Methods and Systems for Fiber Optic Communication

Abstract

The present invention relates in general to communication systems, and more specifically towards methods, systems, and devices that help improve transmission rates and spectral efficiency of intensity modulated (IM) or power modulated channels utilizing multi-level pulse amplitude modulation PAM-M. In an embodiment, the present invention used an iterative algorithm to open the eyes of an eye diagram in a relatively short number of steps. The algorithm, which may not require previous characterization of the channel, utilizes pseudo-random sequences, such as PSBS15 or PRQS10, and adaptive non-linear equalizers to optimize the pre-distortion taps.

We claim: 
     
         1 . An optical communication system for transmitting a communication signal, said optical communication system comprising:
 a first transceiver;   a second transceiver;   an optical medium for transmitting said communication signal between said first transceiver and said second transceiver;   a pre-distortion circuit for conditioning said communication signal prior to a transmission of said communication signal by said first transceiver, said pre-distortion circuit providing linear correction of said communication signal;   a post-equalization circuit for conditioning said communication signal after a receipt of said communication signal by said second transceiver, said post-equalization circuit providing linear correction of said communication signal, at least one of said pre-distortion circuit and said post-equalization circuit further providing non-linear correction of said communication signal; and   a feedback circuit providing at least some information from said post-equalization circuit to said pre-distortion circuit.   
     
     
         2 . The optical communication system of  claim 1 , further comprising a performance estimation circuit, said performance estimation circuit evaluating said communication signal after it has been conditioned by said post-equalization circuit. 
     
     
         3 . The optical communication system of  claim 2 , wherein said performance estimation circuit calculates a bit error rate (BER) of said communication signal after it has been conditioned by said post-equalization circuit. 
     
     
         4 . The optical communication system of  claim 1 , wherein said pre-distortion circuit conditions said communication signal by convolving said communication signal with a linear equalizer vector. 
     
     
         5 . The optical communication system of  claim 4 , wherein said pre-distortion circuit further conditions said communication signal by convolving said communication signal with a non-linear equalizer. 
     
     
         6 . The optical communication system of  claim 1 , wherein said post-equalization circuit conditions said communication signal by convolving said communication signal with a linear equalizer vector. 
     
     
         7 . The optical communication system of  claim 6 , wherein said post-equalization circuit further conditions said communication signal by convolving said communication signal with a non-linear equalizer. 
     
     
         8 . The optical communication system of  claim 1 , wherein said linear correction provided by said pre-distortion circuit depends at least partially on said at least some information provided by said feedback circuit. 
     
     
         9 . The optical communication system of  claim 1 , wherein said system is configured to operate using pulse amplitude modulation (PAM). 
     
     
         10 . The optical communication system of  claim 9 , wherein said PAM is PAM-4.