IMPROVED WAVEFRONT SENSOR USING HYBRID OPTICAL/ELECTRONIC HETERODYNE TECHNIQUES

摘要

A hybrid optical/electronic wavefront includes an electro-acoustical device, such as a Bragg cell, that is used to upshift an optical reference signal. An optical test signal and the frequency upshifted optical reference signal are optically heterodyned to create a signal having a frequency equivalent to the beat frequency of the two signals. The optically heterodyned signal is then converted by a detector to an electronic signal having the same phase as the optical test signal. The output of the detector is a sinusoidal signal having the same phase as the phase of the optical test signal. This signal is filtered by way of an AC filter and mixed with a second clock signal. The low frequency product of the mixer is passed by way of a filter and converted to a square wave by way of a comparator. The output of the comparator is applied to a simple pulse counter and used to disable the pulse counter. An electronic reference signal formed by mixing the two RF signals, filtering the output, and squaring up the output by way of another comparator. The reference signal is used to start the pulse counter. A clock signal for the pulse counter is developed by squaring up the RF driving signal applied to the electro-acoustical device by a comparator. The pulse counter counts the clock pulses while it is enabled. The pulse count is linearly related to the difference in phase between the optical test signal and the frequency upshifted signal.