Optical amplifier, optical amplifying repeater and transmission apparatus of wavelength division multiplexed signal light using the same

Abstract

Flatness of a gain (optical output level) is maintained even when a wavelength division multiplex signal light (WDM signal light) is amplified in an optical amplification utilizing Raman amplification function. The optical amplifier comprises: two (first and second) pumping light sources for Raman amplification for outputting first and second pumping lights; the wavelength multiplexer for Raman amplification for allowing the first and second pumping lights to be incident on optical fiber transmission paths, where the WDM signal light propagates, in the direction opposite to the propagation direction of the signal light. The signal lights are Raman amplified by the both pumping lights. A wavelength of the first pumping light is set such that the gain of the Raman amplified signal light declines in the right direction, and, on the other side, the wavelength of the second pumping light is set such that the gain declines in the left direction. Gradients for showing a relation between the wavelength and the gain in Raman amplification by the first and second pumping lights are made to be in opposite directions from each other. Optical output levels and the wavelengths of the first and second pumping lights are set such that the gains for the signal lights included in the Raman amplified WDM signal light become substantially equal to each other.

1 . An optical amplifier, comprising: 
 a first pumping light source for Raman amplification, which outputs a first pumping light having a first wavelength;    a second pumping light source for Raman amplification, which outputs a second pumping light having a second wavelength; and    a wavelength multiplexer for Raman amplification, which allows said first and second pumping lights to be incident on an optical fiber transmission path where a signal light propagates,    wherein said signal light is Raman amplified in said optical fiber transmission path by said first and second pumping lights.    
   
   
       2 . The optical amplifier according to  claim 1 , 
 wherein said wavelength multiplexer for Raman amplification allows said first and second pumping lights to be incident on said optical fiber transmission path in an opposite direction to a propagation direction of said signal light.    
   
   
       3 . The optical amplifier according to  claim 1 , 
 wherein said wavelength multiplexer for Raman amplification allows said first and second pumping lights to be incident on said optical fiber transmission path in the same direction as the propagation direction of said signal light.    
   
   
       4 . The optical amplifier according to  claim 1 , 
 wherein said signal light comprises a wavelength division multiplexed signal light (a WDM signal light), in which the signal lights having a plurality of wavelengths different from each other are wavelength division multiplexed.    
   
   
       5 . The optical amplifier according to  claim 4 , 
 wherein said first wavelength comprises the wavelength to allow said signal light to be Raman amplified such that the wavelength having a gain by Raman amplification as a peak becomes shorter than the wavelength of the signal light included in said WDM signal light, and    said second wavelength comprises the wavelength to allow said signal light to be Raman amplified such that the wavelength having the gain by Raman amplification as a peak becomes longer than the wavelength of the signal light included in said WDM signal light.    
   
   
       6 . The optical amplifier according to  claim 5 , 
 wherein a gradient showing a relation between the wavelength and the gain in Raman amplification by said first pumping light and a gradient showing the relation between the wavelength and the gain in Raman amplification by said second pumping light are in opposite directions from each other, and    an optical output level and the wavelength of said first and second pumping lights are respectively set such that the gains for signal lights included in said WDM signal light, on which Raman amplification was performed by said first and second pumping lights, become substantially equal to each other.    
   
   
       7 . The optical amplifier according to  claim 4 , 
 wherein said first pumping light source for Raman amplification comprises: 
 a first laser diode for oscillating a first light; and  
 a first wavelength selective optical reflector for transmitting said light of a first wavelength in a specified ratio and reflecting a residual light, which is arranged in a previous step of said first laser diode, and  
   said second pumping light source for Raman amplification comprises: 
 a second laser diode for oscillating a second light; and  
   a second wavelength selective optical reflector for transmitting said light of a second wavelength in a specified ratio and reflecting a residual light, which is arranged in a previous step of said second laser diode.    
   
   
       8 . The optical amplifier according to  claim 4 , 
 wherein said first pumping light source for Raman amplification comprises: 
 a first laser diode for oscillating a first light; and  
 a first optical filter for selectively transmitting said light of a first wavelength, which is arranged in a previous step of said first laser diode, and  
   said second pumping light source for Raman amplification comprises: 
 a second laser diode for oscillating a second light; and  
 a second optical filter for selectively transmitting said light of a second wavelength, which is arranged in a previous step of said second laser diode.  
   
   
   
       9 . The optical amplifier according to  claim 4 , 
 wherein said wavelength multiplexer for Raman amplification comprises: 
 a first pumping light multiplexer for Raman amplification, which transmits said signal light and allows said first pumping light to be incident on an optical fiber, the multiplexer being arranged by connecting to said optical fiber connected to said optical fiber transmission path; and  
 a second pumping light multiplexer for Raman amplification, which transmits said signal light and allows said second pumping light to be incident on the optical fiber, the multiplexer being arranged by connecting to said optical fiber connected to said optical fiber transmission path.  
   
   
   
       10 . The optical amplifier according to  claim 4 , 
 wherein said wavelength multiplexer for Raman amplification comprises: 
 a pumping light multiplexer for Raman amplification, which multiplexes said first and second pumping lights and outputs a multiplexed pumping light; and  
 a pumping light multiplexer for Raman amplification, which transmits said signal light and allows said multiplexed pumping light to be incident on an optical fiber, the multiplexer being arranged by connecting to said optical fiber connected to said optical fiber transmission path.  
   
   
   
       11 . The optical amplifier according to  claim 4 , 
 wherein said wavelength multiplexer for Raman amplification comprises: 
 a polarization combiner for Raman amplification for performing a polarization combination on said first and second pumping lights and outputs the multiplexed pumping light, where said first and second pumping lights respectively output from said first and second pumping light sources for Raman amplification are perpendicular to each other, that is, in a polarization state; and  
 a pumping light multiplexer for Raman amplification, which transmits said signal light and allows said multiplexed pumping light to be incident on an optical fiber, the multiplexer being arranged by connecting to said optical fiber connected to said optical fiber transmission path.  
   
   
   
       12 . The optical amplifier according to  claim 4 , further comprising: 
 an optical splitter for splitting a part of said WDM signal light and outputting a split WDM signal light;    signal light extracting means for extracting two signal lights, which have wavelengths different from each other, from each signal light included in said split WDM signal light;    an optical receiver for detecting an optical output level of each of the two signal lights extracted by said signal light extracting means; and    a pumping light output control circuit for controlling any one of the optical output levels and the wavelengths of said first and second pumping lights for Raman amplification according to an amount of difference between said two optical output levels.    
   
   
       13 - 27 . (canceled)