Abstract:
A method for manufacturing optical components having a periodic or quasi-periodic structure such as diffraction gratings, volume holograms or distributed feedback mirrors in optical fibers. An optical medium is subjected to acoustic waves which induce periodic or quasi-periodic changes in the optical properties of the medium, the changes being at least partially retained on removal of the waves. The changes may result from stress associated with the antinodes of an acoustic standing wave, alteratively the stress distribution associated with a travelling acoustic wave in an electro-viscous liquid may be semi-permanently retained by the solidification of the material resulting from the application of an electric field.
Abstract:
The method of uniquely identifying a product for subsequent recycling includes marking a surface of the product with a first trace signature being representative of the manufacturer of the product.
Abstract:
A method for eliciting or inducing an immune response in a human or animal subject, comprises administering to said subject a composition comprising an antigen and an adjuvant, wherein the composition is administered to the subject by the intra-lung route.
Abstract:
A method for eliciting or inducing an immune response in a human or animal subject, comprises administering to said subject a composition comprising an antigen and an adjuvant, wherein the composition is administered to the subject by the intra-lung route.
Abstract:
A plastics or rubber kerbstone (10) has a body which defines a flange for assisting retention of the kerbstone, in use. A kerb race reinforcement structure (80) is also disclosed. The kerb race reinforcement structure has a preformed body which defines a base and a kerb carrying surface displaced from the base so as to define a cavity between the base and the carrying surface.
Abstract:
Light from a laser (10) is divided by a beam splitter (12) to provide signal (15) and reference (14) channels. The signal channel light is expanded (11) to illuminate an acousto-optic (AO) device (13). This leads to a spatial distribution of Doppler shifted frequencies. This spatial distribution then illuminates a spatial light modulator (SLM) (19) such that a number of parallel and discrete optical channels (112) emerge. In a local area network (LAN) the optical signal channels are coupled into a single mode optical fibre (22) and then heterodont to the reference laser light from a further optical fibre (23) in an optical coupler (25). In a receiver the modulated light is detected (32) and the detected signal connected to the transducer of an AO device (35). The AO device (35) is illuminated by a receiver laser light (36) and the emerging modulated light is incident on a focal plane detector array (39) where each detector (310) then receives light corresponding to each of the transmitted channels (311). A secure free space communications system is possible by separate transmission of a delayed (43) unmodulated reference signal. The receiver is then arranged to include an identical delay (55) in the signal channels before coupling together the signal and reference channels (56) for modulating the AO cell (35). By this means the transmission delay lines (43) and the reference delay lines (55) must have delays which are equal within the coherence length of the source laser.
Abstract:
A filter for removing coherent radiation from a source in a field of view, substantially independent of the size of the source, comprises a first reticle 22 located in the path of received light 21, a first lens 23 producing an optical transform of the first reticle 22 at a second reticle 24 located in the image plane of the first lens 23, a second lens 25 producing an optical transform of the second reticle 24 and a third reticle 26 located in the image plane of the second lens 25. The arrangement is such that the spatial transmittance of the third reticle 26 is selected to block at least part of the diffracted image of the first reticle 22 produced in the image plane of the second lens 25 and characteristic of the coherent radiation. Preferably the optical transforms are Fourier Transforms. A monochromatic coherent source in the field of view produces a pattern of diffracted energy in the image plane of the second lens which is independent of the size of the source. Thus, by providing a suitable reticle 26 in the image plane of the second lens light from a coherent source in the field of view can be blocked while polychromatic light is transmitted. The first and second reticles may be periodic picket-fence reticles or different spatial frequencies may be used for the first and third reticles so as to vary the stop-band characteristics of the filter.
Abstract:
An electro-optical detection system for detecting objects embedded in a partially transmitting medium. The system includes a receiver for receiving electromagnetic radiation and a device for separating the received radiation into two separate spectral channels. A detector in each of the spectral channels for providing a signal indicative of the received radiation in each spectral channel. A signal processor, responsive to the outputs of the detectors, having a signal channel where transmission of light of the signal channel wavelength in the medium is high and having a reference channel where attenuation of light of the reference channel wavelength in the medium is high. The signal processor ensures that the reflected light at both signal and reference wavelengths are of similar intensity and geometric distribution. A subtractor provides a difference output in which the signal and reference channels are subtracted, removing the effect of reflected light.
Abstract:
An interference device for discriminating between radiation sources of differing coherence length comprises means to divide received radiation from a source into two components. A path difference, defining a coherence length cut-off, is introduced into the path of one component and the components are brought together for interference. The recombined light passes through a reticle with alternate opaque and tranparent bars and an optical band-pass filter to a detector. Interference fringes present in the plane of the reticle are swept across the reticle by the action of the collection optical system of the device which includes a scanning rotating mirror. Two similar devices can be arranged for band-pass coherence length filtering and when used in conjunction with a light soruce whose coherence is modulated the device can be used for signalling.