Abstract: A method of measuring a height of a fuel in an aircraft fuel tank (21)b including illuminating the fuel in the aircraft fuel tank and detecting reflected light from the fuel. Optical coherence tomography is used to determine the height of a surface of fuel in the fuel tank. An apparatus (30) is used to measure a height of a surface of fuel in an aircraft fuel tank, and an aircraft fuel tank system with a fuel tank and an apparatus for measuring a height of a surface of fuel in the aircraft fuel tank.

Abstract: A method of measuring a height of a fuel in an aircraft fuel tank (21) b including illuminating the fuel in the aircraft fuel tank and detecting reflected light from the fuel. Optical coherence tomography is used to determine the height of a surface of fuel in the fuel tank. An apparatus (30) is used to measure a height of a surface of fuel in an aircraft fuel tank, and an aircraft fuel tank system with a fuel tank and an apparatus for measuring a height of a surface of fuel in the aircraft fuel tank.

Abstract: An improved photocell offering efficient power generation from broadband incident radiation, the photocell includes a first diode formed in single crystal silicon and one or more further diodes each formed in a single crystal Group II-VI semiconductor. In a preferred embodiment, a tandem photocell is provided that incorporates a first diode formed in single crystal silicon, a second diode formed in a Group II-VI semiconductor, an optional buffer layer and a highly doped layer of silicon acting as an optional tunnel junction between the two diodes. The device can additionally include a layer of silicon deposited at the rear of the structure to maximise current collection of longer wavelength light, and top and bottom (front and back) electrical contacts. In use, light impinges on the top (front) surface of the photocell and is absorbed (in turn) by diodes.

Abstract: A photocell which operates at multiple wavelengths for efficient power generation from broadband incident radiation. According to a preferred embodiment, the photocell is a multi-layer device that includes a first outer layer, a middle layer and an inner layer disposed on a substrate. All three layers are formed from II-VI semiconductor layers. The device is arranged such that the outer layer has a high band gap, the middle layer has a band gap which is less than half the band gap of the outer layer and the inner layer has a band gap which is less than half that of the substrate. Thus, there is a step change in band gap between various layers.

Abstract: A communications system incorporates a transmitter a receiver. The transmitter includes an infrared light emitting diode (LED). The LED output is positive or negative luminescence, i.e. above or below an equilibrium background intensity level respectively, according to the polarity of its bias signal. The receiver contains a lens to focus light from the LED onto a diode detector, from which signals pass to an amplifier, decoder and printer. Output signals from the LED have an average intensity equal to the equilibrium background intensity level and a frequency greater than 100 Hz or byte rate greater than 100 bytes/sec. They are not discernible by conventional thermal infrared imagers with frame rates of 50 Hz or less because integration in such an imager renders them indistinguishable from background.

Abstract: A multi-layer semiconductor diode having a layer of wide bandgap material located between the active layer and a first contact zone, where the active layer and additional wide bandgap layer are of one dopant type, and the first contact zone is of the opposite dopant type. A specific embodiment of the invention comprises a stack formed from a first contact zone (4) of p-type material, a lightly doped p-type active layer (2), an additional p layer (20) and a second contact zone (6) of n-type material. The diode may be used as an infrared detector or a negative luminescent source.

Abstract: A multi-layer semiconductor diode having a layer of wide bandgap material located between the active layer and a first contact zone, where the active layer and additional wide bandgap layer are of one dopant type, and the first contact zone is of the opposite dopant type. A specific embodiment of the invention comprises a stack formed from a first contact zone (4) of p-type material, a lightly doped p-type active layer (2), an additional p layer (20) and a second contact zone (6) of n-type material. The diode may be used as an infrared detector or a negative luminescent source.

Abstract: An infrared optical system incorporates a lens for imaging a remote scene onto a detector within a cold shield. Stray radiation incident on the detector is reduced by an optical stop in the form of a light emitting diode producing negative luminescence. The LED emits less radiation than background, and contributes less to the detector photon noise than an optical stop not exhibiting negative luminescence.