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Fiber Optic Flip Flop

IP.com Disclosure Number: IPCOM000050965D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Gupta, OR: AUTHOR [+3]

Abstract

A logic memory cell is provided consisting of a set/reset flip-flop having input and output light pulse signals connecting through fiberoptic waveguides. The device uses a combination of optical and electrical positive feedback to maintain the switchable bistable output states Q and (Q). The electro-optical gate used in this device is a liquid crystal (L-C) cell using the dynamic scattering effect.

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Fiber Optic Flip Flop

A logic memory cell is provided consisting of a set/reset flip-flop having input and output light pulse signals connecting through fiberoptic waveguides. The device uses a combination of optical and electrical positive feedback to maintain the switchable bistable output states Q and (Q). The electro-optical gate used in this device is a liquid crystal (L-C) cell using the dynamic scattering effect.

Fig. 1 illustrates a typical device configuration in which the cell has been "set" by a pulse of light through fiber-optic waveguide 1. Both light-emitting diodes (LEDs) 3 and 4 are maintained by current from supply V(B) through resistors R1 and R2. Since liquid crystal cell 6 is in the opaque or "off" state, no light emerges from output fiber 12, the Q logic output. In this state no light falls on the surface photodiode 8, and output voltage V1 of transimpedance amplifier 10 is at ground. This voltage is used to drive liquid crystal cell 5.

Fig. 2 illustrates the construction of an L-C cell. Two glass plates 13 are separated by a ring spacer 14 and filled with a nematic liquid crystal 15 having a negative anisotropy. When a voltage is applied between the transparent electrodes 16 made from a thin coating of tin indium oxide, there is a random state in the liquid crystal that scatters and absorbs almost all of the light entering the cell. When the voltage is removed, the liquid crystal molecules again align themselves parallel to the electrodes an...