Abstract: In a process and arrangement for measuring a physical quantity using an optical sensor, for imparting a power modulation proportional to the measured quantity on an effective light flux, the physical quantity being obtained from a ratio of the luminous power of the effective light flux to that of a reference light flux, to achieve a high path neutrality of an optical transmission path, the spectral distribution S(.lambda.) of the effective light flux and the spectral distribution R(.lambda.) of the reference light flux is selected according to the relation: ##EQU1## with .lambda.min<.lambda..sub.1 <.lambda..sub.2 <.lambda. max, the light source being emitting in the wave range between the wavelengths .lambda.min and .lambda.max.

Abstract: A bidirectional three-way star splitter for optical wave guides having coupler connections for the optical wave guides and output and input coupling elements between the individual coupler connections. Three coupling elements are provided and include a plane-parallel glass or synthetic glass element of homogeneous composition. Additionally, each coupling element has a longitudinal inside surface which is constructed as a plane reflector and a longitudinal outside surface which is constructed as an elliptical reflector, the two longitudinal surfaces being joined at both ends by planar coupling surfaces adjoining the respective optical wave guides.

Abstract: An electrically dimmable rear-view mirror for motor vehicles of simple and robust construction, suitable for use as an outside mirror or as an interior mirror possessing a transmission layer which is composed of a PLZT ceramic, on which a linear birefringence can be imposed by means of a controlling electric field. The transmission layer is located between a linear polarizer and a reflective layer, the latter being designed as a dielectric multilayer arrangement. Suitable comb-type electrodes are located on that side of the reflective layer which faces away from the transmission layer and, if appropriate, on that side of the polarizer which faces the transmission layer, the function of these comb-type electrodes being to generate the controlling field. The polarizer defines the direction of polarization, which is inclined at 45.degree. with respect to the field direction and/or the optical axis of the transmission layer.