Abstract: In a data transmission system where a computer side and a terminal side are connected with the aid of an optical fiber cable (FK), unauthorized tapping of light energy from some fiber in the cable can be detected. The transmitted signals are assumed to be shot-noise limited, i.e. the transmitted light is heavily superposed, whereby a large part of the transmitted light must be tapped off for listening. The computer side and terminal side contain level-sensing circuits (NVK1,NVK2) connected to respective receiver units (MD,MT) which send an alarm when tapping takes place. An optical fiber relay (RK) is connected between the fiber cable (FK) and the terminal side for short-circuiting this side in the case where a power failure can occur.

Abstract: A fibre-optical relay for switching optical signals between signal paths contains a fixed first holder (12) with parallel optical fibres (13, 14, 15) and a movable slide (8), similarly with parallel optical fibres (19, 20, 21). The slide can be displaced by an actuating arm (7) at right angles to the axial direction of the fibres from an initial position to a final position situated at a fibre spacing (d) from each other. The fibres (19, 20, 21) on the slide (8) are further arranged in a fixed second holder (16) displaced in the transverse direction of the fibres by half a fibre spacing (d/2).

Abstract: A device for tapping scattered light from a joint in an adjustable connector for two optical fibre waveguides having a first and a second cylindrical jointing tube for the fibre waveguides and a jointing sleeve for the jointing tube, at least one of the fibre waveguides being, inside its jointing tube, enclosed by a capillary tube of a transparent material.