Abstract: A digital data transmission system by modulating a coherent light wave is provided using modulation of the MSFK type with N frequencies for modulating the light wave. The transmitter comprises a coherent light source, a modulator, an output optical means and an MSFK modulation signal generator. The receiver comprises an input optical means, local light wave source and a heterodyne mixer for creating an electric signal of intermediate frequency. A demodulation and detection circuit comprises filtering means for separately selecting the N frequencies before detection. A processing cirucit puts the data back into its initial form. A circuit for compensating for the drift of the light sources is used for preserving lock on to the intermediate frequency.

Abstract: The diffraction grating principle is used to deflect an infrared beam in a series of discrete predetermined directions. A periodic control voltage having a staircase waveform with N steps is applied across a liquid crystal layer to create local variations of refractive index therein, thereby setting up an infrared diffraction grating of adjustable pitch.

Abstract: The rotary-joint device has the design function of maintaining accurate positioning of the ends of optical fiber conductors during relative rotation of external bodies to which the joint is coupled. The device comprises a male ferrule and a female ferrule so arranged as to form a shaft rotatably mounted within a sleeve with a close but compliant fit, an abutment device for limiting the axial displacement of the sleeve, means for centering the ends of the conductors, and means for securing said ferrules to external connector bodies so as to form a rigid coupling and a semi-rigid coupling respectively.

Abstract: A light retro-reflective responser and data modulator arrangement which, in particular, allows expected incident radiation to be reflected back with no contour field within the operating field and which enables an optical modulator of very small size to be used. It comprises a retro-reflective system formed by an optical objective and in the corresponding focal zone, a lens, an electronically controlled optical modulator, and a reflective mirror, the two latter items being produced as layers deposited on at least one face of the lens and preferably on the plane face of a plano-convex lens.

Abstract: A coupler for coupling the end of an optical signal transmission line comprising at least one optical waveguide, to a solidstate converter device such as a light emitting diode or a photosensitive diode according to the case, the converter device presenting a refractive index N3 higher than the refractive index N1 of the optical waveguide. The coupler comprises a transparent matching medium having at least a refractive index N4 of value intermediate between the values N1 and N3 and forming a thin parallel faced plate whose maximum thickness is determined on the basis of the numerical aperture of the guide.