Abstract: A line monitoring arrangement of an optical fibre communications system carrying system data signals includes a test sequence generator, an optical transmitter and a correlator. The generator generates a sequence of test pulses, and the optical transmitter repeatedly launches the sequence of test pulses into a first end of a transmission line forming part of the communications system. The correlator correlates signals received at the first end of the transmission line with the sequence of test pulses to identify returned test pulse sequences. The test pulse sequences and system data signals are superimposed onto the transmission line.

Abstract: Apparatus is provided for detecting losses in a branched optical fibre network comprising a first optical fibre and a plurality of second optical fibres each of which is coupled to the first optical fibre. The first optical fibre constitutes a main line, and the second optical fibres constitute branch lines. The apparatus comprises launch means for launching a carrier wave into the main line, respective modulators in each of the branch lines for modulating the carrier wave in that branch line, returns for returning the modulated signals along the branch lines to the main line, and monitors for monitoring the main line for changes in the modulation of the returned signals. The modulators are such that each modulates the carrier wave differently.

Abstract: An optical tap comprises a transparent acrylic block (1) having a single V-shaped recess (2) into which an optical fibre (3) is urged by a member (4). The resulting kink in the fibre (3) enables light to couple between the core of the fibre and the block (1) from what is substantially a point source defined by a tight curve of short arcuate length at the kink.

Abstract: An optical power meter is used to measure the optical power of optical energy passing along an optical fibre (11). The power meter includes means (12,13) for tapping optical radiation from the optical fibre (11), a transducer (1) for converting the tapped optical radiation into an electrical signal, and means (5,6) for displaying the amplified signal.

Abstract: Apparatus for handling an optical fibre (13) comprises a casing (1) defining a substantially light-proof enclosure surrounding an optical fibre operating position, and mechanical means (4 to 8) for picking up an optical fibre and transporting that optical fibre to the operating position. The operating position is defined by a secondary waveguide (2) which defines a curved optical waveguiding path. The mechanical means (4 to 8) is such as to position the optical fibre (13) in a curved position which at least substantially conforms to the inner side of the curved optical waveguiding, path whereby optical energy passing along the optical fibre is tapped into the curved waveguiding path.

Abstract: A coupling device couples low power levels of optical radiation out of an optical fibre (3) for maintenance and fault-finding purposes. The assembled coupling device acts to clamp a fibre (3), with its primary plastics coating still in place, against the inner side of a gently curved silica rod (1). The rod (1) is strongly waveguiding and, picking up radiation leaked from the fibre (3), directs it to a photodetector (6). The device finds particular application in optical communications systems.