Experimental set up for characterization of acousto-optic modulator system

Abstract

Acousto-optic effect can be used in many useful devices such as modulators, switches, filters, frequency shifters and spectrum analyzers. In this study, the modulating effect was generated by low cost SF6 glass with a lithium niobate transducer. Tunable Helium Neon Laser was used as the main light source. The function generator was used to generate external input signal and to vary the amplitude of acoustic wave. The modulated output signal was measured and analyzed using laser beam profiler, spectrometer, Si photo detector and power meter. The investigation shows that there was a shift of the horizontal main beam spot position when the driving frequency of the modulator is changed. A shift of beam spot between 4.0 mm to 5.5 mm was observed for a frequency range between 70 MHz to 90MHz. This is accordance with the expected theoretical model of the modulator. Results also show that a modulator can produce output signals, which are of the same type as the input signal. Increasing the amplitude of modulating signal in the range of 119 mV to 196 mV decreases the amplitude of modulated square wave signal from 2.6 V to 0.4 V. There was a decrease in the output power of the zero order diffraction but an increase in the first order diffraction with respect to the increase of the RF driving power.