Abstract: An integrated optic device includes a waveguide which is curved and includes a section at the bend which is capable of supporting more than one waveguide mode at the opearting frequency. This enables bend angles of greater than 5.degree. be to accommodated without excessive power losses.

Abstract: In a head-up display system of the kind utilizing a holographic combiner (17) constructed to operate at a relatively large off-axis angle and an aberration compensating optical arrangement (19) in the path between an object surface (21) at which display data originates and the combiner, the light rays from the optical arrangement are redirected upwardly onto the combiner via an arrangement (25) comprising an upper optical surface (29) having both light-reflective and light-transmissive properties and a lower fully reflective optical surface (27), the two surfaces defining a space (S) forwardly tapering in the direction of ray propagation from the object surface. In operation, rays from the object surface are reflected first at the lower surface and then reflected, in part, at the upper surface back to the lower surface where they are again reflected to the upper surface for transmission therethrough to the combiner for reflection thereby to an observer.

Abstract: A helmet supported optical system which provides an eye of a wearer (11 or 49) of a helmet (7 or 35) with a direct view of the scene forward of the wearer (11 or 49) on which is superimposed collimated optical imagery. The system comprises: an eyepiece (1 or 47a, 47b); means (5 or 37a, 37b, 39a, 39b, 41a, 41b, 43a, 43b) operable to develop a bright data representation at a plane (31or 44a, 44b) substantially congruent with the principal focal plane of an element (21 or 46a, 46b) of the eyepiece (1 or 47a, 47b); and, disposed between the means (5 or 37a, 37b, 39a, 39b, 41a, 41b, 43a, 43b) operable and the eyepiece (1or 47a, 47b), a body (3 or 45a, 45b) of light refractive material.

Abstract: A thin film optical waveguide made of a polymeric waveguiding film supported on a substrate, the film being made of a homopolymer of vinylpyridine or of a derivative or vinylpyridine in which the pyridine heterocyclic nucleus is substituted. Alternatively, a copolymer containing a major proportion of vinlypyridine, or of said derivative thereof, may be used in the film. A layer of a material having a lower refractive index may cover the film. The polymer may be modified to increase its capacity for refractive index variation in response to an electric field, by inclusion in the structure of the polymer of at least one optically nonlinear moiety. The polymer may also include cross-linking. The thin film optical waveguide may incorporate a laser dye in the film, for use with laser devices.

Abstract: In order to correct the swathe related banding effect often seen on swathe-scanned imagers a vertical smoothing function separates out artifact detail from the idealized image and derives, from this, proportional corrections for each channel within a swathe. In cases where the artifact varies from swathe to swathe a second algorithm is used to obtain correction values for each line of the image.

Abstract: An infra-red imaging system is operable selectively in wide and narrow field of view modes. Radiation from the object is imaged onto an infra-red CCD staring focal plane array (SFPA) which provides an output representing the image. In the narrow field of view mode, operative on detection of a particular target by target detection electronics, the image is not scanned but is made to follow any movement of the target, and the SFPA stares at the target to build up an image. In the wide field of view mode, the same SFPA is used to provide the image, but the image is scanned along a swath. Smearing of the image is minimized by driving the IRCCD array such that the image-bearing charge is passed down the array from element to element at a speed equal to the scanning speed, so that the output signal from the end element represents the intensity of radiation from a given portion of the object time-integrated by all the elements of the array in succession.

Abstract: An optical in-line filter comprises a first waveguide whose output end is coupled to a second, narrower waveguide such that light from the first waveguide of a predetermined waveband or wavebands only is passed to the second waveguide light of other wavebands emerging elsewhere from the open end of the first waveguide.

Abstract: Catadioptric optical systems are generally arranged to view a fixed large field of view. Apparatus for steering a field of view includes a pair of Risley prisms, which are disc shaped prisms having a generally shallow wedge like side cross-section, arranged in the path of the incoming radiation. The prisms are rotatable with respect to each other and to the optical axis of the system so as to steer the field of view.By utilizing such steering in a dual waveband system then a system having two fields of view and two magnifications may be achieved in which an image over a smaller field of view but of high magnification may be steered within a larger image of large field of view but low magnification.

Abstract: An equipment housing assembly includes: an equipment housing (11); a rack (13) for supporting the housing (11); and two spaced hold-down devices (17a, 17b) each comprising two co-operating separable parts (19a, 19b) secured respectively to the rear (21) of the housing (11) and the rack (13). The two parts (19a, 19b) of each device (17a, 17b) have co-operating parallel inclined planar surfaces (23a, 23b) angled to provide a hold-down force (H), and one part (19b) of each device is spring loaded to accommodate manufacturing variations in the front-to-back dimensions of the housing (11) and the rack (13).

Abstract: A thermal imager including a cryogenically cooled detector element array and a scanning element has an optical system with a field of view limited by a field stop (2). A retroreflective region (6) is provided on part of the field stop to act as a temperature reference by allowing the detector array to "look at" itself. A second, different temperature reference (5) is provided on another part of the field stop and the two references are used to equalize and adjust the output characteristics of the elements in the detector array.

Abstract: A lens system for imaging infra-red radiation comprises two elements, one of Zinc Selenide and the other of either Zinc Sulfide or Cesium Bromide (5). Lens configurations are shown which allow imaging at a common image plane over at least both the 3-5 .mu.m and 8-12 .mu.m optical wavebands.

Abstract: An imaging system, which improves the optical revolution and reduces optical alias of a solid state imager comprises a lens and a modulating element, which alters incident radiation in such a manner as to displace the image by fractions of a pixel between adjacent fields by either mechanically shifting the elements or by electro-optic variations of refractive index. A processing system is also provided, in which alternate fields are interlaced and output to a monitor. The modulator is arranged in a demountable manner, so that it can be "bolted on" as an additional attachment to a standard camera. The processing system is attached via the original CCD output terminal.

Abstract: A sensor apparatus for detecting sludge in a tank e.g. an oil storage tank, wherein sonar tarnsmission and reception is effected by a transducer (29) whose acoustic center is coincident with the center of curvature of a liquid filled part spherical sonar dome part (15) of a housing (13) for the apparatus. The acoustic pressure waves consequently pass through the dome part of the housing in a direction normal to its surfaces thus minimizing velocity, amplitude and phase changes of the waves as they pass to and from the transducer, and avoiding blind spots in the area monitoried by sensor apparatus. Preferably, the apparatus further includes an arrangement (31, 33, 35, 37) within the housing for angularly moving the transducer (29) about two orthogonal axes which intersect at said center of curvature.

Abstract: A helmet display system including a display arrangement (5) located between a helmet body (1) and a helmet visor (3). The display arrangement (5) includes right and left collimating eyepieces (7,9) and a projector (11) which in operation projects bright data for reflection by the eyepieces (7,9) to respective right and left eye positions (13,15). The user 17 of the helment display system is therefore presented with a display of bright data superimposed on the view of the distant scene. Each eyepiece (7,9) is supported at a respective one of two ports (27,29) of a housing arrangement (31) containing light paths leading from a bright data source (33) of the projector (11) to the eyepieces (7,9) by way of an optical system (35) of the projector (11) including a Petzval relay lens (55,57) and reflective elements (37,45,47,49,51,53). At the right port (27) there is a clear light transmissive portion (34) which is contiguous with the right eyepiece (7).

Abstract: A display device for use as an attitude display in an aircraft comprising a circular array (5) of selectively activatable display elements, the elements being disposed in equally angularly spaced radially extending lines, each line having the same number of elements with corresponding elements in the different lines at the same radial distance from the center of the array (5); and a controller (3) for selectively activating said display elements in accordance with aircraft attitude whereby the selected elements form a visible pattern indicative of the aircraft attitude.

Abstract: A video imaging system comprising: a detector with an odd number of elements for the simultaneous scanning of a swath consisting of a corresponding odd number of parallel horizontal image lines; a variable vertical scanning device for causing the detector to scan the image repeatedly over an image frame; and a scan controller arranged to control the variable scanning device to select the scan rate to provide an overlap between adjacent swaths, and selectively to stagger in the vertical direction the starting points of successively scanned frames by a simple fraction, for example 1/2, of the perpendicular distance (.alpha.) between adjacent image lines. The scan controller is capable of effecting either an interlaced scan or a non-interlaced scan without the need to switch mechanical or optical components of the imaging system.

Abstract: An applied magnetic field direction indicating device comprising a magnetic sensor (1) having an omnidirectional characteristic and an output which is non-linearly related to the magnitude of the applied field. The sensor (1) is subjected to two mutually perpendicular sinusoidal magnetic biassing fields of the same frequency and in time quadrature relationship. A characteristic of the output of the sensor (1) is indicative of the direction of the applied field.

Abstract: A night vision gunsight providing an intensified image of an external scene and an image of an illuminated reticle (13,88) superimposed on the user's (14) direct view of the external scene through the sight. The sight utilizes an eyepiece (39) through which the user (14) views the external scene directly and which also incorporates an internal curved surface (57) possessing both light reflecting and light transmitting properties which serves as a collimating reflector for light rays from an image intensifier (31) viewing the external scene. Light from the illuminated reticle (13,88) may also be collimated and reflected to the user's eye (14) by the curved surface (57) in the eyepiece (39), or alternatively by a similar surface (22) incorporated in an optical element (21,23) in the user's (14) line of sight through the eyepiece (39).

Abstract: Scanning imagers often comprise a plurality of detector elements which may be scanned in swathes to produce an image. To match the offsets or sensitivities of such elements the mean values of the channels adjacent each swathe boundary are compared, and an error signal produced which is fed back to equalize the values across each boundary. Proportionally smaller corrections are applied to the intermediate channels in each swathe. In this way the swathing or banding effect often associated with such imagers is much reduced.

Abstract: An optical projector (11) for a two-color head-up display wherein light of a first color from a first data source (15) passes through a first lens arrangement (23) into a first wedge-shaped body (27) wherein the light is, in turn, internally reflected at first and second angled faces (35 and 33) of the body and then exits the body at the first face (35) to pass via a second lens arrangement (25) to the system combiner (13) in a direction at an angle to that which light enters the body, and light of a second color from a second data source (37) passes through a third lens arrangement (41) into a second wedge-shaped body (43) wherein the light is reflected at one (49) of first and second angled faces (47, 49) of the second body and then exits the body at the other angled face (47), which is adjacent the second angled face of the first body, and then passes through the first body to the second lens arrangement, there being a dichroic coating at the interface of the two bodies to effect reflection of light of the