Removal of the zero order in optical fourier transformers.

For coherent optical fourier transformers, aperture tapering (apodization) has been discussed' as a method of improving the detectability of low spatial frequency signals that would other­ wise be obscured by zero-order light. By zero-order light we mean the light distribution in the transform plane, centered at the zero frequency point, due to the average of dc bias light at the input aperture. In this letter, two methods for elim­ inating the entire zero order are described. The detectability of low spatial frequency components is thereby greatly improved and is now limited only by the background due to scattered light.