Element for optical logic

1,056,638. Electro-optic logic systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. June 8, 1965 [June 29, 1964], No.24140/65. Heading G1A. The electro-optical logic system, shown in Fig. 1, contains two electro-optic active elements 15 and 16 each of which when a voltage is applied to them retard by 90 degrees the wave polarization in one direction with respect to that in the other, in the case shown x' retarded with respect to y', and which are combined with a further quarter wave retarding plate 26 and a plane polarizer 13 and analyzer 27. For various combinations of the values of the parameters of the system, all representing inputs to the system, viz. the directions of the polarizing axes of the polarizer, analyzer and electro-optic active elements and the absence or presence of a signal voltage applied to the elements, three levels of intensity of radiation can be received by the photo-multiplier 30 viz. zero of the axis of polarization of the radiation prior to the analyzer is at 90 degrees to the axis of the analyzer, I/2 of the radiation prior to the analyzer is circularly polarized and I of the axis is the same as the analyzer. By using two photomultipliers one with a threshold between zero and I/2 and the other between I/2 and I, or a single photo-multiplier the threshold of which can be switched, two logic output signals can be derived for whatever level of intensity is created by the inputs to the system. Increasing the number of active elements will increase the number of logical functions the system can perform. Compounds suitable for forming the active crystals are ammonium dehydrogen phosphate, potassium dideuterium phosphate and cuprous chloride.