Abstract: There is disclosed two helmet systems, each comprising a helmet (11) and, carried by the helmet (11), an optical arrangement (13). In each system, the optical arrangement (13) both provides a collimated display superimposed on the helmet wearer's view of the forward scene through an eyepiece (15 or 50) of the arrangement (13), and senses the angular position of that eye of the helmet wearer looking through the eyepiece (15 or 50) with respect to the helmet axes. The optical arrangement (13) senses such angular position by sensing the position, within a sensing area of a sensor (37 or 72), of the point focus of infra-red radiation, from an infra-red point source (35 or 71A), reflected by the eye, and producing an electrical output representative of this position. In one helmet system the eyepiece (15) is of the open optics type and in the other the eyepiece (50) is of the solid optics type.

Abstract: An integrated optical device including a direction coupler between first and second waveguides whereby to transfer light energy between the first and second waveguides, the directional coupler including a first region in which the first and second waveguides converge towards one another while the electromagnetic field regions associated with the waveguides interact, and a second region in which the first and second waveguides are merged into a single waveguide structure having at least twice the width of the first or second waveguide, the first and second regions being dimensioned to control or eliminate the dependence of the directional coupler upon polarization of light in the waveguides.

Abstract: Pictorial data from a thermal imager is applied on a line to a RAM at which a histogram representing the numerical distribution of pixel values is produced. This is applied to a microprocessor which uses the histogram to produce a transform to control the gain and offset of the data output of the processor. The microprocessor sets a look-up table to apply the transform to the received data, the output of the table being converted to analogue form at an analogue-to-digital converter.

Abstract: A method is described of manufacturing perovskite lead scandium tantalate comprising the pre-reaction of scandium and tantalum oxides at temperatures between 1000.degree. C. and 1400.degree. C. to form scandium tantalate. The scandium tantalate is then reacted with lead oxide to form the desired perovskite phase lead scandium tantalate. In one embodiment there is described a method for the deposition of perovskite lead scandium tantalate films from metal organic precusors. The availability of metal organic precursors allows the deposition of thin films directly from solution or by MOCVD techniques. One particular material, lead scandium tantalate Pb(Sc.sub.0.5 Ta.sub.0.5)O.sub.3, is described. The principal features of the invention are the deposition of scandium and tantalum components from solution or by MOCVD onto the required substrate. These are then prereacted to yield scandium tantalate.

Abstract: The orientation of a helmet is monitored by illuminating the cockpit volume by a moving interference pattern produced by three beams. The sensors detect the varying phase to produce outputs which are compared to determine the orientation of the helmet.

Abstract: A vertical take-off and landing aircraft is configured so as to provide, when landing tail-first with its fuselage (1) in a generally vertical attitude, a touchdown area (21) at the tail of the aircraft at a position offset from a line extending along the length of the fuselage through the centre of gravity (23) of the aircraft such that after the touchdown area contacts a landing surface the aircraft topples under the action of gravity to bring an undercarriage (11, 13) of the aircraft into contact with the landing surface, thereby to attain a stable landed position.

Abstract: An aircraft capture system, e.g. for a radio-controlled pilotless aircraft (19), having at the homing station a boom arrangement (13) mounted for rotation about a vertical hinge axis (A--A) and having appreciable flexibility under forces acting perpendicular to the hinge axis while being substantially inflexible under forces acting parallel to the hinge axis. The flexibility of the boom arrangement cushions the aircraft against shock when an arrester hook (33) deployed from the aircraft engages the boom arrangement via an arrester wire (15) attached to the boom arrangement.

Abstract: A capacitively coupled printed patch (3) as a high efficiency device to couple orthogonally polarized energy between a microstripline (5) and a waveguide (1). Coupling between the microstripline (5) and the patch (3) is achieved by the microstripline terminating in a narrow strip probe (4), the end of which lies close to, but not in contact with, an edge of the patch (3). Two separate probes (4) arranged mutually orthogonally are used to effect independent polarized couplings to produce independent linear orthogonal signals or independent left- and right-handed circularly polarized signals. The microstriplines (5) and patch (3) are supported on a common substrate (8) which extends transversely through the waveguide (1). The waveguide wall has a quarter-wavelength thickness (T) so that its inner edge (10) appears continuous to energy passing through the substrate (8).

Abstract: A smoothing layer is provided between the rough etched sides of a channel in a substrate in which an optical waveguiding material is to be produced. Losses are substantially reduced thereby. For a rectangular or rib waveguide, where the sides of the rib are left rough by etching, a smoothing layer is again provided over the rib. The smoothing layer preferably has a refractive index close to or the same as the materials having surface roughness.

Abstract: An optical phase modulator comprises a body 1 of a matrix material which supports a length of optical fiber 2, the said body including a polymer material having piezoelectric properties and being provided with spaced electrode areas 4 such that the application of an electrical potential between said areas will produce a mechanical strain in the body 1, the said strain affecting the said fiber 2 so as to control phase modulation of light when this is present in the fibre. This can give a device of inexpensive construction which is robust and has high sensitivity.

Abstract: An optical device comprises a heterojunction bipolar transistor which includes a light guiding layer to which the base contact is made. A ridge is included adjacent to the light guiding layer and acts as the emitter or collector of the transistor, the ridge also defining the lateral extent of the light guiding region. Current injected via the base contact controls the electric field in the region of the ridge and hence the refractive index of the layer controlling the passage of light transmitted along it.

Abstract: Analogue signals are converted to digital data by use of a Sigma-Delta modulator including a pair of bandpass filters and a feedback loop including a digital to analogue converter. The tendency of such a circuit to instability is reduced or eliminated by making small variations in the phase of a clock controlling feedback pulses relative to a clock controlling data output pulses. As an alternative, corrections may be made to the feedback pulses by an additional feedback loop providing pulses for correcting the feedback pulses.

Abstract: The engine and other machinery within a marine vessel is mounted on a raft which is relatively flimsy compared with conventional constructions. The raft is supported by electromagnets, the current to which is controlled so as to avoid vibration and flexing which would otherwise take place and so as to reduce transmission of vibration to the hull and other parts of the ship.

Abstract: A thermal imager employs an intermediate field stop (8) which is preferably placed at an intermediate image plane (P) in front of a cryogenically cooled detector (1) mounted on a substrate (2). Radiation gathered by a telescope is directed onto the detector through an aperture (9) in the field stop. The field stop limits the rays which are emitted by the detector and substrate and which are subsequently retro-reflected back to the detector (called narcissus rays).

Abstract: A radar system comprises a radar carrier frequency oscillator for producing a radar carrier signal, a receiver including a mixer for producing Doppler signals, a Doppler filter bank and an alarm circuit, including a series of Doppler bins, having an alarm threshold level. The radar system is provided with a frequency modulator for modulating the radar carrier signal and any interference signal received by the receiver whereby the bandwidth of the frequency modulated interference signal exceeds the bandwidth of a number of Doppler filters in the Doppler filter bank. The alarm circuit may have two threshold levels and may be controlled in dependence upon a predetermined pattern of crossings of the threshold levels.

Abstract: In a communication system having a plurality of base stations for communication with mobile terminals, each station is allocated one of nine communication channels. The allocation is arranged such that adjacent channels are spaced further apart than non-adjacent channels so as to eliminate interference.

Abstract: An arrangement for protecting selected devices of an electronic equipment from radiation, e.g. resulting from a nuclear event, including a timing circuit (13) responsive to the output of a radiation sensing device (11) first to operate a first switch (35a) to isolate a power supply rail for the devices from the power supply to the equipment when the radiation level exceeds a predetermined level, and then to operate a second switch (35b) to ground the supply rail, thereby shunting to ground residual stored energy in devices connected to the rail.

Abstract: A helmet system including a head-up display system wherein the combiner comprises a tuned optical coating (17) carried on the inner surface of a transparent vizor (15) provided on the helmet (13), and light from the display source (27) is directed onto the combiner, for reflection to the helmet wearer's eyes (29), after passing through a body of light refractive material material (25). Light from the display source passes into the body via a cylindrical surface (33), is reflected within the body at a planar surface (35) and exits the body via a convex surface (37). The system provides a high quality collimated display with minimal change of the physical size and aerodynamic performance of the helmet and vizor so as to provide improved fast jet ejection capability.

Abstract: Inertially insensitive optical fibre hydrophones are described, utilizing materials and configurations to obtain acceleration balanced designs suitable for underwater applications where acceleration is a problem. Balancing and/or insensitivity is obtained both in longitudinal and axially perpendicular directions. Acoustic sensitivity of a coil formed by the fibre is maintained by the properties of materials used to provide a rigid former, encapsulant material and secondary material which form the hydrophone.

Abstract: A data display method and apparatus for use in a vehicle, e.g. for use by the pilot of an aircraft, wherein each eye (EL, ER) of the user (23) is presented with a virtual image at infinity of a respective one of two largely identical displays (31L, 31R). By arranging for corresponding elements (33) of the two displays representative of a controller in the vehicle at a position accessible to the user to have a transverse positional disparity the virtual images of the corresponding elements appear to the user to fuse together to form a single image (I2) in a plane of the controller at a finite distance from the user within the vehicle thereby to facilitate operation of the controller by the user. Other corresponding elements (41, 43, 45, 47, 49) of the two displays (31L, 31R) will normally have no such positional disparity so that their virtual images fuse to present an image (I1) at infinity as in known binocular head-up display (HUD) systems.