Abstract: An optical waveguide environmental sensor is provided that is capable of detecting a target gas or liquid in the ambient environment in an advantageously short period of time. The waveguide is preferably in the form of an optical fiber having a cladding that contains a photonic band gap structure which in turn envelopes a light conducting, hollow core portion. The cladding further includes at least one elongated side opening that preferably extends the entire length of the fiber and exposes said hollow core portion to the ambient environment, which provides broad and nearly immediate access of the core portion to gases and liquids in the ambient environment, thereby minimizing sensor response time. The ambient gases or liquids filling the hollow core portion and elongated opening function as a ridge and slab, respectively, of an optical ridge waveguide that effectively supports at least one bound optical mode.

Abstract: An optical fiber includes a glass fiber having a glass core and a cladding that contains voids that are spaced apart from the core, in contact with the core, or form a substantial portion of the core. The voids act as trapping sites for ingressing molecules from the surrounding environment, thereby reducing the effect of such molecules on the fiber's light-transmission properties.

Abstract: In accordance with at least one embodiment of the present invention, a photonic crystal fiber apparatus includes a first cladding layer and a second cladding layer. The first cladding layer includes a plurality of photonic crystal rods disposed in an array along a longitudinal axis. The array has a separation between a first portion of the rods that defines a core region. A second portion of the photonic crystal rods is doped with two rare earth elements. The first cladding layer is configured to propagate signal light. The second cladding layer provides physical support for the plurality of photonic crystal rods and is configured to propagate pump light.

Abstract: A microbend-induced fiber grating is formed from a section of optical fiber configured to exhibit “splitting” between the resonant wavelengths supported by the TE and TM components of the LP1m mode and the resonant wavelength supported by the odd/even HE2m components of the LP1m mode. Since only the TE and TM components are polarization dependent, by splitting and shifting the resonant wavelengths for these modes away from a system-desired wavelength(s) supported by the odd/even HE modes, a polarization insensitive microbend-induced fiber grating can be formed. A fiber core configuration including a central core region, trench and ring is formed to exhibit a large radial gradient in core refractive index profile, with a significantly steep transition between the ring index and the trench index, to provide the desired splitting between the (undesired, polarization sensitive) TE/TM modes and the HE mode.

Abstract: A low-loss photonic waveguide in the form of a Bragg optical fiber is provided that includes a dielectric core region extending along a waveguide axis that is characterized by a low amount of Rayleigh scattering, and a dielectric confinement region surrounding the dielectric core region that includes alternating layers of different glass compositions having relative refractive index differences that are at least 0.10, and preferably at least 0.30. The core region may be formed from air. The confinement region includes alternating high and low index glass layers wherein the high index layers are substantially pure silica mixed with index raising dopants that form enough % of the high index glass layers by weight to achieve the aforementioned 0.10 difference in indices of refraction, while the low index glass layers may be either substantially pure silica, or silica mixed with index lowering dopants to increase the index contrast between the layers.

Abstract: An apparatus including a microchannel plate having a structure that defines multiple microchannels. The structure includes multiple claddings that form the walls of the microchannels, each of the claddings including a semiconducting layer. The claddings are surrounded by a glass having a lower percentage of materials having atomic numbers higher than 34 as compared to the cladding. The glass has a higher percentage of neutron absorbing material than the cladding, the neutron absorbing material capable of capturing neutrons in reactions that result in secondary electron emissions in the microchannels.

Abstract: The present invention is directed to a light pipe having a structure of enhancing an emission of a light. According to one embodiment of the present invention, a hollow light pipe comprises a base pipe comprising a structured inner surface and a substantially smooth outer surface; and a plurality of diffusive particles disposed on the outer surface. According to another embodiment of the present invention, a hollow light pipe comprises a base pipe comprising a structured inner surface and a substantially smooth outer surface; and a film having a plurality of scattering patterns on at least one surface of the film, and being disposed at inside or outside the base pipe. According to further another embodiment of the present invention, a hollow light pipe comprises a base pipe comprising a structured inner surface and a substantially smooth outer surface; and a cone-shaped extractor being disposed inside the base pipe.

Abstract: A hollow core photonic bandgap chalcogenide glass fiber includes a hollow core for passing light therethrough, a Raman active gas disposed in said core, a microstructured region disposed around said core, and a solid region disposed around said microstructured region for providing structural integrity to said microstructured region. A coupler can introduce at least one light signal into the hollow core of the chalcogenide photonic bandgap fiber. The method includes the steps of introducing a light beam into a hollow core chalcogenide photonic bandgap glass fiber filled with a Raman active gas disposed in the core, conveying the beam through the core while it interacts with the gas to form a Stokes beam of a typically higher wavelength, and removing the Stokes beam from the core of the fiber.

Abstract: An optical fiber having an axial direction and a cross section perpendicular to said axial direction, said optical fiber comprising: a first light guiding fiber portion (604) having a cladding region with a plurality of spaced apart cladding voids extending longitudinally in the fiber axial direction and a core region bounded by said cladding region, and a solid light transparent fiber portion (602) having a first end facing the first light guiding fiber portion and a second end forming an end face of the optical fiber, said solid light transparent fiber portion providing a hermetic sealing (601) of the cladding voids of the first light guiding fiber portion; a method of its production, and its use, such as an optical fiber connector and an article comprising a microstructured optical fiber with hermetically sealed end face.

Abstract: The invention relates to the field of chromatic dispersion compensating optical fibers for a wavelength multiplexing transmission network. A chromatic dispersion compensating optical fiber is provided having at least six core slices (1 to 6) and having a negative chromatic dispersion and chromatic dispersion slope.

Abstract: The invention discloses a plastic waveguide for guiding terahertz (THz) wave with a wavelength ranging from 30 to 3000 ?m. The plastic waveguide includes a core and a cladding layer. At least part of the core is made of a first plastic medium having a first refractive index, and the maximum length of a cross-section of the core is smaller than the wavelength of the guided terahertz wave. The cladding layer surrounds the core and has a second refractive index lower than the first refractive index. In the invention, only one wave mode is propagated in the plastic waveguide, and a first attenuation constant of the core for the guided terahertz wave is higher than a second attenuation constant of the cladding layer for the guided terahertz wave.

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: A photonic crystal structural body has a structure that a second mediums whose refractive index changes with an external field is periodically distributed in a first medium whose refractive index changes with the external field. An external field generator applies the external field to the photonic crystal structural body. It is possible to increase a change amount of a photonic band gap.

Abstract: Provided is a method of manufacturing an optical fiber preform from which an optical fiber having the desired characteristics can easily be produced.

Abstract: The present invention relates to the field of radio-frequency (RF) waveguides. More specifically, the present invention pertains to a method and apparatus that provides ultra-low-loss RF waveguide structures targeted between approximately 300 GHz and approximately 30 THz. The RF waveguide includes a hollow core and a flexible honeycomb, periodic-bandgap structure surrounding the hollow core. The flexible honeycomb, periodic-bandgap structure is formed of a plurality of tubes formed of a dielectric material such as of low-loss quartz, polyethylene, or high-resistivity silicon. Using the RF waveguide, a user may attach a terahertz signal source to the waveguide and pass signals through the waveguide, while a terahertz signal receiver receives the signals.

Abstract: A polarization controller includes a plurality of liquid crystal cells positioned as cladding on a waveguide that propagates a beam of light so that the evanescent field extends into the liquid crystal cells, and a ½-wave birefringent retarder for rotating the eigenstates of polarization between the liquid crystal cells. For fast response, the evanescent field preferably extends only into the surface effect region of the liquid crystal cells, where directors in the liquid crystal respond faster to changes in voltages applied across the liquid crystal cells.

Abstract: In general, in one aspect, the invention features a waveguide that includes a core extending along a waveguide axis and a confinement region surrounding the core. The confinement region includes a spiral portion and a non-spiral portion, wherein the spiral portion and the non-spiral portion extend along the waveguide axis.

Abstract: Novel preforms and methods of making novel preforms are described. The preforms are suitable for being drawn into photonic bandgap optical fibres. In one form, the preform comprises a stack of elongate members having, in transverse cross section, a triangular close-packed arrangement of circular cross section capillaries, which define interstitial regions containing solid rods. The stack is supported around a relatively large capillary, which defines an inner region of the stack. The stack may be adapted by varying the number of rods in any given interstitial region, in order to generate various different configurations of cladding structure, which can be made into optical fibres having surprising operational characteristics, such as a split gap.

Abstract: A Electronic/Photonic Bandgap Device (NC#98614). The apparatus includes a substrate; an electronics layer operatively coupled to the substrate; and an optical bus layer operatively coupled to the electronics layer. The optical bus layer comprises at least one 3D photonic bandgap structure having at least one period operatively coupled to the electronics layer and comprising a plurality of honeycomb-like structures having a plurality of high index regions and a plurality of low index regions, wherein the plurality of honeycomb-like structures comprises at least four honeycomb-like structures layered over each other, wherein a second honeycomb-like structure is offset from a first honeycomb-like structure, wherein a third honeycomb-like structure is offset from a second honeycomb-like structure, and wherein a fourth honeycomb-like structure is not offset from the first honeycomb-like structure. The 3D photonic bandgap structure and the electronics layer are monolithically integrated over the substrate.

Abstract: A three-dimensional photonic crystal has periodic-refractive-index structures including a first layer having a periodic structure based on a first rectangular lattice having a period of A along a first axis and a period of B along a second axis orthogonal to the first axis in the plane direction, a second layer having a periodic structure disposed at a position shifted by +3B/8 along the second axis with respect to the position of the first rectangular lattice, a third layer having a periodic structure disposed at a position shifted by A/2 along the first axis and B/2 along the second axis with respect to the position of the periodic structure in the first layer, and a fourth layer having a periodic structure disposed at the same position as the periodic structure in the second layer.

Abstract: An apparatus for inspecting a specimen, such as a semiconductor wafer, is provided. The apparatus comprises a laser energy source, such as a deep ultraviolet (DUV) energy source and an optical fiber arrangement. The optical fiber arrangement comprises a core surrounded by a plurality of optical fibers structures used to frequency broaden energy received from the laser energy source into frequency broadened radiation. The frequency broadened radiation is employed as an illumination source for inspecting the specimen. In one aspect, the apparatus comprises a central core and a plurality of structures generally surrounding the central core, the plurality of fibers surround a hollow core fiber filled with a gas at high pressure, a tapered photonic fiber, and/or a spider web photonic crystalline fiber, configured to receive light energy and produce frequency broadened radiation for inspecting the specimen.

Abstract: A photonic band gap fiber and method of making thereof is provided. The fiber is made of a non-silica-based glass and has a longitudinal central opening, a microstructured region having a plurality of longitudinal surrounding openings, and a jacket. The air fill fraction of the microstructured region is at least about 40%. The fiber may be made by drawing a preform into a fiber, while applying gas pressure to the microstructured region. The air fill fraction of the microstructured region is changed during the drawing.

Abstract: A hole-assisted holey fiber is provided. The holey fiber includes a core region; a cladding region around the core region, and a plurality of holes in the cladding region around the core region. The core region has a higher refractive index than that of the cladding region. The holes form an inner hole layer and an outer hole layer, and the inner hole layer has the same number of holes as the number of the holes in the outer hole layer. The outer layer holes are provided in locations in which inner holes are absent when viewed from the center of the core region, and holes defining the same layer have the same diameter. A distance ?1 from a center of the core region to a center of an inner hole and a distance ?2 from the center of the core region to a center of an outer hole satisfy the relationship ?1<?2, and a diameter d1 of an inner hole and a diameter d2 of an outer hole satisfy the relationship d1?d2.

Abstract: The present invention is directed to a method and an apparatus for analysis of an analyte. The method involves providing a zero-mode waveguide which includes a cladding surrounding a core where the cladding is configured to preclude propagation of electromagnetic energy of a frequency less than a cutoff frequency longitudinally through the core of the zero-mode waveguide. The analyte is positioned in the core of the zero-mode waveguide and is then subjected, in the core of the zero-mode wave guide, to activating electromagnetic radiation of a frequency less than the cut-off frequency under conditions effective to permit analysis of the analyte in an effective observation volume which is more compact than if the analysis were carried out in the absence of the zero-mode waveguide.

Abstract: A connection end portion of a PC fiber 10 is fused by heating to provide a sealing portion 15 which seals holes 12a of a cladding 12. Length L of the sealing portion 15 is determined by calculation based on the conditions such as an incident angle ? [°] of signal light 22 with respect to the PC fiber 10, an outer diameter D [?m] of the fiber, a diameter a [?m] of the core of the fiber and a refractive index n of the sealing portion 15.

Abstract: A photonic crystal fiber includes a core region for propagating light in a longitudinal direction of the fiber, a cladding region surrounding the core region, the cladding region including micro-structural elements extending in the longitudinal direction. The cladding region further includes at least one stress element having a coefficient of thermal expansion ?T,SAP and extending in the longitudinal direction of the photonic crystal fiber, the stress element(s) being located in a cladding background material having a coefficient of thermal expansion ?T,cladback different from ?T,SAP. The location of the at least one stress element relative to the core region and the micro-structural elements and the coefficients of thermal expansion ?T,SAP and ?T,cladback are adapted to provide a stress induced birefringence in the core region of the photonic crystal fiber. An article includes a photonic crystal fiber, a method of manufacturing and the use of a photonic crystal fiber are furthermore provided.

Abstract: A porous optical fiber provided with air holes and a method for manufacturing the same are disclosed. The porous optical fiber includes a core having a first refractivity extended in a longitudinal direction, an external cladding layer having a second refractivity surrounding the core, and an internal cladding layer having a third refractivity formed between the core and the external cladding layer and provided with a plurality of air holes scattered therethrough.

Abstract: This invention pertains to a glass fiber, a Raman device and a method. The fiber is a hollow core photonic bandgap chalcogenide glass fiber that includes a hollow core for passing light therethrough, a Raman active gas disposed in said core, a microstructured region disposed around said core, and a solid region disposed around said microstructured region for providing structural integrity to said microstructured region. The device includes a coupler for introducing at least one light signal into a hollow core of a chalcogenide photonic bandgap fiber; a hollow core chalcogenide photonic bandgap glass fiber; a microstructured fiber region disposed around said core; a solid fiber region disposed around said microstructured region for providing structural integrity to said microstructured region; and a Raman active gas disposed in the hollow core.

Abstract: The invention proposes a double-clad photonic optical fiber presenting: a fiber core, first cladding surrounding the fiber core, and second cladding surrounding the first cladding; at least one hole in the fiber core; and doping using a rare earth ion, at least in the core of the fiber. The invention makes it possible to obtain a double-clad fiber with good overlap between the signal and a pump injected into the core. It improves amplification efficiency in double-clad optical amplifiers where the signal is injected into the core of the fiber and the pump into the first cladding.

Abstract: An extended triangular lattice type photonic bandgap fiber, includes a cladding and a capillary core, the cladding having a plurality of holes disposed within a silica glass portion in a longitudinal direction of the fiber and arranged in an extended triangular lattice shape, the capillary core having a plurality of holes arranged in a triangular lattice shape, wherein the cross-sectional area of the respective holes in the capillary core is smaller than that of the respective holes in the cladding.

Abstract: Electromagnetic radiation sources operating in the Terahertz (THz) region capable of overcoming the Manley-Rowe limits of known optical schemes by achieving phase matching between a THz wave and optical pulse in a nonlinear waveguide, or by achieving both phase and group velocity matching between a THz wave and optical pulse in a nonlinear waveguide to yield even higher efficiencies in converting optical power to the THz region.

Abstract: An in-line, distributed optical fiber filter comprises a core region with a raised refractive index (with respect to the surrounding cladding material) so as to allow for total internal reflection (TIR) of the desired transmission wavelength(s). One or more raised index features are formed within the cladding region and are configured so as to result in mode mixing between the cladding mode and core mode at determined wavelength(s) to be removed by filtering. The parameters associated with determining the proper core specifications and cladding specifications can be separately determined to provide for enhanced performance in terms of both filtering unwanted signals and propagation of desired communication signals.

Abstract: The present invention provides a new and unique method for increasing the photosensitivity of a large diameter optical waveguide having a cross-section of at least about 0.3 millimeters. The method features loading the large diameter optical waveguide with a photosensitizing gas at a pressure at least about 4000 pounds per square inch (PSI) at a temperature of at least about 250° Celsius. The photosensitizing gas may be hydrogen, Deuterium or other suitable gas. The method also includes the step of using a particular large diameter optical waveguide having a core more than 1000 microns from the surface thereof. The method may be used as part of a process for writing a Bragg grating in an inner core or a cladding of the large diameter optical waveguide.

Abstract: An optical fiber having a longitudinal direction and a cross-section perpendicular thereto, said fiber in a cross-section comprising: (a) a core region (11) having a refractive index profile with a highest refractive index nc, and (b) a cladding region comprising cladding features (10) having a center-to-center spacing, ?, and a diameter, d, of around 0.4? or larger, wherein nc, ? and d are adapted such that the fiber exhibits zero dispersion wavelength of a fundamental mode in the wavelength range from 1530 nm to 1640 nm; a method of producing such a fiber; and use of such an optical fiber in e.g. an optical communication system, in an optical fiber laser, in an optical fiber amplifier, in an optical fiber Raman amplifier, in a dispersion compensator, in a dispersion and/or dispersion slope compensator.

Abstract: An optical fiber includes a glass fiber having a glass core and a cladding that contains voids that are spaced apart from the core, in contact with the core, or form a substantial portion of the core. The voids act as trapping sites for ingressing molecules from the surrounding environment, thereby reducing the effect of such molecules on the fiber's light-transmission properties.

Abstract: Fiber Bragg gratings were written in pure silica photonic crystal fibers and photonic crystal fiber tapers with 125 fs, 800 nm IR radiation. High reflectivites were achieved with short exposure times in the tapers. Both multimode and single mode grating reflections were achieved in the fiber tapers. By tapering the photonic crystal fibers scattering that would otherwise have occurred was lessened and light external to the fiber could reach the core effectively to write a grating.

Abstract: A method and apparatus use a photonic-crystal fiber having a very large core while maintaining a single transverse mode. In some fiber lasers and amplifiers having large cores problems exist related to energy being generated at multiple-modes (i.e., polygamy), and of mode hopping (i.e., promiscuity) due to limited control of energy levels and fluctuations. The problems of multiple-modes and mode hopping result from the use of large-diameter waveguides, and are addressed by the invention. This is especially true in lasers using large amounts of energy (i.e., lasers in the one-megawatt or more range). By using multiple small waveguides in parallel, large amounts of energy can be passed through a laser, but with better control such that the aforementioned problems can be reduced. An additional advantage is that the polarization of the light can be maintained better than by using a single fiber core.

Abstract: By writing non-linear chirp into fiber Bragg gratings, greater control over dispersion compensation in CPA systems is obtained, such that, for example, the dispersion profile of the fiber Bragg grating and a bulk compressor may be matched. An iterative method of writing the fiber grating can reduce the group delay ripple to very low levels; and adaptive control of the fiber grating dispersion profile can further reduce these levels, while in addition offering greater acceptable yield in the manufacture of such gratings. Fiber Bragg gratings may be designed so as to provide customized pulse shapes optimized for various end uses, such as micromachining, for example, and may also be used to counteract gain-narrowing in a downstream amplifier.

Abstract: A large mode area (LMA) fiber with improved resistance to bend-induced distortions utilizes highly oscillatory modes such that the effective index of the propagating modes remains less than the bent-fiber “equivalent” refractive index over a greater portion of the core. By providing a signal mode with a reduced effective index, the “forbidden” (evanescent) region of the core is reduced, and bend-induced distortion of the propagating mode is largely avoided.

Abstract: Light transmission is maximized through the pass band of a photonic bandgap (PBG) crystal (having alternating high- and low-index material) while preserving high reflection for stop band. An anti-reflective coating (ARC) is used to coat the PBG crystal wherein the ARC material has a refractive index of n=(nair×nhigh index material)1/2 and thickness around ?c/8 where ?c is center wavelength.

Abstract: A photonic optical fiber and method of making the optical fiber. The method includes assembling a plurality of elongate elements to define an elongate void; forming within the void a material contacting at least some of the elements while maintaining the elongate void; and drawing a preform, including the assembly of elongate elements, into an optical fiber.

Abstract: This invention pertains to fiber termination combination which includes an optical fiber having a fiber core for transmitting a highly energetic optical signal that can damage the fiber and a structured region around the core for directing the optical signal into the core, the structured region being characterized by multiple channels of smaller internal diameter than the core defined by thin walls disposed around said core; a ferrule, with an opening therein for locating said fiber, at the end of said fiber enveloping said fiber extremity which cooperates with said blocking structure to block the optical signal from impinging on said microstructured region of said fiber; and a blocking structure disposed over the end of said fiber with an opening mating with said fiber core, said blocking structure blocking the optical signal from impinging on said microstructured region of said fiber.

Abstract: An optical system comprises an optical fiber with gain producing core with an index of refraction n1, surrounded by at least one cladding with an index of refraction n2, said cladding including at least one index reduced area with an index of refraction n2, such that n1>n2>n2, the core propagating a signal at a spatial fundamental mode at a signal wavelength ?1 and at a power level sufficient to generate optical power at a wavelength ?2, where ?2>?1, and the at least one index reduced area in combination with the core provide has at least one cut-off fundamental spatial mode wavelength ?C, and ?1<?C and ?2>?C.

Abstract: A phase-conjugate mirror has a length of hollow core photonic crystal multi-spatial mode, polarization-maintaining fiber disposed in a vessel, with a compressible and preferably gaseous medium, such as Xe or CH4, occupying the hollow core of the of hollow core photonic crystal fiber and surrounding the exterior of the hollow core photonic crystal fiber. At least one sealed window is provided in the vessel, the at least one sealed window being optically coupled to at least one end of the length of hollow core photonic crystal fiber.

Abstract: An optical fiber having reduced residual stress discontinuity is disclosed. The optical fiber includes a core which is an optical transmission medium and a clad for surrounding the core. The residual stress discontinuity at an interface between the core and the clad is 20.0 MPa or less, which is represented by an absolute value of a difference between a minimum axial stress at (r/a)=0.8-1.1 and a maximum axial stress at (r/a)=1.0-1.2, wherein a is the radius of the core and r is a radius measured from the center of the core.

Abstract: A photonic-bandgap fiber includes a photonic crystal lattice with a first material having a first refractive index and a pattern of a second material formed therein. The second material has a second refractive index lower than the first refractive index. The photonic crystal lattice has a plurality of first regions that support intensity lobes of the highest frequency bulk mode and has a plurality of second regions that do not support intensity lobes of the highest frequency bulk mode. The photonic-bandgap fiber further includes a central core formed in the photonic crystal lattice. The photonic-bandgap fiber further includes a core ring having an outer perimeter. The core ring surrounds the central core, wherein the outer perimeter of the core ring passes only through the second regions of the photonic crystal lattice.

Abstract: A single mode fiber is provided which is suitable for high-speed, large-capacity optical communication and for optical wiring. The single mode fiber has a first cladding region with a uniform refractive index, a core region with a refractive index higher than that of the first cladding region, and a second cladding region including at least four air hole regions placed in the first cladding region. Optimization can be achieved by making the distance from the center of the core region to the air hole regions equal to 2–4.5 times the core radius, and the air hole radius equal to or greater than 0.2 times the core radius. It is preferable the core radius be 3.7–4.8 ?m, the relative index difference of the core region from the first cladding region be 0.3–0.55 %.

Abstract: A payload is enclosed within a container that is dimensioned to fit within the channel that runs through a hollow optical fiber. The container is also adapted to carry a payload. When laser light shines into the optical fiber, some of the laser light strikes the container and propels the container through the channel. As a result, the payload is transported through the hollow fiber.

Abstract: A novel optical plastic fiber comprising a core region and having a center line along a longitudinal axis of the fiber is disclosed. The refractive index of the core region increases along a direction going from a periphery portion to the center line in any plane perpendicular to the center line, and the birefringence index of the core region varies along a direction going from the center line to a periphery portion perpendicular to the center line in any plane parallel to the center line and containing the center line.

Abstract: Photonic crystal fibers that guide light by virtue of a photonic band gap. Fibers that are formed from materials having higher refractive indices than silica are provided using an optical waveguide including a core with a relatively low refractive index and a photonic band gap structure that can substantially confine light to the core. The structure includes elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index, with the band gap residing above the fifth photonic band of the band gap structure.