Broadband Acousto-optic Amplitude Demodulator

Abstract

The scientific and practical significance of the synthesis of demodulators in solving the problem of monitoring unknown radio emissions has been substantiated. Features of the photoelastic effect are discussed in the context of constructing an amplitude demodulator. A mathematical model of the signal generation process at the output of the demodulator has been developed. It is shown that the output signal of this model is a copy of the information contained in the radio signal at the input of demodulator. In this case, the amplitude demodulator also performs the function of a low-pass filter with a characteristic cutoff frequency. A method for calculating the demodulator cutoff frequency based on the transient response is proposed. A breadboard of acousto-optic amplitude demodulator based on Bragg’s cell with the central frequency of 80 MHz has been created. A number of experimental studies were conducted to verify the established concepts. The demodulation processes of signals with amplitude and pulse modulation were considered. It has been proved by experiment that the acousto-optic amplitude demodulator reproduces information with accuracy sufficient for practice. An example of determining the cutoff frequency of acousto-optic amplitude demodulator by employing the shape of the output pulse is presented.