Optical switch with power equalization
View Patent ↗An optical intensity control system for use with an optical switch providing individual signal paths between input and output ports. The system has a optical splitters connectable to output multiplexers of the switch and also has variable optical intensity controllers (VOICs) for insertion into the individual signal paths. The VOICs individually control the intensity of optical signals present in the signal paths in accordance with intensity control signals. An equalizer is connected to the splitters and to the VOICs, for producing an estimate of the optical power of each individual switched optical signal and generating the intensity control signals. The equalizer is adapted to controllably isolate individual switched optical signals. In this way, individual and independent control of the power on each optical channel is provided, wavelength-dependent losses introduced by all the devices in the switch including the WDM devices at the output of the switch are accounted for and one optical coupler is required for each output optical fiber. Coarse equalization may be provided for each multiplexed optical signal either at the switch input or output, permitting a reduction in the dynamic range over which the VOICs inside the switch are required to operate.
1. A method of generating control signals for adjusting intensity of single-carrier optical signals travelling through an optical switch adapted to recombine groups of switched optical signals into multiplexed switched optical signals at an output end of the optical switch, the method comprising the steps of:
a) controllably isolating individual switched optical signals from the multiplexed switched optical signals;
b) estimating a power of the individual switched optical signals isolated at step (a); and
c) generating the control signals as a function of power estimates obtained at step (b) and a reference value.
2. The method of claim 1 , further comprising adjusting each control signal as a function of a wavelength and the multiplexed switched optical signal associated with the corresponding isolated individual switched optical signal.
3. The method of claim 1 , further comprising the steps of:
in advance of a connection map change affecting a subset of the single-carrier optical signals, generating control signals for gradually decreasing the intensity of the affected signals to a nominal value; and
following the connection map change, generating control signals for gradually increasing the intensity of the affected signals to the reference value.
4. The method of claim 1 , further comprising the steps of:
in advance of a connection map change affecting a subset of the single-carrier optical signals, generating control signals for decreasing, to a nominal value, the intensity of the affected signals in groups thereof; and
following the connection map change, generating control signals for increasing, to the reference value, the intensity of the affected signals in groups thereof.
5. An equalizer for generating control signals used in adjusting an intensity of single-carrier optical signals travelling through an optical switch adapted to recombine groups of individual switched optical signals into multiplexed switched optical signals at an output end of the optical switch, the equalizer comprising:
first means for controllably admitting individual switched optical signals from the multiplexed switched optical signals;
second means, connected to the first means, for estimating a power of the admitted individual switched optical signals; and
means, connected to the second means, for generating the control signals as a function of the power estimates and a reference value.
6. A method of individually controlling an intensity of a plurality of optical carrier signals capable of being switched by a switching core and recombined into wavelength-division multiplexed (WDM) optical signals by a plurality of wavelength division multiplexers, comprising:
tapping a portion of each WDM optical signal after recombination by the plurality of wavelength division multiplexers to produce a respective tapped optical signal;
processing each tapped optical signal to produce an estimate of a power of each optical carrier signal contained in the respective WDM optical signal; and
adjusting the intensity of each optical carrier signal prior to recombination by the plurality of wavelength division multiplexers as a function of the power estimates.
7. A method of calibrating power estimates received at a processor connected to an optical carrier selection circuit in an intensity control loop, comprising the steps of:
obtaining a reference estimate of an optical power of a reference light source without an effect of the optical carrier selection circuit;
controlling the optical carrier selection circuit in order to obtain an estimate of the optical power of the reference light source for each of a plurality of possible optical paths through the optical carrier selection circuit;
generating a calibration factor for each path by evaluating a function of a difference between the corresponding received power estimate and the reference estimate; and
adjusting subsequent power estimates for each path by the corresponding calibration factor.
8. A method of controlling an optical switch providing individual signal paths between a plurality of input ports and a plurality of output ports, the method comprising:
producing an estimate of optical power of one or more individual switched optical signals present in one or more signal paths of the optical switch;
generating intensity control signals as a function of the estimates of optical power; and
individually controlling an intensity of the one or more individual switched optical signals present in the individual signal paths of the optical switch in accordance with the intensity control signals.
9. The method of claim 8 , further comprising receiving a power estimate from a power estimator connected to an optical receiver connected to a wavelength division multiplexer of the optical switch and generating the intensity control signals at least in part as a function of the received power estimate.
10. The method of claim 8 , further comprising converting the one or more individual switched optical signals to electrical signals and time-averaging the electrical signals to obtain the estimates of optical power.
11. The method of claim 8 , wherein generating the intensity control signals further comprises generating the intensity control signals sequentially as a time-division-multiplexed intensity control signal.
12. The method of claim 11 , further comprising distributing time-based portions of the time-division-multiplexed intensity control signal.
13. The method of claim 8 , further comprising:
obtaining a reference estimate of the optical power from a power estimator connected to an optical receiver connected to a wavelength division multiplexer of the optical switch;
determining a calibration factor by evaluating a function of the reference estimate and the estimate of optical power; and
adjusting the intensity control signal associated with each individual switched optical signal by the calibration factor.
14. The method of claim 8 , further comprising selectably raising one mirror at a time of a plurality of controllable mirrors in the optical switch in order to isolate selected ones of the one or more individual switched optical signals.
15. The method of claim 14 , further comprising converting the one or more individual switched optical signals to electrical signals and transmitting the converted individual switched optical signals at a changed wavelength to a core optical switching matrix associated with the changed wavelength in the optical switch.
16. The method of claim 8 , further comprising selectively tuning a wavelength-tunable optical bandpass filter in the optical switch.
17. The method of claim 8 , wherein the controlling step is performed by a plurality of variable optical intensity controllers (VOICs) positioned into respective ones of the individual signal paths.
18. The method of claim 17 , wherein the producing and generating steps are performed by an equalizer connected to the plurality of VOICs.
19. The method of claim 8 , wherein the one or more individual switched optical signals are narrow-optical-bandwidth optical signals.