Abstract: There is disclosed an angle selective coupler for coupling optical energy into and/or out of optical fibers. The coupler consists of a section of the optical fiber modified in such a way as to allow optical excitation of a plurality of higher order modes of optical transmission, each mode being defined by a given angle of propagation relative to the fiber axis. In one embodiment the coupling section comprises a single strand of glass fiber waveguide which is tapered along its length. The existence of the tapered section allows coupling of radiation from an external source into a given propagation angle in the fiber. In another embodiment no taper is used, but the fiber cladding is etched down to a thin layer and higher index material is deposited over the thin layer. This allows coherent coupling of radiation into one or more higher order modes in the optical fiber as determined by the angle of the incident light beam with respect to the cladding of the fiber.

Abstract: Methods and apparatus for erasing the stored scattering image in storage-type liquid crystal light valves. Erasure is accomplished by applying a signal from an erasing signal source across the liquid crystal cell where the signal is a voltage which is swept over the audio frequency range of 1 KHZ through 20 KHZ. In another embodiment, the erasing signal source supplies a precursor signal which has an initial frequency below the frequency threshold for scattering. This low frequency signal is maintained for a brief period of time to excite the entire liquid crystal cell into a uniform scattering state. The erasing signal is then swept over the audio frequency spectrum of 1 KHZ through 20 KHZ to cause the cell to return to the non-scattered, translucent state.