Abstract: Apparatus for indicating the departure of a shape of an object from a specified shape is described. The apparatus includes a light source for directing an incident beam of radiation onto the object, and an inspecting device for inspecting the final beam after transmission by or reflection from the object. The apparatus is arranged so that the final beam will have a substantially planar wavefront when the object has the specified shape, and said inspecting device is arranged to determine any departure of the wavefront of the final beam from planarity. In one embodiment, the inspecting device includes a beamsplitter, for example a diffraction grating or hologram, and a detector such as a CCD camera. The beamsplitter is then arranged to split the final beam into two or more beams and to direct the two or more beams to laterally displaced locations on the detector.

Abstract: The invention relates to a method of multiple criteria decision making. In particular, a method of maintaining a complex article is described that includes the steps of; (a) taking a set of options for replacing each of a plurality of components of the complex article, (b) identifying an optimum solution set from the set of possible replacement options of step (a) that best satisfies a plurality of criteria and (c) implementing an optimum solution of the optimum solution set. The step of identifying an optimum solution set comprises the step of evaluating a plurality of potential solutions from the set of possible options defined in step (a) against the plurality of criteria.

Abstract: A method of processing a temporal sequence of base images from a synthetic aperture system such as a synthetic aperture radar is provided that simplifies the task of identifying moving objects. The method comprises the steps of firstly temporally filtering a plurality of the base images to form a reference image, and secondly normalising the reference image with a base image to form a change detection image. The change detection image has the property that all moving objects are emphasised. Further processing can optionally be performed on the change detection image to remove false targets based on characteristics of the highlighted areas or on a temporal track taken over a plurality of change detection images. The invention allows detection of moving objects without requiring a Doppler return from a target. The invention extends to a system adapted to implement the method, and a computer program.

Abstract: This invention relates to the manufacture of Cadmium Mercury Telluride (CMT) on patterned silicon, especially to growth of CMT on silicon substrates bearing integrated circuitry. The method of the invention involves growing CMT in selected growth windows on the silicon substrate by first growing one or more buffer layers by MBE and then growing the CMT by MOVPE. The growth windows may be defined by masking the area outside of the growth windows. Growth within the growth windows is crystalline whereas any growth outside the growth windows is polycrystalline and can be removed by etching. The invention offers a method of growing CMT structures directly on integrated circuits removing the need for hybridisation.

Abstract: This invention relates to coded aperture imaging apparatus and methods. In one aspect a coded aperture imager has at least one detector array and a reconfigurable coded aperture mask means. A reconfigurable coded aperture mask means can display various coded aperture masks to provide imaging across different fields of view and/or with different resolution without requiring any moving parts or bulky optical components. More than one detector array can be used to provide large area imaging without requiring seamless tiling and this represents another aspect of the invention. The present invention also relates to the use of coded aperture imaging in the visible, ultraviolet or infrared wavebands. The use of coded aperture imaging for imaging through a curved optical element is taught as the image decoding can automatically remove any aberrations introduced by the curved element.

Abstract: This invention relates to optoelectronic devices of improved efficiency. In particular it relates to light emitting diodes, photodiodes and photovoltaics. By careful design of periodic microstructures, e.g. gratings, associated with such devices more efficient light generation or detection is achieved.

Abstract: An optical clock for generating a series of optical clock pulses, comprises a laser source for generating output having a plurality of spectral components ?1, ?2, . . . ?N, an amplitude-modulator arranged to cooperate with the laser source to produce a series of intermediate optical pulses each having the plurality of spectral components, and optical fibre arranged to provide dispersion of each intermediate optical pulse to form a plurality of component pulses each corresponding to a spectral component and to compress each component pulse, the spectral width of each spectral component being sufficient to inhibit stimulated Brillouin scattering (SBS) of the component pulses within the optical fibre. The optical clock may be used for analogue-to-digital conversion of an electrical signal, in which application pulses of respective spectral components are demultiplexed and subsequently detected and digitised in parallel, providing for faster conversion.

Abstract: A vehicle arresting device comprises a net intended to be laid flat on the ground in the path of an oncoming vehicle to be arrested. Two rows of barbed spikes are attached to the net along its leading edge. When a vehicle runs over the device the spikes lodge in its front tyres and the net is caused to wrap around the front wheels, eventually being pulled tight under the vehicle so that the tension in the net prevents further rotation of the wheels and the vehicle is brought to a stop. The net is manufactured such that in its deployed condition it has sufficient lateral stretch to allow it to become fully wrapped around the front wheels before the tension builds up to a level at which there might otherwise be a risk of the spikes being pulled from the tyres.

Abstract: Apparatus comprising an optical fibre laser having at least two laser cores and means arranged to combine laser output from the at least two laser cores at a first end of the optical fibre laser to produce a combined laser output having one or more beat signals.

Abstract: This invention relates to an optical star network in which different communities of users, such as different businesses, are provided through use of quantum key distribution (QKD). At least one QKD device is located at the central hub of the star network and communicates with QKD devices at the endpoints to establish a separate quantum key, i.e. a cryptographic key established by QKD, with each endpoint. A separate key manager is provided for each different community and each key manager is arranged to use the appropriate quantum keys for endpoints within that community to deliver the same community key to each endpoint. This community key can be used by for encrypting network traffic between members of the same community with security. Traffic passing through the network switch is encrypted, but the community keys are not delivered via the switch and hence the switch an error in the switch does not compromise security.

Abstract: The invention relates to a device and method for communicating with a thermal detector module and an appropriate thermal detector for a use with such a control device. The device for communicating with a thermal detector module comprises a means for providing a collimated beam of thermal infrared radiation and means for modulating the intensity of the collimated beam of thermal infrared radiation. The intensity modulated thermal infrared beam, when directed on to the thermal detector module from a position within the module's field of view, is suitable for triggering a response from the thermal detector module. The intensity modulated thermal infrared beam may also be encoded with a digital signal to control the function of the thermal detector.

Abstract: A signal separation method for separation of source signals from a composite signal expresses the composite signal as a series of values of signal amplitude. The source signals have periodicities similar or equal to p. The composite signal is portioned into sections which provide respective rows of a matrix X, in which successive rows represent successive sections. A singular value decomposition of the matrix X is performed to obtain two singular vector matrices U, V and a singular value matrix ?. An independent component analysis is performed on one of the singular vector matrices U, V to obtain an independent component matrix UR2T,R1TV and an associated component matrix R2?V,U?R1. One of the component matrices UR2T,U?R1 contains estimated separated signal modulation envelopes and the other component matrix R2?V, R1TV contains estimated separated cyclets.

Abstract: A flextensional transducer that can be stored at room temperature and activated and operated at an elevated temperature in excess of 200° C.

Abstract: A multistage flextensional transducer includes at least one inner elongate driver member within and mechanically coupled to an inner shell that is nested within an outer shell; the inner shell comprising a pair of contact portions abutting the driver member and a pair of transmission portions on opposite sides of the inner shell between the contact portions; the outer shell being arranged so that the transmission portions act as bridging driver members between the said inner and outer shells, flexure of the outer shell being driven, on actuation of the transducer, by movement of the bridging driver members. The transducer may act as a push or pull actuator or sensor, may magnify displacement and may employ smart materials as driver members. Also cylindrical modules containing thin flextensional actuators may provide axial displacement in a downhole environment and may move a device axially along a downhole pipe or close a valve opening or inch along the pipe.

Abstract: A method of performing quantum key distribution across a network. The method involves a first node first agreeing a quantum key with a first intermediate node in the path. Next the intermediate node exchanges a quantum signal with the next node in the path—which is a targeted node. The intermediate node communicates with the first node using the previous established quantum key details of the quantum signal sent or received by the intermediate node. The first node then performs a key agreement step to agree a quantum key directly with the targeted node. Having established a quantum key with the current targeted node the method can be repeated but with the next node in the network path as the targeted node until a destination node is reached. The final quantum key agreed with the destination node can then be used for encrypting communication between those nodes across the network.

Abstract: A measurement device, such as a laser radar, is described that comprises a transmitter portion for transmitting radiation to a remote probe volume, a receiver portion for detecting radiation returned from the remote probe volume and a processor for analysing the detected return radiation. The device is suitable for transmitting and receiving radiation through a window portion having associated window cleaning apparatus (e.g. wiper 62) for cleaning said window portion in response to a cleaning activation signal. The processor is arranged to generate a cleaning activation signal for activating window cleaning apparatus when the properties of said detected return radiation are indicative of a reduction in transmission through at least part of said window portion. In one embodiment, a conically scanned lidar is described that generates a cleaning activation signal when the power of detected return radiation varies as a function of the angle of transmission of radiation from the device.

Abstract: The method involves exchange of a quantum signal between a first quantum node and a second quantum node as is usual in known quantum key distribution (QKD) scheme. The first quantum node communicates details of the quantum signal it sent or received with a first remote node. The first remote node thus has all the information to required to take the place of the first quantum node in the key agreement step with the second quantum node. The first quantum node may be arranged to transmit the quantum signal to the second quantum node, in which ease the invention provides a distributed quantum transmitter with the control logic in the first remote node being distributed remotely from the actual quantum transmitter in the first quantum node. Communications between the first remote node and first quantum node may comprise or be protected by a quantum key derived by conventional QKD.

Abstract: An optical receiver for a quantum key distribution system comprises a plurality of optical components mounted or formed in a substrate and optically coupled by one or more hollow core waveguides formed in the substrate.

Abstract: An iridescent material comprises a diffraction grating incorporating a plurality of sheets (1) of a first substantially transparent material in parallel alignment and spaced away apart by quantities of a second substantially transparent material (2), the second material having a refractive index significantly lower than the refractive index of the first material, the plates being tilted at an angle ? to an axis X and the grating having a period d(X) in the direction of axis X, the angle ? and period d being such that a second diffraction grating is provided along an axis Z, perpendicular to axis X, the second diffraction grating having a period d(Z) and consisting of ten periods or less and whereby, the diffraction conditions of the grating can be simultaneously fulfilled by electromagentic radiation of a range of wavelength thereby causing iridescence.

Abstract: A method of determining the rate of change of optical thickness of a thin-film during deposition comprising the steps of illuminating the thin-film with electromagnetic radiation having a range of wavelengths, measuring the transmission spectrum of the thin-film at least twice during the deposition process to determine the wavelength ?t or turning points in the transmission spectrum, and using the measurements to determine the rate to change of optical thickness of the thin-film as a function of time. The method further comprises the steps of predicting a time T in the growth process at which the wavelength ?t of the turning point in the transmission spectrum of the thin-film will be substantially equal to the wavelength ?d of the turning point in the transmission spectrum of thin-film at its optical design thickness, and interrupting the growth process such that growth ceases at time T.