Abstract: A reversible device for demultiplexing several light signals in integrated optics is more particularly intended to separate n light signals of different wavelengths forming a light beam and transmitted by a first optical fiber and for respectively reinjecting into n second optical fibers the n light signals. Produced in a light guide, it comprises achromatic input optics for rendering parallel said light beam, n gratings arranged in cascade form and operating under Bragg conditions, each grating serving to diffract that part of the light beam carrying one of the n light signals and transmitting the not yet diffracted part of said light beam in the direction of the following grating, as well as n output optics associated with n gratings, each output optics being used for focussing that part of the light beam diffracted by the associated grating.

Abstract: Fresnel lens for integrated optics, wherein it comprises a light guide of effective index n.sub.eff incorporating a guiding layer and a number N of regions of length L(r) measured in the direction of the lens axis as a function of the distance r from the lens axis and disposed in the direction perpendicular to the lens axis, while having a refractive index such that to the right of these regions the effective index of the light guide has a value n'.sub.eff which differs from n.sub.eff in such a way that a light wave propagated to the right of these regions is given a phase displacement .DELTA..phi. due to the effective index difference n'.sub.eff -n.sub.eff and making it possible to obtain constructive light interferences at the chosen image point. The invention also relates to a process for producing a Fresnel lens in which the regions are produced by ion implantation.

Abstract: Fresnel lens for integrated optics of the type having a number of overlayers deposited on the surface of a waveguide propagating a wave in accordance with a given propagation mode, the overlayer of order m starting from the axis is of width 1.sub.m =.sqroot.(m+1).lambda.f - .sqroot.m.lambda.f and is at the distance from the axis r.sub.m =.sqroot.m.lambda.f in which f is the focal distance of the lens, .lambda. the wavelength of the light in the guide and m a parameter successively assuming the different values of the natural sequence of integers from 1 to p+1, wherein the thickness and/or the length of each film is at least equal to the penetration of absorption distance of the wave guided in or beneath the overlayer for the adopted propagation mode.