Abstract: This invention relates to a pattern recognition correlator and method for correlating input data with one or more reference data sets. The input data, which may be for instance digital amplitude modulated optical data, is used to modulate an optical signal to form a phase modulated optical signal. This temporal phase modulated optical signal is then converted into a parallel optical phase signal, preferably through use of an optical delay, and modulated by an optical phase modulator. When there is a correlation between the input data and the reference data the emerging wavefront is plane and can be strongly coupled to a detector. In the absence of correlation the emergent wavefront is not plane and so is not coupled as strongly to the detector. The detector output can therefore be used as an indication of correlation.

Abstract: An apparatus for detecting the presence of one or more images of a known kind in a scene is disclosed which comprises a digital input means and an optical output means. The digital input means comprises a capture means which passes a capture image to a first electronic processing means to produce a scene pattern corresponding to a Fourier Transform of the scene image. This pattern is then digitally combined with one or more reference patterns corresponding to Fourier Transforms of a reference image. The resulting combined patterns are then used to modulate a beam of light which may be focused to perform an inverse Fourier Transform providing correlation information. In a preferred embodiment, the combined pattern is displayed on a spatial light modulator.

Abstract: A vertical cavity surface emitting laser (VCSEL) comprising a one dimensional grating structure configured to act as a waveguide, preferably located at an end surface of the VCSEL, for selectively reflecting more of a first polarisation of light back into the cavity of the VCSEL than a second orthogonal polarisation of light. Preferably the VCSEL comprises an upper Bragg mirror, a gain region, and a lower Bragg mirror, and the one dimensional grating structure is located on a top layer of the upper Bragg mirror and the top layer of the upper Bragg mirror has a thickness such that the reflected light of one polarisation constructively interferes with light of said one polarisation which is reflected by the upper Bragg mirror. The VCSEL will then lase at the polarisation which is more predominantly reflected by the grating structure.

Abstract: An apparatus for detecting the presence of one or more images of a known kind in a scene is disclosed which comprises a digital input means and an optical output means. The digital input means comprises a capture means which passes a capture image to a first electronic processing means to produce a scene pattern corresponding to a Fourier Transform of the scene image. This pattern is then digitally combined with one or more reference patterns corresponding to Fourier Transforms of a reference image. The resulting combined patterns are then used to modulate a beam of light which may be focused to perform an inverse Fourier Transform providing correlation information. In a preferred arrangement, the combined pattern is displayed on a spatial light modulator.

Abstract: An optical analogue to digital (A/D) converter for converting an input analogue voltage signal into a digital output, comprising means for frequency modulating an optical signal with an input analogue voltage signal, delay means for splitting the frequency modulated optical signal and generating at least one differentially delayed signal and at least one reference signal, at least one combining means arranged to combine the or one of the delayed optical signals with the or one of the reference signals, and at least one converter means for converting a combined signal output from an associated one of the combining means to a digital code.

Abstract: An optical filtering device incorporates first and second prisms, the latter prism counteracting the angular dispersion of the former prism. A spatial light modulator provides a positionally variable optical stop located to block radiation within a wavelength interval and received from a location within a scene. Unobscured radiation from that and other scene locations passes to a camera, which produces an image on a display. Opaque pixels in the stop are positioned to block unwanted light sources. The invention attenuates potentially dazzling monochromatic radiation while retaining radiation at other wavelengths for imaging purposes.

Abstract: A color display device (10) incorporates three light sources (12) supplying red, green and blue light respectively. A spatial light modulator (20) is positioned to provide time varying selective blocking of light from the sources (12) under television signal control. Light passes from the sources (12) to a condenser lens (16), then through a liquid crystal display element (22) and a projection lens (18) before reaching a screen (30). The display element (22) is also under television signal control. Signals supplied to the display element (22) provide for successive sets of three frames to be displayed, each set incorporating frame information to be displayed as red, green and blue and combinable to form a colored frame. When the element (22) displays a frame corresponding to one of the three colors red, green and blue, the modulator (20) transmits that color and blocks the others. The screen (30) receives a color image in which red, green and blue are displayed successively for each frame.

Abstract: A device and a process for enabling an incident wide bandwidth (greater than about 1 GHz) short duration (less than about 10 microseconds) individual pulse of electromagnetic radiation to be digitally sampled at a sampling rate that is achievable by available digital sampling circuits. The incident pulse is modulated onto an optical signal to form a modulated optical signal and the whole, or successive or randomly selected parts, of the modulated optical signal are replicated using optical time delay means. The resulting plurality of modulated optical signal representations of the whole or parts of the incident pulse can then be digitally sampled at a sampling rate which is reduced in proportion to the number of replications to obtain a complete digital representation of the incident pulse.

Abstract: An optical time domain reflectometer incorporates a pulse expander (16) arranged to frequency disperse short duration pulses (14) from a pulse generator (12). The pulse expander (16) is a surface acoustic wave (SAW) filter. The frequency dispersed pulses (18) have long duration, and when amplified are employed to modulate the optical output of a laser diode (24). The optical output is fed to an optical fibre (32) for conventional time domain reflectometry measurements, and return signals are detected conventionally. The detected signals are transformed to short pulses (52) by a second SAW filter arranged as a pulse compressor (36).

Abstract: An electro-optic waveguide device (10) comprises an assembly of waveguides (30) connected to a common light input region (41) and forming a common far field diffraction pattern (44). The device (10) comprises an n.sup.+ GaAs substrate (14) bearing a waveguide lower cladding layer (16) of n.sup.+ Ga.sub.0.9 Al.sub.0.1 As, which is in turn surmounted by a waveguide core layer (18) of n.sup.- GaAs. The layer (18) has grooves (20) defining the waveguides (30), each of which has a respective Schottky contact (32). Each contact (32) is biased negative with respect to the substrate (14), which reverse biases the respective Schottky diode waveguide structure. The waveguide core layer (18) has electro-optic properties, and its refractive index varies with electric field. The phase of light emerging from each waveguide is therefore independently variable by means of its applied bias voltage.

Abstract: A single frequency oscillator (10) comprises a laser diode (12), a fibre optic bundle (22) acting as a delay line filter, a photodiode (26) and a feedback loop to the laser diode (12) containing an amplifier (28) and additional low Q filtering (29, 34). The laser diode output (18) bears a modulation signal which is filtered to a series of "resonant" or synchronous frequencies by the bundle (22), converted back to an electrical signal by the diode (26) amplified, and reduced to a single resonant frequency by the low Q filtering (29, 34). It is then applied to the laser diode (12) as positive feedback to modulate the diode output (18). The output of the oscillator (10) can be taken as a microwave signal or on an optical carrier. The invention provides an oscillator incorporating feedback on an optical carrier.

Abstract: An electro-optic waveguide device (10) comprises an assembly of waveguides (30) connected to a common light input region (41) and forming a common far field diffraction pattern (44). The device (10) comprises an n.sup.+ GaAs substrate (14) bearing a waveguide lower cladding layer (16) of n.sup.+ Ga.sub.0.9 Al.sub.0.1 As, which is in turn surmounted by a waveguide core layer (18) of n.sup.- GaAs. The layer (18) has grooves (20) defining the waveguides (30), each of which has a respective Schottky contact (32). Each contact (32) is biased negative with respect to the substrate (14), which reverse biases the respective Schottky diode waveguide structure. The waveguide core layer (18) has electro-optic properties, and its refractive index varies with electric field. The phase of light emerging from each waveguide is therefore independently variable by means of its applied bias voltage.

Abstract: An acoustic transducer is arranged as a ladder having uprights and rungs consisting of contact pads and interdigital fingers respectively. The transducer has inter-rung spaces 17 occupied by arrays of reflector strips. Each reflector strip is offset by .lambda./8 from a respective position distant 1/2n.lambda. from a transducer finger center, .lambda. being the transducer finger center and n as integer. The .lambda./8 offset reflector strips provide constructive interference between transducer output waves travelling in one direction and destructive interference in the opposite direction. This provides a transducer with undirectional properties which can be manufactured in one metal deposition process. Unwanted reflections at fingers may be reduced by additional blooming reflector banks or by repositioning reflector strips to provide both unidirectional and blooming properties.

Abstract: In devices comprising closely spaced metallized regions deposited upon a dielectric substrate, in particular acoustic wave devices, electric fields may arise between the regions due to pyroelectric effects or acquired static charges during production or subsequently. These fields can cause damage by arcing or cracking of the substrate. The present method overcomes this problem by providing resistive links between such regions so that the fields do not arise. Preferably the links are of metallizing formed simultaneously with the metallized regions. Application to a SAW convolver is described in which the links are strips of metallizing (7,8,9).

Abstract: In devices comprising closely spaced metallized regions deposited upon a dielectric substrate, in particular acoustic wave devices, electric fields may arise between the regions due to pyroelectic effects or acquired static charges during production or subsequently. These fields can cause damage by arcing or cracking of the substrate. The present method overcomes this problem by providing resistive links between such regions so that the fields do not arise. Preferably the links are of metallizing formed simultaneously with the metallized regions. Application to a SAW convolver is described in which the links are strips of metallizing (7,8,9).

Abstract: An acoustic wave device comprises a substrate carrying two or more acoustic components aligned in different directions and electrically connected together in parallel. The phase slope of the acoustic components are similar but their temperature coefficients of delay are different whereby their resultant frequency response is compensated over a useful temperature range. The acoustic components may be delay line employing surface waves or surface skimming bulk waves, or one or two port resonators using surface waves.

Abstract: An acoustic wave device employing surface skimming bulk waves comprises a piezo electric substrate having a flat surface which carries an input transducer and an output transducer for respectively lanuching and receiving acoustic waves into and from the bulk of the substrate. The substrate may be of quartz, lithium tantalate, or lithium niobate and has the flat surface orientated so that a surface skimming bulk wave is launched without generation of surface acoustic waves.

Abstract: An acoustic wave device employing surfaces skimming bulk waves comprises a piezo electric substrate having a flat surface which carries an input transducer and an output transducer for respectively lanuching and receiving acoustic waves into and from the bulk of the substrate. The substrate may be of quartz, lithium tantalate, or lithium niobate and has the flat surface orientated so that a surface skimming bulk wave is launched without generation of surface acoustic waves.