An acousto-optic modulator for use in an optical time domain reflectometer to test multimode optical fibers has an active material, such as AS-Se-Ge or As2S3 glass, that has a high figure of merit with a low insertion loss. The transducer for the modulator is configured to have a height that encompasses the multimode beam diameter at the optical wavelength, and a length that is consistent with a theoretical lower limit that is a function of the acoustic and optical wavelengths. Sufficient RF power is applied to the modulator to produce an angular efficiency, or optical throughput, that is sufficient to meet the specifications for the optical time domain reflectometer. Further dead zone correction for the optical time domain reflectometer is obtained by deriving a transient response signal for the optical time domain reflectometer as a function of a measured output electrical signal in response to a known input optical signal, and subtracting the transient response signal from an output electrical signal obtained in response to an unknown input optical signal to derive a corrected measured output electrical signal.
Multimode acousto-optic switch and dead zone correction method