Granted Patent B1

US 8,731,413 · App. 13/356,167 · Granted May 20, 2014

Abstract

Claims (46)

1. A method of demodulating an optical signal, comprising:

sampling a received optical signal comprising pulse-shaped data modulated onto a carrier frequency at a first sampling rate to generate a first digital version of the optical signal;

downsampling the first digital version of the optical signal to generate a second digital version of the optical signal;

filtering the second digital version of the optical signal with at least one discrete pulse shaping filter;

upsampling the filtered second digital version of the optical signal to generate a third digital version of the optical signal;

performing an equalization function on the third digital version of the optical signal; and

demodulating a stream of data from the equalized third digital version of the optical signal.

2. The method of claim 1 , wherein the first sampling rate is twice a symbol rate of the optical signal.

3. The method of claim 1 , the downsampling the first digital version of the optical signal comprising:

downsampling the first digital version to a second sampling rate, the second sampling rate being between 1.0 and 1.3 times a symbol rate of the optical signal.

4. The method of claim 1 , the upsampling the filtered second digital version of the optical signal comprising:

upsampling the filtered second digital version to the first sampling rate.

5. The method of claim 1 , the discrete pulse-shaping filter comprising an inverse of at least one pulse-shaping filter at a transmitter of the optical signal.

6. An optical communication system, comprising:

an optical transmitter configured to:

filter at least one stream of symbol mapped bits with at least a first discrete pulse shaping filter to precompensate for at least one identified non-ideal transmission condition; and

modulate the filtered symbol mapped bits to a first analog optical signal; and

an optical receiver configured to:

sample a second optical signal at a first sampling rate at an analog-to-digital converter to generate a first digital version of the second optical signal;

downsample the first version of the second optical signal to generate a second digital version of the second optical signal;

filter the second digital version of the second optical signal with at least a second pulse shaping filter to compensate for the at least one identified non-ideal transmission condition;

upsample the filtered second digital version of the second optical signal to generate a third digital version of the second optical signal;

perform an equalization function on the third digital version of the second optical signal; and

demodulate a stream of data from the equalized third digital version of the second optical signal.

7. The optical communication system of claim 6 , wherein the non-ideal transmission condition occurs in optical space.

8. The optical communication system of claim 6 , wherein the first sampling rate is twice a symbol rate of the second optical signal.

9. The optical communication system of claim 6 , the downsampling the first digital version of the optical signal comprising:

downsampling the first digital version to a second sampling rate, the second sampling rate being between 1.0 and 1.3 times a symbol rate of the optical signal.

10. The optical communication system of claim 6 , the upsampling the filtered second digital version of the optical signal comprising:

upsampling the filtered second digital version to the first sampling rate.

11. The optical communication system of claim 6 , the second discrete pulse-shaping filter comprising an inverse of the first pulse-shaping filter.

12. The optical transmitter of claim 6 , further comprising:

a precompensation computation module configured to:

predict the non-ideal transmission condition;

determine an inverse filtering function to pre-compensate for the non-ideal transmission condition; and

provide input to the at least the first discrete pulse shaping filter, the input causing the at least the first discrete pulse shaping filter to substantially implement the inverse filtering function.

13. The optical transmitter of claim 12 , wherein the input comprises a tap coefficient for the at least the first discrete pulse shaping filter.

14. The optical transmitter of claim 12 , wherein the precompensation computation module is further configured to:

receive a measurement of the non-ideal transmission condition from the optical receiver of the optical signal;

wherein the predicting the non-ideal transmission condition is based at least partially on the received measurement.

15. The optical communication system of claim 7 , wherein the non-ideal transmission condition comprises a chromatic dispersion occurring in an optical fiber.

16. The optical communication system of claim 6 , wherein the non-ideal transmission condition occurs in electrical space.

17. The optical communication system of claim 16 , wherein the non-ideal transmission condition comprises a roll-off in a digital-to-analog converter.

18. The optical communication system of claim 16 , wherein the non-ideal transmission condition comprises a non-linear amplifier response.

19. The optical communication system claim 6 , wherein the non-ideal transmission condition comprises a timing skew occurring along a signal path.

20. The optical communication system of claim 6 , wherein the at least one discrete pulse shaping filter comprises a root-raised cosine filter.

Assignments (8)