Abstract: A first embodiment of the invention provides a Gires-Tournois etalon (DGTE) 20 comprising a cladding mode suppressed optical fibre 22, including an etalon section 24 in which a weakly reflective optical waveguide grating 26 and a strongly reflective optical waveguide grating 28 are provided. The two gratings 26, 28 are chirped fibre Bragg gratings (FBGs). The chirped FBGs 26, 28 are arranged to together define an etalon cavity. Another aspect of the invention provides a dispersion compensator 60 comprising two DGTEs 62, 64 according to the first embodiment of the invention. The DGTEs 62, 64 have a linearly varying dispersion over a selected optical bandwidth. The first DGTE 62 has a positive dispersion slope and the second DGTE 64 has a negative dispersion slope. The magnitudes of the dispersion slopes of the two DGTEs 62, 64 are substantially equal, so that the dispersion compensator 60 has a constant dispersion across the selected bandwidth.

Abstract: A first embodiment of the invention provides a Gires-Tournois etalon (DGTE) 20 comprising a cladding mode suppressed optical fibre 22, including an etalon section 24 in which a weakly reflective optical waveguide grating 26 and a strongly reflective optical waveguide grating 28 are provided. The two gratings 26, 28 are chirped fibre Bragg gratings (FBGs). The chirped FBGs 26, 28 are arranged to together define an etalon cavity. Another aspect of the invention provides a dispersion compensator 60 comprising two DGTEs 62, 64 according to the first embodiment of the invention The DGTEs 62, 64 have a linearly varying dispersion over a selected optical bandwidth. The first DGTE 62 has a positive dispersion slope and the second DGTE 64 has a negative dispersion slope. The magnitudes of the dispersion slopes of the two DGTEs 62, 64 are substantially equal, so that the dispersion compensator 60 has a constant dispersion across the selected bandwidth.

Abstract: Instead of a single beam, two coherent beams of light are used to illuminate a phase grating in spatially separated zones for writing a Bragg reflection grating in an underlying optical (fiber) waveguide. Close proximity between phase mask and waveguide is not required. This facilitates the use of masking so that only two different diffracted orders contribute to the fringe pattern that generates the Bragg grating, thereby improving fringe contrast and reducing the deleterious spectral effects upon the reflectivity of the Bragg reflector occasioned by the presence of stitch errors in the phase grating.

Abstract: In order to use one dispersion compensating fiber element for selecting a given value of dispersion, one or more frequency or wavelength dependent optical reflection gratings (G1, G2, G3) is located at such a position along the unit (8) that the double traversal of a section results in a desired value of dispersion at a frequency. A directional coupler (9) diverts the reflected wave to utilization means (10) for its recovery. If a different value of dispersion at the same wavelength, or if some value of dispersion at a different frequency, is required, a reflection grating effective to reflect at the appropriate frequency and at the appropriate position, gives the required values.

Abstract: A partially coated optical fiber for laser transmission, is described, wherein the partially coated optical fiber comprises an optical fiber which comprises an optionally clad fiber core and an external coating. The external coating and the fiber core are longitudinally substantially coextensive but circumferentially non-coextensive whereby the coating defines a grating window extending longitudinally for at least the major part of the length of the fiber. The window is optionally interrupted by one or more coating continuities which partition said window. The coating has a thickness such that a plane bridging the circumferential displacement of the grating window is extra-peripheral of the optical fiber.

Abstract: Exposure to UV light of a photosensitive optical fiber through a uniform pitch phase grating is employed to write a chirped Bragg reflection grating in that fiber by imparting tensile strain to the fiber while sections of the Bragg reflection grating are sequentially written, and by altering the magnitude of that strain during the writing process.

Abstract: An active optical fiber for use in an amplifier or laser has an inner cladding and an outer cladding. An index grating is written into the inner cladding to provide coupling between cladding modes of pumping radiation conducted in the inner cladding. The periodicity of the index grating is selected to couple energy from cladding modes having minimal overlap with the core to cladding modes having relatively high overlap. The efficiency of pumping the radiation amplifying medium of the core is thereby improved. The fibre has utility in transmitters for broad band networks.

Abstract: A laser has an optical laser cavity one end of which is constituted by a partial reflector formed in optical waveguide by an unbalanced Michelson interferometer comprising an optical waveguide splitter/combiner (23; 33) and two optical waveguide Bragg grating reflectors (24a, 24b; 34a, 34b; 44a, 44b).

Abstract: Optical FM is converted to AM, for instance for injection laser emission wavelength stabilisation, using an optical arrangement comprising a 2.times.2 3 dB coupler and a pair of monotonically oppositely chirped Bragg fiber grating spectrally selective reflectors connected in Mach Zehnder configuration.

Abstract: An optical wave, guide transmission filter has a 3 dB single mode waveguide coupler that is provided on one side of its coupling region with a spectrally matched pair of retro-reflecting optical waveguide Bragg grating reflectors. The optical path distance of one of the Bragg reflectors from the coupling region is greater than the equivalent distance of the other Bragg reflector by an amount greater than half the coherence length of a signal having a spectral width matched with that of the Bragg reflectors.

Abstract: A phase grating mask is placed in-contact or near contact with an optical waveguide to make a blazed grating in the waveguide. A band of grating elements are defined across a surface of the mask such that in the plane of the surface each element is formed at a predetermined blaze angle to a central longitudinal axis of the band. The grating is made by aligning the waveguide with the axis of the band and irradiating the phase mask. Gratings may be formed in a single step, or in several steps by moving the mask relative to the waveguide after each irradiation. The mask may be formed on a substrate by electron beam lithography.

Abstract: A method of generating a Bragg reflective grating in a photosensitive optical waveguide using a fringe pattern of electromagnetic radiation additionally employs a further beam of radiation to promote differential heating of the fibre in the region where the grating is being generated. The differential heating produces differential photo-sensitivity of the fibre so that the resulting grating, though it has a constant physical pitch, has an effective optical pitch that is a function of position along the length of the grating.

Abstract: A method of generating a Bragg reflective grating in a photosensitive optical waveguide using a fringe pattern of electromagnetic radiation involves positioning a mask in the path of the radiation, and moving that mask during the creation of the grating so that different portions of the grating receive different exposures to the radiation so that the resulting grating, though it has a constant physical pitch, has an effective optical pitch that is a function of position along the length of the grating.

Abstract: An optical waveguide transmission filter has a 3 dB single mode waveguide coupler that is provided on one side of its coupling region with a spectrally matched pair of retro-reflecting optical waveguide Bragg grating reflectors. The optical path distance of one of the Bragg reflectors from the coupling region is greater than the equivalent distance of the other Bragg reflector by an amount greater than half the coherence length of a signal having a spectral width matched with that of the Bragg reflectors.