High dynamic range, bifrequency acousto-optic modulator

Multifrequency acousto-optic interaction is limited mainly by the two-tone, third-order intermodulation products. The tangential phase-matching (TPM) anisotropic interaction can greatly reduce the phase-grating intermodulations. We consider the two operating modes, high or low frequency, for the slow shear wave propagating in paratellurite with an angular tilt from the [110] axis. As two different angles lead to the same central operating frequency, we show that the low-frequency configuration allows one to greatly increase the dynamic range, compared with that obtained in the high-frequency mode. For experimental validation, two bifrequency acousto-optic modulators have been realized and tested. For a central frequency in the low-frequency configuration and a diffraction efficiency , the dynamic range is shown to be enhanced by 5 dB.