Abstract: An optical scanning arrangement for gas sensing, in which scanned light source means produces a spectrum of regularly spaced wavelengths or lines which correspond as regards spacing to the absorption line spectrum of a gas to be monitored and in which the multi-line output from the light source means propagates through a region to be sensed for gas and means for determining the light output from the region for detecting the attenuation of the components of the multi-line output from the light source means due to absorption by said gas being monitored.

Abstract: A multi channel averaging circuit for use with an optical sensing system utilizing back-scattering light for establishing the scattering profile along a fibre sensor, e.g. to determine the temperature distribution along the optical fibre sensor. The circuit comprises a number of connected in parallel, charge coupled devices (3-9) energized by a clock (10) and arranged to store successive elements of a signal waveform derived from the back-scattered light. The stored analogue signals are fed sequentially into the averaging circuit (11), sampled, and then digitized by an A to D converter (13).

Abstract: An optical time domain reflectometry system in which laser level reference signals are derived from the respective laser outputs from the laser sources and fed into a single receiver provided for receiving the back-scattered or returned light along an optical fibre. The receiver is thus continuously calibrated in accordance with the relative intensities of the optical signals at different frequencies being launched into the optical fibre so that the receiver provides an accurate measurement of temperature or other parameter being measured by the system.

Abstract: A Fabry-Perot pressure or displacement sensor comprises an optical fibre which serves to transmit a light beam to the mirrors of the sensor and to receive light which is reflected back from the mirrors. The light beam and the reflected light comprise light at a plurality of wavelengths. The wavelength components of the transmitted light and the wavelength components of the received light are range rated in range gates and are compared in comparators to provide respective ratios of transmitted intensities and received intensities. These ratios are in turn compared in comparator to provide a ratio dependent upon the displacement of the mirrors of sensor due to pressure applied thereto but independent of any changes in the intensities of transmitted light due to reflections from optical components in the pressure or displacement monitoring arrangement.

Abstract: A two-wavelength referencing optical sensing arrangement comprises two laser sources for producing simultaneous optical pulse signals of two different wavelengths for transmission over a plurality of discrete optical fibre paths to the sensors terminating such paths. Time-displaced return signals of different wavelengths received over the optical paths from sensors are fed into a single receiver which uses the intensity of signals of one wavelength in order to compensate for unknown losses in the system when indicating measurement of conditions sensed at the locations of the optical sensors.

Abstract: An optical fiber sensing system for measuring the location and/or magnitude of an external parameter acting at a single point along an optical fiber loop sensor. The system comprises light source means for producing light for propagation in opposite directions around the loop sensor and directional coupler means for coupling the light source means and detector means to the loop sensor and to other optical fiber interfering paths of the system. The detector means are arranged for measuring a phase change (x) between interfering light signals propagating around the sensor loop in opposite directions and for simultaneously measuring a phase change (y) experienced by the light propagating around the loop sensor in one direction. By computation or otherwise, the rate of change of the phase change (x) can be derived and by the use of an algorithm the location and/or magnitude of the applied parameter can be determined.

Abstract: A spectral filtering optical sensor comprises a stationary zone plate and stationary co-terminous ends of input and output fibres with the interposition in the optical path between the zone plate and the optical fibre ends of a variable optical focussing arrangement the focussing characteristics of which change with changes in magnitude of the particular parameter being sensed and thereby vary the effective optical path length between the zone plate and the optical fibre ends and the wavelength of light impinging on the end of the output fibre.

Abstract: An optical fibre sensing system for monitoring and/or measuring temperatures or pressures distributed around an optical fibre sensing loop. Light source and coupler are provided for applying continuous wave light to the loop so that the light propagates simultaneously in opposite directions around the loop with the resultant light output from the loop being detected by a detector. Light pulse generating source and coupler cause light pulses to propagate in one direction only around the loop and by so doing produce transient variations in the propagation constant along the looped fibre in dependence upon the distributed temperature or pressure around the loop. The detector detects the phase changes occurring in the continuous wave light received from the sensing loop due to variations in temperature or pressure around the loop.

Abstract: An optical transmission system comprises a plurality of transducers located at intervals along a continuous optical fibre data transmission path. Data signals are derived from respective transmitters associated with the transducers and are applied to the transducers to produce mechanical stressing or deformation of the data transmission path optical fibre for imparting corresponding modulation of the polarization state of light being propagated along the optical fibre. A receiver connected to the far end of the transmission path includes means for determining the exact state of polarization of the received light and for extracting the modulation information and hence transmitted data therefrom.

Abstract: A temperature measuring arrangement including a relatively long optical fibre temperature sensor doped along its length with material that absorbs light in dependence upon temperature, launcher for launching into one end of the temperature sensor fibre contemporaneous light pulses of two different wavelengths and comparator for comparing variations with time in back-scattered light of the two different wavelengths returned along the sensor fibre in order to provide an indication of the temperature distribution along the fibre, the two wavelengths of the light pulses launched into the fibre sensor being chosen so that they correspond with different absorption bands of the doped material.

Abstract: An optical sensing arrangement suitable for the detection of acoustic waves and/or temperature or magnetic field changes, comprises a laser light source for producing polarized light which in operation of the arrangement will be applied for detection purposes to the input end of an optical sensor for transmission therethrough, whereby a relative phase delay is produced between orthogonal components of the polarized light at the output end of the optical sensor, characterized in that a relative phase delay compensation device is optically coupled to and so orientated with respect to one end of the sensor, that the relative phase delay between the orthogonally polarized components transmitted through the compensation device and the corresponding relative phase delay of these components in the optical sensor are mutually opposite, thereby reducing the noise content of an output signal derived from the arrangement and fed to polarization analyzer for producing an indication of structural changes which have occurr

Abstract: According to the present invention there is provided an optical detecting, monitoring or measuring arrangement, comprising a movable diffraction grating arranged for angular displacement by means responsive for example to changes in one or more parameters, such as temperature or pressure, whereby the color of light being reflected to a light-receiving point from said grating changes and said light is then directed onto a fixed diffraction grating so that the direction of a light beam consequentially reflected from said fixed diffraction grating changes with change in color, such change in direction being dependent upon and providing an indication of the change in said parameter or parameters.

Abstract: A position indicating system for affording an indication of the instantaneous position of a movable member, such as a rotating shaft, comprises means for producing light in different color bands directed on to a suitably coded structure movable in accordance with movement of the movable member or coded structure which itself carried filter means for separating light into different colors. Optical fibre means is located for receiving colored light passing through the movable coded structure and for transmitting light to light detector means for producing an output dependent upon the light received by the optical fibre means and indicative of the instantaneous position of the movable member.

Abstract: An optical fibre connector comprising in respect of each of the optical fibres to be connected, a connector body part formed at one end with a recess which accurately locates a sphere lens relative to an optical fibre receiving hole extending through the body part and terminating at the center of the recess whereby the axis of the optical fibre received by the hole and preferably bonded to the surface of the sphere lens. Connecting means is provided for connecting together in axial alignment two of the body parts with the sphere lenses of the parts arranged in opposed relationship.