Surface stabilized ferroelectric liquid crystal devices with total reflection in one state and transmission in another state

Abstract

A liquid crystal device including a ferroelectric liquid crystal disposed between plates treated to enforce a particular ferroelectric molecular orientation to the plates. The devices employ alone or in combination non-planar boundary conditions, polar boundary conditions, boundaries with multiple physical states, intrinic spontaneous splay distortion of the polarization orientation field, combined ferroelectric and dielectric torques, layers tilted with respect to the plates. The plates are spaced by a distance sufficiently small to ensure unwinding of the helix typical in a bulk of the material to form either monostable, bistable or multistable states which exhibit novel electro-optic properties. The liquid crystal is responsive to an externally applied electric field, temperature or the like to make a light valve or other electro-optical device.

What is claimed is: 
     
       1. An electro-optical device comprising: a pair of substrates;   a ferroelectric liquid crystal having a plurality of layers each comprised of a plurality of molecules, each molecule having a long axis, the long axes of said molecules in a bulk forming helices, said ferroelectric liquid crystal being disposed between said pair of substrates which are spaced by a distance sufficiently small to suppress the formation of said helices, said plurality of layers being aligned parallel to each other, and said substrates and said ferroelectric liquid crystal causing an orientation state of said molecular long axes which corresponds to one of a plurality of different stable states; and   means for directing light at an interface between at least one of said substrates and said liquid crystal so that said light undergoes total reflection at said interface when said long axes are in at least one of said stable states and so that said light at least partially transmits through said interface when said long axes are in at least one other of said stable states.   
     
     
       2. A device as in claim 1 further comprising means for applying an electric field to said liquid crystal in one of two directions to switch said long axes between said one and said other stable states, said light incident on said interface undergoing total reflection at said interface for one direction of said electric field, but partially transmitting for the other direction of said electric field. 
     
     
       3. A device as in claim 2 wherein: said liquid crystal is in a smectic state, having layers normal or nearly normal to the substrates, said layers further oriented so that the layer normal makes an angle θ, equal to or nearly equal to the FLC smectic C tilt angle, with the plane of incidence of light incident on said interface;   said directing means includes means for polarizing said incident light normal to the plane of incidence; and   when said electric field applying means applies said electric field in one direction, the long axes are oriented parallel the plane of incidence and said incident light is totally reflected at said interface by an apparent liquid crystal refractive index of n 0 , and when said electric field applying means applies said electric field in the opposite direction the long axes make an angle of twice θ with the plane of incidence and said light is subject to a larger apparent liquid index refractive index and is at least partially transmitted, where n 0  is the ordinary refractive index.   
     
     
       4. A device as in claim 3 where the angle θ is 45° and the apparent liquid crystal refractive index in the partially transmitting state is n e , where n e  is the extraordinary refractive index. 
     
     
       5. An electro-optical device comprising: a pair of substrates, at least one of which is photoconductive;   a ferroelectric liquid crystal having a plurality of layers each comprised of a plurality of molecules, each molecule having a long axis, the long axes of said molecules in a bulk forming helices, said ferroelectric liquid crystal being disposed between said pair of substrates which are spaced by a distance sufficiently small to suppress the formation of said helices, said plurality of layers being aligned parallel to each other in one direction within the planes of said substrates, and said substrates and said ferroelectric liquid crystal causing an orientation state of said molecular long axes which corresponds to one of a plurality of different stable states;   electrode means, between which said photoconductive substrate and said liquid crystal are disposed, for applying a voltage across the photoconductive substrate and liquid crystal; and   means for illuminating the photoconductive substrate to change the voltage applied across said liquid crystal, said change of voltage causing said long axes to change orientation.   
     
     
       6. A device as in claim 5 wherein said photoconductive substrate includes an additional insulating layer directly adjacent said liquid crystal.