Abstract: An apparatus and method for optical telecommunication includes introducing a laser beam emitted from a light source at a first station into an optical fiber, providing an ultrasonic wave obtained by modulating a voice signal by a signal-applying-device at a work section to the optical fiber, modulating a polarized light passing through the optical fiber in amplitude and frequency, receiving the polarized light with the shifted wave plane at a light-receiving section in a second station, detecting at the light-receiving section in the second station the polarized light which has been modulated by the signal-applying device in the work section, and demodulating the polarized light to obtain a voice signal.

Abstract: A technique for identifying an optical transmission medium from a plurality of single-mode-type optical transmission media by using longitudinal middle portions of the media as an identification section by first exciting a particular optical transmission media by means of a polarized light, next applying either an electromagnetic action or a mechanical action to the particular optical transmission medium to modulate the polarized light and then identifying the particular optical transmission medium based on the deviation of the polarized plane of the polarized light.