Hybrid Optical and Electrical Fiber Optic Link Linearizer

Abstract

Techniques and systems for reducing nonlinear distortions in an output optical beam from an optical transmitter by using both electrical pre-distortion compensation and optical compensation.

1 . A system, comprising:
 an optical transmitter to produce an optical signal in response to a control signal that is modulated to carry information;   an electrical pre-distortion circuit, coupled in an electrical path of said control signal prior to reception by said optical transmitter, to superimpose an electrical predistortion signal to said control signal that reduces nonlinear distortions in said optical signal;   an optical device disposed in an optical path of said optical signal and configured to produce a wavelength-dependent optical transfer profile on said optical signal to reduce residual nonlinear distortions in said optical signal and to produce a linearized optical signal;   an optical transmission line coupled between said optical transmitter and said optical device to transmit said optical signal to said optical device;   an optical detector coupled to receive said linearized optical signal to produce a first detector output and a second detector output, wherein said second detector output includes said information; and   a distortion circuit coupled to said optical detector to receive said first detector output, said distortion circuit processing said first detector output to measure nonlinear distortions in said linearized optical signal and to produce a distortion control signal to control said optical device, said optical device responsive to said distortion control signal to modify said wavelength-dependent optical transfer profile on said optical signal to reduce residual nonlinear distortions in said linearized optical signal.   
   
   
       2 . The system as in  claim 1 , further comprising:
 an optical coupler disposed between said optical transmitter and said optical transmission line to split a fraction of said optical signal to produce an optical monitor signal;   a second optical detector coupled to receive said optical monitor signal to produce a detector output; and   a distortion circuit coupled to said optical detector to receive said detector output, said distortion circuit to measure nonlinear distortions in said linearized optical signal and to produce a distortion control signal to control said optical transmitter to reduce nonlinear distortions in said optical signal.   
   
   
       3 . The system as in  claim 2 , further comprising a wavelength control unit coupled to said optical transmitter that controls a wavelength of said optical signal, wherein said distortion control signal is coupled into said wavelength control unit to adjust said wavelength of said optical signal. 
   
   
       4 . The system as in  claim 2 , further comprising a bias control unit coupled to said optical transmitter that produces an electrical bias to said optical transmitter that affects said optical signal, wherein said distortion control signal is coupled into said bias control unit to adjust said electrical bias. 
   
   
       5 . The system of  claim 1 , further comprising:
 an optical coupler disposed to split a fraction of said optical signal prior to entry of said optical device to produce a first optical monitor signal;   a second optical detector coupled to receive said first optical monitor signal to produce a third detector output; and   another distortion circuit coupled to said second optical detector to receive said third detector output, said another distortion circuit to measure nonlinear distortions in said optical signal and to produce a another distortion control signal to control said optical transmitter to reduce nonlinear distortions in said optical signal.   
   
   
       6 . The system as in  claim 5 , further comprising a fiber link coupled between said optical transmitter and said optical device.