MWS drift feedback compensator using VOA and input power dithering
View Patent ↗The invention relates to a compensator of attenuation drift in an optical multi-wavelength switch (MWS) which uses input signal amplitude dither and external VOA dither cancellation to determine relative position of MEMS micro mirror hence indirectly determining attenuation level.
1. A drift feedback compensator for compensating drift comprising:
an optical switch comprising a plurality of input ports, an output port, and a switch control, wherein an insertion loss between at least one of the input ports and the output port is controllable in response to a control signal applied to the switch control;
a variable optical attenuator having a VOA input port optically coupled the output port of the optical switch, a VOA output port and a VOA control, wherein an attenuation between the VOA input port and VOA output port is settable in response to an attenuation setting signal applied to the VOA control;
an optical splitter optically coupled to the VOA output port for splitting an optical output signal from the VOA output port into a tapped signal and a through signal;
an optical channel monitor optically coupled to the optical splitter for receiving the tapped signal and providing a feedback signal; and
a controller for applying the control signal to the switch control and the attenuation setting signal to the VOA control in response to the feedback signal received from the optical channel monitor;
wherein the control signal modulates the insertion loss to produce an insertion loss modulation at a dither frequency, wherein the attenuation setting signal modulates the attenuation to produce an attenuation modulation at the dither frequency, and wherein the insertion loss modulation is anti-phase to the attenuation modulation.
2. The drift feedback compensator claimed in claim 1 , wherein the optical switch is a MWS.
3. The drift feedback compensator claimed in claim 1 , wherein the controller further comprises a memory unit for storing calibration values.
4. The drift feedback compensator claimed in claim 1 , wherein the controller further comprises a processing unit for calculating a control offset.
5. The drift feedback compensator claimed in claim 1 , wherein the dither frequency has period from about 0.1 millisecond to about 1.0 second.
6. The drift feedback compensator claimed in claim 1 , wherein the insertion loss modulation and the attenuation modulation sum to a residual ripple that has an amplitude which is less than about 0.1 dB.
7. The drift feedback compensator claimed in claim 1 , wherein the insertion loss modulation has an amplitude from about 0.01 dB to about 1.0 dB.
8. The drift feedback compensator claimed in claim 1 , wherein the attenuation modulation has an amplitude from about 0.01 dB to about 1.0 dB.
9. A method of compensating the drift of the optical switch as defined in claim 1 , comprising the steps of:
a) applying a control voltage to the switch control from the controller based on an initial electro-optic characteristic;
b) applying an optical signal to at least one input port of the optical switch;
c) applying by means of the controller a first dither signal having a dither frequency to the VOA control for producing an attenuation modulation;
d) applying by means of the controller a second dither signal at the dither frequency to the switch control for producing an insertion loss modulation with opposite phase to the attenuation modulation;
e) measuring a residual dither signal at the VOA output port with the optical channel monitor;
f) adjusting an amplitude of the second dither signal to reduce the residual dither signal;
g) calculating a set of correction values from the amplitude of the second dither signal;
h) applying a corrected control voltage to the switch control from the controller, based on the correction values and the initial electro-optic characteristic; and i) periodically repeating steps e) through h).
10. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the optical switch is a MWS.
11. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the controller further comprises a memory unit for storing the initial electro-optic characteristic.
12. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the controller further comprises a processing unit for calculating the set of correction values.
13. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the dither frequency has period from about 0.1 millisecond to about 1.0 second.
14. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the insertion loss modulation has an amplitude from about 0.01 dB to about 1.0 dB.
15. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the attenuation modulation has an amplitude from about 0.01 dB to about 1.0 dB.
16. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the residual dither signal has an amplitude that is less than about 0.1 dB.
17. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the initial electro-optic characteristic is stored in a calibration file.
18. The method of compensating the drift of the optical switch claimed in claim 9 , wherein the set of correction values is stored in an offset file.