Digital optical spectral shaping
A method and system for generating an optical channel signal for transmission through an optical fiber link of an optical communications system. A digital filter processes an input data signal using a compensation function and a shaping function to generate a pair of multi-bit sample streams representing a target optical E-field envelope of the optical channel signal. A modulator modulates an optical carrier light using the pair of multi-bit sample streams to generate the optical channel signal. The compensation function is designed to at least partially compensate impairments of the optical fiber link. The predetermined shaping function is designed to modify a baseband spectrum of the target optical E-field envelope.
1. A method of generating an optical channel signal for transmission through an optical fiber link of an optical communications system, the method comprising steps of:
a digital filter processing an input data signal using a compensation function and a spectral shaping function to generate a pair of multi-bit sample streams representing a target optical E-field envelope of the optical channel signal; and
a modulator modulating an optical carrier light using the pair of multi-bit sample streams to generate the optical channel signal;
the compensation function at least partially compensating impairments of the optical fiber link; and
the predetermined spectral shaping function being designed to pre-emphasize predetermined frequency components of a baseband spectrum of the target optical E-field envelope.
2. The method of claim 1 , wherein the pre-emphasized frequency components are selected to at least partially compensate finite roll-off of an analog filter between the digital filter and the modulator.
3. The method of claim 1 , wherein the spectral shaping function is designed to impose a predetermined shape to a predetermined portion of the baseband spectrum.
4. The method of claim 3 , wherein the predetermined shape comprises a detectable peak.
5. The method of claim 4 , wherein the predetermined shape comprises a shoulder at higher frequency components of the baseband spectrum.
6. The method of claim 5 wherein the shoulder of the spectral shaping function is designed to pre-emphasize frequency components used for at least clock recovery in a receiver.
7. The method of claim 5 , wherein the shoulder portion of the spectral shaping function is designed to preserve frequency components used for at least clock recovery in a receiver.
8. The method of claim 1 , wherein spectral the shaping function has different profiles in respective different portions of the baseband spectrum.
9. The method of claim 8 , wherein the spectral shaping function is discontinuous.
10. The method of claim 1 , wherein a magnitude of the spectral shaping function is selected such that imposing the spectral shaping function does not change a total energy of the optical channel signal.
11. The method of claim 1 , wherein the spectral shaping function is designed to optimise a performance of the optical fiber link.
12. A transmitter for generating an optical channel signal for transmission through an optical fiber link of an optical communications system, the transmitter comprising:
a digital filter configured to process an input data signal using a compensation function and a spectral shaping function to generate a pair of multi-bit sample streams representing a target optical E-field envelope of the optical channel signal; and
a modulator configured to modulate an optical carrier light using the pair of multi-bit sample streams to generate the optical channel signal;
wherein the compensation function at least partially compensating impairments of the optical fiber link; and
wherein the predetermined spectral shaping function being designed to pre-emphasize predetermined frequency components of a baseband spectrum of the target optical E-field envelope.
13. The transmitter of claim 12 , wherein the pre-emphasized frequency components are selected to at least partially compensate finite roll-off of an analog filter between the digital filter and the modulator.
14. The transmitter of claim 12 , wherein the spectral shaping function is designed to impose a predetermined shape to a predetermined portion of the baseband spectrum.
15. The transmitter of claim 14 , wherein the predetermined shape comprises a detectable peak.
16. The transmitter of claim 15 , wherein the predetermined shape comprises a shoulder at higher frequency components of the baseband spectrum.
17. The transmitter of claim 16 , wherein the shoulder of the spectral shaping function is designed to per-emphasize frequency components used for at least clock recovery in a receiver.
18. The transmitter of claim 12 , wherein the spectral shaping function has different profiles in respective different portions of the baseband spectrum.
19. The transmitter of claim 18 , wherein the spectral shaping function is discontinuous.
20. A receiver for receiving an optical channel signal through an optical fiber link from a transmitter of an optical communications system, the receiver comprising:
a digital signal processor configured to process sample streams of the optical channel signal using a compensation function and an inverse spectral shaping function to generate a recovered data signal;
the compensation function at least partially compensating chromatic dispersion of the optical fiber link; and
the predetermined inverse spectral shaping function reversing effects of a predetermined shaping function applied to the optical channel signal by the transmitter, the predetermined shaping function being designed to pre-emphasize predetermined frequency components of a baseband spectrum of the optical channel signal transmitted by the transmitter.