OPTICAL FIBER, SLANTED OPTICAL FIBER GRATING, BAND REJECTION OPTICAL FILTER, GAIN EQUALIZING OPTICAL FILTER FOR OPTICAL AMPLIFIER, AND OPTICAL AMPLIFIER MODULE

摘要

Photosensitivity of an inner core (1a) which is disposed in a central portion of a core (1) is low. Photosensitivity of an outer core (1b) which is disposed close to a cladding (2) is high. In the cladding (2), photosensitivity of the inner cladding (2a) which is close to the core (1) is high and photosensitivity of an outer cladding (2b) which is outside of the inner cladding (2a) is low. A plurality of slant optical fiber grating having different optical characteristics by using the optical fiber having such photosensitivity so as to form a gain equalizing optical filter. By doing this, it is possible to provide an optical filter having a slant optical fiber grating which can maintain a filtering characteristics in a narrow bandwidth and enlarge loss area.