Abstract: A hollow fiber has a hollow tube, a reflecting film formed on an inner wall of the hollow tube, and the reflecting film is a first metal film formed by baking a first metal nano particle solution including a first metal nano particle. The hollow fiber may have a transparent film on the first metal film. The transparent film is formed by baking or chemically reacting from a second metal nano particle included in a second metal nano particle solution.

Abstract: Provided is a holey single-mode optical fiber including a core not having holes, and a clad having holes extending in a longitudinal direction, in which a refraction index of the core is larger than that of a portion of the clad other than the holes, a radius r1 of the core is within a range of 2.2 to 3.2 ?m, a relative refraction index difference ? of the core to the clad is within a range of 0.3 to 0.56%, a distance Rin between a center of the core and an inner edge of the holes is 2.0 to 3.5 times the radius r1 of the core, an air-filling fraction F is within a range of 30 to 50%, a cable cut-off wavelength is 1.0 ?m or less, a zero-dispersion wavelength is within a range of 1260 to 1460 nm, and a bending loss characteristic at a bending radius of 10 mm is 10 dB/m or less.

Abstract: An optical fiber connection structure which reduces MPI in the use of an optical fiber with a bend resistance improved by forming holes in the fiber, and a single-mode fiber which reduces MPI are provided. A second cladding portion of a second single-mode fiber 20 includes holes 28, and thus, the second single-mode fiber 20 has low bending loss. A portion of the second single-mode fiber 20 connected to a first single-mode fiber 10a is made solid by filling corresponding portions of the holes 28 over the length L0, and light in a mode LP11 is significantly attenuated in this portion, thereby reducing MPI.

Abstract: An optical fiber includes a cladding, a first core, and a second core. At least one of the first core and the second core is hollow and is substantially surrounded by the cladding. At least a portion of the first core is generally parallel to and spaced from at least a portion of the second core. The optical fiber includes a defect substantially surrounded by the cladding, the defect increasing a coupling coefficient between the first core and the second core.

Abstract: A multi-core holey fiber with suppression of crosstalk deterioration among transmitted optical signals in a plurality of cores, and an optical transmission system using the fiber are disclosed. The multi-core holey fiber comprises a plurality of cores arranged separately from each other, and a cladding surrounding the plurality of cores wherein the cladding has plurality of holes arranged in a triangular lattice shape to create hole layers around the plurality of cores. Additionally, d/? is not more than 0.5, where ? [?m] is lattice constant of the triangular lattice, d [?m] is diameter of each of the holes; a distance between adjacent cores is equivalent to not less than six hole layers; the cores arranged farthest from the center of the multi-core holey fiber is surrounded by not less three hole layers; and the sum of the coupling coefficients between the adjacent cores is not more than 1.6×10?5/m.

Abstract: A double clad fiber includes a core, a first cladding provided so as to cover the core, and a second cladding provided so as to cover the first cladding. The second cladding has a plurality of pores extending in a length direction and arranged so as to surround the first cladding. In at least one fiber end, the second cladding has been removed by mechanical processing so that the at least one fiber end is formed by the core and the first cladding.

Abstract: A hollow fiber has a hollow tube, a reflecting film formed on an inner wall of the hollow tube, and the reflecting film is a first metal film formed by baking a first metal nano particle solution including a first metal nano particle. The hollow fiber may have a transparent film on the first metal film. The transparent film is formed by baking or chemically reacting from a second metal nano particle included in a second metal nano particle solution.

Abstract: A fluid conduit comprises an inner conduit configured for conducting a fluid, and an outer conduit circumferentially enclosing the inner conduit. The outer conduit's inner diameter is larger than the inner conduit's outer diameter, with an interspace being formed between the inner conduit's outer surface and the outer conduit's inner surface. The interspace between the inner conduit's outer surface and the outer conduit's inner surface contains an interspace liquid. The inner conduit is configured for guiding light coupled into the inner conduit, and dependent on the light's angle of incidence, total reflection occurs at a boundary between the inner conduit's outer surface and the interspace between the inner conduit and the outer conduit.

Abstract: Provided is an optical fiber that has a small bending loss, can be securely prevented from being fractured due to accidental bending during installation or other operations, and is compliant with the G. 652 standard. An optical fiber 1 includes a core 11, a first cladding 12, a second cladding 13, and a third cladding 14. The relative refractive index difference ?1 of the core 11 is in the range of 0.3% to 0.38%, the relative refractive index difference ?2 of the first cladding 12 is equal to or smaller than 0%, and the relative refractive index difference ?3 of the second cladding 13 is in the range of ?1.8% to ?0.5%. The inner radius r2 and the outer radius r3 of the second cladding 13 satisfy the expression “0.4r2+10.5<r3<0.2r2+16”, and the inner radius r2 of the second cladding 13 is equal to or greater than 8 ?m. The bending loss at a wavelength of 1550 nm and at a radius of curvature of 7.5 mm is smaller than 0.

Abstract: An optical assembly includes a gas cell and an optical fiber portion in which the gas cell is contiguously attached to the optical fiber portion. The gas cell can be made, for example from hollow-core photonic crystal fiber (HC-PCF).

Abstract: Provided is an optical fiber that has a small bending loss, can be securely prevented from being fractured due to accidental bending during installation or other operations, and is compliant with the G. 652 standard. An optical fiber 1 includes a core 11, a first cladding 12, a second cladding 13, and a third cladding 14. The relative refractive index difference ?1 of the core 11 is in the range of 0.3% to 0.38%, the relative refractive index difference ?2 of the first cladding 12 is equal to or smaller than 0%, and the relative refractive index difference ?3 of the second cladding 13 is in the range of ?1.8% to ?0.5%. The inner radius r2 and the outer radius r3 of the second cladding 13 satisfy the expression “0.4r2+10.5<r3<0.2r2+16”, and the inner radius r2 of the second cladding 13 is equal to or greater than 8 ?m. The bending loss at a wavelength of 1550 nm and at a radius of curvature of 7.5 mm is smaller than 0.

Abstract: An arrangement comprising a fiber-optic waveguide (10) and a detection device (25), wherein the fiber-optic waveguide (10) comprises a core region (10E) and a cladding region (10C) surrounding the core region (10E), wherein the core region has a higher refractive index than the cladding region, and wherein the detection device (25) can detect damage to the fiber-optic waveguide (10).

Abstract: A dispersion-shifted optical fiber (NZDSF) includes a central core (r1, Dn1), an inner cladding having at least three zones with a first intermediate cladding zone (r2, Dn2), a second ring zone (r3, Dn3) and a third buried trench zone (Wtr, Dnt). The buried trench zone has an index difference (Dnt) with the optical cladding between ?5·10?3 and ?15·10?3 and has a width (Wtr) between 2.5 ?m and 5.5 ?m. The present optical fiber, at a wavelength of 1550 nm, has reduced Rayleigh scattering losses of less than 0.164 dB/km, with limited bending losses.

Abstract: Microstructured optical fiber for single-moded transmission of optical signals, the optical fiber including a core region and a cladding region, the cladding region including an annular hole-containing region that contains non-periodically disposed holes. The annular hole containing region is doped with at least one dopant selected from fluorine and chlorine. The optical fiber provides low bend loss as well as low heat-induced splice loss.

Abstract: A multi-core optical fiber includes: a plurality of core portions; and a cladding portion positioned around the plurality of core portions and including a marker for identifying a position of a specific one of the plurality of core portions.

Abstract: A photonic bandgap fiber includes a core and a cladding that surrounds the core. In this photonic bandgap fiber, high refractive index portions which have a refractive index higher than that of a medium of the cladding are provided in the cladding so as to form a triangular lattice structure with a lattice constant ?, and the refractive index of the core is higher than the refractive index of the medium of the cladding and lower than the refractive index of the high refractive index portion. The coupling length between the core and the high refractive index portion that is closest to the core is longer than the coupling length between adjacent high refractive index portions, or a periodic structure formed by the high refractive index portions is not provided around the entirely of the area along the circumference of the core.

Abstract: A photonic band-gap fiber comprises a first core having a refractive index that is not higher than a refractive index of a clad; a second core that is disposed so as to surround the first core and has a refractive index that is lower than the refractive index of the first core; a clad that surrounds the second core; and a periodic structure portion that is disposed in the clad in a vicinity of the second core and is constituted by high-refractive index portions that have a refractive index higher than that of clad and form the periodic structure, and the periodic-structure portion functions as a wave-length filter. By the function of the periodic structure portion as a wave-length filter, it is possible to reduce the propagation loss of the transmission wavelength and increase the propagation loss of the cutoff wavelength.

Abstract: Various embodiments described include optical fiber designs and fabrication processes for ultra high numerical aperture optical fibers (UHNAF) having a numerical aperture (NA) of about 1. Various embodiments of UHNAF may have an NA greater than about 0.7, greater than about 0.8, greater than about 0.9, or greater than about 0.95. Embodiments of UHNAF may have a small core diameter and may have low transmission loss. Embodiments of UHNAF having a sufficiently small core diameter provide single mode operation. Some embodiments have a low V number, for example, less than 2.4 and large dispersion. Some embodiments of UHNAF have extremely large negative dispersion, for example, less than about ?300 ps/nm/km in some embodiments. Systems and apparatus using UHNAF are also disclosed.

Abstract: An optical fiber sensing cable is disclosed. The optical fiber sensing cable comprises a fiber with a core having an index of refraction n1, and a circumferential surface of the fiber including a nanoporous cladding having an index of refraction index n2. The methods of preparing the fiber sensor cable, including forming the nanoporous cladding and the sensor systems incorporating the optical fiber sensing cable of this invention are also disclosed.

Abstract: A 1.55 ?m band dispersion shifted optical fiber is provided which has a low loss and low dispersion slope. A core region “a” is heavily doped with GeO2 . A core region “b” is composed of pure SiO2 glass. A cladding section is arranged around the core region. The cladding section has a lot of holes extending in the longitudinal direction of the optical fiber. The holes of the cladding section are not located at random, but have a honeycomb structure composed of regular hexagons which have a side length of ?, and serve as a primitive lattice. The center of the core section has a region having a refractive index higher than that of the periphery of the core section. The core section has the refractive index distribution in which the group velocity dispersion at the operation wavelength of the region becomes the normal dispersion.

Abstract: The present invention relates to a plastic photonic crystal fiber for terahertz wave transmission and a method for the manufacturing thereof. More particularly, the present invention is directed to a plastic photonic crystal fiber that can be easily manufactured and has low loss characteristics to be used as a waveguide of terahertz waves. The plastic photonic crystal fiber includes a crystal defect component having a longitudinal axis and a photonic crystal component surrounding the crystal defect component. The photonic crystal component has an array of a plurality of plastic elements having longitudinal axes and forming a 2-dimensional photonic crystal structure with a predetermined lattice constant. Further, the plastic photonic crystal fiber of the present invention can be used as a preform from which a plastic photonic crystal fiber for an optical communication (400-800 nm) can be drawn.

Abstract: The present invention relates to a plastic photonic crystal fiber for terahertz wave transmission and a method for the manufacturing thereof. More particularly, the present invention is directed to a plastic photonic crystal fiber that can be easily manufactured and has low loss characteristics to be used as a waveguide of terahertz waves. The plastic photonic crystal fiber includes a crystal defect component having a longitudinal axis and a photonic crystal component surrounding the crystal defect component. The photonic crystal component has an array of a plurality of plastic elements having longitudinal axes and forming a 2-dimensional photonic crystal structure with a predetermined lattice constant. Further, the plastic photonic crystal fiber of the present invention can be used as a preform from which a plastic photonic crystal fiber for an optical communication (400-800 nm) can be drawn.

Abstract: Various embodiments of the present invention are related to photonic systems and methods that can be used to encode data in carrier electromagnetic waves. In one embodiment of the present invention, a photonic switch comprises: a waveguide configured to guide electromagnetic waves; a number of holes in the waveguide that prevent propagation of the electromagnetic waves beyond the holes; a reservoir located beneath the holes and filled with a liquid having the same refractive index as the photonic crystal; and a device for forcing the liquid into the holes so that the refractive index of the holes matches approximately the refractive index of the waveguide and the electromagnetic waves can propagate within the waveguide beyond the holes.

Abstract: A manufacturing method of a photonic band gap fiber which includes measuring a hole diameter d0 and a distance-between-holes ?0 in a preliminary experiment capillary body by first drawing a preliminary experiment preform, calculating a confinement loss to a normalized wavelength ?/? being a wavelength ? normalized by an optional distance-between-holes ? using a ratio d0/?0 and the optional distance-between-holes ? as design parameters, setting a distance-between-holes by calculating the set distance-between-holes ?1 to a desired transmission wavelength ?1 of a photonic band gap fiber to be manufactured using a value of the normalized wavelength ?/? in which the confinement loss becomes about a minimum value, and second drawing a preform for a photonic band gap fiber by using the same members as those of the preliminary experiment preform and by setting a distance-between-holes to the set distance-between-holes ?1, in a drawing temperature condition used for the first drawing.

Abstract: An exemplary refractive-index sensor includes a photonic crystal microcavity structure, a light source, and a detector. The photonic crystal microcavity structure includes a photonic crystal layer having first holes and a second hole defined therein. The first holes are arranged in a regular pattern of staggered parallel rows. The second hole is at an approximate center of the regular pattern, instead of a first hole. A diameter of the second hole is different from that of the first holes. The first holes at each of opposite ends of the row having the second hole are omitted, thereby defining an input waveguide and an output waveguide. The light source is adjacent to the input waveguide. The detector is adjacent to the output waveguide.

Abstract: An optical fiber includes a glass fiber having a glass core and a cladding which contains voids spaced apart from 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: A photonic bandgap fiber includes a first core having a refractive index equal to or smaller than a refractive index of a cladding, a second core that is provided to surround the first core and has a refractive index smaller than the refractive index of the first core, the cladding that surrounds the second core, and a periodic structure portion that is provided in the cladding around the second core, and in which high-refractive index portions having a refractive index larger than the refractive index of the cladding form a periodic structure. The periodic structure is configured such that at least the propagation constant of the fundamental mode at a wavelength to be used is in a photonic bandgap, and the propagation constant of a higher-order mode at the wavelength to be used is outside of the photonic bandgap.

Abstract: Included among the many structures described herein are photonic bandgap fibers designed to provide a desired dispersion spectrum. Additionally, designs for achieving wide transmission bands and lower transmission loss are also discussed. For example, in some fiber designs, smaller dimensions of high index material in the cladding and large core size provide small flat dispersion over a wide spectral range. In other examples, the thickness of the high index ring-shaped region closest to the core has sufficiently large dimensions to provide negative dispersion or zero dispersion at a desired wavelength. Additionally, low index cladding features distributed along concentric rings or circles may be used for achieving wide bandgaps.

Abstract: A liquid core waveguide assembly includes: a waveguide-forming body formed with a waveguide channel and first and second fiber channels, transparent first and second partition walls, and a liquid inlet in fluid communication with the waveguide channel, the waveguide channel having a first end spaced apart from the first fiber channel by the first partition wall, and a second end spaced apart from the second fiber channel by the second partition wall; and at least one first optical fiber and at least one second optical fiber extending into the first and second fiber channels, respectively. A detecting system including the liquid core waveguide assembly is also disclosed.

Abstract: An all-fiber optical pulse compression arrangement comprises a concatenated arrangement of a section of input fiber (e.g., a single mode fiber), a graded-index (GRIN) fiber lens and a section of pulse-compressing fiber (e.g., LMA fiber). The GRIN fiber lens is used to provide mode matching between the input fiber (supporting the propagation of chirped optical pulses) and the pulse-compressing fiber, with efficient pulse compression occurring along the length of the LMA fiber. The dispersion and length of the LMA fiber section are selected to provide the desired degree of pulse compression; for example, capable of reconstituting a femtosecond pulse as is used in supercontinuum generation systems.

Abstract: An optical fiber, which has a zero-material dispersion wavelength equal to or greater than 2 ?m, and a high nonlinear susceptibility ?3 equal to or greater than 1×10?12 esu, and uses tellurite glass having sufficient thermal stability for processing into a low loss fiber, employs a PCF structure or HF structure having strong confinement into a core region. This enables light to propagate at a low loss. The size and geometry of air holes formed in the core region, and the spacing between adjacent air holes make it possible to control the zero dispersion wavelength within an optical telecommunication window (1.2-1.7 ?m), and to achieve large nonlinearity with a nonlinear coefficient ? equal to or greater than 500 W?1 km?1.

Abstract: Apparatus and method for chemical and biological agent sensing. An example sensing apparatus includes a resonator having a resonance frequency. The resonator includes a coil of a photonic crystal fiber. The photonic crystal fiber has a solid region configured to guide a substantially single optical mode of light having, a cladding surrounding an exterior of the solid region, and at least one hollow core within the cladding. The cladding contains at least one hollow core. The photonic crystal fiber is configured to introduce a fluid that may contain an analyte to the hollow core. The photonic crystal fiber is configured so that the light interacts with the fluid. The resonator is configured to produce a resonance signal centered at the resonance frequency. A predetermined change in the resonance signal indicates a presence of a quantity of the analyte in the fluid.

Abstract: An embodiment of a sensor fiber includes: at least two fiber sections with a plurality of holes; and at least one other fiber section situated between said at least two fiber sections, wherein the at least one other fiber sections being without the plurality of holes.

Abstract: An optical fiber that has no bubbles in the ultraviolet ray curable resin filled inside the air holes to seal the end parts thereof, an end part processing method of the optical fiber, and an end part processing apparatus of the optical fiber, are provided. In an end part processing method of an optical fiber that is comprised of a core and a cladding formed around the core, the cladding having a refraction index lower than that of the core and has a plurality of air holes formed therein along the axis of the core, wherein the end part process of the optical fiber is to form sealed portions on the ends of the air holes by sealing them with ultraviolet ray curable resin, the method is characterized in that the sealed portion is formed by heating the end of the optical fiber.

Abstract: An optical fiber comprising: a core formed in a center axis area; an inner clad layer, disposed around the core, having a refractive index smaller than that of the core; a pore layer, disposed around the inner clad layer, having a plurality of elongated pores; and an outer clad layer, disposed around the pore layer, having a refractive index equal to or smaller than the refractive index of the core, wherein a length of the elongated pores is not larger than 200 m.

Abstract: Optical fiber probe tips and methods for fabricating the same are presented. One method entails immersing a distal end of an optical fiber having a cladding and a core into an etching solution and simultaneously etching the cladding and the core using the etching solution for tapering the cladding and the core to form a tapered cladding and a tapered core tip. The optical fiber probe tips are suitable for near-field, scanning, optical microscopy (NSOM).

Abstract: A holey fiber with significantly large effective core area is provided. The holey fiber comprises a core portion and a cladding portion at the circumference of the core portion. The cladding portion has plurality of holes distributed to shape triangular lattices around the core portion; wherein d/? is less than or equal to 0.42, the diameter of the holey fiber is larger than or equal to 580 ?m, an effective core area is larger than or equal to 15000 ?m2 at 1064 nm and a confinement loss is less than or equal to 0.1 dB/m at 1064 nm; where d is the hole diameter in ?m and ? is a lattice constant of the triangular lattice in ?m.

Abstract: According to the electronic apparatus and cellular phone of the present invention, in an optical waveguide forming body of a flexible cable, an air layer is provided in a deforming section which experiences bending deformation as a result of the movement of a second body relative to a first body (either a pivoting or sliding movement), and the position of this air layer becomes located on the outer circumferential side of a core when the deforming section undergoes bending deformation. As a result of this, it is possible to ensure sufficient flexibility and to also achieve a sufficient improvement in the folding endurance of the core portion for this optical waveguide forming body to be utilized in practical applications. Moreover, it is possible to suppress light loss and achieve high-speed, large-capacity transmissions even when the optical waveguide forming body of a flexible cable experiences bending deformation due to the relative movement of the second body relative to the first body.

Abstract: The present invention relates to a single mode optical fiber comprising a first central region having a radius r1, a maximum refractive index value n1 and at least one second ring surrounding said first central region, which second ring has a radius r2 and a minimum refractive index value n2, wherein n2<n1. The present invention furthermore relates to an optical communication system for multi-channel signal transmission.

Abstract: A holey fiber has: a core region at a center of the holey fiber; a cladding region around the core region; a plurality of holes included in the cladding region, formed in layers around the core region, arranged to form a triangular lattice having a lattice constant ? of 2 micrometers to 5 micrometers, and each having a diameter of d micrometers; and a wavelength dispersion value of ?10 ps/nm/km to 10 ps/nm/km at a wavelength of 1050 nanometers when d/? is 0.3 to 0.47.

Abstract: An optical fiber laser, according to the present invention, has an optical fiber including a core to which a rare earth element is added and a clad disposed around the core, and also has an excitation light source for emitting excitation light incident on a side of the optical fiber. The optical fiber has a corrugated shape on the outer circumference of the clad along the longitudinal direction thereof; and the optical fiber is wound in a spiral form and is bundled in such a way that adjacent sides of the clad are brought into contact with one another.

Abstract: The invention relates to an optical waveguide capable of extracting light especially from arbitrary positions of the same. An object of the invention is to provide an optical waveguide capable of extracting light efficiently from arbitrary positions of the same. To achieve the above object and according to one aspect of the invention, an optical waveguide is provided with a core for guiding light, a clad and a displacing structure for the core to contact the clad. The core has a first refractive index. The clad has a second refractive index higher than the first refractive index.

Abstract: An optical fiber preform comprising a plurality of longitudinal air holes is subjected to a thermal treatment (i.e., heating), coupled with the application of a compressive force on either end of the heated preform to compress the entire preform structure a predetermined amount. The thermal compression treatment has been found to smooth any roughened glass surfaces and heal microcracks that may have formed during the preform fabrication process, essentially “knitting” the glass material back together and forming a preform of improved quality over the prior art microstructured preforms.

Abstract: A guiding nonlinearity cell. The novel nonlinearity cell includes a nonlinear medium and a waveguide adapted to guide input electromagnetic energy through the nonlinear medium. In an illustrative embodiment, the cell includes a thin layer of a liquid or solid nonlinear medium disposed between two parallel plates adapted to guide energy through the length of the medium by total internal reflection. The plates can be made from a material having a refractive index less than a refractive index of the medium to provide total internal reflection within the liquid, or they can be made from a material matching the refractive index of the medium such that outer walls of the plates provide total internal reflection, allowing energy to leak into the plates.

Abstract: A geometrically shaped optical waveguide crossing with minimal transmission loss is described. A symmetrically tapered waveguide intersection is used to minimize loss in the intersecting region where at least two optical waveguides cross one another. The present invention embodies a waveguide crossing that includes tapering the width of the waveguides as they approach the intersecting region, forcing the field of light to contract, reducing asymmetric field distortions, and thus reducing transmission loss and effectively minimizing crosstalk. This is accomplished by focusing light through a perpendicular or near perpendicular intersection by simple linear tapering rather than by the use of a lens or other previously used devices.

Abstract: A double-clad optical fiber includes a core, an inner cladding and an outer cladding of silica-based glass. The core may have a radius of less than about 5 ?m, a first index of refraction n1 and does not contain any active rare-earth dopants. The inner cladding may surround the core and includes a radial thickness of at least about 25 ?m, a numerical aperture of at least about 0.25, and a second index of refraction n2 such that n2<n1. The relative refractive index percent (?%) of the core relative to the inner cladding may be greater than about 0.1%. The outer cladding may surround the inner cladding and include a radial thickness from about 10 ?m to about 50 ?m and a third index of refraction n3 such that n3<n2. The relative refractive index percent (?%) of the inner cladding relative to the outer cladding may be greater than about 1.5%.

Abstract: A holey fiber with significantly large effective core area is provided. The holey fiber comprises a core portion and a cladding portion at the circumference of the core portion. The cladding portion has plurality of holes distributed to shape triangular lattices around the core portion; wherein d/? is less than or equal to 0.42, the diameter of the holey fiber is larger than or equal to 580 ?m, an effective core area is larger than or equal to 15000 ?m2 at 1064 nm and a confinement loss is less than or equal to 0.1 dB/m at 1064 nm; where d is the hole diameter in ?m and ? is a lattice constant of the triangular lattice in ?m.

Abstract: An optical transmission system employs an optical fiber as an optical transmission path that includes a holey fiber and a dispersion-compensating optical fiber. The holey fiber includes a core region that is formed at a center of the holey fiber and a cladding region having a plurality of holes around the core region at regular intervals. The dispersion-compensating optical fiber is connected close to the holey fiber and that collectively compensates wavelength dispersion of the holey fiber at an operation wavelength in at least two wavelength bands out of O band, E band, S band, C band, and L band within a predetermined range depending on a transmission rate.

Abstract: A photonic band gap fiber and method of making thereof is provided. The fiber is made of a germanate glass comprising at least 30 mol % of a germanium oxide 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 90%. 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: In accordance with one aspect of the invention, the core and cladding regions of a hollow-core optical fiber are configured so that a signal mode is coupled to a cladding mode in order to exploit polarization-dependent properties. In general, the fiber comprises a hollow-core region surrounded by a cladding region, which includes a localized hollow-waveguide region. The core and waveguide regions are configured so that the coupling between a signal mode in the core region and a cladding mode in the waveguide region are phase-matched for efficient coupling, and the phase-matching condition is made polarization-dependent to provide improved control of the fiber's polarization dependent properties.