Abstract: An optical fiber interface includes a detector assembly, which may include an integral fiber, for detecting an optical signal carried on a single fiber in an outbound direction and a piezo electric transducer or the like for providing relative movement between the fiber and the detector assembly to produce a modulated return optical signal in reflections of the outbound signal. The return optical signal has a lower frequency or data rate than the outbound signal. Several embodiments modulate the return signal by relative movement either perpendicular to or parallel to the fiber. The perpendicular movement modulates the reflected signal by varying alignment of the fiber and detector assembly, while the parallel movement modulates by varying a Fabry-Perot gap formed between the fiber and the detector assembly. One embodiment includes a cantilever beam of semiconductor material attached to the detector surface. The beam providing an integrated transducer and reflecting surface.

Abstract: Optical communications fibers extend from a central office to subscribers' premises for carrying signals in both directions between optical transmitters and receivers. Each subscriber's optical receiver continuously reflects back to its fiber, and then to the central office, about 20 percent of the light which it receives. At the central office the reflected light is monitored in turn for each subscriber, and is correlated with the signal transmitted to that subscriber to provide a signal for optical time domain reflectometry of the respective subscriber's fiber connection.

Abstract: A bandwidth limiter for an optical fiber transmission path comprises a four-port optical coupler via which an optical signal is passed. A spliced optical fiber provides a loop, from an output to an input of the coupler, with a predetermined propagation delay and attenuation. An alternative arrangement uses two couplers which are coupled together via fibers of different length and hence propagation delay.

Abstract: An optical fiber having a core and a cladding has its cladding interrupted and an electro-optic crystal disposed at the interruption, a modulating electric field being applied via electrodes to the crystal to control its refractive index and thereby modulate an optical signal carried by the fiber. In one embodiment the interruption in the cladding extends all around the core. In another embodiment the fiber is embedded in a curved position in epoxy material, and the epoxy material and fiber are ground down on the outside of the curve to interrupt the cladding and expose the core, the electro-optic crystal being provided on the ground surface. A second fiber can be inverted on the crystal to provide an optical coupler. The electro-optic crystal is for example a single crystal of a tetragonal phosphate.

Abstract: An order wire system which can be used during installation and maintenance of an optical fiber communication system comprises an optical fiber order wire to which engineers can connect at remote sites communication sets each of which includes a microphone and earphone allowing the engineers to communicate with each other. Full duplex and multi-party operation can be achieved with the sets according to the invention and, because the signals are regenerated, the range of operation is considerable. Both analog and digital communication is contemplated and different specific circuits are proposed. In a typical analog configuration, the microphone output is fed to first and second frequency modulators operating respectively at first f.sub.1 and second f.sub.2 center frequencies. The outputs of the modulators are summed and passed to a laser driver and laser which is optically coupled both to the upstream and the downstream side of the order wire.

Abstract: In the formation of a splice between two optical fibers, the splice loss is determined by locally supplying an optical signal to each fiber, in a direction towards the end to be spliced, and measuring the signal level at the end of the fiber before making the splice, and using a symmetric detector to measure in one of the fibers the signal level passing in one direction towards the splice and in the opposite direction after passing through the splice, the splice loss being calculated from differences between the measurements. Alternative forms of symmetric detector, which is substantially equally responsive to optical signals in either direction in a fiber, are also described.

Abstract: An attenuator for an optical fiber has a tapered screw around which the fiber is looped, the fiber engaging within the screw thread. The fiber is held fixed in position by a spring so that as the screw is rotated the radius of curvature of that part of the fiber held against the screw is altered. Light propagating along the fiber is radiated out at the fiber bend, the level of radiation loss depending on the bend radius of curvature. The attentuator elements are mounted within a light-tight box with the fiber terminating at optical connector components mounted within a wall of the housing. The connector components enable rapid insertion of the attenuator into an optical transmission line to provide an accurate reproducible level of attenuation.

Abstract: A battery powered portable test instrument for detecting whether light is propagating in an optical fiber has a jaw into which the fiber is placed, the jaw being closable to press a section of the fiber into a bend having predetermined radius of curvature. If light is propagating through the fiber it is scattered and detected in a detection circuit. If the detected light is greater than the predetermined threshold, an indicator circuit is energized.