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When a piezoelectric transducer is bonded to an acousto-optic (A-O) crystal, it will generate an acoustic traveling wave or standing wave in the medium as illustrated in Fig. 35. The elasto-optic interaction then sets up a periodic variation in refractive index characterized by acoustic angular frequency W and wave vector K of magnitude 2p/L where sound velocity V = W/K. The incident optical wave (ki) will be diffracted by K into a wave kd = ki K. However, only a fraction of the incident optical or acoustic beam will be effective in the process.

Fig.35.JPG (20437 bytes)

The diffraction efficiency of the process is a function of the product of the acoustic power and figure of merit M = n⁶p²/rV³ where p is the appropriate photoelastic coefficient and r is the density of A-O material. Thus, an acousto-optic light modulator can be produced by modulating the acoustic power.