Nonlinear optical processing: nonmonotonic halftone cells and phase halftones.

The halftone screen process has proven to be a useful, flexible technique for achieving general nonlinear functions in coherent optical systems. The two steps to the process involve making a binary pulse-width modulated copy of the continuous-level input using a halftone screen and spatial filtering of single diffraction orders of the image to produce the nonlinearly transformed output. The halftone screens are usually monotonic nondecreasing functions; thus the fundamental sampling periodicity of the screen is maintained. This paper describes some generalizations of the process using nonmonotonic periodic halftone screens. With this new type of screen, functions with an arbitrary number of slope changes can be obtained in the first diffraction order. A detailed synthesis algorithm for specifying the screen shape is given, along with examples and experimental realization of irradiance notch filter and quantization functions. A technique for making the halftone process more resistant to line blooming is descr bed, and a binary phase system made by bleaching ordinary halftoned input is analyzed.