Nonlinearity cancellation in fiber optic transmission based on frequency-mutually-referenced carriers

Abstract

A system and method for mitigating nonlinearity in an optical communication link with multiple carriers uses mutual frequency referencing to stabilize at least a portion of the multiple carriers. Using at least one frequency-referenced signal, carrier nonlinearity can be determined and compensated within the link by pre-distortion, back-propagation, or a combination of both. Mutual frequency referencing may be performed at the emitting end of the link, at the receiving end, or a combination of both.

1 . A method for mitigating nonlinearity in an optical communication link comprising multiple carriers, the method comprising:
 applying mutual frequency referencing to at least a portion of the multiple carriers by one or more of frequency locking free running lasers, generating the multiple carriers using a frequency comb, and generating the multiple carriers using stabilized independent lasers;   using at least one frequency-referenced carrier, determining nonlinearity within the link; and   compensating for the determined nonlinearity, wherein compensating comprises canceling the nonlinearity by one or more of applying a pre-distortion to the carriers, applying back propagation, using a nonlinear equalizer, generating a feedback correction signal with a frequency-locked local oscillator, and applying calculated phase conjugation of a received signal.   
     
     
         2 . The method of  claim 1 , wherein applying mutual frequency referencing is performed at a transmitting end of the link. 
     
     
         3 . (canceled) 
     
     
         4 . The method of  claim 1 , wherein applying mutual frequency referencing comprises applying frequency locking, and wherein frequency locking is selected from injection locking, current injection, laser cavity control, opto-electronic phase-locked loops, frequency-locked loops and cavity-based wavelength lockers. 
     
     
         5 - 6 . (canceled) 
     
     
         7 . The method of  claim 1 , wherein the independent lasers are locked in frequency to a frequency reference. 
     
     
         8 . The method of  claim 7 , wherein the frequency reference is located at one of a receiving end and an emitting end of the link. 
     
     
         9 - 10 . (canceled) 
     
     
         11 . The method of  claim 1 , wherein applying a pre-distortion comprises generating a virtual link characterized by opposite sign physical constants and negative gain relative to the link. 
     
     
         12 - 14 . (canceled) 
     
     
         15 . The method of  claim 1 , wherein compensating comprises generating a feedback correction signal and wherein the frequency-locked local oscillator is selected from the group consisting of frequency comb, injection locking, current injection, laser cavity control, opto-electronic phase-locked loops, frequency-locked loops, and cavity-based wavelength locker. 
     
     
         16 . (canceled) 
     
     
         17 . The method of  claim 1 , wherein compensating comprises applying calculated phase conjugation, and wherein phase conjugation is implemented all-optically, electro-optically, or a combination thereof. 
     
     
         18 . The method of  claim 1 , wherein applying mutual frequency referencing to at least a portion of the multiple carriers comprises defining subsets of neighboring carriers within the multiple carriers, wherein the carriers within each subset are mutually frequency locked. 
     
     
         19 . The method of  claim 18 , wherein the subsets are at least partially overlapping. 
     
     
         20 . The method of  claim 19 , wherein the subsets are defined by a sliding window. 
     
     
         21 . The method of  claim 1 , wherein applying mutual frequency referencing is non-continuous. 
     
     
         22 . An optical fiber transmission system, the system comprising:
 a carrier source configured for generating a plurality of channels, wherein the channels are configured for imprinting with information-containing waveforms, wherein the carrier source comprises one or more of a frequency comb, a frequency-referenced carrier source wherein the plurality of channels are at least partially mutually frequency locked, and independent stabilized lasers;   a multiplexer configured for receiving the plurality of channels and outputting a multiplexed signal;   one or more transmission links for transmitting the multiplexed signal, the transmission link comprising an optical fiber and an amplifier;   a demultiplexer configured for receiving an optical signal at a receiving end of the transmission link;   a plurality of receivers for receiving demultiplexed signals, each receiver configured for receiving one of the plurality of wavelengths; and   a processor for detecting nonlinearity within the transmission link and calculating compensation for substantially cancelling the nonlinearity;   wherein at least one of the carrier source and the plurality of receivers comprises a frequency-referenced oscillator.   
     
     
         23 . The system of  claim 22 , wherein the frequency-referenced oscillator is stabilized by one or more of injection locking, current injection, laser cavity control, opto-electronic phase-locked loops, frequency-locked loops and cavity-based wavelength lockers. 
     
     
         24 . (canceled) 
     
     
         25 . The system of  claim 22 , wherein a least a portion of the plurality of channels comprises subsets of neighboring channels, wherein the channels within each subset are mutually frequency locked. 
     
     
         26 . (canceled) 
     
     
         27 . The system of  claim 22 , further comprising a pre-distortion processor configured for providing input to the carrier source. 
     
     
         28 . The system of  claim 27 , wherein the pre-distortion processor generates a virtual link characterized by opposite sign physical constants and negative gain relative to the transmission link. 
     
     
         29 . The system of  claim 22 , wherein the plurality of receivers comprise frequency-locked local oscillators, and wherein the processor comprises a back-propagation block. 
     
     
         30 . The system of  claim 22 , wherein the optical fiber comprises one or more fiber selected from the group consisting of single mode fiber, multi-mode fiber, and multi-core fiber. 
     
     
         31 . The system of  claim 30 , wherein the system is a polarization multiplexed system.