Abstract: The present invention relates to communication, in particular to communication involving analogue-like signals that are multiplexed together. There is provided a method of communicating with a plurality of devices, each of which of which provides a signal whose amplitude varies in an analogue fashion, the method including the steps of: temporally interleaving the signals from the devices so as to form a multiplexed signal having a plurality of sequential pulses, which pulses can, in an analogue fashion, each have an amplitude within a continuous range, each pulse originating from a respective device, and each pulse having a plurality of temporal portions; and, forming a synchronisation signal within the multiplexed signal for demultiplexing the multiplexed signal, the synchronisation signal being formed by reducing the amplitude within a temporal portion of at least some of the pulses.

Abstract: The present invention relates to communication, in particular to communication involving analogue-like signals that are multiplexed together. There is provided a method of communicating with a plurality of devices, each of which of which provides a signal whose amplitude varies in an analogue fashion, the method including the steps of: temporally interleaving the signals from the devices so as to form a multiplexed signal having a plurality of sequential pulses, which pulses can, in an analogue fashion, each have an amplitude within a continuous range, each pulse originating from a respective device, and each pulse having a plurality of temporal portions; and, forming a synchronisation signal within the multiplexed signal for demultiplexing the multiplexed signal, the synchronisation signal being formed by reducing the amplitude within a temporal portion of at least some of the pulses.

Abstract: The present invention relates to a communication system having a central station and a plurality of outstations. The central station is configured to execute a compensation procedure for compensating for degradation of data from the outstations, the compensation procedure having a plurality of adjustable characteristics, which characteristics are governed by a parameter set. The central station stores a respective parameter set in respect of each outstation; and, for each outstation, applies the compensation algorithm to data from that outstation using the parameter set associated with that outstation. In an initialization phase, the central station tests a plurality of starting parameter sets on data from a given outstation and selects the set providing the best compensation. The selected set is stored for subsequent compensation of data from that outstation.

Abstract: A tunable optical filter includes an array of optical fibre located within a capillary tube and mounted on a solenoid movable support and positioned in front of a lens and diffration grating. The filter provides simultaneous tuning filtering between fibres. By coupling fibres to a ring laser and fibre to an optical receiver simultaneous tuning of a laser and receiver is possible. The filter finds particular application in passive optical networks.

Abstract: A communications network in which a central switching node (70) has at least two sets of both input ports (52) and output ports (56) coupled to respective sets of transmitters (T.sub.ij) and receivers (R.sub.ij) by passive optical networks (54) and (58) and demultiplexers (52) and multiplexers (59). The transmitters (T.sub.ij) are tunable so that each can be selectively the input ports (52). The receivers (R.sub.ij) are also tunable so the output ports (56) can be selectively coupled to the one or more of the receivers (R.sub.ij). Alternatively, the demultiplexers (55) and multiplexers (59) can be tunable. This devolves some of the switching function outside the central switching node (50) thereby reducing the component count.

Abstract: An optical 1.times.N star coupler has a single mode input fibre (I) and N single mode output fibres (O.sub.1) forming an output fibre assembly. The output fibres (O) are tapered within a former (2) which holds each output fibre (O) so it is positioned substantially identically relative to the remaining output fibres. The input fibre (I) is also tapered such that the fundamental mode field of the input fibre (I) and output fibre assembly are substantially equal. The identical relative positions of the output fibres (O) provides a wavelength independent 1.times.N star coupler.

Abstract: A two way transmission system has a source at one terminal and a fibre loop at the other terminal. Conventional modulation techniques are used at the terminal with the source, whereas at the other terminal modulation is achieved by modulation of the birefringence of the loop.

Abstract: An optical filter includes a volume diffraction grating provided within a waveguide. The grating has a thickness T sufficient such that when an optical beam R is incident on the grating from outside the waveguide, wavelengths at or near the Bragg wavelength for the grating are diffracted and coupled into the waveguide, all but the first order interferences being substantially eliminated, while wavelengths away from the Bragg wavelength pass through the waveguide substantially undiffracted. The grating pitch L may be varied to permit tuning of the filter response.

Abstract: A technique for reducing splice loss between similar or dissimilar optical fibres. Two fibers (10,11) are joined by fusion splicing and the joint region is tapered until the cladding assumes a guiding function. This produces a mode transformer which covers the fundamental mode of one fibre to that of the other with little or negligible loss.

Abstract: An optical fiber laser comprises an optical resonant cavity defined by an optical fiber (1). First and second reflectors (8, 13; 14, 19) are optically coupled with respective ends of the fibre. The first reflector is adapted to reflect radiation at the lasing wavelength and the second reflector to be partially transparent to radiation at the lasing wavelength. Each reflector comprises a directional coupler (8; 14) having first and second pairs of ports. One each of the one pair of ports (11; 16) of each coupler (8; 14) is optically coupled with the cavity (1) while both ports of the other pair (9, 10; 17,18) are coupled with a respective loop of optical fibre (13, 19). The remaining port (12) of one coupler (8) is connected with a source of pumping radiation (6), and the remaining port (15) of the other coupler (14), is available to output laser radiation.

Abstract: A technique for aligning and coupling dielectric optical waveguides comprises threading the end of a waveguide through the central opening of a triad ball connector and forming by fusion a generally spherical glass bead on the end of the waveguide using, for example, an electric arc. The waveguide is then drawn back so that the bead contacts the balls of the triad connector to accurately locate the waveguide. The bead acts as a locating element and also has beneficial focussing properties.

Abstract: A pair of optical fibres which are to be joined are located with their end portions in coupling elements one of which is transparent to light. The coupling elements are located such that the ends of the fibres are in approximate alignment. Light is transmitted along one fibre so that it is received by the fibre in the transparent coupling element. Light which is not coupled into the core of the fibre is sensed by a sensor and the relative position of the fibres is adjusted until the level of sensed light is a minimum. The sensing of the light is carried out at positions spaced angularly about the waveguide so that an indication of the direction of any misalignment is obtained. The coupling elements are then secured in this position. The adjustment of the fibres can be carried out using a linear translation stage and a microprocessor which controls the stage in accordance with signals from the sensor.