We report a novel means of measuring the acoustic velocity based on a well-known acousto-optic interaction. With an acousto-optic modulator (AOM), we construct an optoelectronic oscillator (OEO) that can measure the acoustic velocity in the AOM directly. The free spectral range between the modes is a function of the total loop length of the OEO, which is mainly dependent on the propagation time of the acoustic wave through the AOM. By changing the propagation time, we measured the acoustic velocity from the variation of the free spectral range. The results are reported and compared with earlier results. This method is insensitive to the variation of the optical phase shift. In addition, the high frequency-stability and microwave spectral purity of the OEO allow reliable and precise measurements.
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