Abstract: A tunable optical filter comprises optical waveguides separated by a space filled with liquid crystal material which is oriented by an alignment layer or grating to form a Fabry Perot resonant cavity, where the resonant condition is set up by a reflective coating or grating in the optical waveguide, and the refractive index of the liquid crystal may be altered by the application of a voltage across the cavity by means of electrodes. The filter or an array of filters may be constructed using optical fibers between a substrate and a superstrate, preferably with the fibres being located by means of grooves formed in the substrate and superstrate, with individual electrodes in the space between aligned fibres enabling independent tuning of each filter, typically for use in wavelength division multiplexing communication systems. The liquid crystal molecules may be aligned parallel or perpendicular to the length of the fibres.

Abstract: A liquid crystal display device comprises a reflective type liquid crystal panel with pixels which are arranged in two-dimentionally and which modulate irradiated light utilizing polymer dispersed liquid crystal capable of exhibiting two conditions including scattering and unscattering. The device is provided with an optical member having a multiple-interference effect at a predetermined angle with respect to the surface of the reflective type liquid crystal panel.

Abstract: This invention provides a phase modulator comprising an electro-optically rotatable smectic liquid crystal half-wave retarder in combination with a cholesteric liquid crystal circular polarizer. Rotation of the half-wave retarder varies the phase delay of the modulator. A polarizing interferometer is provided utilizing the phase modulator of this invention in combination with a second cholesteric circular polarizer and a linear polarizer. A tunable Fabry-Perot resonator which does not require ordinary mirrors is provided utilizing the phase modulator of this invention in combination with a second cholesteric circular polarizer.

Abstract: This invention provides polarization-independent optical filters that are Fabry-Perot filters. The inventive filters incorporate a phase modulator within the FP cavity and two quarter-wave plates, one on either side of the phase modulator, in the cavity. The quarter-wave plates are perpendicular to each other and oriented at .+-.45.degree. with respect to the optic axis of the phase modulator. A variety of phase modulators including those that incorporate nematic and smectic liquid crystal optical modulators can be employed in these FP filters. The filters of this invention are particularly useful in fiber optic systems and in telecommunications applications at 1550 nm.

Abstract: An electrically-controllable liquid crystal filter device comprises two partially-reflecting substrate structures mounted substantially parallel to each other with a space therebetween to form a Fabry-Perot filter. A layer of ferroelectric liquid crystal material is disposed in the space, the liquid crystal material being switchable, by application of an electric field, between different refractive index values whereby the device is switchable between transmissive and reflective states for light of a particular narrow wavelength band. The spacing of the substrate structures is selected in relation to the wavelength of light to be transmitted, such that the Fabry-Perot filter operates in a low order state, which may be the first order.

Abstract: An erasable display medium comprising a substrate having thereon at least one liquid crystal polymer layer comprising a side chain type liquid crystal polymer which repeatedly and reversibly switches from a transparent state and a light-scattered state by the action of at least one of heat, an electrical field, and a magnetic field is disclosed, said side chain type liquid crystal polymer being a copolymer comprising a repeating unit represented by formula (I): ##STR1## and a repeating unit represented by formula (II): ##STR2## or a copolymer comprising a repeating unit represented by formula (III): ##STR3## and a repeating unit represented by formula (IV): ##STR4## wherein R.sup.a and R.sup.