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 method of identifying a particular optical cable C1 out of a set of optical cables C1, C2 by applying an external signal by means of a signal applying apparatus 16 while an optical signal is transmitted from means for transmitting optical signals and monitoring changes in the signals received by means for receiving optical signals. Since the difference in the frequencies and the levels of the higher harmonics generated by the external signal in the particular cable and the other cable(s) that are laid so close to one another that the phenomenon of cross talk remarkably appears, the optical cable in question can be identified almost without fail.

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.

Abstract: A optical talk set has a talk set including bending means for bending an optical fiber of an optical cable, vibration applying means for applying vibration to the optical fiber, and a light-receiving element for receiving light leaking upon bending of the optical fiber and for converting the light into electricity, a signal transmitting/receiving line having an input/output terminal, for enabling transmission of signals to be input to the bending means and the vibration applying means and a signal output from the light-receiving element, and a housing enclosing the converter, the signal transmitting/receiving line, and the light-receiving element. The input/output terminal of the signal transmitting/receiving line is provided so as to be exposed to the outside of the housing, by virtue of which a call can be made without opening the housing, facilitating maintenance, etc. of an optical fiber path.

Abstract: The invention relates to a single-mode optical fiber used in a long wavelength band range for optical telecommunication. The core and the cladding of this optical fiber contain P.sub.2 O.sub.5 as a dopant selected to lower the deposition temperature and to hasten the deposition speed so as to result in low absorption loss.