Novel space-integrating acousto-optic correlator: amplitude and phase information from intensity only measurements

A novel form of twin Bragg cell, nonheterodyning, space-integrating optical correlator convolver has been built and tested using digitally generated signals. The system is fundamentally a convolver but may be made to act as a correlator by time-reversing the signal to one of the Bragg cells. It is found that the nature of the correlation/convolution function obtained depends upon the way in which the signals are amplitude modulated onto the Bragg cell carrier frequency. If a suppressed carrier form of modulation is used the correlation/convolution of the squares of the signals is obtained but when a large carrier modulation is used the true correlation/convolution of the signals may be extracted from the detector output by highpass filtering. The experimental results obtained from the system are shown to be in agreement with theory. A unique feature of the system is that it enables both the amplitude and phase of the correlation function to be obtained but requires only the intensity of the light at the output of the system to be measured. Previous systems to obtain the same result have involved heterodyning (interferometric) techniques which are significantly more complex and difficult to use than the system described.