Abstract: In a laser radar system, in which pulses from a laser are focused by a telescope onto a target, the back-scattered radiation being deflected by polarizing beam splitter onto a detector in conjunction with a reference beam, the reference beam being produced from pulses derived from the pulse laser by the beam splitter, the pulses making repeated journeys around a cavity and a proportion of the pulse being emitted each time so that each input pulse produces a multiplicity of output pulses to form the reference beam, thereby avoiding the need for a separate laser for the reference beam.

Abstract: Fault location apparatus is disclosed for use in an optical signal transmission network which comprises a main optical fibre having a plurality of branch fibres, and in which each final branch fibre of a chain of branches ends in a terminal unit. The fault location apparatus comprises OTDR equipment connected to the network so as to transmit an output signal through the main fibre and the branch fibres, and a filter incorporated in each of the final branch fibres. The filter is capable of reflecting back towards the OTDR equipment at least one wavelength in the OTDR band, but not traffic wavelengths. The OTDR equipment is operative to make measurements on the mirror or "virtual" image of the path from the terminal unit incorporating the filter returning a signal to the equipment.

Abstract: A changeover device provides for contactless interchange of power between an r.f. source such as a transmitter Tx.sub.1 and two loads, such as an aerial 2 and a test load 3. The device may be used in a changeover system for exchanging main and standby transmitters in the event of failure of the main transmitter between the aerial and a test load, or for connecting transmitters in parallel in such a way as to leave them well matched in the event of failure of one while permitting half power operation from the surviving transmitter.

Abstract: A variable area convergent-divergent nozzle for use as an attitude control thruster on a VTOL aircraft is formed by a curved wall forming a chamber a convergent section a throat section and a divergent section and a pair of parallel side plates, one of the side plates being movable to alter the area of the nozzle.

Abstract: A reflective liquid crystal display device includes a ferroelectric liquid crystal cell, a first polarizer through which light from a light source passes before passing through the cell, a second polarizer through which the light passes after passing through the cell, and a reflective layer which reflects the light back through the second polarizer, the cell and the first polarizer, in that order, for viewing by an observer. In order to obtain a bright image, the first and second polarizers are orientated with their directions of polarization at angles of .alpha. and .beta., respectively, relative to the alignment direction, the value of .alpha.+.beta. being determined from ##EQU1## where the optic axes in the two switching states of the liquid crystal material are at angles of +.theta..sub.c, and -.theta..sub.c, respectively, to the alignment direction wherein angle .theta..sub.c is in a range wherein .theta..sub.c <22.5.degree..

Abstract: A helmet mounted display system comprising an eyepiece (3) through which a wearer of the helmet directly views a forward scene (13). The eyepiece also serves to combine an intensified image of the forward scene with the wearer's direct view of the scene. The intensified image is produced by an optical arrangement including an image intensifier (6) from which light is passed to the eyepiece via a prism (2). The prism serves to compensate for orientation of the intensified image in other parts of the optical arrangement so that the intensified image is in the same orientation as the wearer's direct view of the forward scene. In addition the prism allows the various components in the system light path to conform to the profile of the helmet thereby making the helmet more comfortable for a wearer.

Abstract: A system for generating, in an aircraft, a warning signal whenever the aircraft is on a potentially hazardous course with respect to the terrain and obstacles thereon imminently to be overflown. The system involves the computation of pull-up trajectories which the aircraft could carry out at a reference point (RP) on the current aircraft flight path (FP) forward of the aircraft current position (CP), taking account of uncertainties of at least aircraft position, which trajectories define collectively a region moving notionally forwardly of the aircraft at a spacing ahead of the aircraft which is a function of aircraft velocity and acceleration and aircraft dynamic response to pilot demands and pilot reaction time, and therefore constitutes a region which the aircraft can imminently overfly. A warning signal is produced if any point on the trajectories has a predetermined relationship with data stored in a map data storage means containing height data relating to the region defined by the trajectories.

Abstract: A mixer of the commutating type using FETs to switch between the primary of a transformer for an r.f. input and the secondary of a transformer 2 for an i.f. output. The mixer has high linearity and low power consumption of the local oscillator drive because the gate electrodes of the FETs are switched using pulse waveforms from driving transistors.

Abstract: A large number of processor cells 11, the majority of which are standard cells 12 and others special cells 13, are connected to a communication network 14 in the form of several binary trees. The cells 11 are connected at the leaf positions of the binary trees, and the nodes of the binary trees are formed by switching circuits that allow individual cells to control the formation of signal paths through the nodes. In operation, cells may be in a waiting state, a free state, a calling state, searching state, a communicating state, or an internal operation state. Cells 12 in the free state transmit a free signal into the network 14. Cells 12 or 13 in a searching state transmit a searching signal into the network 14 where, on meeting a free signal at a node, a route is formed from the searching state cell to a free state cell. A calling state cell 12 establishes, with a calling signal, a route through the network 14 to another cell identified by destination information in the calling signal.

Abstract: An optical device comprising an optical waveguide (13) on a substrate (11) which over part of its length forms one of a stack (15) of coupled optical waveguide sections of the same length, the stack being of a length such that a light wave of predetermined frequency propagating along the waveguide (13) to enter the stack (15) at one end thereof produces light waves at the other end of the stack which are substantially in phase adjacent each waveguide section. The device finds particular application for coupling light from a substrate waveguide into another waveguide, e.g. an optical fibre (27), off the substrate (11).

Abstract: An optical filter comprises a light waveguide and an electrode structure located adjacent the waveguide. The electrode structure comprises a first ladder arrangement having a plurality of rungs disposed along the length of the waveguide and spaced apart from each other, each rung of the first ladder arrangement comprising a plurality of interdigitated electrode pairs. A second ladder arrangement has a plurality of rungs interleaved with the rungs of the first ladder arrangement and spaced apart from each other by a second pitch spacing that is different from the first pitch spacing.

Abstract: A high voltage pulse generator for providing a high voltage pulse across a dielectric switch comprises a main high voltage pulse generator, an energy storing pulse forming line connected at one end to the main pulse generator and connected at the other end to an electrode of the dielectric switch, a high voltage trigger pulse generator and a ferrite loaded shock line. The ferrite loaded shock line, preferably located within the pulse forming line (or within a line on the output side of the switch), is connected at one end to the trigger pulse generator via a coaxial inner conductor and connected at the other end to a trigger electrode located within the dielectric switch. The pulse forming line enables a high voltage pulse to build up on the electrode of the dielectric switch, the trigger pulse having its edges sharpened by the shock line and triggering a discharge across a dielectric to an output line. This produces an extremely fast, high voltage pulse, e.g., for radar transmitter.

Abstract: A bare die testing apparatus comprising a multilayer interconnection structure 10 having a testing station 11 for testing the bare die 20, testing circuits and components 12 arranged in said structure adjacent the testing station 11, said testing station 11 having a plurality of microbumps 17 of conductive material soldered onto wettable metallization pads 18 located on interconnection trace terminations of the interconnection structure, said terminations being connected through the interconnections of the multilayer structure to said testing circuits and components 12. The microbumps 17 are distributed in a pattern corresponding to the pattern of contact pads 19 on a bare die 20 to be tested.

Abstract: An arrangement for protecting an integrated circuit device (11) against latch up during a nuclear event comprising a capacitance (15) and a switch (17) connected in parallel across the power supply lines (13) of the device. When the power supply lines are connected to a power supply (19) the capacitance stores energy sufficient to supply necessary operating currents to the device during its normal operation. The switch is arranged so that, under a transient gamma pulse incident thereon during a nuclear event, its impedance is set to a low value at such a rate that the energy stored by the capacitance is discharged through the switch and the voltage applied to the device via the power supply lines is pulled down to such a level and at such a rate as to prevent transient gamma pulse induced latch-up in the device.

Abstract: This invention provides imaging apparatus in which an image is scanned over an array of sensing elements 2, the outputs of which form a plurality of channels. Signal processing means 6 adds a noise signal to at least some of the channels to more closely match the signal to noise ratio of the channels and reduce linear noise structures, to which the eyebrain is particularly sensitive, in the output signal 10 of the processing means.

Abstract: In order to measure the relative proportions of oil, water and gas passing along a pipe, the pipe is passed through the coils of a number of coil resonators having different resonant frequencies. By measuring changes in the resonant frequencies of the coil resonators the proportions of oil, water and gas in the flow through the pipe can be calculated.

Abstract: Directional couplers 7.sup.1 -7.sup.20 are used to couple power from r.f. power amplifier modules 5.sup.1 -5.sup.20 to a transmission line 6 or other type of resonator, from which it is withdrawn by directional coupler 8. The power withdrawn from the continuous transmission line, which is an integral number of wavelengths at the operating frequency of the modules in length, is less than the power circulating around the transmission line 6. The balance load may be removed to enable the output load to be combined with the output of another r.f. power amplifier operating a different frequency so that e.g. sound and vision signals can be combined at an aerial and, in the latter case, means may be provided for improving the resonance of the main loop 6.

Abstract: An optical analysis or processing system for use, for example, in the analysis of microscopic spots of material by their effect on a very fine polarized beam of light (e.g., FPIA). For multiple "spot" analysis the spot samples are disposed on a substrate in predetermined relation with an optical pattern, bars, chevrons, etc. The substrate is mounted in the path of the fixed and focused beam with three degrees of freedom of movement. A video camera records the optical pattern very accurately and controls the substrate mounting to position a selected sample spot at the beam focus. Multiple and rapid sample analysis can thus be performed.

Abstract: An exhaust gas particle sensor has an inlet tube and a sensing region having different cross sections and linked by a transition region including a number of baffles arranged so that the time taken for gas to travel from the inlet tube to the sensing region is substantially independent of the position of the gas across the inlet tube. The sensor operates by measuring the opacity of the exhaust gas using a light beam which passes in and out of the sensing region through windows, the exhaust gas being prevented from impinging on each window by a double air curtain.

Abstract: A circuit 8 reduces noise on a video signal from an imager 6 for a TV monitor 7. The noise reduction circuit includes a video frame store connected so as to integrate the corresponding picture elements of several frames in order to reduce noise. The amount of noise reduction applied depends on the noise on the incoming video signal but, whereas this has been assessed previously by comparing differences between incoming frames, in the invention it is assessed from the gain, information on which is encoded on the video signal. The gain of the imager gives a more accurate reflection of video noise than does comparing successive frames, since movements on the image can produce the same effect as noise fluctuations.