Variable gain optical amplifier and control method

Abstract

A variable gain optical amplifier and method for control thereof is provided that includes an amplifier stage having a light pump, and a power source for the pump, and a variable optical attenuator connected to the amplifier stage and having a movable controller that changes attenuation of the amplifier output when moved to a different position. The dynamic controller of the amplifier includes gain detecting circuits that generate signals indicative of input and output signal strengths of the amplifier stage, and a circuit that provides a signal indicative of a position of the attenuator controller, as well as a digital signal processor connected to the outputs of the gain detecting circuits and position indicating circuit. The digital process maintains a selected gain setpoint for the amplifier in accordance with a predetermined relationship between amplifier gain and the signal input and output strengths, and a position of the attenuator controller and signal attenuation. The use of a position indicating circuit in the dynamic controller obviates the need for one of the gain detecting circuits normally used in such a controller, and thus simplifies the structure and reduces expense of the dynamic controller of the amplifier with no sacrifice in performance.

1 .- 34 . (Canceled)  
     
     
         35 . A variable gain optical amplifier, comprising: 
 a first amplifier stage including an input, an output, an optical pump, and a power source for the optical pump;    a second amplifier stage including an input, an output, an optical pump, and a power source for the optical pump;    a variable optical attenuator coupled to the output of the first amplifier stage and the input of the second amplifier stage, the variable optical attenuator including a setting indicative of an attenuation of the variable optical attenuator;    a first optical tap indicative of an optical power of the input of the first amplifier stage;    a second optical tap indicative of an optical power of the output of the second amplifier stage; and    controller circuitry including: 
 one or more inputs coupled to the first optical tap, the second optical tap, and the setting of the variable optical attenuator,  
 one or more outputs coupled to one or more of the power source for the optical pump of the first amplifier stage and the power source for the optical pump of the second amplifier stage,  
 wherein the controller circuitry maintains a flat total gain of the first amplifier stage and the second amplifier stage, based at least on the optical power of the input of the first amplifier stage, the optical power of the output of the second amplifier stage, and the setting indicative of the attenuation of the variable optical attenuator.  
   
     
     
         36 . The amplifier of  claim 35 , further comprising: 
 a third optical tap indicative of an optical power of the input of the second amplifier stage, the third optical tap coupled to the one or more inputs of the controller circuitry,    wherein the controller circuitry is maintains a flat total gain of the first amplifier stage and the second amplifier stage, further based at least on the optical power of the input of the second amplifier stage.    
     
     
         37 . The amplifier of  claim 35 , further comprising: 
 a third optical tap indicative of an optical power of the output of the first amplifier stage, the third optical tap coupled to the one or more inputs of the controller circuitry,    wherein the controller circuitry is maintains a flat total gain of the first amplifier stage and the second amplifier stage, further based at least on the optical power of the output of the first amplifier stage.