Optical amplification monitoring apparatus

Abstract

In an optical amplification monitoring apparatus of the invention, the number of signal light beams actually being transmitted is detected and an optical amplifier is controlled in accordance with the detected number. There is provided a means for monitoring intermodulation light beams resulting from signal light beams of two wavelengths which means includes a nonlinear medium and a WDM coupler that are provided on a light transmission path, an optical fiber grating for allowing passage of only intermodulation light components among the branched light beams, and a photodetector for converting the detected intermodulation light components into currents. A dispersion-shift optical fiber having a zero-dispersion wavelength in the 1.55-.mu.m band is used as the nonlinear medium. Intermodulation light beams are generated only when both signal light beams having different wavelengths w1 and w2 exist in the nonlinear medium. Since the intermodulation light beams have different wavelengths than the signal light beams, the number of signal light beams can be detected by monitoring the intermodulation light beams separated from the signal light beams. Thus, in wavelength-multiplexed transmission, optical amplification can be performed independently of the number of signal light beams actually being transmitted.