LIGHT MONITORING CIRCUIT

PROBLEM TO BE SOLVED: To provide a light monitoring circuit which can detect a noise light power, a signal light power and the like generated in amplifying signal light with high precision by a simple constitution of an optical circuit, at a low cost. SOLUTION: In the light monitoring circuit, a tilted chirped fiber grating is formed as an optical reflection medium 2 on an optical fiber to transmit signal light; lights of a first and a second wavelength band are reflected with different reflectances, and radiated outside the core of the optical fiber; and powers of the lights of the wavelength bands are detected by a first and a second light receiving unit arranged corresponding to focal distances of the reflected lights from the tilted chirped fiber grating. Thereby, the light power of each wavelength band can be monitored with high precision owing to a desired wavelength resolution corresponding to the arrangement of the each light receiving unit. COPYRIGHT: (C)2009,JPO&INPIT