Acousto-optic FM demodulation

This thesis describes the operation of a frequency demodulator using optical signal processing principles. The frequency dependent deflection properties of an acousto-optic cell are harnessed to demonstrate a means of demodulating narrow-band frequency modulated RF signals at high modulation rates (β small). Theory is developed to predict the linear operating range, absolute frequency sensitivity, frequency and transient response of the demodulator and results are presented to support all aspects of the theory discussed. Investigations are carried out into other effects on the demodulator performance including external noise, degradation in the carrier to noise ratio and unwanted AM modulation on the signal of interest. An improved system which offers enhanced sensitivity and improved noise rejection performance is then described. Theory is developed and further results are presented to demonstrate the improvements over the original system. Detailed studies of the engineering requirements of both types of system are presented and suggestions are made on optimum component choice and system construction. Comparisons are drawn with conventional electronic methods of FM demodulation and advantages and disadvantages of the acousto-optic FM demodulator are highlighted. Novel uses for the demodulator are suggested which exploit the system's unique characteristics and advantages over conventional electronic demodulation techniques.