METHOD FOR IDENTIFYING OPTICAL FIBER

PURPOSE:To avert the effect of an adverse influence upon the optical fiber circuit under operation even if this circuit is erroneously subjected to an identification operation by applying ultrasonic oscillation to the optical fiber from the outside thereof. CONSTITUTION:Ultrasonic waves are applied from the outside of the optical fiber 1 to the identifying part 5 at the intermediate point in the longitudinal direction of the optical fiber 1 by an ultrasonic wave applying device 6. This applying device 6 is designed to allow the modulation of the intensity and phase of ultrasonic oscillation by changing the intensity and period of ultrasonic oscillation by means of a controller 10. Even if ultrasonic oscillation are applied to the other optical fiber 1 during use, this method is of an intensity modulation/ direct detection system and, therefore, no adverse influences are exerted at all upon the circuit. The optical fiber 12 for input and the optical fiber 13 for output are connected by a looped wire 14 in a folding station 11. The optical circuit under operation is kept free from the adverse influence even if this circuit is subjected to the identifying operation.