Abstract: An arrangement has a WDT (Wavelength-Dependent Tap) coupled in an OCS (Optical Communication System) and an OPM (Optical Performance Monitoring) function coupled to the WDT. The WDT is adapted to receive from the OCS an input optical signal having noise and channels at respective channel wavelengths. The WDT couples to an output some of the input optical signal at the channel wavelengths and most of a noise power at wavelengths between the channel wavelengths, and couples a remaining portion of the input optical signal back into the optical communication system. The optical performance monitoring function determines a power characteristic of the input optical signal as a function of a power from the output. The power characteristic may be an OSNR (Optical Signal-to-Noise Ratio) determined as a function of a signal power and a noise power of the output optical signal.

Abstract: An optical amplifier system and controller and a method for automatically controlling the usable signal power of an optical amplifier are provided. The method differentiates between the total optical power that includes the amplified spontaneous emission (ASE), and the useful amplified optical signal power at the output of the amplifier. The optical amplifier system comprises an optical amplifier, a first and a second photodetector operable to measure the power of the input and output signals of the optical amplifier and an amplification controller with a control input. The amplification controller is operable to compensate for the ASE power when operating in automatic signal power control mode.

Abstract: An optical amplification apparatus is provided comprising a plurality of fiber amplification media segments which are concatenated in series wherein subsequent to each fiber amplification media segment one or more wavelengths is dropped so as to exploit a gain versus fiber amplification media physical length characteristic. By exploiting the gain versus fiber amplification media physical length characteristic in such a manner it is possible to achieve a substantially flat gain response for a multi-wavelength output of the optical amplification apparatus. Some embodiments of the invention combine noise suppression and additional gain flattening on one or more wavelengths. Embodiments of the optical amplification apparatus can be used in red-band wavelength range applications of coarse wavelength division multiplexing (CWDM). Some embodiments of the invention also provide that the optical amplification apparatus can be used as a hybrid dense wavelength division multiplexing (DWDM) and CWDM optical amplifier.

Abstract: An optical amplifier system and controller and a method for automatically controlling the usable signal power of an optical amplifier are provided. The method differentiates between the total optical power that includes the amplified spontaneous emission (ASE), and the useful amplified optical signal power at the output of the amplifier. The optical amplifier system comprises an optical amplifier, a first and a second photodetector operable to measure the power of the input and output signals of the optical amplifier and an amplification controller with a control input. The amplification controller is operable to compensate for the ASE power when operating in automatic signal power control mode.

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: A fiber optic coupler has a cylindrical rod protruding along the apex of an angled block. An optical waveguide is mounted to extend around part of the circumferential of the rod. A transparent body is located on the side of the fiber remote from the rod, and the rod and the body are biased together to bend the fiber around the rod surface and to form an intimate contact between the transparent body and the curved part of the fiber. A light input or output device is positioned to direct light at or receive light from the curved fiber part through the transparent body.

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: Light reflected at an optical fiber connector is monitored to test the connector. Light entering an optical fiber via the connector under test is attenuated in the fiber to prevent undesired reflections.

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.

Abstract: The chromatic dispersion of an optical fiber such as a 10 to 50 km length of single mode fiber is measured by launching into the fiber the outputs of at least three commonly modulated semiconductor lasers having output wavelengths close to a region of minimum chromatic dispersion of the fiber. At a remote end of the fiber the relative phases of the signals from the three lasers are determined and a chromatic dispersion profile of the fiber is derived from the measured relative phases and the output wavelenghts of the lasers by assuming a parabolic relationship between signal propagation times and wavelength. The profile can be determined by defferentiating a parabolic function fitted to the three date points derived using said three lasers or by directly generating a linear relationship between chromatic dispersion and wavelength on the basis of two values of chromatic dispersion derived from these three data points.