Patent ID: 6891659
Filing Date: 2005-05-10
Classification: H01S,H04B

Abstract:
1. An optical amplifier coupled to a source of Raman pump waves, comprising; an input end of an optical signal; an output end of the optical signal; optical gain mediums placed between the input end and the output end; at least one member selected from a group consisting of a first light detector for detecting intensity of reflected light from the output end of the optical signal that is input from said input end and a second light detector for detecting light intensity of the optical signal that is input from said input end; means for preventing reflections of said Raman pump waves from preventing proper operation of said first and second light detectors, said means including a band-pass filter that blocks substantially all of the Raman pump waves from passing through the band-pass filter, and that allows substantially all of the optical signals, which are input from the input end and amplified by one of the optical gain mediums, to pass through the band-pass filter, said band-pass filter being located at least either between said light output end and the first light detector for detecting intensity of reflected light from the output end of the optical signal, or between said light input end and the second light detector for detecting light intensity of the optical signal that is input from the input end; and at least one gain control circuit which reduces or turns off an optical gain of a corresponding optical medium, either when the reflected light intensity and/or the light reflection ratio from the output end measured by the first light detector exceeds a specified threshold value, or when the input light from the input end intensity measured by the second light detector become smaller than a specified threshold value.