This paper is concerned with a systematic approach to the design of the “linear channel” of a repeater for a digital fiber optic communication system. In particular, it is concerned with how one properly chooses the front‐end preamplifier and biasing circuitry for the photodetector; and how the required power to achieve a desired error rate varies with the bit rate, the received optical pulse shape, and the desired baseband‐equalized output pulse shape. It is shown that a proper front‐end design incorporates a high‐impedance preamplifier which tends to integrate the detector output. This must be followed by proper equalization in the later stages of the linear channel. The baseband signal‐to‐noise ratio is calculated as a function of the preamplifier parameters. Such a design provides significant reduction in the required optical power and/or required avalanche gain when compared to a design which does not integrate initially. It is shown that, when the received optical pulses overlap and when the optical channel is behaving linearly in power,1 baseband equalization can be used to separate the pulses with a practical but significant increase in required optical power. This required power penalty is calculated as a function of the input and equalized pulse shapes.

No abstract

No abstract

This paper applies the results of Part I to specific receivers in order to obtain numerical results. The general explicit formulas for the required optical average power to achieve a desired error rate are summarized. A specific receiver is considered and the optical power requirements solved for. The parameters defining this receiver (e.g., bit rate, bias resistance, dark current, etc.) are then varied, and the effects on the required optical power are plotted.

This paper describes an optical time‐domain reflectometer that incorporates a gated photomultiplier receiver. The instrument can detect extremely weak reflections from fiber breaks (more than 65 dB below the 4‐percent reflection of a perfect break) with 0.5‐m distance resolution. In addition, backward Rayleigh scattering, which occurs roughly uniformly along a fiber, can be used to estimate the attenuation us position within a fiber. Therefore, regions of high attenuation can be located nondestructively from one end of the fiber.