Optical signal transmitter with active optical e-field degradation
View Patent ↗A method and system for controlling optical signal to noise ratio (OSNR) of an optical signal at a receiver end of an optical link. A multi-bit sample stream is generated using a compensation function adapted to compensate impairments of the optical link A digital noise signal is generated and added to the multi-bit sample stream, and the resulting signal used to generate a degraded optical signal, which is then transmitted through the optical link.
1. A method of controlling a signal to noise ratio of an optical signal at a receiver end of an optical link, the method comprising steps of:
generating a degraded optical signal based on a compensation function adapted to compensate impairments of the optical link and a predetermined degradation function for producing a predetermined residual distortion in the optical signal at the receiver end of the optical link; and
transmitting the degraded optical signal through the optical link.
2. A method as claimed in claim 1 , wherein the degradation function is substantially constant in time.
3. A method as claimed in claim 1 , wherein the degradation function varies in time.
4. A method as claimed in claim 1 , wherein the degradation function comprises a predetermined error of the compensation function.
5. A method as claimed in claim 4 , wherein the predetermined error comprises an offset of either one or both of: a chromatic dispersion parameter; and a polarization mode dispersion parameter.
6. A method as claimed in claim 1 , wherein the step of generating a degraded optical signal comprises steps of:
generating a multi-bit sample stream using the compensation function;
applying the degradation function to the sample stream; and
generating a degraded optical signal based on the degradation function result.
7. A method as claimed in claim 6 , wherein the step of applying a degradation function to the sample stream comprises steps of:
generating a degradation signal; and
applying the degradation signal to the multi-bit sample stream.
8. A method as claimed in claim 7 , wherein the degradation signal comprises variations in either one or both of phase and amplitude.
9. A method as claimed in claim 7 , wherein the degradation signal is spectrally white.
10. A method as claimed in claim 7 , wherein the step of applying the degradation signal to the multi-bit sample stream comprises a step of adding the degradation signal to the sample stream.
11. A method as claimed in claim 7 , wherein the step of applying the degradation signal to the multi-bit sample stream comprises a step of multiplying the sample stream by the degradation signal.
12. A method as claimed in claim 1 , further comprising a step of controlling a strength of the degradation function based on a desired Bit Error Rate (BER) at the receiver end of the link.
13. A method as claimed in claim 12 , wherein the step of controlling the strength of the degradation function comprises steps of:
receiving a measured BER value from a receiver;
comparing the measured BER value to the desired BER value; and
adjusting the strength based on the comparison result.
14. A method as claimed in claim 12 , wherein the desired BER value is based on either one or both of: a design of a BER-based control loop of the receiver; and a BER tolerance of a Forward Error Correction (FEC) circuit of the receiver.
15. A method as claimed in claim 12 , wherein the step of controlling the strength of the degradation function comprises steps of:
setting the strength to zero during a continuity testing and training mode; and
increasing the strength following completion of continuity testing and training.
16. A method as claimed in claim 15 , wherein the step of setting the strength to zero comprises a step of disabling generation of a degradation signal.
17. A method as claimed in claim 16 , wherein the step of increasing the strength comprises a step of re-enabling generation of the degradation signal.
18. A method as claimed in claim 16 , wherein the step of increasing the strength comprises a step of progressively increasing the strength until at least one BER-based control loop of a receiver converges to an optimum control point.
19. A method as claimed in claim 18 , comprising a further step of adjusting the strength based on a BER tolerance of a Forward Error Correction (FEC) circuit of the receiver.
20. A system for controlling a signal to noise ratio of an optical signal at a receiver end of an optical link, the system comprising:
an optical signal generator for generating a degraded optical signal based on a compensation function adapted to compensate impairments of the optical link and a predetermined degradation function for producing a predetermined residual distortion in the optical signal at the receiver end of the optical link; and
means for transmitting the degraded optical signal through the optical link.
21. A system as claimed in claim 20 , wherein the degradation function is substantially constant in time.
22. A system as claimed in claim 20 , wherein the degradation function varies in time.
23. A system as claimed in claim 20 , wherein the degradation function comprises a predetermined error of the compensation function.
24. A system as claimed in claim 23 , wherein the predetermined error comprises an offset of either one or both of: a chromatic dispersion parameter; and a polarization mode dispersion parameter.
25. A system as claimed in claim 20 , wherein the optical signal generator comprises:
a digital filter for generating a multi-bit sample stream using the compensation function;
means for applying the degradation function to the sample stream; and
an optical modulator for generating the degraded optical signal based on the degradation function result.
26. A system as claimed in claim 25 , wherein the means for applying the degradation function to the sample stream comprises steps of:
a digital noise generator for generating a degradation signal; and
a combiner block for applying the degradation signal to the multi-bit sample stream.
27. A system as claimed in claim 26 , wherein the degradation signal comprises variations in either one or both of phase and amplitude.
28. A system as claimed in claim 26 , wherein the degradation signal is spectrally white.
29. A system as claimed in claim 26 , wherein the combiner block comprises a digital adder for adding the degradation signal to the sample stream.
30. A system as claimed in claim 26 , wherein the combiner block comprises a digital multiplier for multiplying the sample stream by the offset value.