Development is underway to realize practical application of optical fibers for optical communications in a low loss wavelength region (1.3 μm or 1.55 μm). Regarding optical cable fault location measured in the low loss wavelength range, the conventional isolated pulse method was inadequate for long-distance measurements because of the small light source power, lowered sensitivity of the light receiver, and feeble backscattering light. The technique described here using pseudo-random noise (PN) pulses has realized a long-distance measurement of 10 km in an optical cable of 0.8 dB/km in optical loss at 1.3μm wavelength.
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