System and method for training an optical cross-connect comprising steerable switching elements
First Claim
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.
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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.
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Citations
24 Claims
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1. A method of training an optical cross-connect having one or more steerable mirrors for routing optical signals, the method comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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.
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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.
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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.
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6. The method according to claim 1, wherein controllably adjusting comprises incrementally adjusting a tilt position of the at least one steerable mirror.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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:
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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.
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16. The method according to claim 15, further comprising:
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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.
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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:
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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. - View Dependent Claims (18, 19, 20)
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.
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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.
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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.
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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:
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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. - View Dependent Claims (22, 23)
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.
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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.
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24. A system for training steerable switching elements in an optical cross-connect comprising:
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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.
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Specification