Abstract: Means for digitizing and averaging the signals in an optical time domain reflectometer are disclosed in which a comparator is used to output a 1 or 0 into an arbitrarily large number of successive time-bins. In each comparator choice, the analog voltage signal from the OTDR receiver is compared to a selected analog voltage value. The selected value is chosen randomly from the range of available signals in the interval of interest; and each such valve is used to provide a comparator input into every time-bin during one waveform recovery.Each comparator output signal (1 or 0) is directed to a separate time-bin (counter), representing the desired time interval (resolution). Subsequent comparator output signals are added to each time bin. The waveform recovery runs are repeated until an acceptable signal-to-noise result is achieved. Each waveform run uses a different voltage for comparison to the receiver voltage.

Abstract: This application discloses a system in which a single optical time domain reflector is used to monitor a plurality of cables. In one embodiment two lasers having different wavelengths are separately fired into different cables, and the returning signals are fed into the appropriate port of a wavelength dependent coupler. In another embodiment, each laser simultaneouly checks two cables having different lengths, the length difference permitting identification of the cable in which a fault has occurred.

Abstract: The present invention provides a radiation source which essentially matches the throughput radiation of the source to the throughput radiation of the interferometer; and it provides the maximum throughput usable by the interferometer with a minimum use of power at the source. The infrared source in this invention combines a radiating element having the optimum area with a hollow, inwardly-reflecting sphere, whose center is at the radiating element and whose exterior has a single aperture which causes radiation to fill the entrance field of view of the spectrometer.