Abstract: The present invention provides a bistable optical device in which the active medium is a polymer material of thermo-optical effect inserted into a cavity resonator, preferably a FABRY-PEROT resonance cavity, in said cavity the polymer material transmitting and reflecting an incident light wave with bistable values and values variable according to its thermal state. This latter is varied by the absorption of a fraction of the incident light wave, which transfers heat to the polymer material to generate therein an increase in the transmission of the incident light and a variable refractive index in response to the increase in its temperature, to thus provide a positive response effect which enables the device of the present invention to vary between two bistable states.

Abstract: A nonlinear all-optical switching device including a waveguide of an organic conjugated material which forms a nonlinear optical medium. The nonlinear material has an index of refraction which is a function of the local intensity of light. Light beams passing through the waveguide intersect and interact causing diffraction into secondary beams. The intensity of the diffracted beams is a function of the intensity and frequency of the intersecting light beams. The nonlinear material can respond extremely fast and provide a bandwidth exceeding 500 GHz.

Abstract: A hollow glass waveguide such as an optical fibre comprises a glass cladding containing in excess of 90 mole % germanium dioxide, the balance of the cladding being made up of modifying oxides such as network modifiers and intermediate modifiers. The use of high concentrations of germanium dioxide results in the waveguide having good optical properties in the 9-11 .mu.m wavelength range e.g. low transmission losses. The incorporation of small quantities of modifying oxides produces improved physical properties e.g. better fibre drawing capability and reduced tendency to devitrification. A particularly preferred cladding contains 94 mole % GeO.sub.2, 3 mole % Na.sub.2 O and 3 mole % Al.sub.2 O.sub.3.