Abstract: Multi-cladding optical fibers to be used in the context of fiber amplifiers and fiber lasers are described herein. Embodiments of optical fibers include a rare-earth doped core into which the signal field is to be amplified. The doped core is surrounded by multiple claddings that guide the pump field to be absorbed by the reactive core material. The first cladding has a depressed refractive index to improve high-order mode bending losses without incurring significant fundamental mode bending losses.

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: The present invention embraces a multimode optical fiber that includes a glass-based central core having an alpha-index profile and a glass-based cladding immediately surrounding the optical fiber's central core. Typically, the refractive index difference between the central core's minimum refractive index and the cladding's maximum refractive index is greater than 2×10?3. The multimode optical fiber exhibits reduced bending losses and reduced coupling losses when connected to a standard graded-index fiber.

Abstract: A single mode fiber having a core, an inner cladding, a depressed cladding, and an outer cladding composed of pure silica glass. The core is surrounded in sequence with the inner cladding and the depressed cladding. The core has silica glass doped with germanium and fluorine, with a diameter (a) of 8.0-8.8 ?m, a relative refractive index difference (?1) of 0.35-0.38%, and the contribution of fluoride (?F) is ?0.09±0.02%. The inner cladding has silica glass doped with germanium and fluorine, with a diameter (b) of 18-21 ?m and a relative refractive index difference (?2) of 0±0.02%. The depressed cladding has silica glass doped with fluorine, with a diameter (c) of 26-36 ?m and a relative refractive index difference (?32) at the external interface thereof is between ?0.22 and ?0.35%, and a relative refractive index difference (?31) at the internal interface thereof is between ?0.20 and ?0.35%, and ?32??31.

Abstract: According to one embodiment a method of making optical fibers comprises: (i) manufacturing a core cane; (ii) situating a plurality of microstructures selected from rods, air filled tubes and glass filed tubes and placing said microstructures adjacent to the core cane, said microstructures forming no more than 3 layers; (iii) placing the core cane with said adjacent microstructures inside a holding clad tube; and (iv) placing interstitial cladding rods inside the holding (clad) tube, thereby forming an assembly comprising a tube containing a core cane, a plurality of microstructures and interstitial cladding rods. The assembly is then drawn into a microstructured cane and an optical fiber is drawn from the microstructured cane. According to several embodiments, the method of making an optical fiber includes providing at least one air hole and at least one stress rod adjacent to the core.

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 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: Optical waveguide fiber that is bend resistant and single mode at 1260 nm and at higher wavelengths. The optical fiber includes a core of radius R1 and cladding, the cladding having an annular inner region of radius R2, an annular ring region, and an annular outer region. The annular ring region starts at R2, and the ratio R1/R2 is greater than 0.40.

Abstract: Bend resistant optical fibers which are multi-moded at 1300 nm include a core, an inner cladding, a low index ring and an outer cladding. The core has a graded index of refraction with a core alpha profile where 1.9??C?2.1, a maximum relative refractive index percent ?1Max%, and a numerical aperture NA of greater than 0.23. The inner cladding surrounds the core and has a maximum relative refractive index percent ?2Max%, a minimum relative refractive index percent ?2Min%, and a radial thickness ?0.5 microns, wherein ?1Max%>?2Max%. The low index ring surrounds the inner cladding and has a relative refractive index percent ?3%, a radial thickness of at least 0.5 microns, a profile volume with an absolute magnitude of greater than 50%-?m2, wherein ?2Min%??3%. The outer cladding surrounds the low index ring and has a relative refractive index percent ?4%, such that ?1Max%>?4%??2Max%.

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 multimode fiber including a core and a cladding. The core has a radius (R1) of 24-26 ?m, the refractive index profile thereof is a parabola, and the maximum relative refractive index difference (?1) is 0.9-1.1%. The cladding surrounds the core and includes from inside to outside an inner cladding, a middle cladding, and an outer cladding; a radius (R2) of the inner cladding is 1.04-1.6 times that of the core, and a relative refractive index difference (?2) thereof is ?0.01-0.01%; the middle cladding is a graded refractive index cladding whose radius (R3) is 1.06-1.8 times that of the core, and a relative refractive index difference thereof is decreased from ?2 to ?4; and a radius (R4) of the outer cladding is 2.38-2.63 times that of the core, and a relative refractive index difference (?4) thereof is between ?0.20 and ?0.40%.

Abstract: The present invention relates to a transmission optical fiber. The optical fiber includes, from its center to its periphery a central core, an intermediate cladding, and a depressed cladding. The optical fiber has an effective area (Seff) of at least about 120 ?m2 at a wavelength of 1550 nm and an effective cutoff wavelength (?Ceff) of less than 1600 nm. The optical fiber has an effective area of more than 120 ?m2 with a cutoff wavelength limited to less than about 1600 nm without degradation of other optical parameters (e.g., attenuation losses and dispersion).

Abstract: The present invention relates to an optical fiber which has a structure for further increasing an FOM (=|dispersion|/loss) and which can be applied to a dispersion compensation module. The optical fiber is mainly composed of silica glass and has a core region including a center of an optical axis, a depressed region surrounding the core region, a ring region surrounding the depressed region, and a cladding region surrounding the ring region and doped with F. As compared with the refractive index of pure silica glass, a relative refractive index difference of the core region is greater than 2% but less than 3%, a relative refractive index difference of the depressed region is ?1% or more but ?0.5% or less, a relative refractive index difference of the ring region is 0.01% or more but 0.24% or less, and a relative refractive index difference of the cladding region is ?0.3% or more but ?0.1% or less. The FOM at the wavelength of 1550 nm is 250 ps/nm/dB or more.

Abstract: The present invention provides a resin composition and film for forming a cladding layer of an optical waveguide, which composition contains (A) a (meth)acrylic polymer having a weight average molecular weight more than 100,000, (B) a urethane (meth)acrylate, and (D) a radical polymerization initiator; and an optical waveguide and an optical module produced by use of the composition or film. There can be provided a resin composition for forming a cladding layer and a resin film for forming a cladding layer, which exhibit excellent bending durability and twisting durability, and an optical waveguide and an optical module each produced therefrom.

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: In certain embodiments, an optical device and a method of use is provided. The optical device includes a fiber Bragg grating having a substantially periodic refractive index modulation along a length of the fiber Bragg grating. The fiber Bragg grating has a power transmission spectrum with a plurality of local transmission minima, wherein each pair of neighboring local transmission minima has a local transmission maximum therebetween. The local transmission maximum has a maximum power at a transmission peak wavelength. The optical device further includes a narrowband optical source in optical communication with a first optical path and a second optical path.

Abstract: A graded index multimode optical fiber (10) includes: a core (11) having an outside diameter of 45-65 ?m; a first cladding (12) surrounding the core (11); a second cladding (13) surrounding the first cladding (12) and made of a material having a lower refractive index than the first cladding (12); and a third cladding (14) surrounding the second cladding (13) and made of a material having a higher refractive index than the second cladding (13). The ratio of the outside diameter of the first cladding (12) to the outside diameter of the core (11) is 1.15-1.25.

Abstract: A large mode area fiber amplifier suitable for high power applications includes a core region specifically configured to allow for high power operation while also limiting the amount of SBS that is generated. The composition of the core region is selected to include a dopant (such as aluminum) in selected areas to reduce the acoustic refractive index of the core and limit the spatial overlap between the acoustic and optical fields. The acoustic refractive index is also structured so that the acoustic field is refracted away from the central core area. In one embodiment, the core may comprise a depressed index center portion and surrounding ring core area, with the center portion including the aluminum doping and the ring formed to have a diameter less that the phonon decay length for the operating wavelength(s).

Abstract: A single mode optical fiber comprises: (i) a segmented core having at least three segments and (ii) a silica based clad layer surrounding and in contact with the core, the clad layer having a refractive index nc. The first segment has a ?max % in the range of about 0.75 to 1.1, and ?0%?0.6?max %, and an outer radius r1 in the range of about 1.5 to 3.0 ?m. The second segment has a ?2% in the range of 0.00 to 0.15%. The third segment has a ?3% in the range of less than 0.35%, an outer radius r3 in the range of about 7 ?m to 11 ?m, a width w3 in the range of about 1.5 to 3 ?m, and volume V3<7% ?m2. The refractive index profiles of the core segments are selected to provide: zero dispersion wavelength in the range of about 1565 nm to 1600 nm; total dispersion at 1550 nm in the range of about ?6 to ?0.5 ps/nm-km; and dispersion slope at 1550 nm is greater than 0.1.

Abstract: An apparatus includes a medium that is a metamaterial over a frequency range. The medium includes a stack of layers or slabs. A mechanical, electrical, or magnetic property of the layers or slabs of the stack varies monotonically between neighboring ones of the layers or slabs.

Abstract: Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular region, wherein the inner boundary of said depressed index region is an extension of the graded index core, the depressed region having a moat volume greater than 105%-um2.

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: A powerful fiber laser system is configured with at least one gain block. The gain block includes an input fiber guiding a pump light, a multiclad active fiber receiving the pump light so that a major portion is absorbed in the core of the active fiber while a minor portion of the pump light propagates in the inner cladding of the active fiber, and a multiclad output fiber. The multiclad output fiber is configured with a core, guiding a signal lased by the core of the active fiber upon absorption of the major portion of the pump light, an inner cladding receiving the minor portion of the pump light and an outer cladding. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding.

Abstract: Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular portion comprising a depressed relative refractive index.

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: An optical component including an acceptance fiber, e.g. a photonic crystal fiber, for propagation of pump and signal light, a number of pump delivery fibers and a reflector element that reflects pump light from the pump delivery fibers into the acceptance fiber. An optical component includes a) a first fiber having a pump core with an NA1, and a first fiber end; b) a number of second fibers surrounding the pump core of the first fiber, at least one of the second fibers has a pump core with an NA2 that is smaller than NA1, the number of second fibers each having a second fiber end; and c) a reflector element having an end-facet with a predetermined profile for reflecting light from at least one of the second fiber ends into the pump core of the first fiber.

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: Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region having a radius greater than 25 microns and a polymer coating applied to the outside of the fiber, the coating spaced from the core no more than 15 microns. The fiber exhibits an overfilled bandwidth at 850 nm greater than 400 MHz-km.

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: An optical fiber, made of silica-based glass, comprising a core and a cladding, each of the optical fiber having a mode field diameter of 5.5 ?m or larger at a wavelength of 1100 nm, transmitting light with a wavelength of 1250 nm in a single mode, and having a bending loss of 1 dB/turn or smaller at a wavelength of 1100 nm when the optical fiber is bent with a curvature radius of 2 mm.

Abstract: Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular portion comprising a depressed relative refractive index.

Abstract: In a LMA optical fiber the index of the core region is graded (i.e., as viewed in a radial cross-section) and has a grading depth of ?ng, as measured from a central maximum at or near the axis to a lower level that is not greater than the central maximum and not less than the index of the cladding region. When the fiber is to be bent at a bend radius, the grading depth, the radius of the core region, and the difference between the central maximum index and the cladding region index are configured to reduce bend distortion. They may also advantageously be configured to maximize the effective mode-field area of the fundamental mode, suppress higher order modes, and reduce bend loss. In a preferred embodiment, the core region includes a centralized gain region, which in turn includes a dark region that is no more than 30% of the area of the gain region. Also described is a method of making such LMA fibers.

Abstract: The present invention relates to an active energy ray-curable organopolysiloxane resin composition that comprises an organopolysiloxane resin having an epoxy group and an aromatic hydrocarbon group and a photopolymerization initiator, as well as to a light-transmitting component that comprises cured bodies produced by irradiating the aforementioned organopolysiloxane resin with active-energy rays in the presence of the aforementioned photopolymerization initiator, and to a method for manufacturing the aforementioned light-transmitting component.

Abstract: An optical fiber transmits at least a signal light having a wavelength of 1550 nanometers in a fundamental propagation mode. The optical fiber has a cutoff wavelength equal to or longer than a wavelength of 1550 nanometers, a wavelength dispersion in the fundamental propagation mode at the wavelength of 1550 nanometers larger than 0 ps/nm/km, and a dispersion slope in the fundamental propagation mode at the wavelength of the signal light equal to or smaller than ?0.05 ps/nm2/km.

Abstract: An optical device includes an optical material comprising active dopant ions and absorber dopant ions spaced apart from the active dopant ions. The active dopant ions are provided to absorb a first radiation and convert a portion of the first radiation into sensible heat. A concentration profile of the absorber dopant ions is selected to absorb a second radiation different from the first radiation and optionally the first radiation in at least one direction of the optical material so as to control a refractive index profile in the at least one direction of the optical material.

Abstract: An optical fiber that exhibits reduced mode distortions as the fiber is bent is formed by properly defining its refractive index profile during fabrication. The as-fabricated profile is defined as a “pre-distorted” profile that takes into account the gradient introduced by bending the fiber. A parabolic index profile is one exemplary bend-resistant profile that exhibits a quadratic form. A raised-cone index is another profile that may be used as the “as-fabricated” profile. In any properly configured form, factors such as bend loss and mode distortion are significantly reduced, since the profile undergoes a shift of essentially constant gradient as a bend is introduced. The resultant effective area of the inventive fiber is substantially improved over state-of-the-art fiber that is subjected to bending during installation. The as-fabricated profile may be incorporated into various types of fibers (birefringent, photonic bandgap, etc.), and is particularly well-suited for use in a fiber amplifier arrangement.

Abstract: Step-index optical waveguides are made of multicomponent glass containing a core glass and an outer glass which entirely surrounds the core class. A fiber-optic cable for conducting electromagnetic radiation, contains at least one bundle of individual fibers which encompass the step-index optical waveguides that are made of multicomponent glass containing a core glass and an outer glass that entirely surrounds the core glass on the circumferential wall thereof. These step-index optical waveguides provide great transmission capacity for transmitting data while keeping the transfer characteristics sufficiently durable. Furthermore, the fiber-optic cable is resistant against physical and chemical environmental influences and be protected against radical ambient chemicals.

Abstract: Disclosed is a low bend loss optical fiber including: a core; an inner layer disposed at outside of the core, which has a refractive index lower than a refractive index of the core, the refractive index of the inner layer gradually decreasing as it becomes farther from the core; and a trench layer disposed at outside of the inner layer, which has a lowest refractive index.

Abstract: A silica-based optical fiber includes a core and a cladding that is formed on an outer circumference of the core. The core includes three or more layers including a layer doped with at least one of germanium and fluorine, and a concentration of the germanium or the fluorine in each of the layers is controlled in such a manner that a Brillouin gain spectral peak is spread into a plurality of peaks on a Brillouin gain spectrum. With this scheme, an optical fiber is provided, which has stable characteristics in the longitudinal direction, and which has a high SBS threshold so that generation of the SBS can be effectively suppressed.

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 powerful fiber laser system is configured with at least one gain block. The gain block includes an input fiber guiding a pump light, a multiclad active fiber receiving the pump light so that a major portion is absorbed in the core of the active fiber while a minor portion of the pump light propagates in the inner cladding of the active fiber, and a multiclad output fiber. The multiclad output fiber is configured with a core, guiding a signal lased by the core of the active fiber upon absorption of the major portion of the pump light, an inner cladding receiving the minor portion of the pump light and an outer cladding. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding.

Abstract: Disclosed is a method of producing a planar multimode optical waveguide by direct photo-patterning and, more particularly, to an optical waveguide material and a method of producing the same. It is possible to control the refractive index of the optical waveguide, and the optical waveguide has a desirable refractive index distribution throughout different dielectric regions. In the method, it is unnecessary to conduct processes of forming a clad layer and of etching a core layer, thus a production process is simplified. The method comprises coating a photosensitive hybrid material having a refractive index or a volume changed by light radiation, in a thickness of 10 microns or more, and radiating light having a predetermined wavelength onto the coated photosensitive hybrid material to form the multimode optical waveguide due to a change in refractive index of a portion onto which light is radiated.

Abstract: An optical fiber includes: a first core portion doped with rare earth ions; a second core portion having a lower refractive index than that of the first core portion, provided along an outer circumference of the first core portion, and doped with the rare earth ions; and a clad portion having a lower refractive index than that of the second core portion and provided along an outer circumference of the second core portion, and is configured such that a concentration of the rare earth ions added to the second core portion is higher than that to the first core portion. With this configuration, it is possible to suppress an amount of FWM crosstalk in an optical amplification by decreasing the length of a fiber while alleviating efficiency deterioration due to concentration quenching.

Abstract: A lens, a lens array and imaging device and system containing a lens, and a method of forming a lens array and an imaging device and system containing a lens. Each lens has varying reflection indices in a radial direction.

Abstract: A laser amplifier includes a pump source and an optically active fiber having an input portion configured to receive a signal source and an output portion. The pump source is optically coupled to the optically active fiber. The laser amplifier also includes an output fiber optically coupled to the output portion of the optically active fiber. The output fiber includes a rare-earth element. The laser amplifier further includes a beam expansion section joined to the output fiber.

Abstract: An optical fiber is described in which the cladding is provided with a refractive index that increases in a radially outward direction. In particular embodiments the refractive index of the cladding increases monotonically from a low value to a value close to or higher than the refractive index of the core. Such a fiber can be formed that can be operated in an effective single mode manner or in multimode operation and which is very suitable for use in high-bit-rate communication systems.

Abstract: An optical multimode fiber including a graded index core and an extended gradient core which has a negative refractive index difference with respect to the cladding. The fiber improves the bandwidth, reliability and complexity of the telecommunication systems that are based on multimode fibers. The fiber reduces the differential mode delay among modes. The fiber thereby allows achieving large bandwidth even in the case when the highest order modes are excited. This has positive effects to the conditions that need to be fulfilled by the components such as optical sources, connectors, fiber couplers, other optical components, cables, etc. The fiber eliminates negative impact of the cladding that allows for reduction of fiber core size and the difference between the cladding and the core and thereby allows for achieving the larger bandwidth of optical fiber at lower fiber production cost.

Abstract: A method for manufacturing a final optical fiber preform via overcladding of a primary preform having a cross section area is disclosed. The method includes at least one manufacturing step of the primary preform by deposit of an inner cladding and of a central core inside a tube of fluorine-doped silica, the tube being chosen such that it has a cross section area that is maximally about 15% less than the cross section area of the primary preform. With the method of the invention it is possible to manufacture a preform of large capacity at reduced cost which allows the drawing of an optical fiber having reduced transmission losses.

Abstract: An optical fiber, comprising: (i) a core having a core center and a radius or a width a, (ii) a cladding surrounding the core, and (iii) at least one stress member situated proximate to the fiber core within the cladding, said stress member comprising silica co-doped with F and at least one dopant selected from the list consisting of: GeO2, P2O5, Y2O3, TiO2 and Al2O3, wherein distance b between the stress member and the core center satisfies the following equation: 1?b/a<2.

Abstract: A distributed fiber optic sensor device that employs a photonic band gap fiber as a sensing medium, in which: the photonic band gap fiber, which is the sensing medium, includes: a quartz section; and a plurality of high refractive index portions provided in the quartz section along the longitudinal direction of the fiber, the high refractive index portions being photonic band gaps periodically arranged to form a triangular-lattice pattern; the photonic band gap fiber has a bandwidth in which a wavelength band of a Stokes beam generated due to stimulated Raman scattering is included; and the photonic band gap fiber has a band gap width in which a wavelength band of an anti-Stokes beam generated due to the stimulated Raman scattering and a wavelength band of an optical signal incident into the photonic band gap fiber are included.