Abstract: Multiplexer-demultiplexer device for wavelengths in an optical transmission fiber (6) for introducing therein a wavelength from an emitter (18) and for extracting wavelengths therefrom towards receivers (19), comprising several spherical mirrors (13-14) at least one of which (3) is a selective mirror with dielectric layers, selected to segregate by transmission or reflection a band containing only one of the wavelengths transmitted, or to be transmitted, by the fiber (6). The invention applies to telecommunications employing optical fibers.

Abstract: A multiplexer-demultiplexer for different wavelengths carried by optical fibers (10) the ends of which are disposed in the immediate vicinity of the focus of a concave mirror (18) associated with a plane diffraction grating (15) is disclosed.The multiplexer-demultiplexer consists of four elements that are adhesively attached to one another, namely, a fiber-carrying element (1); a grating-carrying element (15); an intermediary element (3) of the same index as the element (2); and a mirror element (4) having an index of refraction different from that of element (3) and selected to compensate for longitudinal spherical aberration of the mirror (18) for at least one of the wavelengths being utilized.

Abstract: Selector for separating at least two wavelength bands from a complex light introduced into the apparatus through the end of an optical fiber (12) arranged in the immediate vicinity of the focal point of a concave mirror (5) producing a parallel beam directed towards a plane reflecting device, the return beam being focused towards an output optical fiber. It comprises at least one plane multidielectric layer (8) interposed between the concave mirror (5) and the plane reflecting device (10) and forming, with the vertex axis (6) of the concave mirror, an angle which is slightly different from that of the plane reflecting device, each multidielectric layer having a discontinuity in the vicinity of the vertex axis of the concave mirror.

Abstract: Monochromator comprising a concave grating, the lines of which are situated at the intersection of the concave surface with a family of surfaces geometrically like the equiphasic surfaces obtained as loci of the luminous intensity maxima produced by the interference of two beams from two point sources C and D, an entry slit A and an exit slit B, wherein the polar coordinates of the points C and D and of the entry slit A and exit slit B in a system of polar coordinates having as its origin the apex of the grating and as reference axis the axis of the grating in a plane of reference passing through this axis are connected by the following relationships: ##EQU1## in which (.alpha., l.sub.A), (.beta., l .sub.B), (.beta., l.sub.C) and (.delta., l.sub.D) are the polar coordinates of A,B,C and D, respectively, R is the radius of curvature of the grating, .omega.=(.alpha.+.beta.) /2 and .phi.=(.alpha.-.beta.)/2.