We report a tunable narrow-band light source with a spectral width of
0.26 +/- 0.04 nm, a 0-dBm output power, and a reduced background spect
rum in the 1.5-mu m band, which we have developed for optical low cohe
rence reflectometry. The Rayleigh backscatter signal fluctuations were
reduced to within +/-0.4 dB by using this source. The source will als
o be used in a system for measuring optical waveguide circuits. This i
s because the coherence length is about 1 cm and, by using a fiber-opt
ic depolarizer, the degree of polarization is less than 0.016.