DAC-based optical modulator and demodulator
View Patent ↗Methods, systems, and devices are described for modulating and demodulating data on optical signals. During modulation, at least one stream of symbol mapped bits is filtered with at least one pulse shaping filter to reduce a bandwidth of the stream of bits and to pre-compensate for at least one identified non-ideal transmission condition. The filtered bits are modulated onto a waveform in the digital domain, and the modulated filtered bits are transmitted to digital-to-analog converter. The output of the digital-to-analog converter is converted to an optical signal. During demodulation, a received optical signal is sampled at a first sampling rate at an ADC, downsampled to a lower sampling rate for filtering, filtered with at least one discrete pulse-shaping filter, upsampled for equalization and demodulation, and then equalized and demodulated.
1. An optical communication system, comprising:
an optical transmitter comprising:
a precompensation computation processor to:
predict at least one non-ideal transmission condition;
determine an inverse filtering function to precompensate for the at least one non-ideal transmission condition;
a first discrete pulse-shaping filter to filter, based on input from the precompensation computation processor, at least one stream of symbol mapped bits to precompensate for the at least one non-ideal transmission condition, the input causing the first discrete pulse-shaping filter to substantially implement the inverse filtering function; and
a modulator to modulate the filtered symbol mapped bits to a first 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, wherein the first sampling rate is at or near a symbol rate of the second optical signal;
filter the first digital version of the second optical signal with at least a second discrete pulse-shaping filter;
upsample the filtered first digital version of the second optical signal to generate a second digital version of the second optical signal;
perform an equalization function on the second digital version of the second optical signal; and
demodulate a stream of data from the equalized second digital version of the second optical signal.
2. The optical communication system of claim 1 , wherein the at least one non-ideal transmission condition occurs in optical space.
3. The optical communication system of claim 1 , wherein the optical receiver is configured to upsample the filtered first digital version to a second sampling rate, the second sampling rate being twice the symbol rate of the second optical signal.
4. The optical communication system of claim 1 , wherein the input comprises a tap coefficient for the first discrete pulse-shaping filter.
5. The optical communication system of claim 1 , wherein the precompensation computation processor is further configured to:
receive a measurement of the at least one non-ideal transmission condition from a second optical receiver of the first optical signal,
wherein the predicting the at least one non-ideal transmission condition is based at least partially on the received measurement.
6. An optical communication system, comprising:
an optical transmitter comprising:
a precompensation computation processor to:
predict at least one non-ideal transmission condition;
determine an inverse filtering function to precompensate for the at least one non-ideal transmission condition;
a first discrete pulse-shaping filter to filter, based on input from the precompensation computation processor, at least one stream of symbol mapped bits to precompensate for the at least one non-ideal transmission condition, the input causing the first discrete pulse-shaping filter to substantially implement the inverse filtering function; and
a modulator to modulate the filtered symbol mapped bits to a first optical signal; and
an optical receiver configured to:
sample a second optical signal comprising pulse-shaped data modulated onto a carrier frequency at a first sampling rate to generate a first digital version of the second optical signal;
downsample the first digital 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 one discrete pulse shaping filter;
upsample the filtered second digital version of the second optical signal to generate a third digital version of the second optical signal; and
demodulate a stream of data from the third digital version of the second optical signal.
7. The optical communication system of claim 6 , wherein the input comprises a tap coefficient for the first discrete pulse-shaping filter.
8. The optical communication system of claim 6 , wherein the precompensation computation processor is further configured to:
receive a measurement of the at least one non-ideal transmission condition from a second optical receiver of the first optical signal,
wherein the predicting the at least one non-ideal transmission condition is based at least partially on the received measurement.
9. The optical communication system of claim 6 , wherein the first sampling rate is twice a symbol rate of the second optical signal.
10. The optical communication system of claim 6 , wherein the optical receiver is configured to downsample 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 second optical signal.
11. The optical communication system of claim 6 , wherein the optical receiver is configured to upsample the filtered second digital version to the first sampling rate.
12. The optical communication system of claim 6 , wherein the at least one non-ideal transmission condition occurs in optical space or in electrical space.
13. The optical communication system of claim 6 , wherein the at least one non-ideal transmission condition comprises a chromatic dispersion occurring in an optical fiber, a roll-off in a digital-to-analog converter, a non-linear amplifier response, a timing skew occurring along a signal path.
14. The optical communication system of claim 1 , wherein the first sampling rate is between 1.0 and 1.3 times the symbol rate of the second optical signal.
15. The optical communication system of claim 1 , wherein the optical receiver is configured to upsample the filtered first digital version to a second sampling rate, the second sampling rate being twice the symbol rate of the second optical signal.
16. The optical communication system of claim 1 , wherein the at least one non-ideal transmission condition comprises a chromatic dispersion occurring in an optical fiber, a roll-off in a digital-to-analog converter, a non-linear amplifier response, a timing skew occurring along a signal path.
17. The optical communication system of claim 1 , wherein the at least one non-ideal transmission condition occurs in electrical space.
18. A method for optical communications, comprising:
predicting, at a precompensation computation processor of an optical transmitter, at least one non-ideal transmission condition for a first optical signal;
determining, at the precompensation computation processor, an inverse filtering function to precompensate for the at least one non-ideal transmission condition;
filtering at least one stream of symbol mapped bits with a first discrete pulse-shaping filter to precompensate for the at least one non-ideal transmission condition by substantially implementing the inverse filtering function;
modulating the filtered symbol mapped bits to the first optical signal;
transmitting the first optical signal;
sampling, at an optical receiver, 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, wherein the first sampling rate is at or near a symbol rate of the second optical signal;
filtering the first digital version of the second optical signal with a second discrete pulse-shaping filter;
upsampling the filtered first digital version of the second optical signal to generate a second digital version of the second optical signal;
performing an equalization function on the second digital version of the second optical signal; and
demodulating a stream of data from the equalized second digital version of the second optical signal.
19. The method of claim 18 , further comprising:
updating at least one tap coefficient for the first discrete pulse-shaping filter to implement the inverse filtering function.
20. The method of claim 18 , further comprising:
receiving a measurement of the at least one non-ideal transmission condition from a second optical receiver of the first optical signal,
wherein the predicting the at least one non-ideal transmission condition is based at least partially on the received measurement.
21. The method of claim 18 , wherein the first sampling rate is between 1.0 and 1.3 times the symbol rate of the second optical signal.
22. The method of claim 18 , the upsampling the filtered first digital version of the second optical signal comprising:
upsampling the filtered first digital version to a second sampling rate, the second sampling rate being twice the symbol rate of the second optical signal.
23. The method of claim 18 , wherein the at least one non-ideal transmission condition occurs in optical space or in electrical space.
24. The method of claim 18 , wherein the at least one non-ideal transmission condition comprises a chromatic dispersion occurring in an optical fiber, a roll-off in a digital-to-analog converter, a non-linear amplifier response, a timing skew occurring along a signal path.
25. A method for optical communications, comprising:
predicting, at a precompensation computation processor of an optical transmitter, at least one non-ideal transmission condition for a first optical signal;
determining, at the precompensation computation processor, an inverse filtering function to precompensate for the at least one non-ideal transmission condition;
filtering at least one stream of symbol mapped bits with at least a first discrete pulse-shaping filter to precompensate for the at least one non-ideal transmission condition by substantially implementing the inverse filtering function;
modulating the filtered symbol mapped bits to the first optical signal;
transmitting the first optical signal;
sampling, at an optical receiver, a second optical signal comprising pulse-shaped data modulated onto a carrier frequency at a first sampling rate to generate a first digital version of the second optical signal;
downsampling the first digital version of the second optical signal to generate a second digital version of the second optical signal;
filtering the second digital version of the second optical signal with at least one discrete pulse shaping filter;
upsampling the filtered second digital version of the second optical signal to generate a third digital version of the second optical signal;
demodulating a stream of data from the third digital version of the second optical signal.
26. The method of claim 25 , further comprising:
updating at least one tap coefficient for the first discrete pulse-shaping filter to implement the inverse filtering function.
27. The method of claim 25 , further comprising:
receiving a measurement of the at least one non-ideal transmission condition from a second optical receiver of the first optical signal,
wherein the predicting the at least one non-ideal transmission condition is based at least partially on the received measurement.
28. The method of claim 25 , wherein the first sampling rate is twice a symbol rate of the second optical signal.
29. The method of claim 25 , wherein the downsampling comprises 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 second optical signal.
30. The method of claim 25 , wherein the upsampling comprises upsampling the filtered second digital version to the first sampling rate.
31. The method of claim 25 , wherein the at least one non-ideal transmission condition occurs in electrical space or in optical space.
32. The method of claim 25 , wherein the at least one non-ideal transmission condition comprises a chromatic dispersion occurring in an optical fiber, a roll-off in a digital-to-analog converter, a non-linear amplifier response, a timing skew occurring along a signal path.