PURPOSE: To detect the abnormality of an optical fiber securely by detecting the output of a laser oscillator and the intensity of laser beam passed through the optical fiber, operating their ratio, and comparing it to the value in normal operation.
CONSTITUTION: Part of laser beam emitted by oscillation 11 is transmitted 12 and photodetected by the 1st detector 13 to detect an electric output I0, which is inputted to a signal processing part 14. Further, laser beam after reflection 12 is converged 15 and passed through the optical fiber 6 to form an image through a lens 17. Laser beam reflected by the surface of the lens 17 is photodetected by the 2nd detector 18, which detects its intensity Ir. When this intensity Ir is inputted to the signal processing part 14, the processing part 14 operates a=Ir/I0. This ratio (a) is compared with the value in normal operation and when the ratio (a) is much larger than the value in normal operation, it is judged that the optical fiber 16 is abnormal, so that a signal for stopping the laser oscillation is outputted to a laser controller 19.
FUJIMORI YASUTOMO
SHIMOI TAISUKE
