Chirp measurement method, chirp measurement apparatus and their application

Abstract

A chirp measurement apparatus includes a splitting section for splitting input signal light to two paths; a first dispersion medium with a total dispersion amount of +D (≠0) at a used wavelength, and a second dispersion medium with a total dispersion amount of −D (≠0) at the used wavelength; first and second nonlinear photo-detecting sections for receiving the signal light beams passing through the first and second dispersion media, and for outputting electric signals with the intensities proportional to nth power of the intensities of the signal light beams, where n is greater than one; and a difference detecting section for computing a difference between the electric signals output from the first and second nonlinear photo-detecting sections, and for outputting a differential signal corresponding to the difference as a chirp signal of the input signal light.

1 . A chirp measurement apparatus comprising: 
 splitting means for splitting input signal light to two paths;    a first dispersion medium with a total dispersion amount of +D (≠0) at a wavelength of the input signal light, and first nonlinear photo-detecting means for receiving the signal light passing through the first dispersion medium, and for outputting an electric signal with the intensity proportional to nth power of the intensity of the signal light, where n is greater than one, said first dispersion medium and said first nonlinear photo-detecting means being placed on a first path of the two paths;    a second dispersion medium with a total dispersion amount of −D (≠0) at the wavelength of the input signal light, and second nonlinear photo-detecting means for receiving the signal light passing through the second dispersion medium, and for outputting an electric signal with the intensity proportional to nth power of the intensity of the signal light, where n is greater than one, said second dispersion medium and said second nonlinear photo-detecting means being placed on a second path of the two paths; and    difference detecting means for obtaining a difference between the electric signals output from said first nonlinear photo-detecting means and said second nonlinear photo-detecting means, and for outputting a differential signal corresponding to the difference as a chirp signal of the input signal light.    
   
   
       2 . The chirp measurement apparatus as claimed in  claim 1 , wherein said first and second nonlinear photo-detecting means are each composed of a nonlinear photo-detecting device exhibiting two-photon absorption.  
   
   
       3 . The chirp measurement apparatus as claimed in  claim 1 , wherein said first and second nonlinear photo-detecting means are each composed of a nonlinear medium for generating second harmonic light of input light to said nonlinear photo-detecting means, and photo-detecting means for converting the second harmonic light to an electric signal.  
   
   
       4 . The chirp measurement apparatus as claimed in  claim 3 , wherein said first and second nonlinear photo-detecting means each comprise, between said nonlinear medium and said photo-detecting means, a filter for passing only the second harmonic light.  
   
   
       5 . The chirp measurement apparatus as claimed in  claim 1 , wherein said splitting means splits the input signal light into two equal powers (50:50) at the wavelength of the input signal light and supplies them to the two paths.  
   
   
       6 . The chirp measurement apparatus as claimed in  claim 1 , further comprising, in said two paths, first and second optical signal intensity adjusting means for adjusting, when the input signal light unaffected by dispersion is input, signal light intensities supplied to said first and second nonlinear photo-detecting means such that intensities of the electric signals supplied from the two paths to said difference detecting means become equal.  
   
   
       7 . The chirp measurement apparatus as claimed in  claim 6 , further comprising control means for controlling the differential signal output from said difference detecting means such that the differential signal becomes minimum by feeding the differential signal back to at least one of said first and second optical signal adjusting means.  
   
   
       8 . The chirp measurement apparatus as claimed in  claim 1 , further comprising, in said two paths, first and second electric signal intensity adjusting means for adjusting, when the input signal light unaffected by dispersion is input, electric signal intensities supplied to said first and second nonlinear photo-detecting means such that the electric signal intensities supplied from the two paths to said difference detecting means become equal.  
   
   
       9 . The chirp measurement apparatus as claimed in  claim 8 , further comprising control means for controlling the differential signal output from said difference detecting means such that the differential signal becomes minimum by feeding the differential signal back to at least one of said first and second electric signal adjusting means.  
   
   
       10 . The chirp measurement apparatus as claimed in  claim 1 , further comprising: 
 linear photo-detecting means for dividing part of the input signal light supplied to said splitting means, and for outputting an electric signal V 1  proportional to the optical intensity of the signal light; and    normalization means for normalizing the electric signal V 21  output from said first nonlinear photo-detecting means and the electric signal V 22  output from said second nonlinear photo-detecting means to electric signals V 21 /V 1   n  and V 22 /V 1   n  by the electric signal V 1 , and supplies the normalized electric signals to said difference detecting means.    
   
   
       11 . The chirp measurement apparatus as claimed in  claim 1 , further comprising, in the two paths, a first linear photo-detecting means and a second photo-detecting means for dividing parts of the signal light supplied to said first and second nonlinear photo-detecting means, and for outputting electric signals V 11  and V 12  proportional to the optical intensity of the signal light, respectively; and 
 normalization means for normalizing the electric signals V 21  and V 22  output from said first and second nonlinear photo-detecting means into electric signals V 21 /V 11   n  and V 22 /V 12   n  by the electric signals V 11  and V 12 , and for supplying the normalized electric signals to said difference detecting means.    
   
   
       12 . A dispersion compensating apparatus comprising the chirp measurement apparatus as defined in  claim 1 , and tunable dispersion equalization means for canceling the chirp of the input signal light measured by said chirp measurement apparatus.  
   
   
       13 - 17 . (canceled)  
   
   
       18 . A chirp measurement method comprising: 
 a first step of splitting input signal light to two paths;    a second step of supplying signal light beams traveling through the two paths to first and second nonlinear photo-detecting means through first and second dispersion media with total dispersion amounts of +D (≠0) and −D (≠0) at the wavelength of the input signal light beams, respectively, to convert the individual signal light beams traveling through the two paths to electric signals with intensities proportional to nth power of input optical intensities, where n is greater than one; and    a third step of outputting a differential signal corresponding to a difference between the electric signals of the two paths as a chirp signal of the input signal light.    
   
   
       19 . The chirp measurement method as claimed in  claim 18 , further comprising: 
 a fourth step of inputting the input signal light unaffected by the dispersion; and    a fifth step of adjusting signal light intensities of the two paths or electric signal intensities output from said first and second nonlinear photo-detecting means such that the differential signal becomes minimum by using first and second signal intensity adjusting means provided in the two paths.    
   
   
       20 . (canceled)