Abstract: A method of determining Inter-Symbol Interference (ISI) in transmission systems first measures, for each of a plurality of received signal having different Signal-to-Noise (S/N) ratio, the minimum Bit-Error Rate (BER) as a function of the threshold level of a decision circuit at the system receiver. The measurements are then repeated on the system or on a simulated system where one or more segments of the transmission facility has been replaced with one or more non-ISI producing attenuators. The ISI levels for a given BER value is determined from the first and second sets of measurements. An alternate method measures minimum BER values of the system and the simulated system, as a function of the received signal power, for received signals having different S/N ratios. The ISI levels for a given BER value is then determined from these two sets of measurements.

Abstract: An optical communication system uses adjustable dispersion compensating fibers to compensate for dispersion in system fibers. The amount of dispersion introduced by the dispersion compensating fibers is varied depending upon the amount of compensation required. The amount of compensation may be determined automatically and the amount of compensation introduced by the fibers may be adjusted automatically by a controller.

Abstract: Dispersion compensation is achieved in an optical communications system by using an optical circulator with first, second, and third ports. The first and third ports are connected to system optical fibers. The second port is connected to a dispersion compensating fiber and return means. The signal passes through the dispersion compensating fiber twice permitting shorter dispersion compensating fibers to be used than were previously used. A Faraday rotator may be used compensate for the polarization mode dispersion of the fiber.

Abstract: A terminating portion of an optical fiber waveguide having a polished beveled end is laterally disposed directly on the light-emitting surface of a light-emitting diode (LED). The light power coupled into the fiber consists of two components: the light power directly coupled into the fiber all along the region of contact between the fiber and the light-emitting surface; and the light power reflected by the beveled end and directed along the fiber axis.