Abstract: This invention provides a method for identifying a compound which inhibits HIV-1 entry into a cell. This invention also provides a compound which inhibits the cavity binding interaction between HIV-1 gp120 and CD4. This invention further provides a method of inhibiting HIV-1 infection of a cell, a method of preventing HIV-1 infection in a subject and a method of treating HIV-1 infection in a subject comprising contacting the cell or administering to the subject an amount of the compound which inhibits the cavity binding interaction between HIV-1 gp120 and CD4 effective to inhibit HIV-1 infection, thereby inhibiting HIV-1 infection of the cell, preventing HIV-1 infection in the subject and treating HIV-1 infection in the subject.

Abstract: Optical device and method for protecting an optical communications route A section of tapered optical fiber is provided to protect optical components from catastrophic damage that may propagate within an optical route. The tapered section functions as a fuse to arrest the propagation of optical power induced damage by leaking optical power from a waveguiding region to below a threshold, below which further propagation of damage is not supported.

Abstract: A thulium doped silica based glass capable of supporting lasing activity including Tm3+as a lasing species disposed in a host composition, including oxides of germanium, silicon and tantalum. The preferred concentration of silicon in the host composition being between 15-25 weight percent. The preferred concentration of germanium in the host composition being between 0.1-1 weight percent. The preferred concentration of tantalum in the host composition is greater than 15 weight percent. The preferred concentration of thulium ions being in the range of 500-1000 parts per million by weight.

Abstract: In a gain-controlled erbium-doped optical amplifier, gain control is achieved by clamping the gain of a laser cavity to be equal to the overall cavity loss and by fixing the resonant wavelength of the amplifier to be at a first wavelength. When an optical signal to be amplified having a second wavelength different from the first wavelength passes through the amplifier the gain experienced by the signal depends entirely on the gain of the cavity, and not on the intensity of the signal. If the first wavelength is arranged to be at the peak of the sum of the absorption and emission cross sections of erbium, the amplifier exhibits minimum sensitivity to ambient changes in temperature.

Abstract: A laser includes first and second feedback elements defining a laser cavity, and a gain medium within the laser cavity. The gain medium has first and second facets and an optical waveguide for guiding optical radiation between said first and second facets. The second feedback element is wavelength selective, and the optical waveguide is configured to direct optical radiation at an angle .theta. to the normal of the second facet.

Abstract: Immunogenic peptides containing amino acid residues which define a binding site to a CD4 receptor are disclosed. Antibodies to these peptides are also disclosed. Methods of reducing the ability of a gp120 env protein to bind to CD4 are also disclosed. Methods of treatment and prophylaxis using these antibodies and peptides are also described.

Abstract: A high power monomode laser arrangement is able to manipulate the output from a high power laser diode array pump source using a computer-generated hologram to launch a high proportion of the pump source light into a multimode fibre portion including input reflector. A monomode fibre portion with the same fundamental-mode spot size as the multimode fibre portion is optically coupled to the multimode fibre portion and includes a reflector which reflects only the fundamental mode of the multimode and monomode fibre portions. The fundamental mode reflection forced by the monomode fibre portion provides the feedback necessary to force predominantly fundamental mode oscillation which enables stimulated emission in only the fundamental mode.

Abstract: A filter has a preselected attenuation/wavelength characteristic, in which spatially separated parts of the filter attenuate different wavelengths. The spatially-separated parts have different attenuation characteristics to attenuate different wavelengths in a predetermined manner to provide a selected attenuation/wavelength characteristic. In one arrangement an interference type filter includes a grating, the pitch of which varies spatially. In one instance, the structure to determine the proportion of radiation subject to interference includes a grating of spatially-varying effectiveness, but alternatively it may include an attenuation filter, the attenuation effect of the attenuation layer varying spatially. In another arrangement, the filter may include structure to separate received radiation into a spatially-disposed spectrum, and to attenuate different parts of the spatially-disposed spectrum in such a manner as to provide the selected attenuation/wavelength characteristic.

Abstract: An optical fibre amplifier (50) comprises a SiO.sub.2 --Al.sub.2 O.sub.3 --GeO.sub.2 single-mode optical fibre (52) doped with E.sub.r.sup.3+. It is pumped by 1.55 .mu.m and 1.47 .mu.m optical sources (54 and 56) whose optical outputs are combined by an optical coupler (58) and are then coupled to the fibre (52) by a further optical coupler (50). A source of optical signals to be amplified (62) is also coupled to the fibre (52) by the further coupler (60). The E.sub.r.sup.3+ ions provide a three-level lasing scheme with a fluorescence peak at about 1.53 .mu.m. Low noise amplification of optical signals in the long-wavelength tail of the fluorescence spectrum with suppressed ASE at the fluorescence spectrums peak wavelength is obtained as follows. The 1.47 .mu.m pump provides some low noise amplification of the optical signal but preferentially amplifies the 1.55 .mu.m pump source. The resultant 1.55 .mu.

Abstract: A high power monomode laser arrangement is able to manipulate the output from a high power laser diode array pump source 3 using a computer-generated hologram 4 to launch a high proportion of the pump source light into a multimode fiber portion including in input reflector 6. A monomode fiber portion 2 with the same fundamental-mode spot size as the multimode fiber portion 1 is optically coupled to the multimode fiber portion and includes a reflector 5 which reflects only the fundamental mode of the multimode and monomode fiber portions. The fundamental mode reflection forced by the monomode fiber portion 2 provides the feedback necessary to force predominantly fundamental mode oscillation which enables stimulated emission in only the fundamental mode.

Abstract: An external cavity laser assembly in which the laser chip is within a hermetically sealed package and the external cavity is outside the hermetic package. A collimating lens in a screw threaded mounting is disposed outside the hermetic package, the screw thread permitting focussing. The cavity is turned by rotation and translation of a grating, the position of which is electrically controlled via piezoelectric stacks. Thermal expansion of the stacks is compensated by mounting the grating on a rod of suitable material (e.g., ceramic) which also serves to reduce the cavity length while allowing maximum piezoextension. In a second embodiment the assembly is a tunable laser amplifier, with a grating being driven in a similar manner to provide the tuning.

Abstract: An optical resonant device comprises a laser diode (14), a graded-index collimating lens (11) and a prism grating (17). The lens (11) is rigidly connected to the prism grating (17). Coarse tuning by adjustment of the angle of incidence of light on the grating (17) is achieved by laterally offsetting the laser (14) relative to the central optical axis C of the lens (11). The grating (17) is angled relative to the optical axis C so that the tuned position of the laser (14) is at or close to the optical axis C.

Abstract: A method and apparatus for generating a plurality of electromagnetic signals, primarily optical signals, having linewidths centered on frequencies fixed relatively to a reference frequency. The apparatus comprises a reference frequency signal source such as a gas laser (1) which generates a reference signal having a frequency f.sub.p. This reference signal is fed to a leading one (3) of a plurality of optical fibre ring lasers (3, 11, 16) connected together in series by optical fibres (6, 12). The characteristics of the injected signal and the form of the waveguide ring (5) defined by the ring laser (3) is such that stimulated Brillouin scattering occurs in the waveguide ring to generate a scattered signal with a frequency f.sub.p -f.sub.A traveling in an opposite direction to the injected signal. This scattered signal is passed by the optical fibres (6) via an isolation device (7) to the next ring laser (11) in series.

Abstract: A method and apparatus for generating relatively narrow linewidth radiation, for example having a 1 MHz linewidth. The apparatus comprises a source of relatively broad linewidth, coherent radiation such as a semiconductor laser (1) generating optical radiation having a linewidth of 10 MHz. The broad linewidth radiation is injected into a waveguide ring (5), the characteristics of the radiation and the form of the waveguide ring (5) being such that stimulated Brillouin scattering occurs in use to generate the relatively narrow linewidth of the order of kHz, coherent wave travelling in an opposite direction to the broad linewidth radiation. A directional coupler (3) between the source (1) and the waveguide ring (5) separates the narrow linewidth wave from the injected radiation.

Abstract: A light source comprises a semiconductor laser and a gas laser. The semiconductor laser is injection locked using the highly coherent output from the gas laser. The output from the semiconductor laser has a narrow linewidth and a high stability.The invention has a major application in optical fibre communications systems.

Abstract: An extension of the noncollinear second harmonic generation technique for lse autocorrelation measurements is described. A diffraction-grating is used to produce a tailored, expanded beam, with a differential time delay along its expanded axis. When this beam is combined with an inverted replica of itself at the frequency-doubling crystal, the monitored spatial profile of the generated second harmonic beam gives directly the duration of the incident laser pulse. A time resolution of better than 1 picosecond (ps) is obtained at 500 nanometers (nm), and a total measurement range of .about.80 ps. The optical system here described enables the extension of the measurement range in a simple manner.