An optical directional coupler in which a TeO2 acoustooptical deflector (AOD) is employed has been designed and developed for use in an optical time-domain reflectometer (OTDR). A low roundtrip insertion loss of 4.6 dB and low crosstalk of below -48 dB were attained for the fabricated coupler. Signals of large amplitude, such as Fresnel reflection, could be suppressed to less than - 33 dB by switching of the optical directional coupler. Amplitude fluctuation of the backscattered signal due to polarization fluctuation in single-mode fibers is reduced to a negligible extent. Copyright é 1984 by The Institute of Electrical and Electronics Engineers, Inc.
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