We report an optical time-domain reflectometer that employs an ultrafa
st optical switch based on nondegenerate four-wave mixing in a semicon
ductor laser amplifier. Two-point spatial resolution on the order of 1
mm over 2 m is demonstrated; Fresnel reflections with optical return
losses greater than 53 dB are detected. Submillimeter-resolution optic
al time-domain reflectometery over a 100-m range should be possible wi
th modifications to the pulse sources.