Optical fiber amplifier circuit comprising a control circuit for controlling a plurality of excitation light sources

Claim 1

An optical fiber amplifier circuit including an optical fiber amplifier for amplifying input light to produce amplified output light and which comprises an optical fiber doped with a rare-earth element and first through m-th excitation light sources for generating first through m-th excitation lights, where m represents a positive integer greater than unity, and for supplying said first through said m-th excitation lights to said optical fiber, said optical fiber amplifier circuit further comprising: first through m-th driving circuits for driving said first through said m-th excitation light sources, respectively; first through m-th transducers coupled to said first through said m-th excitation light sources, respectively, each of said first through said m-th transducers being supplied with a part of each of said first through said m-th excitation lights and tansducing said part of each of the first through the m-th excitation light into first through m-th electrical signals having first through m-th signal values; and a control circuit connected to said first through said m-th transducers and said first through said m-th driving circuits for controlling said first through said m-th driving circuits in response to said first through said m-th electrical signals by supplying first through m-th control signals to said first through said m-th driving circuits, respectively, said first through said m-th excitation light sources thereby generating said first through said m-th excitation lights having first through m-th output power ratios, said control circuit comprising: first through m-th primary multipliers connected to said first through said m-th transducers for multiplying said first through said m-th signal values by first through m-th primary factors, respectively, to produce first through m-th primary multiplied signals representative of first through m-th primary multiplied values; a calculator connected to said first through said m-th primary multipliers for calculating a mean value of said first through said m-th primary multiplied values to produce a mean value signal representative of said mean value; first through m-th subtracters connected to said first through said m-th primary multipliers, respectively, and connected to said calculator for calculating first through m-th difference between said mean value and said first through said m-th primary multiplied values to produce first through m-th difference signals representative of said first through said m-th differences; first through m-th secondary multipliers connected to said first through said m-th subtracters for multiplying said first through said m-th differences by first through m-th secondary factors, respectively, to produce first through m-th secondary multiplied signals representative of first through m-th secondary multiplied values; and first through m-th adders connected to said first through said m-th secondary multipliers, respectively, for calculating first through m-th sums of said first through said m-th secondary multiplied values and first through m-th set values, respectively, to produce first through m-th sum signals, as said first through said m-th control signals, representative of said first through said m-th sums.