Abstract: A birefringent elongate waveguide for guiding light, comprises: a core region (110), comprising an elongate region of relatively low refractive index; and a cladding region (100), comprising elongate regions (105) of relatively low refractive index interspersed with elongate regions (117,120) of relatively high refractive index. In a transverse cross-section of the waveguide, a (5) relatively high refractive index boundary region (115) is provided that surrounds the core region and has either (1) at most two-fold rotational symmetry or (2) a rotational symmetry that reduces the rotational symmetry of the waveguide to at most two-fold rotational symmetry. The symmetry of the boundary region (115) results at least in part from azimuthal variations therein, which are substantially uncharacteristic of the cladding region (100).

Abstract: A method of manufacturing an optical fibre, comprises: (i) forming a preform (10) for drawing into the fibre, the preform (10) comprising a bundle of elongate elements, (20,50) arranged to form a first region that becomes a cladding region of the fibre and a second region that becomes a core region of the fibre; (ii) drawing the preform (10) into the fibre. The bundle of elongate elements (20,50) comprises a plurality of elongate elements (20) of a lower purity dielectric material and at least one elongate element (50) of a higher purity dielectric material. The first region comprises a plurality of the lower purity elements (20) and the second region comprises the higher purity element (50).

Abstract: This invention relates to an optical fibre that comprises a core (4) of lower refractive index that is surrounded by a cladding which includes regions of a higher refractive index and is substantially periodic, where the core (4) has a longest transverse dimension that is longer than a single, shortest period of the cladding. In a fibre of this type light is substantially confined to the core area by virtue of the photonic band gap of the cladding material. The invention also relates to a method of manufacturing such an optical fibre, comprising the steps of forming a stack of canes (5), the stack (5) including at least one truncated cane (6) that defines an aperture (7), and then drawing the stack (5) into a fibre having an elongate cavity. The fibre is suitable for high power uses, but is equally suitable for other areas, e.g. optical amplifiers, spectral filters, lasers, gas sensors and telecommunications networks.

Abstract: An elongate waveguide for guiding light includes a core having an elongate region of relatively low refractive index; a microstructured region around the core having elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index; and a boundary at the interface between the core and the microstructured region, the boundary including in the transverse cross-section, a region of relatively high refractive index, which is connected to the microstructured region at a plurality of nodes, at least one relatively enlarged region around the boundary (and excluding a boundary having twelve nodes and six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes).

Abstract: The present invention relates to photonic crystal fibers, in particular to photonic crystal fibers that guide light by virtue of a photonic band gap. It is an object of the present invention to provide such fibers that are formed from materials having higher refractive indices than silica. The object is achieved by an elongate waveguide comprising a core with a relatively low refractive index and a photonic band gap structure that can substantially confine light to the core, the structure comprising elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index wherein the band gap resides above the fifth photonic band of the band gap structure. Alternatively the photonic band gap may have a V0-value in the range 130?V02?160. Alternatively the waveguide has a lattice pitch ? and the elongate regions have a transverse dimension d, wherein the photonic band gap has a normalized centre frequency k0? in the range 5?k0??6, when d/?=0.

Abstract: A method of manufacturing a microstructured fibre, comprises: providing a preform comprising a plurality of elongate holes; mating at least one, but not all, of the holes with a connector to connect the hole(s) to an external pressure-controller; drawing the preform into the fibre whilst controlling gas pressure in the hole(s) connected to the pressure-controller. The connector is also claimed.

Abstract: An optical fibre comprises: (i) a plurality of elongate, tubular, higher-refractive-index regions (20,50) of dielectric material, the regions being concentric about a longitudinal axis; (ii) a plurality of elongate, tubular lower-refractive-index regions, arranged between the higher-index regions (20,50), and comprising bridging regions (30), of a solid dielectric material, and a plurality of elongate holes (40); and (iii) a core region (10). The higher-index regions (20,50) and the lower-index regions (40) together define a cladding structure arranged to guide light in the core region (10). The elongate holes (40) are arcuate in cross-section.

Abstract: A nonlinear optical device, comprises a source of input light having a first spectrum and an optical fibre 10 arranged so that in use the light propagates through the fibre 10, the optical fibre 10 comprises a tapered region including a waist 30, the waist 30 having a diameter smaller than 10 microns for a length of more than 20 mm, wherein the propagating light is converted by nonlinear optical processes into output light having a spectrum different from the first spectrum.

Abstract: A large core photonic crystal fiber for transmitting radiation having a core comprising a substantially transparent core material and having a core diameter of at least 5&mgr;. The fiber also comprises a cladding region surrounding the length of core material, wherein the cladding region comprises a first substantially transparent cladding material, having a first refractive index, and wherein the first substantially transparent cladding material has embedded along its length a substantially periodic array of holes, wherein the holes are filled with a second cladding material having a second refractive index less than the first refractive index, such that radiation input to the optical fiber is transmitted along the length of the core material in a single mode of propagation. In a preferred embodiment, the core diameter may be at least 20&mgr;, and may be as large as 50&mgr;. The fiber is capable of transmitting higher power radiation than conventional fibers, whilst maintaining propagation in a single mode.

Abstract: A composite material for supporting propagation of light of a wavelength &lgr;, comprising a plurality of cylinders each having a longitudinal axis, the cylinders being separated from each other by regions of a matrix material and the cylinders having their longitudinal axes substantially parallel to each other, and each cylinder having a diameter, in the plane perpendicular to the longitudinal axis, that is small enough for the composite material to be substantially optically homogeneous in respect of light of wavelength &lgr;.

Abstract: A large core photonic crystal fibre for transmitting radiation having a core comprising a substantially transparent core material and having a core diameter of at least 5&mgr;. The fibre also comprises a cladding region surrounding the length of core material, wherein the cladding region comprises a first substantially transparent cladding material, having a first refractive index, and wherein the first substantially transparent cladding material has embedded along its length a substantially periodic A array of holes, wherein the holes are filled with a second cladding material having a second refractive index less than the first refractive index, such that radiation input to the optical fibre is transmitted along the length of the core material in a single mode of propagation. In a preferred embodiment, the core diameter may be at least 20&mgr;, and may be as large as 50&mgr;.

Abstract: A large core photonic crystal fiber for transmitting radiation having a core comprising a substantially transparent core material and having a core diameter of at least 5 &mgr;. The fiber also comprises a cladding region surrounding the length of core material, wherein the cladding region comprises a first substantially transparent cladding material, having a first refractive index, and wherein the first substantially transparent cladding material has embedded along its length a substantially periodic array of holes, wherein the holes are filled with a second cladding material having a second refractive index less than the first refractive index, such that radiation input to the optical fiber is transmitted along the length of the core material in a single mode of propagation. In a preferred embodiment, the core diameter may be at least 20 &mgr;, and may be as large as 50 &mgr;.

Abstract: An optical fiber for transmitting radiation comprising two or more core regions, two or more core regions, each core region comprising a substantially transparent core material and having a core refractive index, a core length, and a core diameter, wherein said core regions are arranged within a cladding region, said cladding region comprising a length of first substantially transparent cladding material, having a first refractive index, wherein said first substantially transparent cladding material has an array of lengths of a second cladding material embedded along its length, wherein the second cladding material has a second refractive index which is less than said first refractive index, such that radiation input to said fiber propagates along at least one of said core regions. The cladding region and the core regions may be arranged such that radiation input to said optical fiber propagates along one or more said lengths of said core regions in a single mode of propagation.