Raman excitation control method and optical transmission system using the same

Abstract

A Raman excitation control method enabling to reduce the number of couplers and photodetectors (PD) for providing an optical transmission unit with reduced cost The method is provided for use in optical amplification to amplify an optical signal using Raman excitation light fed into an optical transmission line. A backward light of a laser diode producing the Raman excitation light is monitored by an optical back power monitor. The monitored power value is compared with an initial set value stored in a memory for the laser diode. Based on this comparison result, a feedback control is performed against the light emission power of the laser diode.

1 . A Raman excitation control method for use in optical signal amplification by a Raman excitation light fed into a transmission line, comprising the steps of: 
 detecting, with aback power monitor circuit, backward lights produced by a laser diode circuit for Raman excitation; and    controlling light emission power of the laser diode circuit according to level of the detected backward lights detected by the back power monitor circuit.    
   
   
       2 . The Raman excitation control method according to  claim 1 , wherein the laser diode circuit includes a plurality of laser diodes, which produce Raman excitation lights having respectively different wavelengths, and 
 in the step of detecting, the back power monitor circuit detects the back power lights produced by the plurality of laser diodes; and    in the step of controlling, light emission power of each of the laser diodes is controlled according to each of the back power lights detected.    
   
   
       3 . A Raman excitation control method for use in optical signal amplification by Raman excitation lights fed into a transmission line, comprising the steps of: 
 detecting, with a power monitor, a Raman excitation light produced by a laser diode;    comparing the power value detected by the power monitor with an initial set data for the laser diode producing the Raman excitation light being stored in a memory; and    controlling light emission power of the laser diode according to the result of the comparison.    
   
   
       4 . The Raman excitation control method according to  claim 3 , wherein the initial set data indicates an initial power of the laser diode, and 
 in the step of comparing, a difference value is obtained between the initial power and a power value detected by the power monitor; and    in the step of controlling, the light emission of the laser diode is controlled by using the difference value added to the initial power value.    
   
   
       5 . A Raman excitation control method for use in optical signal amplification by Raman excitation lights fed into a transmission line, comprising the steps of: 
 detecting, with a power monitor, the Raman excitation lights having different wavelengths produced by a plurality of laser diodes;    comparing respective power values detected by the power monitor with initial set data stored in a memory corresponding to each of the plurality of laser diodes producing the Raman excitation lights; and    performing a feedback control of light emission power of each of the plurality of laser diodes according to the result of the comparison.    
   
   
       6 . The Raman excitation control method according to  claim 5 , wherein the initial set data indicates each initial power of the plurality of laser diodes, and 
 in the step of comparing, difference values between each of the initial power of the plurality of laser diodes and each of the power value detected by the power monitor are obtained, and    in the step of performing a feedback control, the light emission of the plurality of laser diodes is controlled by using each difference value added to the initial power value corresponding to each of the plurality of laser diode.    
   
   
       7 . A Raman excitation control method for use in optical signal amplification by Raman excitation lights fed into a transmission line comprising the steps of: 
 detecting, with a power monitor, each of the Raman excitation lights respectively having different wavelengths produced by a plurality of laser diodes;    further, detecting an input level of the optical signal to a reception amplifier; and    performing a feedback control of light emission power of each of the plurality of laser diodes by either adding or subtracting a predetermined correction value to each detected optical level of the plurality of laser diodes when the detected input optical signal level exceeds either upper limit or lower limit of an input dynamic range for the reception amplifier.    
   
   
       8 . A Raman excitation control system for use in optical signal amplification by a Raman excitation light fed into a transmission line, comprising: 
 a back power monitor circuit detecting backward lights produced by a laser diode circuit for Raman excitation; and    a control circuit controlling light emission power of the laser diode circuit according to level of the detected backward lights detected by the back power monitor circuit.    
   
   
       9 . The Raman excitation control system according to  claim 8 , wherein the laser diode circuit includes a plurality of laser diodes, which produce Raman excitation lights having respectively different wavelengths, 
 wherein the back power monitor circuit detects the back power lights produced by the plurality of laser diodes, and light emission power of each of the laser diodes is controlled according to each of the back power lights detected.