Patent ID: 8822895

Claim:
A fiber fuse detecting apparatus that detects fiber fuse in an optical fiber that propagates laser light, comprising light input means that is arranged on a laser light incidence side of the optical fiber and that inputs at least a portion of the laser light propagating in a reverse direction to a direction of the laser light incident on the optical fiber, a light receiving element that photo-electrically converts light input by the light input means, an electric band-pass filter that extracts from an output of the light receiving element a prescribed frequency band component that contains a periodic signal due to fiber fuse, the prescribed frequency band component being in a range from 10 kHz to 500 kHz, detecting means that detects an output level of the electric band-pass filter, and compares the output level or a change of the output level with a prescribed value, and warning circuit that emits a warning signal in response to an output of the detecting means indicating the output level or the change of the output level is above the prescribed value.