An optical timehyphen;domain reflectometer (OTDR) with minus;136 dB minimum detectable reflectivity and 14 mgr;m spatial resolution is developed based on low coherence interference. The high sensitivity was accomplished by using a highhyphen;power superluminescent diode module with a 1.5 mW fiber output and a new system configuration, both for effectively operating the balanced heterodyne detection. The reflectivity of minus;136 dB is only 6 dB above the shot noise limit. The first observation of 1.3 mgr;m wavelength Rayleigh backscattering in singlehyphen;mode fibers was successfully made by the OTDR with a 17 dB dynamic range and 14 mgr;m spatial resolution.
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