Abstract: Apparatus and method for 3R regeneration of optical digital signals in which a modulator, preferably an electroabsorption modulator, is driven by an electrical clock synchronised with optical input pulses (preferably by a phase-locked-loop controller) and is located downstream of a 2R regenerator so as to receive its output.

Abstract: An optical interconnect is formed form a series of coaxially aligned lenses. The lenses are spaced apart along a planar substrate and form repeated images of an optical array at the input to the interconnect. Outputs ports are located at different points along the interconnect. Each of the pair of lenses enclosing one of the repeated images is formed as a single physically integral member. This member may take the form of a transparent rod having spherical end surfaces. Each of the spherical end surfaces then provides one of the pair of lenses.

Abstract: A Sagnac interferometer (19) is defined by four port, 50:50 optical fiber coupler (20), two output ports (38, 40) of which are coupled together by a non-linear semiconductor laser amplifier (3) in series between a pair of optical fibres (22, 24). The coupling losses between the ports (38, 40) and the amplifier (30) are different. An input pulse coupled to port (34) of the coupler (20) is split into two portions which counterpropagate from one of the output ports (38, 40) to the other. The portions return to the coupler (20) with an intensity dependent relative phase shift. This provides switching of an input pulse at the input port (34) between the input ports (34 and 36) dependant on the intensity of the input pulse. The device can provide intensity dependent switching at optical power levels of less than 250 .mu.W.

Abstract: A neural network has inputs formed by square array of optical modulators M.sub.ij and outputs by optical detectors D.sub.ij coupled to threshold comparators. A holographic plate includes a spatial modulator whose elements are controlled by a controller to form an array of optical beams from a coherent optical source. Each optical beam optically interconnects a modulator M.sub.ij with a respective detector D.sub.ij. The weight values of the neural network are provided by the intensities of the optical beams. This obviates the need for an optical weighting mask between an array of light emitting diodes and a detector array allowing a higher density of lower power consumption components and reprogrammability of the network.

Abstract: An optical signal regenerator has a semiconductor laser in a resonant cavity defined by a mirror and a semireflective facet of the laser to form a resonant, non-linear, optical amplifier. A polarization beam splitter allows resonance in one polarization mode only. A clock signal generator provides clock signals in the resonant polarization mode of a power just below the optical power bistable threshold of the amplifier. An information signal coupled to the laser by a lens and the beam splitter is in a non-resonant mode of the amplifier and will give rise to a regenerator output by triggering the bistability. Because the information signal is in a non-resonant mode its wavelength need not be controlled to lie near a resonance peak of the amplifier so reducing control requirements.

Abstract: An optical signal regenerator includes an optical coupler having a first input for an optical information signal, a second input for optical clock pulses and an output for a combined signal. A resonant laser amplifier is located downstream of the output of the coupler and arranged to receive the combined signal and, in use, output a regenerated optical information signal. The bias current applied to the laser amplifier, in use, biases the amplifier to a level below its lasing threshold, and the power of the optical clock pulses is just below the bistable threshold of the amplilfier, so that, when an optical information signal is fed into the first input during the application of an optical clock pulse to the second input, the bistable threshold of the amplifier is exceeded causing a sudden jump in the power of the optical output of the amplifier to provide a regenerated optical information signal.

Abstract: An optically controlled selector comprises an optical coupler having a first input for an optical input signal, a second input for an optical control signal and an output for a combined signal, and a resonant cavity downstream of the output of the coupler and arranged to receive the combined signal. The resonant cavity contains an optically non-linear material so that changes in the power of the optical control signal result in changes in the resonant frequency of the cavity. In use, the power of the optical control signal controls transmission or suppression of the optical input signal through the optical cavity. Such a selector acts as a simple switch or to select one from a number of optical signals of different wavelength. Preferably the optical material is active and the optical cavity formed by semiconductor laser amplifier.

Abstract: An optical communication system is disclosed comprising a transmission assembly including a semiconductor laser amplifier. The laser amplifier superimposes onto an amplitude modulated signal a phase modulation corresponding to the amplitude modulation. The optical communication system may further include a separation device for filtering out the amplitude modulation. A receiving assembly is provided for detecting the phase modulation of a transmitted signal.

Abstract: A signal level stabilizer includes two amplifier stages, each stage having a respective feed-back loop to control its gain. The gains of the amplifiers are varied in response to variations in the level of the input signal to give a substantially constant output signal. At low levels of the input signal the gain of one of the amplifiers only is varied in response to variations of the input signal and at high levels of the input signal the gain of the other amplifier is varied. The amplifiers may be part of a repeater in an optical communications linkage and one of the amplifiers may then be a photodiode and the other a power amplifier.