Array Illuminators For The Optical Computer

Abstract

ABSTRACT An array illuminator provides the holding beam for an array of optical switches. The transformation of an incoming light beam can be brought about by several optical arrangements as are: telescopic arrays of lenses or holograms, phase contrast, Fraunhofer or Fresnel diffraction at periodic phase masks. The phase contrast illuminator will be discussed in more detail. 1.INTRODUCTION Optical bistable devices need strong holding beams to keep their stored information. The necessary amount of light energy can be provided for a periodic structure of switches by array illuminators. The array illuminator transforms a beam of parallel light into a set of sub-beams separated by a dark surrounding almost without loss of light energy.Different systems for array generation have been proposed [1-9] and have to be compared with respect to different parameters. Here a list of the most important properties of an array generator for digital optical data processing:The splitting ratio is the number of beams generated out of one incoming beam. A splitting ratio of 100 = 10 x 10 is considered small, since for highly parallel optical processing schemes splitting ratios of 10^ or more might be necessary, depending on the size of the arrays.The compression ratio is the quotient of the area of the elementary cell of the periodic intensity distribution to the area of the bright spot. It measures how well the beams of an array are separated. Obviously, this parameter depends on the requirements posed by the devices, which we intend to use, their active area and the distance in between different devices.The inhomogeneity is the maximum deviation in intensity between different spots within an array. For example, bistable optical devices usually require quite accurate biasing (critical biasing). Specifi­ cally, no overall envelope function should be present over the array, such as a Gaussian envelope of a laser beam.The light: efficiency specifies how much energy of the incoming laser beam is converted into the array and how much is lost.The modal shape describes the shape of the individual beams of an array. Needless to say, that for arrays of identical nonlinear devices all the power supply beamlets should have identical shape. In addition, for small devices (low switching energy!) the actual shape of the beamlets becomes important: As the device gets smaller, it supports less and less optical modes and we have to be careful to offer to the device the power supply beam in an acceptable mode.