Practical considerations for the use of spatial carrier-frequency filters.
The article discusses several practical problems in the use of spatial carrier-frequency filters in coherent optical systems, and describes an interferometric system that offers many practical advantages in constructing such filters. Also described is an optical configuration that can easily search for the scale of a signal, as well as its location and orientation. The use of a prism in the optical configuration simplifies the search for the orientation and scale of the signal. The spatial carrier-frequency filter introduces some aberrations, but only astigmatism and distortion remain uncorrected. The necessary magnitude of the spatial carrier frequency depends upon the size of the signal and of the input data. A natural extension of this consideration leads directly to a corresponding requirement on the spatial carrier frequencies for multiplexed filters.
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Radar and Optics Laboratory, Willow Run Laboratories, Institute of Science and Technology, The University of Michigan, Ann Arbor, Michigan 48107, USA.