Instrument for measuring dispersional distortions in optical fibers and cables

An instrument was developed and built for measuring the dispersional distortions in optical fibers and cables on the basis of pulse widening. The instrument consists of a laser as a light source, a master oscillator, an optical transmitter, an optical shunt with mode mixer, an optical receiver, a fiber length measuring device, a smoothly adjustable delay line, and a stroboscopic oscillograph. The optical transmitter contains a semiconductor laser with GaAs-GaAlAs diheterostructure and modulator with pulse generating avalanche-breakdown transistors. The optical receiver contains a germanium photodiode with internal amplification and photoreceiver amplifier with microwave bipolar germanium transistors. Matching of the instrument to the tested fiber line is done by passing radiation into the latter from an auxiliary small He-Ne laser through a directional coupler.