Abstract: A multi-host subscriber loop (10, 70) includes N central office terminals (22-26, 78) coupled to a local exchange (20, 76), where one of the N central office terminals (22, 110) is directly coupled to all other central office terminals (24-26, 112-114). M remote terminals (40-46, 100-104) are coupled to a plurality of telephone service subscribers. A single network facility (16, 76) is coupled between the M remote terminals and N central office terminals. The single network facility concentrates subscriber traffic, control information and associated signaling onto one message structure (60, 140). Messages in this message structure are transmitted between the remote terminals and central office terminals. The message structure includes a plurality of time slots, a first predetermined number of the time slots being allocated to N control channels, at least one time slot being allocated to associated signaling, and remaining time slots being allocated to subscriber traffic.

Abstract: A multi-host subscriber loop (10, 70) includes N central office terminals (22-26, 78) coupled to a local exchange (20, 76), where one of the N central office terminals (22, 110) is directly coupled to all other central office terminals (24-26, 112-114). M remote terminals (40-46, 100-104) are coupled to a plurality of telephone service subscribers. A single network facility (16, 76) is coupled between the M remote terminals and N central office terminals. The single network facility concentrates subscriber traffic, control information and associated signaling onto one message structure (60, 140). Messages in this message structure are transmitted between the remote terminals and central office terminals. The message structure includes a plurality of time slots, a first predetermined number of the time slots being allocated to N control channels, at least one time slot being allocated to associated signaling, and remaining time slots being allocated to subscriber traffic.

Abstract: A method of forming low loss splices between single-mode optical fiber ends involves taking prepared fiber ends and aligning the one with the other by inserting them into opposite ends of the bore of a ferrule, and fusing the fiber ends together by applying thermal energy thereto by means of an aperture in the wall of the ferrule. Splices prepared in this way have losses of less than 0.5 dB. The use of a precisely dimensioned ceramic ferrule enables the use of splicing apparatus which does not incorporate means for 3-dimensional micromanipulation.

Abstract: Apparatus for measuring the endface angle of a cleaved optical fibre (1) includes a light source (3) for injecting optical energy into that end (1a) of the optical fibre (1) opposite to that whose endface angle is to be measured. Means are provided for tapping optical energy passing along the optical fiber (1) in both directions. Photodetectors (5,6) measure the signal strength of the optical energy tapped from the optical fibre (1) in both directions. The ratio of these measured signal strengths is compared with a known relationship between endface angles and the ratio of said measured signals to provide a measure of the endface angle.

Abstract: An optical space switch comprising an optical output; three optical deflection stages each having a twisted-nematic liquid crystal polarization rotator responsive to a respective bi-state control signal and a calcite crystal deflection means for selectively deflecting optical signals according to their polarization. The deflection stages are arranged serially to define eight distinct source locations from where an optical signal is selectively deflectable successively by the deflection stages to the optical output. A distinct combination of states of the three control signals corresponds to each location. Each input is formed from an array of fibers so as to be capable of launching an optical signal which is spatially modulated transverse to the signal propagation direction. Each deflection stage preserves the spatial integrity of the deflected optical signals.

Abstract: An optical switch includes a series of 2(n-1) macro-cells each having a variable polarization rotating cell and a birefringent cell. Each rotating cell is divided into individually addressable and switchable sub-cells. Some of the macro-cells have birefringent cells having a first orientation. In these macro-cells, sub-cells switch light passing through position Pi to either position Pi or Pi+1 of the rotating cell of the next macro-cell in the series. Other macro-cells have birefringent cells having a second orientation. In these macro-cells, the sub-cells switch light passing through position Pi to either position Pi or Pi-1 of the rotating cell of the next macro-cell in the series. The sub-cells of the macro-cells are positioned such that light from any one of several inputs is switchable independently to any one of several outputs.

Abstract: A liquid crystal device (5) having smectic phase liquid crystal material in two transparent states of differing molecular orientation, each state presenting a different refractive index to polarized light transmitted therethrough, may be utilized to perform various optical functions. For example, switchable waveguides (6, 7) a ring resonator or a diffraction grating may be produced by appropriate arrangement of the material in the two states.

Abstract: An optical device comprises an optical waveguide, such as a single mode optical fiber (11), underlying a first layer (2) of material, such as a thin film, which has a refractive index higher than the refractive index of the waveguide (11) and which forms a planar waveguide capable of supporting and guiding at least one propagation mode of a higher order than, but matching the phase velocity of, the propagation mode or modes in the underlying waveguide. A reflection diffraction grating (4) is provided on or adjacent to the surface of the first layer (2) remote from the waveguide (11). The arrangement is such that an optical signal which is coupled from the waveguide (11) into the first layer (2) is reflected by the reflection diffraction grating (4) and is coupled back into the waveguide.

Abstract: An optical coupler device comprises a waveguide structure underlying a first layer of material which has a refractive index higher than the effective refractive index of the waveguide structure and which is capable of supporting propagation modes of a higher order than, but matching the phase velocity of, the propagation mode or modes in the underlying waveguide structure, said layer thereby forming a wave guiding structure.

Abstract: A micro-optic lens is formed by making a lens element (20) having a length less than the required lens length. Adhesive (22) is attached to the rear of the lens element and a glass plate (21) attached to the adhesive. An optical fibre (26) is located against the plate (b 21), light is transmitted along the fibre, the beam emerging from the element (20) is sensed and the axial position of the plate (21) adjusted until the beam is sensed to be collimated. The adhesive (22) is then cured.

Abstract: A selective filtering device for use in optical communications systems takes the form of a transversely coupled Fabry-Perot interferometer. One described embodiment comprises a first length of monomode optical fiber transversely coupled to a second fiber in a coupling region. One end of each fiber at opposite respective ends of the coupling region is provided with a suitable highly reflective surface, or example, an evaporated gold/aluminum deposit. In operation, a light input may be modified by the resonant cavity behavior of the Fabry-Perot cavity formed between the mirrored ends to provide filtered or enhanced outputs. The outputs may be further modified by alternative or additional light input via the ends of the fibers.

Abstract: A Fabry-Perot interferometer comprises a single crystal silicon substrate (1) with an integrally formed diaphragm (6) supported between walls (2-5). A glass superstrate (14) is mounted adjacent the substrate (1) with a spacer (13) sandwiched therebetween. Facing surfaces (12, 16) of the diaphragm (6) and superstrate (14) are polished and suitably coated to define reflective surfaces and the position of the diaphragm may be altered to vary the response of the interferometer.

Abstract: An optical fibre termination is machined to provide a locating surface having improved concentricity with a therein-mounted optical fibre by more accurately locating the optical fibre at the rotational center of a machining tool. Light transmitted through the optical fibre is monitored while the termination is adjusted, in response to such monitoring, to accurately coincide with the rotational machining axis.

Abstract: An optical fibre connector to connect two optical fibres comprises a ferrule secured to each fibre end, and a clamping sleeve of shape memory effect metal to align and clamp the ferrules. The shape memory effect metal is selected and trained to expand on heating above its transformation temperature. The bore of the clamping sleeve is arranged to make an interference fit with the ferrules when below the transformation temperature, and a clearance fit when above the transformation temperature. An elastic titanium alloy compression sleeve surrounding the clamping sleeve provides for long-term integrity of the connector and reinforces the clamping action of the clamping sleeve when below its transformation temperature.