Abstract: A holey optical fibre for supporting propagation of light of a wavelength &lgr;,comprises a plurality of cylinders (10) each having a longitudinal axis, the cylinders (10) being separated from each other by regions of a matrix material (20) and having their longitudinal axes substantially parallel to each other. Each cylinder (10) has a diameter, in the plane perpendicular to the longitudinal axis, that is small enough for the composite material of the ensemble of cylinders and matrix material to be substantially optically homogenous in respect of light of wavelength &lgr;.

Abstract: In a method of producing a photonic crystal fibre, a preform (300) that includes holes is formed and the preform (300) is drawn into a fibre. The method includes the step of applying a pressure differential to certain of the holes to control changes in the fibre structure during the draw.

Abstract: A photonic crystal fiber including a plurality of longitudinal holes (220), in which at least some of the holes have a different cross-sectional area in a first region (200) of the fiber, that region having been heat-treated after fabrication of the fiber, from their cross-sectional area in a second region of the fiber (190), wherein the optical properties of the fiber in the heat-treated region (200) are altered by virtue of the change in cross-sectional area of holes (230) in that region (200).

Abstract: A photonic-crystal fibre comprises a core (20) and a cladding (10) with longitudinal holes. The refractive index of the core is lower than that of the cladding bulk material, e.g. by fluorine doping of the core material. The holes are air-filled cavities extending along the longitudinal direction of the fibre. One property of the fibre is that a guided mode having longer wavelength is more confined in the core than a mode with a shorter wavelength. Such a fibre may have a cut-off wavelength &lgr;c? such that the fibre is unable to guide in its core light of wavelengths shorter than &lgr;c.

Abstract: A photonic crystal fibre comprising a bulk material having an arrangement of longitudinal holes, the fibre including a cladding region and a guiding core (280), the cladding region having an effective-refractive-index which varies across the fibre's cross section, wherein, in use, the effective-refractive-index variation causes light propagating in the fibre to have a different transverse profile from the profile that it would have if the cladding region were of a substantially uniform effective refractive index.

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;.