Jaggedness-free millimeter-resolution low coherence reflectometry

We report a millimeter resolution optical low coherence reflectometer (OLCR) that exhibits reduced jaggedness in the Rayleigh backscatter signal. This OLCR was achieved by using an erbium-doped superfluorescent fiber source that can tune narrow-band superfluorescence (~0.2 nm full-width at half-maximum) over a 3-nm range with an output of -8 dBm, The signal averaging that resulted from wavelength tuning with this source efficiently reduced the jagged fluctuation to ±1.4 dB. The spatial resolution was 1.2 mm, and the hidden spaces defined by the full-widths at -20 dB and -60 dB maximum of a Fresnel response of the OLCR were 6 mm and 1.2 cm, respectively. These two hidden spaces are at least ten times narrower than those of a previously reported photon-counting OTDR, although their spatial resolutions are roughly the same. The OLCR enabled the weak Rayleigh backscattering near a connector joint to be measured with a dynamic range of 18 dB without any deconvolution. We confidently expect that this OLCR will be applied to short-haul optical fiber fault location