Abstract: An optical waveguide having a cladding layer formed of high-purity glass, or a cladding layer formed of high-purity isotope-proportion modified glass, and with a core of high-purity isotope-proportion-modified glass with the index of refraction of the core glass greater than the index of refraction of the cladding glass, said high-purity isotope-proportion-modified core material having a Si-29-isotope proportion at most 4.447% Si-29 (atom/atom) of all silicon atoms in said core, or at least 4.90% of Si-29 (atom/atom) atoms in said core, or having a Ge-73 isotope proportion of at most 7.2% Ge-73 (atom/atom) of all germanium atoms in said core, or at least 8.18% of Ge-73 (atom/atom) of Germanium atoms in said core region.

Abstract: A multimode optical fiber, and a method of making the fiber, are provided according to the following steps and elements: forming a core preform with a graded refractive index that includes silica and an up-dopant; drawing the core preform into a core cane; forming an inner annular segment preform that includes silica soot and an up-dopant surrounding the core cane; and forming a depressed-index annular segment preform that includes silica soot surrounding the inner annular segment preform. The method also includes the steps: forming an outer annular segment preform that includes silica soot and an up-dopant surrounding the depressed-index annular segment preform; doping the inner, depressed-index and outer annular segment preforms simultaneously or nearly simultaneously with a down-dopant; and consolidating the segment preforms simultaneously or nearly simultaneously into inner, depressed-index and outer annular segments.

Abstract: Gradient index optical materials are formed by drop by drop dispensing of nanoparticle/monomer suspensions. Refractive index variations are defined by nanoparticle concentrations that can vary in three dimensions. Droplets of differing compositions can be mixed, and droplets or layers or droplets are partially cross-linked by exposure to ultraviolet radiation prior to dispensing additional droplets. Gradient index optical elements such as lenses, prisms, and waveguides can be formed in flexible polymer layers.

Abstract: A core layer (13) of an optical waveguide (1) includes a plurality of core groups (140) disposed so as to mutually intersect on the same plane, each core group (140) being an assembly of a plurality of core portions (14), at least some of which are arranged in parallel, and side cladding portions (15) provided so as to adjoin the side surfaces of each core portion (14). A transverse cross-section of the optical waveguide (1) includes a high refractive index region (WH) in a position corresponding with each core portion (14) and having a relatively high refractive index, and a low refractive index region (WL) in a position corresponding with each side cladding portion (15) and having a lower refractive index than the high refractive index region (WH), and a refractive index distribution is formed in which the refractive index varies continuously across the entire distribution.

Abstract: The invention relates to a fiber structure (700), which has one or more refractive index disturbances (750, 760) outside a fiber core (710) for discriminating one or more high order modes in the fiber structure. The invention also relates to a method for discriminating one or more high order modes, an arrangement having the high order modes discriminating fiber structure, and a device having the high order mode discriminating fiber structure.

Abstract: An optical waveguide having a cladding layer formed of high-purity glass, or a cladding layer formed of high-purity isotope-proportion modified glass, and with a core of high-purity isotope-proportion-modified glass with the index of refraction of the core glass greater than the index of refraction of the cladding glass, said high-purity isotope-proportion-modified core material having a Si-29-isotope proportion at most 4.447% Si-29 (atom/atom) of all silicon atoms in said core, or at least 4.90% of Si-29 (atom/atom) atoms in said core, or having a Ge-73 isotope proportion of at most 7.2% Ge-73 (atom/atom) of all germanium atoms in said core, or at least 8.18% of Ge-73 (atom/atom) of Germanium atoms in said core region.

Abstract: In one embodiment, an apparatus may include a first capillary component. A second capillary component may be disposed outside of the first capillary component and may have an inner surface, wherein a portion of the inner surface may be heat-fused to an outer surface of the first capillary component. The apparatus may also include a portion of an optical fiber disposed inside of the first capillary component and the portion of the optical fiber can have an outer surface. A portion of the outer surface of the optical fiber may be heat-fused to an inner surface of the first capillary component. The optical fiber may have a distal surface configured to reflect electromagnetic radiation propagated along a longitudinal axis of a distal end portion of the optical fiber in a lateral direction through the inner surface of the first capillary component and the inner surface of the second capillary component.

Abstract: The invention relates to a mode filter for reducing higher-order modes, with an optical fibre (1), which has a core (2) and a cladding (3) surrounding the latter, wherein the cladding (3) and core (2) have refractive indices that differ from one another. In order to develop an alternative to the prior art, the mode filter according to the invention is designed in such a manner that the fibre (1) has, in a transition region (4) between core (2) and cladding (3), at least one local refractive index modification region (5) which is arranged in the radially outer region of the core (2) and extends into the region of the cladding (3).

Abstract: A mode filter for eliminating the propagation of higher-order modes along a section of optical multimode fiber comprises a graded index (GRIN) lens, preferably of a quarter-pitch length, and a pinhole element in the form of a small core fiber. This configuration creates a Fourier spatial filter assembly that removes higher order modes propagating along an optical fiber while capturing the fundamental mode of the optical signal. A section of GRIN fiber is preferably used as the lens, with the small core fiber disposed at the output of the GRIN fiber lens to collect substantially only the on-axis fundamental mode of the optical signal. Since the higher order modes are shifted away from the origin by the GRIN fiber lens, only the fundamental mode signal is captured by the small core fiber.

Abstract: An optical fiber according to an embodiment of the present invention is provided with a center core, a side core, and a cladding. The center core includes a ring part where a relative index difference varies discontinuously, in its peripheral region, and when a is a radius from a core center to an outside of the ring part and c is a radius to a position where the relative index difference is maximum in the side core, an index profile is realized in a shape where c/a is in the range of 2.25 to 2.50, so as to enable setting of a dispersion value, a cable cutoff wavelength, a bending loss in the diameter of 20 mm, and an effective area in desired ranges.

Abstract: The invention relates to a multimode optical fibre having a refractive index profile, comprising a light-guiding core surrounded by one or more cladding layers. The present invention furthermore relates to an optical communication system comprising a transmitter, a receiver and a multimode optical fibre.

Abstract: The invention relates to a bend insensitive gradient index multi-mode light conducting fiber comprising a leakage mode dependent optical core diameter that is uniform over its length and a numerical aperture that is uniform over its length, a core (1), an inner cladding (2), a refraction index trench (3) and an outer cladding (4), wherein the core (1) includes a core radius R1, an alpha-refraction index profile and a core refraction index difference dn1 with respect to the outer cladding (4), wherein the refraction index trench (3) includes a refraction index trench radius R3 and a trench refraction index difference dn3 with respect to the outer cladding (4), wherein the outer cladding (4) includes an outer cladding radius R4 and a refraction index between 1.40 and 1.55, wherein for a light wavelength of 850 nm and a full core excitation (OFL), the optical core diameter for a fiber length in a range between 2 m and 300 m decreases by less than 5% and the numeric aperture decreases by less than 2.

Abstract: An optical fiber includes a core region having a longitudinal axis. A cladding region surrounds the core region. The core region and cladding region are configured to support and guide the propagation of signal light in a fundamental transverse mode in the core region in the directions of the axis. The fiber has a bend-induced gradient of its equivalent index of refraction indicative of a loss in guidance of the mode. At least a portion of cladding region has a graded index of refraction opposite the bend-induced gradient. The cladding region is configured to have a substantially flat equivalent index in response to a bend of the optical fiber.

Abstract: The present invention relates to a multimode optical fiber which can provide a smooth cut face suitable for fusion splicing between fibers. The multimode optical fiber has at least a core extending along a central axis and having an ?-power refractive index profile, and a cladding, and a residual stress distribution in the core along a radial direction from the central axis has a shape with a maximum at a position intersecting with the central axis.

Abstract: A multimode optical fiber includes a central core having a radius (r1) and an alpha-index profile. The multimode optical fiber further includes a depressed trench, which surrounds the central core, that has a width (wt) and a refractive index difference (?nt) with an outer optical cladding. Typically, the central core's diameter is between about 47 and 53 microns, and the depressed trench's width (wt) is between 0.5 micron and 2 microns. The depressed trench's refractive index difference (?nt) with the outer optical cladding is typically between ?4×10?3 and ?1×10?3.

Abstract: Small-radius coated optical fibers having large mode field diameter and low bending losses. The coated fiber may have an outer radius of 110 ?m or less, while providing a mode field diameter of 9.0 ?m or greater and a bending loss when wrapped about a 15 mm mandrel of 0.5 dB/km or less at wavelength of 1550 nm. The coated fiber may have a mode field diameter of 9.2 ?m or greater and may have a bending loss at 1550 nm of 0.25 dB/km or less when wrapped about a 20 mm mandrel or a bending loss at 1550 nm of 0.02 dB/km or less when wrapped about a 30 mm mandrel.

Abstract: Holey fibers provide optical propagation. In various embodiments, a large core holey fiber comprises a cladding region formed by large holes arranged in few layers. The number of layers or rows of holes about the large core can be used to coarse tune the leakage losses of the fundamental and higher modes of a signal, thereby allowing the non-fundamental modes to be substantially eliminated by leakage over a given length of fiber. Fine tuning of leakage losses can be performed by adjusting the hole dimension and/or spacing to yield a desired operation with a desired leakage loss of the fundamental mode. Resulting holey fibers have a large hole dimension and spacing, and thus a large core, when compared to traditional fibers and conventional fibers that propagate a single mode. Other loss mechanisms, such as bend loss and modal spacing can be utilized for selected modes of operation of holey fibers.

Abstract: The present disclosure relates to a multimode optical waveguide comprising a cladding and a core. The core of the multimode optical waveguide has a polygonal cross-section. The core forms a coil spun around the longitudinal axis of the cladding. The multimode optical waveguide may be used to realize a mode scrambler and a mode conditioner.

Abstract: An optical fiber comprising: (I) a germania doped central core region having outer radius r1 and (II) a maximum relative refractive index ?1max and a cladding region including (i) a first inner cladding region having an outer radius r2>5 microns and refractive index ?2; (ii) a and a second inner cladding region having an outer radius r3>9 microns and comprising refractive index ?3; and (iii) an outer cladding region surrounding the inner cladding region and comprising refractive index ?4, wherein ?1max>?4, ?2>?3, and wherein 0.01%??4??3?0.09%, said fiber exhibits a 22 m cable cutoff less than or equal to 1260 nm, and 0.25?r1/r2?0.85.

Abstract: According to some embodiments, a multimode optical fiber comprises a graded index glass core with refractive index ?1, a maximum refractive index delta ?1MAX, and a core radius between 10 and 40 microns; and cladding region surrounding the core comprising refractive index ?4, wherein the fiber exhibits an overfilled bandwidth at an operating wavelength in a 900 to 1250 nm wavelength range of greater than 2.5 GHz-km. According to some embodiments the fiber exhibits an overfilled bandwidth at a wavelength between 950 and 1100 nm which is greater than 4 GHz-km. According to some embodiments the fiber exhibits an overfilled bandwidth at a wavelength between 950 and 1100 nm which is greater than 10 GHz-km.

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: An optical transmission fiber comprises a central core having an index difference ?n1 with an outer optical cladding; a first inner cladding having an index difference ?n2 with the outer cladding; and a second buried inner cladding having an index difference ?n3 with the outer cladding of less than ?3·10?3. The second buried inner cladding moreover contains Germanium in a weight concentration of between 0.5% and 7%. The fiber shows reduced bending and microbending losses while exhibiting the optical performances of a standard single-mode fiber (SSMF).

Abstract: A multimode optical fiber includes a graded index glass core having a diameter in the range of 41 microns to 80 microns, a graded index having an alpha less than 2.04 and a maximum relative refractive index in the range between 0.6% and 1.8%. The cladding includes a depressed-index annular portion. The fiber has an overfilled bandwidth greater than 2.5 GHz-km at 1310 nm.

Abstract: An optical fiber comprising a first core, a second core, a third core, and a cladding, wherein the expressions 0.30%??1?0.45%, ?0.05%??2?0.05%, ?0.35%??3??0.15%, 2.5?b/a, 3.5 ?m?a?4.2 ?m, 9 ?m?b?13 ?m, and 4.5 ?m?c?b?7.0 ?m are satisfied, a zero-dispersion wavelength is no less than 1300 nm and no greater than 1324 nm, and transmission loss increase for a wavelength of 1550 nm when the optical fiber is wound around a mandrel with a diameter of 10 mm is no greater than 1 dB/turn.

Abstract: A leaky travelling wave array of optical elements provide a solar wavelength rectenna.

Abstract: The present invention relates to a multimode optical fiber having a stably manufacturable structure as a transmission medium suitable for wide-band multimode transmission. In the multimode optical fiber, a core has a refractive-index profile a shape of which is defined by the exponent ? which varies along a radial direction from a center of the core and an average of radial variation of which is positive in a predetermined range in the radial direction.

Abstract: The present invention generally relates to the field of fiber optics, and more specifically to optical fibers, methods of manufacturing optical fibers, and methods of classifying optical fibers. In an embodiment, the present invention is a multimode optical fiber which comprises a core and clad material system where the refractive indices of the core and cladding are selected to minimize chromatic dispersion in the 850 nm wavelength window and the refractive index profile is optimized for minimum modal-chromatic dispersion in channels utilizing VCSEL transceivers. Multimode optical fibers according to this embodiment may have increased channel bandwidth.

Abstract: An optical fiber is provided that includes a fiber configured to transmit optical data in a plurality of modes or in a single mode; a core region in the fiber that comprises fluorine-doped silica; and a cladding in the fiber that surrounds the core region and that comprises fluorine-doped silica. The core region has a graded refractive index profile with an alpha of about 0.5 to 5. The core of the fiber may be set with a radius of approximately 6 to 50 microns. The cladding may also comprise one or a plurality of layers, including trench or moat regions of a relatively lower refractive index. Still further, an inner cladding may be doped with fluorine at a concentration greater than that in the core region. An outer cladding can comprise silica with fluorine at a concentration below or equal to that in the inner cladding.

Abstract: The present invention relates to a multi-core optical fiber including a plurality of cores, in each of which an effective area at the wavelength of 1550 nm, a transmission loss at the wavelength of 1550 nm, a chromatic dispersion at the wavelength of 1550 nm, a cable cutoff wavelength, and a bending loss in a bending radius of 30 mm at the wavelength of 1625 nm are set so as to increase a transmission capacity in each core in a state in which a difference of the transmission loss at the wavelength of 1550 nm between different cores is controlled to at most 0.02 dB/km or less.

Abstract: The multi-core fiber of the present invention uses a multi-core fiber configuration, compatible with the “coupled” operation mode in which coupling between cores is positively utilized, to carry out mode division multiplexing transmission via a multi-core fiber that contains multiple single-mode cores in one optical fiber. The multi-core fiber of the present invention uses a configuration in which mode multiplexing transmission is carried out using a multi-core fiber that contains multiple single-mode cores in one optical fiber, wherein multiple cores are strongly coupled intentionally to form a coupled multi-core fiber that makes the coupled modes correspond, one to one, to the transmission channels.

Abstract: The invention relates to a bend insensitive gradient index multimode light conducting fiber comprising a leakage mode dependent optical core diameter that is uniform over its length and numerical aperture that is uniform over its length, a core (1), an inner cladding (2), a refraction index trench (3) and an outer cladding (4), wherein the core (1) includes a core radius R1, an alpha-refraction index profile and a core refraction index difference dn1 with respect to the outer cladding (4), wherein the refraction index trench (3) includes a refraction index trench radius R3 and a trench refraction index difference dn3 with respect to the outer cladding (4), wherein the outer cladding (4) includes an outer cladding radius R4 and a refraction index between 1.40 and 1.55, wherein for a light wavelength of 850 nm and an overfilled launch (OFL), the optical core diameter for a fiber length in a range between 2 m and 300 m decreases by less than 5% and the numerical aperture decreases by less than 2.

Abstract: Compact laser systems are disclosed which include ultrafast laser sources in combination with nonlinear crystals or waveguides. In some implementations fiber based mid-IR sources producing very short pulses and/or mid-IR sources based on a mode locked fiber lasers are utilized. A difference frequency generator receives outputs from the ultrafast sources, and generates an output including a difference frequency. The output power from the difference frequency generator can further be enhanced via the implementation of large core dispersion shifted fibers. Exemplary applications of the compact, high brightness mid-IR light sources include medical applications, spectroscopy, ranging, sensing and metrology.

Abstract: An optical system comprising: a light source providing light in 300-700 nm range; and an optical fiber optically coupled to the source; the optical fiber is structured to transmit the light provided by the source and comprises Al doped silica based core with 0 to 1 wt % of Ge and no rare-earth metal(s); and at least one silica based cladding surrounding the core. According to some embodiments the fiber includes: a core having a radius of no more than 2.0 ?m and having a first index of refraction n1 and a relative refractive index delta with respect to the cladding between 0.15 and 1.0%. The Al doped silica core comprises less than 0.5 wt % of Ge and includes no rare-earth metals; and the silica based cladding surrounding the core has a second index of refraction n2, such that n1>n2, the cladding having an outer diameter of 80 ?m or greater.

Abstract: Device for the emission or amplification of a signal, comprising an optical fiber (1) having a solid core (2) of refractive index nc, made of a silica glass doped with a rare earth, such as erbium, ytterbium or neodymium, said core being surrounded by an optical cladding (3, 4, 5, 6, 7, 8) comprising at least a pair of silica layers composed of a first, inner layer (3), having a refractive index greater than the refractive index nc of the core (2), covered by a second, outer layer (4). The optical fiber (1) comprises several pairs of silica layers (3, 4; 5, 6; 7, 8) around the core (2), each pair comprising an inner layer (3, 5, 7) of refractive index ni and an outer layer (4, 6, 8) of refractive index ne, the refractive index ne of the outer layer being lower that the refractive index ni of the inner layer of the same pair.

Abstract: Provided is an extreme bending insensitive optical fiber. The optical fiber includes a core comprising a maximum refractive index difference ?n1 in the optical fiber, an inner layer comprising a refractive index difference ?n2 that is smaller than the maximum refractive index of the core and decreases in a direction away from the core, the inner layer being positioned outside the core, and a trench layer comprising an inner-circumference refractive index difference ?n3 that is smaller than the refractive index difference of the inner layer and an outer-circumference refractive index difference ?n4 that is a minimum refractive index difference in the optical fiber.

Abstract: Optical fibers that provide stable output beam sizes have core refractive indices that decrease non-monotonically from a core center to a core/cladding interface. A maximum refractive index of the core is situated at a radius of between about ½ and ¾ of the core radius so that a core center has a depressed refractive index. Such fibers are included in diode pumped solid state lasers to deliver pump laser power to a laser medium.

Abstract: In one aspect of the invention, the bend insensitive single-mode optical fiber includes a core layer and cladding layers having an inner cladding layer, a trench cladding layer and an outer cladding layer sequentially formed surrounding the core layer from inside to outside. For the core layer, the diameter is 7-7.9 ?m, and the relative refractive index difference ?1 is between 4.6×10?3 and 6.5×10?3. For the inner cladding layer, the diameter is 16.5-20 ?m, and a relative refractive index difference ?2 is between ?3×10?4 and 3×10?4. For the trench cladding layer, the diameter is 33-40 ?m, and the relative refractive index difference ?3 is between ?2.9×10?3 and ?7.3×10?3, changes in a gradient manner and increases gradually from outside to inside, where a relative refractive index difference ?32 at an outermost interface is smaller than a relative refractive index difference ?31 at an innermost interface.

Abstract: The specification describes an optical fiber color coding scheme that uses two colors, where each of the two colors constitutes one half of the surface of the optical fiber coating. If a longitudinal portion of the coating is considered a hollow cylinder, then each of the two colors is a hollow hemi-cylinder. To ensure that each of the two colors is always plainly visible to an installer, the two colors are formed with a twist. Using two colors for coding substantially increases the number of available unique color codes. Coloring the entire coating reduces the chances of error in identifying the optical fibers.

Abstract: The present invention relates to a multimode optical fiber including a glass fiber, and a coating member provided on an outer periphery of the glass fiber. The glass fiber extends along a predetermined central axis, and includes at least a core region having a GI-type refractive index profile. The coating member has a refractive index that is higher than a minimum refractive index of the core region. According to this configuration, leakage of a higher-order mode with a large group delay difference to the coating member side is facilitated.

Abstract: Multimode optical fiber is disclosed herein having a core surrounded by first and second annular cladding regions. The second annular cladding region has a maximum relative refractive index that is at least 0.05% higher than the minimum relative refractive index of the first annular cladding region.

Abstract: Certain embodiments of the invention may include optimized trench-assisted ultra large area (ULA) optical fibers. According to an example embodiment of the invention, a trench-assisted optical fiber, optimized for figure-of-merit (FOM) performance, is provided. The optical fiber includes a core region having a longitudinal axis, a shelf region surrounding said core region, a cladding region surrounding said shelf region, said core and shelf and cladding regions configured to support and guide the propagation of signal light in a fundamental transverse mode in said core and shelf regions in the direction of said axis. The optical fiber further includes a core effective area (Aeff) of between 135 ?m2 and about 170 ?m2; and an index profile having a figure of merit (FOM) frontier distance less than about 0.7 dB.

Abstract: A bridge fiber includes a core layer 31 and an outer layer 32 which has an index of refraction higher than that of the core layer 31 and covers the outer peripheral surface of the core layer 31. The outer layer 32 is surrounded by a substance such as the atmosphere having an index of refraction lower than an index of refraction n2 of the outer layer 32. An area AR1 of the outer layer 32 at one end face of the bridge fiber is an area that is to be optically coupled to an end face of a core of each of a plurality of pumping light inputting optical fibers, while an area AR2 of the core layer 31 at another end face of the bridge fiber is an area that is to be optically coupled to an end face of a core of an amplification optical fiber 40.

Abstract: A light source is coupled to an input facet that directs light from the light source to a core layer of a waveguide and a gradient index material layer disposed beside the core layer along a portion of a propagation length of the waveguide. Light is launched from the light source into the input facet. In response, the gradient index material layer directs light to the core layer at least along the portion of the propagation length.

Abstract: Optical fiber refractive index profile designs having an alpha core profile and a negative index trench to control bend loss, are modified by truncating the edge of the alpha core profile and adding a ledge to the truncated core. The result is low bend loss and preservation of low differential mode delay and high bandwidth.

Abstract: The invention relates to an electro-static variable optical attenuator suitable for use in a small form factor pluggable module. A short cladding suppressing fiber, such as a double clad optical fiber, dissipates attenuated light coupled to the cladding to reduce modal interference in the output light, while also reducing PDL and WDL introduced by the off set attenuation mechanism.

Abstract: The present invention relates to a preform manufacturing method and others for effectively reducing variation in refractive index due to chlorine used in manufacture of an optical fiber preform. The manufacturing method includes a dechlorination step carried out between a point of an end time of a dehydration step and a point of a start time of a sintering step, the dechlorination step being a step of heating a porous preform after dehydrated, in an atmosphere containing no chlorine-based dehydrating agent, for a given length of time while maintaining a temperature lower than a sintering temperature, thereby removing chlorine from the porous preform after dehydrated.

Abstract: An optical fiber includes a core section and a cladding section. A k value expressed by k=4Aeff/(?MFD2) is 1.08 or larger, Aeff being an effective area and MFD being a mode field diameter, at a wavelength of 1550 nm, a chromatic dispersion is in a range from +19.0 ps/nm/km to +21.9 ps/nm/km, and MFD is in a range from 10.3 ?m to 13.0 ?m. The inequality, r1<r2<r3, is established, R=r3/r2 is larger than 1.0 and equal to or smaller than 5.4, and a relative refractive index difference ?12 of the maximum value N2 with respect to the minimum value N1 is 0.05% or higher, r1 and r2 being radial positions respectively with minimum and maximum value N1 and N2 of a refractive index in the core section and r3 being a radius of the core section.

Abstract: A multimode optical fiber comprises a central core having an alpha profile, a depressed cladding having a portion in continuity with the alpha profile of the central core and a stepped portion, and an outer cladding. The alpha profile is obtained by co-doping at least two dopants. A multimode fiber for Ethernet optical system with an improved bandwidth is thus obtained.

Abstract: The invention aims to provide an optical fiber in which light that is input to the clad is easily released to the outside of the clad, and a laser device using the optical fiber. An optical fiber (50) includes a core (51), and a clad (52) coating the core (51). The clad (52) includes a refractive-index varying region (56) in which the refractive index increases in the direction from the inner circumferential side toward the outer circumferential side. In this structure, even when light is input to the clad (52), the light that has reached the refractive-index varying region (56) of the clad (52) is refracted and propagates from the inner circumferential side toward the outer circumferential side of the clad (52). Accordingly, light that is input to the clad (52) is easily released to the outside of the clad (52).

Abstract: According to one example of the invention an optical fiber comprises: (i) a core comprising Al doped silica but essentially no Er or Yb, and having a first index of refraction n1; (ii) at least one F doped silica based cladding surrounding the core and having a second index of refraction n2, such that n1>n2, wherein the cladding comprises essentially of SiO2 and 0.2-5 wt % F; (iii) a hermetic carbon based coating surrounding said cladding, said hermetic coating being 200 to 1000 Angstroms thick; and (iv) a second coating surrounding said hermetic coating, said second coating being 5 ?m to 80 ?m thick.