input to the output of the cross-connect by at least one steerable mirror; and

controllably adjusting the alignment of the at least one steerable mirror as a function of the input signal power and output signal power of the optical signal while maintaining an active cross-connection of the optical signal.

2. The method according to claim 1, wherein the one or more steerable mirrors are micro-electromechanical system (MEMS) mirrors.

3. The method according to claim 1, wherein controllably adjusting comprises:

retrieving a stored value that corresponds to an expected signal power loss for the active cross-connection;

determining an actual signal power loss based on the measured input signal power and measured output signal power; and

comparing the actual signal power loss to the expected signal power loss to determine a difference value.

4. The method according to claim 3, further comprising the step of maintaining present alignment settings of the at least one steerable mirror if the difference value is less than a prescribed threshold.

5. The method according to claim 3, further comprising the step of initiating adjustment of alignment settings of the at least one steerable mirror if the difference value exceeds a prescribed threshold.

6. The method according to claim 1, wherein controllably adjusting comprises incrementally adjusting a tilt position of the at least one steerable mirror.

7. The method according to claim 6, wherein incrementally adjusting a tilt position comprises applying control voltages in a prescribed manner to control electrodes associated with the at least one steerable mirror.

8. The method according to claim 7, wherein incrementally adjusting comprises the step of determining a control voltage step size as a function of control voltage settings that align the at least one steerable mirror to one or more next nearest neighbor mirrors.

9. The method according to claim 6, further comprising the step of monitoring output signal power to identify a tilt position that provides increased optical signal power in the active cross-connection.

10. The method according to claim 9, wherein the step of incrementally adjusting is terminated when the increased optical signal power exceeds a predetermined threshold.

11. The method according to claim 6, wherein the optical signal is routed from the input to the output of the cross-connect by a first steerable mirror and a second steerable mirror, and wherein the first steerable mirror and the second steerable mirror are incrementally adjusted on a sequential basis.

12. The method according to claim 6, wherein the optical signal is routed from the input to the output of the cross-connect by a first steerable mirror and a second steerable mirror, and wherein the first steerable mirror and the second steerable mirror are incrementally adjusted on a simultaneous basis.

13. The method according to claim 6, wherein the optical signal is routed from the input to the output of the cross-connect by a first steerable mirror and a second steerable mirror, and wherein the first steerable mirror and the second steerable mirror are incrementally adjusted on a simultaneous basis with corresponding adjustments in tilt position.

14. The method according to claim 6, wherein the optical signal is routed from the input to the output of the cross-connect by a first steerable mirror and a second steerable mirror, and wherein the first steerable mirror and the second steerable mirror are incrementally adjusted on a simultaneous basis with diametrically opposite adjustments in tilt position.

15. The method according to claim 6, wherein the optical signal is routed from the input to the output of the cross-connect by a first steerable mirror and a second steerable mirror, and wherein the step of controllably adjusting comprises a walk and dither sequence comprising:

determining a baseline output signal power for the active cross-connection;

walking the first steerable mirror to a first tilt position;

dithering the second steerable mirror through a plurality of tilt positions while the first steerable mirror is at the first tilt position;

monitoring output signal power for each of the plurality of tilt positions; and

terminating the walk and dither sequence if the monitored output signal power exceeds the baseline output signal power by a prescribed amount.

16. The method according to claim 15, further comprising:

if the monitored output signal power does not exceed the baseline output signal power by a prescribed amount, walking the first steerable mirror to a second tilt position; and

repeating the dithering and monitoring steps.

17. A method of increasing optical signal power of an optical signal routed through an optical cross-connect having a plurality of steerable switching elements, the method comprising:

measuring input signal power of an optical signal at an input of the cross-connect;

measuring output signal power of the optical signal at an output of the cross-connect, wherein the optical signal is routed from the input to the output of the cross-connect by at least one steerable switching element; and

controllably adjusting the alignment of the at least one steerable switching element as a function of the input signal power and output signal power of the optical signal while maintaining an active cross-connection of the optical signal.

18. The method according to claim 17, wherein controllably adjusting the alignment includes:

comparing an actual optical power loss associated with the active cross-connection with a previously stored value representing the expected optical power loss for the active cross-connection; and

adjusting the alignment of the at least one steerable switching element if the difference between the actual power loss and expected power loss exceeds a prescribed threshold.

19. The method according to claim 18, wherein the actual optical power loss is calculated by subtracting the measured output signal power from the measured input signal power.

20. The method according to claim 19, wherein adjusting the alignment includes walking the at least one steerable switching element through alternate positions to identify a position that provides increased optical signal power in the optical signal associated with the active cross-connection.

21. A system for increasing optical signal power of an optical signal routed through an optical cross-connect having a plurality of steerable switching elements, the system comprising:

an input signal monitor for measuring input signal power of an optical signal at an input of the cross-connect;

an output signal monitor for measuring output signal power of the optical signal at an output of the cross-connect, wherein the optical signal is routed from the input to the output of the cross-connect by at least one steerable switching element; and

a controller for controlling alignment adjustments to the at least one steerable switching element as a function of the input signal power and output signal power of the optical signal while maintaining an active cross-connection of the optical signal.

22. The system according to claim 21, wherein the input signal monitor and output signal monitor each comprise:

an optical tap for tapping off a portion of optical signal power of the optical signal;

a photodetector coupled to the optical tap for supplying an electrical signal indicative of the tapped optical signal power;

a transimpedance amplifier circuit coupled to the photodetector for translating current to voltage in the electrical signal; and

an analog to digital converter for producing a digital representation of the electrical signal.

23. The system according to claim 22, wherein the controller is responsive to an electrical signal supplied by each of the input and output signal monitors to initiate alignment adjustments.

24. A system for training steerable switching elements in an optical cross-connect comprising:

an input signal monitor for measuring input signal power of an optical signal at an input of the cross-connect;

an output signal monitor for measuring output signal power of the optical signal at an output of the cross-connect, wherein the optical signal is routed from the input to the output of the cross-connect by at least one steerable switching element; and

a controller for controlling dither of the at least one steerable switching element as a function of the input signal power and output signal power of the optical signal while maintaining an active cross-connection of the optical signal.