Abstract: An optical masking apparatus of an OTDR capable of lowering insertion loss and of easily aligning optical axes and of being structured at low cost. The apparatus comprises an optical pulse generating means, an optical branching coupler for permitting an optical pulse generated by the optical pulse generating means to be incident to an optical fiber to be measured, and an optical chopper means to which a reflected light from the optical fiber is incident by way of the optical branching coupler wherein the optical chopper means operates in synchronization with the optical pulse to remove a desired range of the reflected light. A light signal supplied to an optical/electric transducer from the optical chopper means is converted into an electric signal, which is displayed on an indicator by way of a signal processing circuit.

Abstract: The purpose of the present invention is to provide a time domain reflectometer in which the system cost is low and the dynamic range is wide. In accordance with the present invention, an excitation light source for generating continuous light of a predetermined frequency (e. g., 1.48 .mu.m), and a ring laser part for generating a high power light pulse in accordance with the continuous light are provided. A light branch device is held in common by the ring laser part and a measurement part. The light branch device makes the light pulse which has been incident on one of its end parts to be incident on a light cable to be measured; and the light branch device also receives response light and supplies the response light to a light receptor in the measurement part. In the measurement part, the response light is converted to a corresponding electric signal and the signal is amplified to be supplied to a measurement circuit.

Abstract: An optical pulse tester capable of displaying Raman scattered light is disclosed. An optical pulse with the specified wavelength is injected into an optical fiber to be measured via a directional coupler and an optical demultiplexer/multiplexer. The demultiplexer/multiplexer demultiplexes returning light from the optical fiber into Raman scattered light different from the optical pulse in wavelength. The directional coupler divides returning light from the optical fiber into Fresnel reflection light and Rayleigh scattered light with the specified wavelength. The switcher supplies the Rayleigh scattered light to a display In the case of long distance measurement or precise loss measurement of the optical fiber. Therefore, the display displays the characteristic waveform of the optical fiber with the Rayleigh scattered light.

Abstract: A bidirectional light transmission system comprises a transmitting station having a light source for intensity-modulating a transmission signal, a first light branching portion for branching intensity-modulated light of the light source in a predetermined ratio and a first light receiving portion, and a receiving station having a second light branching portion, a light phase-modulating portion, a light reflecting portion and a second light receiving portion.

Abstract: A resonant type constant voltage supply apparatus has a LC series resonance circuit. Energy stored in both a resonance capacitor and a resonance inductor is directly transferred to the output or input terminal of the apparatus. A control transformer is provided in parallel with the resonance capacitor for deriving the energy stored in the resonance capacitor. The amount of the energy stored in the resonance capacitor can be controlled by changing the switching frequency of the apparatus or the inductance of the control transformer, so as to thereby control the amount of energy transferred to the output or input terminal of the apparatus and thereby stabilize the output voltage of the apparatus.

Abstract: A self-oscillating DC to DC converter which includes either two or four transistors, three transformers (a converting transformer, a driving transformer and a current transformer) and an inductance.The operating frequency of the converter is fixed by the saturation time of the driving transformer. The base currents of the transistors are mainly supplied by the current transformer so as to be in proportion to the collector currents of the transistors. The operating frequency of the converter is kept constant in spite of load fluctuations. The inductance which is connected in series between a winding of the converting transformer and a winding of the driving transformer. The inductance prevents the two or four transistors from being `on` simultaneously.