Abstract: An optical waveguide including a core, a buffer surrounding the core, and a cladding surrounding the buffer. The core, the buffer and the cladding include silica glass. A refractive index of the buffer is substantially equal to a refractive index of pure amorphous silica glass. The buffer may reduce bubble formation during manufacturing and may facilitate splicing of the waveguide. A numerical aperture of the waveguide may be fine-tuned by adjusting a radial dimension of the buffer in order to compensate variations in the refractive index of the core.

Abstract: An optical fiber has: a core made of silica glass in which a rare earth element and aluminum have been added; an inner cladding layer that is formed around the core, is made of silica glass in which at least any one of an alkali metal and an alkali earth metal has been added, and has a refractive index lower than a refractive index of the core; and an outer cladding layer that is formed around the inner cladding layer and has a refractive index lower than the refractive index of the inner cladding layer.

Abstract: An optical fiber (10) includes: a core (11); a first cladding (12) surrounding the core (11) and having a lower refractive index than the core (11); and a second cladding (13) surrounding the first cladding (12) and having a lower refractive index than the first cladding (12). The first cladding (12) is doped with light attenuating dopant so that a concentration of the light attenuating dopant in the first cladding (12) increases from an inner surface of the first cladding (12) toward an outer surface of the first cladding (12).

Abstract: A method of coupling a spliceable optical fiber includes (A) providing the spliceable optical fiber, the spliceable optical fiber including (a) a core region; and (b) a microstructured cladding region. The cladding region surrounds the core region and includes (b1) an inner cladding region having a refractive index formed by inner cladding features arranged in an inner cladding background material with a refractive index n1, the inner cladding features including thermally collapsible holes or voids, and (b2) an outer cladding region with an outer cladding background material with a refractive index n2, the spliceable optical fiber having at least one end. (B) Collapsing the thermally collapsible holes or voids by heating the at least one end of the spliceable optical fiber thereby increasing the refractive index of the inner cladding providing an expanded core. And, (C) coupling the collapsed spliceable optical fiber end to the optical component.

Abstract: A high confinement nonlinear optical fiber is provided along with methods of parametric amplification for use thereof The nonlinear optical fiber may include a plurality of concentric layers which are configured to provide different guiding regimes to low-frequency and high-frequency components through transverse geometry and refractive index profiling, thus reducing waveguide dispersion. The resulting optical fiber provides a parametric device with phase-matching in any spectral region of interest, such that a fiber optic parametric amplifier (FOPA) implementing the optical fiber can amplify in any spectral window of interest. A narrow-band FOPA configured to minimize phase mismatching is also provided for use with the optical fiber, and may be implemented as a light source or a monochromator.

Abstract: A polarization-maintaining optical fiber of the present invention includes a core, a pair of stress-applying parts provided on both sides of the core, and a cladding surrounding the core and the stress-applying parts, and is used in a wavelength range of 400 to 680 nm. The diameter of the cladding is 125 ?m, the diameter of the stress-applying part is 33 to 37 ?m, a distance between the pair of stress-applying parts is 8.6 to 15.4 ?m, a relative refractive index difference between the core and the cladding is 0.35 to 0.45%, and a cut-off wavelength is less than or equal to 400 nm.

Abstract: The present invention relates to a multi-core optical fiber enabling calculation effectively using the MEMO technology. The multi-core optical fiber has a plurality of cores and a cladding and the cores rotate around a fiber axis. A conditional expression defined by an average twist rate ? (rad/m), the shortest distance ? (m) between centers of the cores, a group index ng, an in-use bending radius R (m), the speed of light in vacuum c (m/s), and the ratio of the circumference of a circle to its diameter ? is not more than 7.91×10?12 (s/m1/2) as an example.

Abstract: A multi-core optical fiber has: a plurality of core portions; a cladding portion that is positioned around each of the plurality of core portions and has a refractive index lower than that of each of the plurality of core portions; and a separation distance between adjacent ones of the plurality of core portions being set so that crosstalk of light between the adjacent core portions over an entire length thereof becomes ?15 dB or greater at a wavelength of 1550 nm and a cable cut-off wavelength becomes 1530 nm or less.

Abstract: The invention relates to optical fiber communications. A multicore optical fiber comprises at least two light-guiding cores made of doped fused silica with refractive indices nc1, nc2, nck, each light-guiding core of the at least two light-guiding cores being surrounded by a respective arbitrarily shaped inner reflecting cladding made of fused silica or doped fused silica with refractive indices nc11, nc12, nclk, which are less than the refractive indices nc1, nc2, nck of respective light-guiding cores; a continuous or intermittent barrier region made of fused silica and having an arbitrary cross-sectional shape, the barrier region being formed in the space between the inner reflecting claddings and an outer cladding of fused silica with refractive index n0, the barrier region having refractive index nb, which is less than the refractive index of each of the inner reflecting claddings; and an external protective coating.

Abstract: There is provided a multi-core fiber that can reduce both skew and crosstalk between cores. The multi-core fiber includes a plurality of cores extending along a fiber axis, and optical claddings surrounding the plurality of cores. The skew between optical signals propagating through the plurality of cores is 1 ps/m or less, and the propagation constant difference between two adjacent cores of the plurality of cores is more than 0.

Abstract: Various embodiments include large cores fibers that can propagate few modes or a single mode while introducing loss to higher order modes. Some of these fibers are holey fibers that comprising cladding features such as air-holes. Additional embodiments described herein include holey rods. The rods and fibers may be used in many optical systems including optical amplification systems, lasers, short pulse generators, Q-switched lasers, etc. and may be used for example for micromachining.

Abstract: A bending-resistant large core diameter high numerical aperture multimode fiber includes a core and a cladding surrounding the core. The core has a radius R1 in a range of 28 to 50 microns, a refractive index profile of a parabola shape with ? being in a range of 1.9 to 2.2, and a maximum relative refractive index difference ?1% max being in a range of 1.9% to 2.5%. The cladding includes an inner cladding and/or a trench cladding, and an outer cladding disposed from the inner to the outer in sequence. The radius R2 of the inner cladding is in a range of 28 to 55 microns, and the relative refractive index difference ?2% is ?0.1% to 0.1%. The radius R3 of the trench cladding is in a range of 28 to 60 microns, and the relative refractive index difference ?3% is in a range of ?0.15% to ?0.8%.

Abstract: A photonic bandgap fiber includes a core of a solid material; a first cladding provided around the core; a low-refractive-index region provided in a part of a core vicinity portion of the first cladding and whose average refractive index is lower than that of the core; and a periodic structure region that is arranged in another part of the core vicinity portion of the first cladding which is made of a great many high-refractive-index portions whose refractive index is higher than that of the first cladding arranged in a periodic structure. According to the invention, it is possible to provide a photonic bandgap fiber which, when arranged in a double-clad structure, enables pump light to efficiently pump signal light.

Abstract: A multimode optical fiber includes a central core, an inner cladding, a buried trench, and an outer cladding (e.g., an outer optical cladding). Typically, the optical fiber's central core is a glass-based central core having an alpha-index profile (i.e., a graded-index profile), an outer radius r1, and a maximum refractive index difference ?n1 with respect to the outer cladding. The central core's alpha-index profile has a minimum refractive index at the central core's outer radius r1 that corresponds to a refractive index difference ?nend with respect to the outer cladding. The inner cladding has an outer radius r2, a width w2, and a refractive index difference ?n2 with respect to the outer cladding. The buried trench has an outer radius rext, a width w3, and a refractive index difference ?n3 with respect to the outer cladding. The multimode optical fiber typically has reduced bending losses, a high bandwidth at wavelengths of both 850 nanometers and 1300 nanometers, and a reduced cladding effect.

Abstract: A multi-core optical fiber according to an embodiment of the present invention is provided with a plurality of core parts, a common cladding, and a coating. Particularly, in order to improve a spectral efficiency per unit sectional area, optical properties typified by the number of core parts, a sectional area of the entire multi-core optical fiber, the sum of power coupling coefficients to a core part n from all the other core parts, and a transmission loss, a non-linear refractive index, an effective area, and a chromatic dispersion of the core part n with the largest crosstalk from other core parts are set so as to satisfy a predetermined relation.

Abstract: A multicore fiber includes a plurality of core elements; and a clad surrounding an outer periphery surface of each of the core elements, and each of the core elements includes a core, a first clad surrounding the outer periphery surface of the core and a second clad surrounding an outer periphery surface of the first clad, and when a refractive index of the core is n1, a refractive index of the first clad is n2, a refractive index of the second clad is n3 and a refractive index of the clad is n4, all of n1>n2>n3, n1>n4 and n3<n4 are satisfied.

Abstract: A multi-core optical fiber includes a plurality of core portions. The diameter of each of the core portions is 12 micrometers or smaller, the relative refractive-index difference of the core portions with respect to the cladding portion is 0.2% or larger, the cut-off wavelength is 1.53 micrometers or smaller, the bending loss at a 1.55-micrometer wavelength is 10 dB/m or smaller, the effective core area at a 1.55-micrometer wavelength is 30 ?m2 or larger, and the cross-talk of light between the core portions is ?35 decibels or smaller.

Abstract: An optical fiber includes a core (1a) having an oblong rectangular or square cross section and made of quartz, a cladding (2) surrounding the core (1a), having a circular outer cross-sectional shape, having a lower refractive index than the core (1a), and made of resin, and a support layer (3) surrounding the cladding (2) and made of quartz.

Abstract: The invention concerns a method for generating a laser beam (3) with different beam profile characteristics, whereby a laser beam (2) is coupled into one fibre end (1a) of a multi-clad fibre (1), in particular a double-clad fibre, and emitted from the other fibre end (1b) of the multi-clad fibre (1) and whereby, to generate different beam profile characteristics of the output laser beam (3), the input laser beam (2) is electively coupled either at least into the inner fibre core (4) of the multi-clad fibre (1) or at least into at least one outer ring core (6) of the multi-clad fibre (1), as well as a corresponding arrangement (10).

Abstract: Systems and devices enabling a highly compact design for a fiber-based lasing and/or amplifying system are disclosed. In some instances, a tightly-coiled active optical fiber may be coupled with a seed source and a pump source for optical amplification and other applications. Such systems can be disposed in a small footprint package such as a butterfly package or a high heat load package. In some instances, the tightly-wound active optical fiber may further include a fiber Bragg grating adapted to accommodate bends in the active optical fiber. The active optical fiber may further utilize a cladding shaped to maintain an orientation of the active optical fiber in relation to a bend in the fiber.

Abstract: The specification describes multimode optical fibers with specific design parameters, i.e., controlled refractive index design ratios and dimensions, which render the optical fibers largely immune to moderately severe bends. The modal structure in the optical fibers is also largely unaffected by bending, thus leaving the optical fiber bandwidth essentially unimpaired. Bend performance results were established by DMD measurements of fibers wound on mandrels vs. measurements of fibers with no severe bends.

Abstract: The present disclosure provides an approach to more efficiently amplify signals by matching either the gain materials or the pump profile with the signal profile for a higher-order mode (HOM) signal. By doing so, more efficient energy extraction is achieved.

Abstract: Described is a method of fabricating an optical fiber preform that includes a deep index trench comprising a shallower outer trench portion formed on a substrate tube and a deeper inner trench portion formed on the shallower outer trench portion. Each of the shallower outer trench and deeper inner trench portions comprises multiple silica layers. The method comprises the steps of: (1) forming each layer of the shallower outer trench portion in a single-pass deposition of a F-containing silica layer; and (2) forming each layer of the deeper inner portion in a double-pass deposition in which, in a first pass, a layer of silica soot is deposited and then, in a second pass, the soot is sintered in the presence of SiF4.

Abstract: An embodiment of an apparatus includes an optical fiber for which a complete orthogonal basis of propagating modes at an optical telecommunication frequency includes ones of the propagating modes with different angular momenta. The optical fiber has a tubular optical core and an outer optical cladding in contact with and surrounding the tubular optical core. The tubular optical core has a larger refractive index than the optical cladding. The tubular optical core is configured such that those of the propagating modes whose angular momenta have the lowest magnitude for the propagating modes have substantially the same radial intensity profile.

Abstract: An amplifying optical fiber includes a core containing oxides of elements selected from the group consisting of silicon, germanium, phosphorus, bismuth, aluminum, gallium with a concentration of bismuth oxide of 10-4-5 mol %, a total concentration of silicon and germanium oxides of 70-99.8999 mol %, a total concentration of aluminum and gallium oxides of 0.1-20 mol % wherein both aluminum and gallium oxide are present and a ratio of aluminum oxide to gallium oxide is at least two, and a concentration of phosphorus oxide from 0 to 10 mol %, and provides a maximum optical gain at least 10 times greater than the nonresonant loss factor in the optical fiber. An outside oxide glass cladding comprises fused silica. The core has an absorption band in the 1000 nm region, pumping to which region provides an increased efficiency of power conversion of pump light into luminescence light in the 1000-1700 nm range.

Abstract: An apparatus includes an optical fiber having a plurality of optical cores therein. Each optical core is located lateral in the optical fiber to the remaining one or more optical cores and is able to support a number of propagating optical modes at telecommunications wavelengths. Each number is less than seventy.

Abstract: An optical fiber containing an alkali metal element and exhibiting low attenuation as well as excellent radiation resistance is provided. The optical fiber of the present invention has a core region and a cladding region enclosing the core region. The core region contains alkali metal elements by an average concentration of 0.2 atomic ppm or more. The attenuation at a wavelength of 1550 nm after irradiating with the radiation of 0.10 Gy or more of cumulative absorbed dose increases by 0.02 dB/km or less as compared with the attenuation exhibited prior to radiation exposure.

Abstract: A multi-core optical fiber includes: a plurality of core portions; and a cladding portion positioned so as to surround each of the core portions, wherein each core portion includes a center core portion that has a refractive index greater than that of the cladding portion, a second core portion that is formed so as to surround the center core portion and that has a refractive index less than that of the center core portion, and a depressed portion that is formed so as to surround the second core portion and that has a refractive index less than those of the second core portion and the cladding portion, and an interval distance between the adjacent core portions is set such that optical cross-talk between the core portions for a total length of the multi-core optical fiber is equal to or less than ?30 dB at a wavelength of 1.55 ?m.

Abstract: An optical fiber having a core and an outer cladding, the core including from its center outward a central core having a radius and a refractive index difference with respect to the outer cladding, and a depressed inner cladding. The depressed inner cladding includes at least a first portion having a radius and a refractive index difference with respect to the outer cladding, the first portion preferably being adjacent to the central core, and a second portion adjacent to the first portion constituting a depressed trench having a radius, and a refractive index difference with respect to the outer cladding. The first portion of the inner cladding has a refractive index below the refractive index of the outer cladding, and the depressed trench has a refractive index that is lower than the refractive index of the first portion of the depressed inner cladding.

Abstract: An optical fiber having increased mechanical strength is provided. The optical fiber includes an over cladding layer that has a compressive stress of at least 100 MPa.

Abstract: A high confinement nonlinear optical fiber is provided along with methods of parametric amplification for use thereof. The nonlinear optical fiber may include a plurality of concentric layers which are configured to provide different guiding regimes to low-frequency and high-frequency components through transverse geometry and refractive index profiling, thus reducing waveguide dispersion. The resulting optical fiber provides a parametric device with phase-matching in any spectral region of interest, such that a fiber optic parametric amplifier (FOPA) implementing the optical fiber can amplify in any spectral window of interest. A narrow-band FOPA configured to minimize phase mismatching is also provided for use with the optical fiber, and may be implemented as a light source or a monochromator.

Abstract: Optical illuminators comprise optical fibers having a gradient index core and a cladding selected so that a refractive index difference at a core/cladding interface provides a numerical aperture less than, greater than, or equal to a numerical aperture of the gradient index core. In some examples, a maximum refractive index difference in the gradient index core is substantially the same as, less than, or greater than the refractive index difference at the core/cladding interface. Illuminators based on such fibers are configured to produce optical beams with a laser diode or diode array, and to provide stable, approximately Gaussian optical fluxes at a fiber output surface.

Abstract: Various embodiments include photonic bandgap fibers (PBGF). Some PBGF embodiments have a hollow core (HC) and may have a square lattice (SQL). In various embodiments, SQL PBGF can have a cladding region including 2-10 layers of air-holes. In various embodiments, an HC SQL PBGF can be configured to provide a relative wavelength transmission window ??/?c larger than about 0.35 and a minimum transmission loss in a range from about 70 dB/km to about 0.1 dB/km. In some embodiments, the HC SQL PBGF can be a polarization maintaining fiber. Methods of fabricating PBGF are also disclosed along with some examples of fabricated fibers. Various applications of PBGF are also described.

Abstract: Optical fiber comprises core and a cladding configured to support and guide a fundamental transverse mode, the cladding including (i) an outer cladding having an index nout less than the index n1 of the core, (ii) an inner cladding having an index n2<nout, (iii) a pedestal having an index n4˜nout, (iv) an inner trench disposed between the inner cladding and the pedestal, the inner trench having an index n3<<n4, and (iv) an outer trench disposed between the pedestal and the outer cladding, the outer trench having an index n5<n4 and relatively close to nout. To suppress unwanted HOMs the pedestal is configured to resonantly couple at least one unwanted transverse mode of the core (other than the fundamental mode) to at least one transverse mode of the pedestal. Also described is a modular method of making the optical fiber of silica glass.

Abstract: An optical fiber with a glass core extending from a centerline to a radius R1 wherein R1 is greater than about 5 ?m; a glass cladding surrounding and in contact with the core. The cladding has a depressed annular region, the inner radius of said depressed annular region is spaced from said core a distance greater than 1 ?m and less or equal to than 5 ?m. The core and the cladding provide a fiber with cable cutoff less than 1550 nm, and an effective area at 1550 nm greater than 120 ?m2 and bend loss of ?0.7 dB/turn on a 20 mm diameter mandrel.

Abstract: According to some embodiments the triple-clad optical fiber comprises a core, a first inner cladding, a second inner cladding, and an outer cladding wherein: (i) the core comprises a radius r0 a first index of refraction n0; (ii) the first inner cladding surrounds the core and has a numerical aperture of at least about 0.12, and a second index of refraction n1 such that n1<n0, (iii) the second inner cladding surrounds the first inner cladding a numerical aperture of at least about 0.2, and a second index of refraction n2 such that n2>n1, wherein a relative refractive index percent (?%) of the second cladding relative to the outer cladding is greater 1%; and (iv) the outer cladding surrounds the second inner cladding and has a third index of refraction n3 such that n3<n2, and n3<n1.

Abstract: A light emitter according to one embodiment has a fiber shape. And it includes a core portion containing a light emitting material, the material absorbing excitation light and emitting light having a wavelength longer than a wavelength of the excitation light. And also it includes a clad portion provided outside the core portion, the clad portion having a first region and second regions, the second regions being periodically formed in the first region, the second regions having a refractive index higher than a refractive index of a first region, the refractive index of the first region being equal to or higher than a refractive index of the core portion.

Abstract: The present invention relates to a multi-core optical fiber having a structure to effectively reduce crosstalk between adjacent core regions among a plurality of core regions. The multi-core optical fiber (1) has a leakage reduction portion (50), at least a portion of which is arranged at a position on a straight line connecting adjacent core regions together among a plurality of core regions (10). The leakage reduction portion (50) reduces leakage light in the multi-core optical fiber (1) from each of the core regions (10), thereby effectively reducing crosstalk between adjacent core regions.

Abstract: An optical fiber that is relatively insensitive to bend loss comprises a core region and a cladding region configured to support and guide the propagation of light in a fundamental transverse mode, the cladding region including (i) an outer cladding region having a refractive index less than that of the core region, (ii) an annular cladding pedestal region having a refractive index higher than that of the outer cladding region and comparable to that of the core region, and (iii) an annular cladding inner trench region disposed between the core region and the pedestal region, the inner trench region having a refractive index less than that of the outer cladding region. In one embodiment, the fiber also includes a (iv) an annular cladding outer trench region disposed between the pedestal region and the outer cladding region, the outer trench region having a refractive index less than that of the outer cladding region.

Abstract: A compact, light weight laser beam combiner includes a pair of concentric annular shells defining an annular cavity of an annular ring resonator having an annular solid laser gain medium disposed therein. The output ends of a plurality of low power and brightness fiber lasers are coupled into the cavity of the resonator such that fiber laser beams cause the gain medium in the resonator cavity to lase and produce an annular beam of laser light. Optical elements of the resonator are operable to feed a first portion of the laser light back through the resonator cavity to support regenerative lasing of the laser medium and to couple off a second portion of the laser light in the form of a circular beam of high power and high brightness laser light. A fluid may be circulated through the resonator cavity to cool the laser medium.

Abstract: A multi-core optical fiber 1A in which a plurality of cores can easily be identified even in the case where they are symmetrically arranged in its section has seven cores 10 to 16, a visual recognition marker 20, and a shared cladding 30 enclosing the seven cores 10 to 16 and the visual recognition marker 20. The cores 10 to 16 and the visual recognition marker 20 extend along the fiber-axis direction. The respective refractive index of the cores 10 to 16 is higher than the refractive index of the cladding 30. The refractive index of the visual recognition marker 20 differs from that of the cladding 30. In the cross-section perpendicular to the fiber-axis, the cores 10 to 16 are arranged such that they have 6-fold rotational symmetry and line symmetry. The visual recognition marker 20 is arranged at a position which breaks such symmetry.

Abstract: A section of active optical fiber (11) which comprises an active core (1), an inner cladding layer (2) and an outer cladding layer (3). The diameter of said core 1) and the thickness of said inner cladding (2) change gradually along the length of said section of active optical fiber (11). This forms tapered longitudinal profile enabling a continuous mode conversion process along the length of the section of fiber (11). The method for fabricating a section of tapered active optical fiber comprises the steps of fabricating a preform for drawing active optical fiber from said preform, installing said preform into a drawing tower, drawing optical fiber in said drawing tower and altering at least one of the two parameters including the take-off preform speed and the take-up fiber speed during drawing of the optical fiber.

Abstract: An optical waveguide has a refractive index variation that is structured to provide the fiber, over a wavelength operating range, with an effective area supporting multiple Stokes shifts and with a negative dispersion value at a target wavelength within the wavelength operating range. The refractive index variation is further structured to provide the fiber with a finite LP01 cutoff at a wavelength longer than the target wavelength, whereby the LP01 cutoff wavelength provides a disparity, for a selected bending diameter, between macrobending losses at the target wavelength and macrobending losses at wavelengths longer than the target wavelength, whereby Raman scattering is frustrated at wavelengths longer than the target wavelength.

Abstract: A stretcher fiber has a core region, inner trench region, ring region, outer trench region, and outer cladding region. The fiber regions are structured to provide the stretcher fiber with a relationship between dispersion and wavelength, such that the second and third derivatives of the stretcher fiber's propagation constant with respect to angular frequency have a shape and wavelength range matching those of a selected compressor module.

Abstract: A single-mode optical fiber includes a central core, an intermediate cladding, a depressed trench, and an external optical cladding. The central core has a radius r1 and a positive refractive index difference ?n1 with the optical cladding. The intermediate cladding has a radius r2 and a refractive index difference ?n2 with the optical cladding, wherein ?n2 is less than ?n1. The depressed trench has a radius r3 and a negative index difference ?n3 with the optical cladding. At a wavelength of 1310 nanometers, the optical fiber has a mode field diameter (MFD) between 8.6 microns and 9.5 microns and, at a wavelength of 1550 nanometers, the optical fiber has bending losses less than about 0.25×10?3 dB/turn for a radius of curvature of 15 millimeters. At a wavelength of 1260 nanometers, attenuation of the LP11 mode to 19.3 dB is achieved over less than 90 meters of fiber.

Abstract: The present invention embraces a single-mode optical fiber typically having reduced bending losses. The optical fiber includes a central core, an intermediate cladding, a buried trench, and an outer cladding. The optical fiber typically has (i), at a wavelength of 1310 nanometers, a mode field diameter with a nominal value of between about 8.6 microns and 9.5 microns (and a tolerance of ±0.4 micron), (ii) a cable cut-off wavelength of no more than 1260 nanometers, and (iii), for a bending radius of 15 millimeters at a wavelength of 1550 nanometers, bending losses of no more than 0.03 dB/turn.

Abstract: A trench optical fiber that stably realizes a small transmission loss includes (1) a core extending in an axial direction while containing an axial center of the fiber, the core having a diameter d1 of 7.0 ?m to 7.4 ?m; (2) a first optical cladding layer surrounding the core and having an outside diameter d2 of 1.67 dl to 2.5 dl; (3) a second optical cladding layer surrounding the first optical cladding layer; and (4) a jacket layer surrounding the second optical cladding layer and containing fluorine having a concentration of 0.06 wt % or higher. A relative refractive index difference ?1 of the core with respect to the jacket layer is 0.31% to 0.37%. A relative refractive index difference ?2 of the first optical cladding layer with respect to the jacket layer is +0.02% or larger and smaller than ?1. A relative refractive index difference ?3 of the second optical cladding layer with respect to the jacket layer is ?0.2% or smaller.

Abstract: Embodiments of the present invention provide a plastic fiber coupler. The plastic fiber coupler includes a bundle of plastic optical fibers (POFs) arranged in a ring-shape; and an optical mixing tube attached to a cross-section of the bundle of POFs. In one embodiment, a cross-section of the optical mixing tube may be coated with a reflective film forming a reflective type plastic fiber coupler; in another embodiment, the optical mixing tube is attached to a second bundle of plastic optical fibers forming a transmissive type plastic fiber coupler.

Abstract: An optical fiber-type optical filter includes: two fiber regions, namely, the first and second PBGF regions, each of which includes: a core section extending in a waveguide direction of incident light; and a clad section extending in the waveguide direction and surrounding the core section, wherein the clad section includes a plurality of high rods which have a refractive index higher than that of a base material of the clad section, extend in the waveguide direction, and are arranged periodically in a cross section perpendicular to the waveguide direction, and a light loss region between mutually-facing end surfaces of the first and second fiber regions, for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section.

Abstract: According to one example of the invention an optical fiber comprises: (i) silica based, rare earth doped core having a first index of refraction n1; (ii) at least one silica based cladding surrounding the core and having a second index of refraction n2, such that n1>n2; wherein at least one of the core or cladding is doped with Al2O3, such that the ratio of max wt % to min wt % of Al2O3 concentration is less than 2:1.