An acoustooptical directional coupler for an optical time-domain reflectometer

An optical directional coupler in which a TeO2acoustooptical deflector (AOD) is employed has been designed and developed for use in an optical time-domain reflectometer (OTDR). A low round-trip 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 back-scattered signal due to polarization fluctuation in single-mode fibers is reduced to a negligible extent.