Abstract: Surface plasmon generation on a metal or semiconductor layer at an outer surface of an optical waveguide, using light reflected or scattered from inside the optical waveguide. One aspect provides a main optical waveguide (11) (e.g. optical fibre) having a second optical waveguide (18) adhered thereto, the second optical waveguide including an optically transparent material (610) separating two surface plasmon supporting layers (600, 620). Another aspect provides a surface plasmon supporting layer of material(s) adhered to the main optical waveguide, the layer having photo-induced regions of material compaction. The regions of compaction may cause un-inscribed refractive index modulations in the main optical waveguide. The surface plasmons are coupled to the guided mode(s) in the main optical waveguide. Surface plasmon resonance depends on sample material in contact with an outermost surface plasmon supporting layer.

Abstract: The generation of surface plasmons on a metal layer arranged upon an outer surface of an optical waveguide, using light reflected from inside the optical waveguide. The reflected light may be a reflected part of guided light travelling along the optical waveguide and may be a back-reflected (e.g. obliquely back-reflected) part of the guided light. The reflected part of guided light may form a radiative optical mode(s) which is used to excite surface plasmons and which is also coupled to the remaining guided mode(s) of the light from which it derives. This coupling of the radiation mode(s) and the guided mode(s) enables changes in the radiation mode(s) to cause consequential changes in the guided mode(s) of light. Such changes in the radiation mode(s) may occur due to the coupling of the reflected mode(s) to the surface plasmons they excite at the metal layer.

Abstract: A Gires-Tournois etalon (GTE) (10) comprising an optical fiber (12) in which a primary chirped fiber Bragg grating (FBG) (16) is provided, an RF signal generator (20), a piezoelectric transducer (22), and a glass horn (24), for coupling an acoustic wave (26) into the fiber (12). The acoustic wave (26) causes a periodic compression within the fiber (12), which induces a low frequency periodic refractive index modulation within the grating section (14) of the fiber (12). This causes two side frequency components to be generated for each high-frequency component of the FBG (16). Two secondary grating are thus excited, having the same spectral bandwidth as the FBG (16), but a lower reflectivity and different central wavelengths. The free spectral range of the GTE (10) can be adjusted by varying the frequency of the acoustic wave (26). The reflectivity of the excited secondary gratings can be adjusted by adjusting the amplitude of the acoustic wave (26).

Abstract: A torsion sensor using an optical waveguide in optical communication with a diffraction grating, preferably a tilted grating, and most preferably a tilted Bragg grating, which provides the optical waveguide and grating with a torsion-dependent collective optical transmission spectrum. Changes in the collective optical transmission spectrum of the waveguide and grating, induced by changes in the amount of torsion applied to the waveguide, may be detected by detecting a corresponding change in the intensity of optical radiation transmitted through the grating from a controlled optical source. The degree of change in the collective optical transmission spectrum is dependent upon the degree of torsion (twist) applied to the optical waveguide. Measuring the magnitude and/or sense (i.e. increase/decrease) in the intensity of optical radiation transmitted through the grating from an optical source enables torsion to be sensed.

Abstract: A fiber (Bragg) laser comprising a fiber with a cladding and a core having a (Bragg) grating inscribed in the core forming a laser cavity.

Abstract: A Gires-Tournois etalon (GTE) (10) comprising an optical fibre (12) in which a primary chirped fibre Bragg grating (FBG) (16) is provided, an RF signal generator (20), a piezoelectric transducer (22), and a glass horn (24), for coupling an acoustic wave (26) into the fibre (12). The acoustic wave (26) causes a periodic compression within the fibre (12), which induces a low frequency periodic refractive index modulation within the grating section (14) of the fibre (12). This causes two side frequency components to be generated for each high-frequency component of the FBG (16). Two secondary grating are thus excited, having the same spectral bandwidth as the FBG (16), but a lower reflectivity and different central wavelengths. The free spectral range of the GTE (10) can be adjusted by varying the frequency of the acoustic wave (26). The reflectivity of the excited secondary gratings can be adjusted by adjusting the amplitude of the acoustic wave (26).

Abstract: An optical fiber or waveguide having a core and a cladding, the fiber/waveguide including a modified region or regions with a modified optical property that differs from the surrounding optical fiber/waveguide, wherein the cross sectional area of the modified region(s) is considerably smaller than the cross sectional area of the core of the fiber or waveguide.

Abstract: Surface profiling apparatus (10) according to one embodiment comprises three long period gratings (LPGs) (12, 14, 16) fabricated in progressive three layered (PTL) fibre (18) and embedded within a deformable carrier member (40) comprising a skeleton (42) provided between two sheets of flexible rubber skin (44, 46). The LPGs (12, 14, 16) are illuminated by three wavelength modulated, narrow bandwidth optical signals, each having a different wavelength and modulation frequency. A photodetector (26) connected to three lock-in amplifiers (28, 30, 32) measures the amplitudes of the first and second harmonic frequency components of the photodetector output signal corresponding to each LPG (12, 14, 16). Similar surface profiling apparatus (10) forms the basis for respiratory function monitoring apparatus (100) in which five LPGs are provided within each of four PTL fibres (104, 106, 108, 110) and embedded in four carrier members (40a–d) attached to a garment (114) to be worn by a subject.

Abstract: Surface profiling apparatus (10) according to one embodiment comprises three long period gratings (LPGs) (12, 14, 16) fabricated in progressive three layered (PTL) fibre (18) and embedded within a deformable carrier member (40) comprising a skeleton (42) provided between two sheets of flexible rubber skin (44, 46). The LPGs (12, 14, 16) are illuminated by three wavelength modulated, narrow bandwidth optical signals, each having a different wavelength and modulation frequency. A photodetector (26) connected to three lock-in amplifiers (28, 30, 32) measures the amplitudes of the first and second harmonic frequency components of the photodetector output signal corresponding to each LPG (12, 14, 16). Similar surface profiling apparatus (10) forms the basis for respiratory function monitoring apparatus (100) in which five LPGs are provided within each of four PTL fibres (104, 106, 108, 110) and embedded in four carrier members (40a-d) attached to a garment (114) to be worn by a subject.

Abstract: A regenerated optical waveguide is fabricated by hydrogenating an optical waveguide (12) and exposing a grating section (28) to a UV laser beam interference fringe pattern (14) to form a Type I grating. The grating section (28) is exposed for a second period to erase the Type I grating, and then a third period to cause a regenerated optical waveguide grating to form. The resonant wavelength increases during the third period from being substantially the same as the final wavelength of the Type I grating.

Abstract: In the present invention an optical waveguide grating sensing device for a dual-parameter optical waveguide grating sensor includes a first optical waveguide grating of a first resonant wavelength provided in a first section of an optical waveguide and a second optical waveguide grating of a second resonant wavelength provided in a second of an optical waveguide. The first and second gratings have different coefficients of rate of change of wavelength as a function of temperature and have substantially the same coefficient of rate of change of wavelength as a function of stain.

Abstract: An optical pulse transmission line portion is provided, having dispersion slope compensation, including an optical waveguide (length L1, dispersion parameter D1) having a dispersion slope parameter (S1) of a first sign, and a dispersion compensation unit (length L2, dispersion parameter D2) having a dispersion slope parameter (S2) of the opposite sign.

Abstract: A strain sensor comprises an optical waveguide having a plurality of reflecting structure (Bragg grating) along its length. Each structure reflects light at a different characteristic wavelength (&lgr;1 to &lgr;n+1) which changes in dependence on a change of physical length of at least part of the reflecting structure. The reflectivity of reflecting structures which reflect at characteristic wavelengths which are adjacent to each other (&lgr;1 and &lgr;2 or &lgr;n and &lgr;n+1) are configured to be different such that the intensity of light reflected from adjacent structures can be used to discriminate between them.

Abstract: In the present invention an optical waveguide grating sensing device for a dual-parameter optical waveguide grating sensor includes a first optical waveguide grating of a first resonant wavelength provided in a first section of an optical waveguide and a second optical waveguide grating of a second resonant wavelength provided in a second of an optical wavelguide. The first and second gratings have different coefficients of rate of change of wavelength as a function of temperature and have substantially the same coefficient of rate of change of wavelength as a function of stain.

Abstract: A regenerated optical waveguide is fabricated by hydrogenating an optical waveguide (12) and exposing a grating section (28) to a UV laser beam interference fringe pattern (14) to form a Type I grating. The grating section (28) is exposed for a second period to erase the Type I grating, and then a third period to cause a regenerated optical waveguide grating to form. The resonant wavelength increases during the third period from being substantially the same as the final wavelength of the Type I grating.

Abstract: A dispersion compensation apparatus (10) includes a chirped fibre Bragg grating (CFBG) (12) coupled to a mechanical support (16) within a bending apparatus (14). The bending apparatus (14) is operable to bend the mechanical support (16) and hence the grating (12). Bending the grating (12) changes the periodicity, and thus the group delay characteristic, of the grating. The group delay characteristic of an initially linearly CFBG can thereby be made nonlinear. The grating (12) may be used to simultaneously compensate for chromatic dispersion and dispersion slope, and can therefore be used to recompress optical pulses.

Abstract: An optical pulse transmission line portion 10, having dispersion slope compensation, comprising an optical waveguide 12 (length L1, dispersion parameter D1) having a dispersion slope parameter (S1) of a first sign, and dispersion compensation means 14 (length L2, dispersion parameter D2) having a dispersion slope parameter (S2) of the opposite sign.

Abstract: Apparatus for sensing temperature and/or strain in an object includes a broadband light source (1), connector means (2) in the form of an optical circulator or an optical coupler to which at least two substantially identical optical fiber Bragg gratings (4, 5) are connected. Grating (4) receives the broadband light from the connector means (2) and functions as a sensor of temperature and/or strain in an object. Light is reflected back from the grating (4) to the connector means (2) and then passed to the grating (5) which acts as a reference grating through which a light output signal is transmitted to a detector (8) which is conveniently a photodetector. Means are provided for chirping the two gratings (4, 5) at the same bandwidth and the detector (8) measures the intensity of the received light output signal, with the intensity being monotonically related to the change in temperature and/or strain sensed by the grating (4) in the object.

Abstract: The invention describes an optical data storage medium in which the optical contrast of stored data bits is enhanced by the use, as a photosensitive material or as an additional photosensitive material, of a layer of a photochromic fulgide.

Abstract: An optical resonant assembly which comprises a plurality of partially light-transmitting mirrors, a layer of photochromic material disposed between the mirrors, a light source providing a light beam of variable intensity incident on the layer of photochromic material and detecting means for determining transmittance values of said incident beam at different intensity levels, said photochromic material having a low quantum yield for bleaching with light of a wavelength corresponding to said light beam and being selected from pyran compounds of the general formula (I) below: ##STR1## wherein X and Y together represent a spiro-adamantylidene group or a spiro-carbocyclic or heterocyclic group or X and Y independently represent hydrogen, alkyl (preferably lower alkyl having 1 to 5 carbon atoms) or phenyl and R.sub.3 and R.sub.4 each independently represent hydrogen, alkyl, aralkyl, aryl, halogen or a heterocyclic group and R.sup.