A single crystal photo-elastic modulator

摘要

We present theoretical and experimental data and possible applications of a photo-elastic-modulator (PEM) made of LiTaO_3. The device with dimensions 13.2×7.1×5.5 mm in x-, y- and z-direction and electrodes on the zx-surfaces offers basic modulation frequencies at 199,348 and 377 kHz corresponding to the longitudinal oscillations in x- and y-direction and to a yz-shear oscillation mode. The light travels along the optical axis. At the main resonance at 199 kHz the voltage amplitude to achieve a quarter wave retardation amplitude is only ～2.5 V, a very low value due to the strong piezo-electric response and the low loss of LiTaO_3. Hence when compared to a conventional photo-elastic modulator, which is made out of at least two components, the device is extremely compact, cheap and easy to operate, especially when placed in a feedback loop of an amplifier such that it operates on one fixed frequency.