Optical signal generating circuit and optical transmission line

Abstract

An optical transmission line allows optical signals to be transmitted with higher stability over longer distances. According to a first aspect, an optical NRZ signal is split in two, one half is presented to a clock extraction circuit, and the other half is presented to an EA modulator. An optical RZ signal is obtained as an output because the EA modulator is energized by the provided clock component. According to a second aspect, a nonlinear phase shift based on cross-phase modulation is induced in an RZ pulse train by an optical NRZ signal, and only the RZ pulses corresponding to the optical NRZ signal are extracted. According to a third aspect, first dispersion compensator is provided to a preceding stage of an optical fiber transmission line for transmitting optical pulses, and second dispersion compensation compensator is provided to a subsequent stage. Pulse widening in the optical fiber transmission line is controlled by a nonlinear chirp induced in the first dispersion compensator.

1 - 9 . (canceled)  
   
   
       10 . An optical signal generation circuit, comprising a light waveguide and a polarizer connected to this light waveguide, wherein: 
 said light waveguide receives an optical NRZ signal having a first polarization direction and an RZ pulse train having a second polarization direction at 45° to the said first polarization direction;    a nonlinear phase shift based on cross-phase modulation is induced in said RZ pulse train by said optical NRZ signal inside said light waveguide; and    said polarizer extracts pulses corresponding to said optical NRZ signal from the individual RZ pulses constituting the RZ pulse train.    
   
   
       11 . An optical signal generation circuit, comprising a light waveguide and a polarization beam splitter connected to this light waveguide, wherein: 
 said light waveguide receives an optical NRZ signal having a first polarization direction and an RZ pulse train having a second polarization direction at 45° to the said first polarization direction;    a nonlinear phase shift based on cross-phase modulation is induced in said RZ pulse train by said optical NRZ signal inside said light waveguide;    said polarization beam splitter transmits pulses corresponding to said optical NRZ signal from among the individual RZ pulses constituting said RZ pulse train, and reflects pulses that do not correspond to said optical NRZ signal from among the individual RZ pulses constituting said RZ pulse train; and    the RZ pulses that do not correspond to said optical NRZ signal and that have been reflected by said polarization beam splitter are received by a receiver.    
   
   
       12 . An optical transmission line, comprising an optical fiber transmission line for transmitting optical pulses; 
 first dispersion compensation means connected to a preceding stage of the optical fiber transmission line; and    second dispersion compensation means connected to a subsequent stage of the optical fiber transmission line; wherein:    said first dispersion compensation means is composed of a dispersion-shifted fiber, and said second dispersion compensation means is composed of a dispersion-compensated fiber.    
   
   
       13 . An optical transmission line as defined in  claim 12 , wherein the dispersion value of said first dispersion compensation means is set to near-zero level, and the dispersion value of said second dispersion compensation means is set to a negative value.  
   
   
       14 . An optical fiber transmission line as defined in  claim 12 , wherein the dispersion value of said first dispersion compensation means is set to normal dispersion, and the dispersion value of said second dispersion compensation means is set to a negative value.  
   
   
       15 . An optical transmission line as defined in  claim 13 , wherein the pulse widening in said optical fiber transmission line is controlled by a nonlinear chirp induced in said first dispersion compensation means.  
   
   
       16 . An optical transmission line, comprising: 
 an optical fiber transmission line for transmitting optical pulses;    first dispersion compensation means connected to a preceding stage of the optical fiber transmission line; and    second dispersion compensation means connected to a subsequent stage of the optical fiber transmission line; wherein:    said first dispersion compensation means is composed of two optical fibers, which are combined to provide, on average, zero dispersion;    the optical fibers are capable of providing said first dispersion compensation means with a very low pre-chirp as an input; and    the widening of said optical pulses in said transmission fiber is controlled by the effect of this pre-chirp and of a chirp based on self-phase modulation and induced in said fist dispersion compensation means.    
   
   
       17 . An optical transmission line as defined in  claim 16 , wherein: 
 a variable optical attenuator is provided to a preceding stage of said transmission fiber; and    the pulse interaction that accompanies the nonlinearity of said transmission fiber is reduced by controlling the optical intensity of the optical pulses inputted to said transmission fiber.    
   
   
       18 . An optical transmission line as defined in  claim 14 , wherein the pulse widening in said optical fiber transmission line is controlled by a nonlinear chirp induced in said first dispersion compensation means.  
   
   
       19 . An optical transmission line as defined in  claim 12 , wherein the pulse widening in said optical fiber transmission line is controlled by a nonlinear chirp induced in said first dispersion compensation means.