Abstract: An electro-optical memory cell having a non-volatile programmable refractive index and a method of making. The memory cell includes: a waveguiding structure having a transition metal oxide with oxygen vacancies; a plurality of electrodes for applying an electrical field; and an optical detector for detecting a state of the memory cell. The method includes: fabricating a waveguiding structure having a transition metal oxide with oxygen vacancies; positioning a plurality of electrodes for application of an electric field; arranging the transition metal oxide and the electrodes such that when an electric field is applied, the oxygen vacancies migrate in a direction that has a component which is radial relative to a center of the beam path; applying the electric field thereby programming the refractive index to set a state of the memory cell; and detecting the state of the memory cell using an optical detector.

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: Disclosed is an optical fiber for a current sensor, the optical fiber comprising a core doped with CdSe quantum dots and a current sensor using the same.

Abstract: The invention consists in an amplifying optical fiber comprising a core containing a dopant and a cladding, wherein said core comprises a monomode core intended to propagate an optical signal, quantum dots of a semiconductor material being disposed in or near said monomode core, and a multimode core surrounding the monomode core, intended to receive a pumping signal.

Abstract: The invention relates to coated optical fibers comprising soft primary coatings and to such primary coatings for protecting glass optical fibers having a sufficient high resistance against cavitation. In particular, the primary coatings have a cavitation strength at which a tenth cavitation appears (?10cav) of at least about 1.0 MPa as measured at a deformation rate of 0.20% min?1 and of at least about 1.4 times their storage modulus at 23° C. The coating preferably shows strain hardening in a relative Mooney plot, preferably has a strain energy release rate Go of about 20 J/m2 or more, and preferably has a low volumetric thermal expansion coefficient. The invention furthermore provides a method and apparatus for measuring the cavitation strength of a primary coating.

Abstract: The invention relates to an optical fibre comprising a gain medium which is equipped with: a core (22) which is formed from a transparent material and nanoparticles (24) comprising a doping element and at least one element for enhancing the use of said doping element; and an outer cladding (26) which surrounds the core. The invention is characterised in that the doping element is erbium (Er) and in that the enhancing element is selected from among antimony (Sb), bismuth (Bi) and a combination of antimony (Sb) and bismuth (Bi). According to the invention, one such fibre is characterised in that the size of the nanoparticles is variable and is between 1 and 500 nanometres inclusive, and preferably greater than 20 nm.

Abstract: A novel polyimide compound which has a lower linear expansion coefficient and permits film formation by a spin coating method or the like, a preparation method for the polyimide compound, and an optical film and an optical waveguide produced by employing the compound. The polyimide compound has a structural unit represented by the following general formula (1): wherein X and Y are each a covalent single bond, —CO—, —O—, —CH2—, —C(CF3)2— or —CR(R?)— (wherein R and R?, which may be the same or different, are each a linear or branched C1 to C4 alkyl group); A and B are each a halogen group; a and b, which are the numbers of the groups A and B, respectively, are each 0 or an integer of 1 or 2; and R1, R2, R3 and R4, which may be the same or different, are each a hydrogen atom or a linear C1 to C4 alkyl group.

Abstract: A novel polyimide compound which has a low linear expansion coefficient and permits film formation by a spin coating method or the like, a preparation method for the polyimide compound, and an optical film and an optical waveguide produced by employing the compound. The polyimide compound has a structural unit represented by the following general formula (1): wherein X is a covalent single bond, —CH2—, —C(CF3)2— or —CR(R?)— (wherein R and R?, which may be the same or different, are each a C1 to C6 alkyl group or an aryl group); A and B, which may be the same or different, are substituents each selected from a hydroxyl group, a halogen group and a C1 to C4 alkyl group; a and b, which are the numbers of the substituents A and B, respectively, are each an integer of 0 to 2; and o, p and q are each an integer of 1 to 5.

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 method is provided for eliminating crystals in non-oxide optical fiber preforms as well as optical fibers drawn therefrom. The optical-fiber-drawing axis of the preform is aligned with the force of gravity. A magnetic field is applied to the preform as it is heated to at least a melting temperature thereof. The magnetic field is applied in a direction that is parallel to the preform's optical-fiber-drawing axis. The preform is then cooled to a temperature that is less than a glass transition temperature of the preform while the preform is maintained in the magnetic field. When the processed preform is to have an optical fiber drawn therefrom, the preform's optical-fiber-drawing axis is again aligned with the force of gravity and a magnetic field is again applied along the axis as the optical fiber is drawn from the preform.

Abstract: Disclosed is an optical fiber having a silica-based core comprising an alkali metal oxide a silica-based core, said core comprising an alkali metal oxide selected from the group consisting of K2O, Na2O, Li2O, Rb2O, Cs2O and mixtures thereof in an average concentration in said core between about 10 and 10000 ppm by weight, and a silica-based cladding surrounding and directly adjacent the core, the cladding including a region having a lower index of refraction than the remainder of such cladding. By appropriately selecting the concentration of alkali metal oxide dopant in the core and the cladding, a low loss optical fiber may be obtained which exhibits a cable cutoff less than 1400 nm chromatic dispersion at 1550 nm between about 13 and 19 ps/nm/km, and a zero dispersion wavelength less than about 1324 nm.

Abstract: A thermally stable chalcogenide glass, a process for making the same, and an optical fiber drawn therefrom are provided. A chalcogenide glass having the composition Ge(5?y)As(32?x)Se(59+x)Te(4+y) (0?y?1 and 0?x?2) is substantially free from crystallization when it is heated past the glass transition temperature Tg or drawn into optical fibers. A process for making the thermally stable chalcogenide glass includes purifying the components to remove oxides and scattering centers, batching the components in a preprocessed distillation ampoule, gettering oxygen impurities from the mixture, and heating the components to form a glass melt. An optical fiber formed from the chalcogenide glass is substantially free from crystallization and exhibits low signal loss in the near-infrared region, particularly at wavelengths of about 1.55 ?m.

Abstract: A composite material with at least one of a negative effective permittivity and a negative effective permeability for incident radiation of at least one wavelength is described. The composite material comprises conductive structures that are substantially random with respect to at least one of size, shape, orientation, and location.

Abstract: The invention aims to provide a method by which a solution of polyimide can be easily obtained. Further, the invention aims to provide a fluorinated polyimide solution by which fluorinated polyimide excellent especially as an optical material and an electronic functional material can easily be produced. The production method of the soluble polyimide solution according to invention is characterized by mixing a mixture containing a polyamide acid, a cyclodehydration reagent, and a solvent by a rotation-revolution mixing method. Further, the fluorinated polyimide solution of the invention is a solution of polyimide defined by the following formula (II): wherein, X and Y independently represent divalent organic groups; Z represents chlorine atom, bromine atom, or iodine atom; p represents an integer of 1 to 3; q represents an integer of 0 to 2; and p+q=3.

Abstract: A waveguide core made of hydrogel serves as an immobilization matrix having receptor molecules embedded therein.

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

Abstract: Stimulated Brillouin scattering (SBS) in a photonic crystal fiber is suppressed by doping the individual core segments such that the Brillouin frequency of each segment is sufficiently different from the neighboring segments that Brillouin scattered light from one core segment sees negligible gain from the other core segments, whereby higher power narrow-linewidth optical fiber amplifiers and lasers may be obtained. The optical properties of the guiding medium are preserved through the careful design of the core and the lattice structure.

Abstract: Planar waveguides having quantum dots and methods of manufacture of the planar waveguide are described.

Abstract: According to one example of the invention an optical fiber comprises: (i) a core comprising of Al doped silica 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; (iii) a hermetic carbon based coating surrounding said cladding, said hermetic coating being 300 nm-1000 nm thick; and (iv) a second coating surrounding said hermetic coating, said second coating being 5 ?m to 80 ?m thick.

Abstract: The present invention relates to a resin composition for an optical waveguide comprising (A) a photopolymerizable monomer, (B) a binder polymer and (C) a photoinitiator, wherein the photopolymerizable monomer (A) contains a hydroxyl group-containing fluorinated mono(meth)acrylate base compound. Provided are a resin composition for an optical waveguide which has a high transparency in a wavelength of 1.3 ?m and which is excellent in formation of a thick film and an adhesive property and an optical waveguide prepared by using the same.

Abstract: An electro-optic waveguide device comprising an electro-optic polymer core and at least one crosslinked polymer clad, wherein the crosslinked polymer clad is comprised of a first constitutional unit derived from a compound having the formula wherein, m=0-6; n=0-1; q=1-3; y=0-3; Ar1 is an aryl or heteroaryl group; and independently at each occurrence p=0-1; R is an alkyl, heteroalkyl, aryl, or heteroaryl group; Ar2 is an aryl or heteroaryl group; and X is a crosslinkable group. The R group may be an alkyl or heteroalkyl group with at least 6 atoms in a straight chain. In some embodiments, the R group is an alkoxy capped oligoalkylene group. Other embodiments include a polymer comprising a first constitutional unit derived from a compound having the formula described above.

Abstract: An optical waveguide includes a cladding film and a core formed integrally with the cladding film. The core includes a light guide portion formed on one surface of the cladding film, a light input portion, and a light output portion, the light input portion and the light output portion being formed in through-holes formed in the cladding film. A mirror surface is respectively formed at a connecting portion between the light guide portion and the light input portion and a connecting portion between the light guide portion and the light output portion. In manufacturing the optical waveguide, the cladding film is brought into close contact with a surface of a mold, the surface having a recessed groove thereon, and a UV-curable resin is injected under pressure through one of the through-holes opened in the cladding film into the recessed groove.

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: A plurality of optical members (lenses) for use in ultraviolet region are mutually stuck. A fluorine-based organic compound (for example, fluorine-based oil) is provided between them. The periphery of the optical members is sealed with a sealant. As the sealant, an adhesive fluorine resin, for example, a soluble fluorine resin is used.

Abstract: A waveguide structure includes a SOI substrate. A core structure is formed on the SOI substrate comprising a plurality of multilayers having alternating or aperiodically distributed thin layers of either Si-rich oxide (SRO), Si-rich nitride (SRN) or Si-rich oxynitride (SRON). The multilayers are doped with a rare earth material so as to extend the emission range of the waveguide structure to the near infrared region. A low index cladding includes conductive oxides to act as electrodes.

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: 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 electro-optical device having a non-volatile programmable refractive index. The device includes: a waveguiding structure with waveguiding material, the waveguiding structure defining an optical beam path, where the waveguiding structure includes a transition metal oxide with oxygen vacancies that migrate when exposed to an electric field; and a plurality of electrodes for applying an electric field to a region including the transition metal oxide with oxygen vacancies; where the transition metal oxide and the electrodes are arranged such that under the applied electric field the oxygen vacancies migrate in a direction that has a component which is radial relative to a center of the beam path. Further, there is provided a method for making the electro-optical device, including: fabricating the waveguiding structure; positioning a plurality of electrodes for application of an electric field; and arranging the transition metal oxide and the electrodes.

Abstract: Disclosed is an amplifying optical fiber having a central core and an optical cladding surrounding the central core. The central core is based on a silica matrix that includes nanoparticles, which are composed of a matrix material that includes doping ions of at least one rare earth element. The amplifying optical fiber can be employed, for example, in an optical amplifier and an optical laser.

Abstract: The present invention provides a rare earth element-doped optical fiber amplifier having a function which allows to omit an optical isolator component, and a method for providing the optical non-reciprocity using the same. In the optical fiber, the optical fiber matrix material is a ferroelectric solid state material, and the ferroelectric solid state material is doped by a rare earth element such as erbium (Er) or thulium (Tm). The optical fiber is characterized by an optical amplification function and an optical non-reciprocity function.

Abstract: The present invention relates to an assembly of multiple waveguides which includes a substrate and a plurality of waveguides positioned on said substrate at locations effective to suppress cross-talk between different waveguides. The plurality of waveguides each comprise an elongate array of quantum dots extending between sets of first and second locations on the substrate. The waveguides are positioned to receive: (1) pumped light uniformly applied to the array to produce electron-hole pairs and to enable optical gain and (2) signal light at the first location to trigger an emission from the quantum dot at the first location and transmission of photons along the array to the second location. A light transmission system which includes this assembly as well as methods of making and using the assembly are also disclosed.

Abstract: The invention relates to coated optical fibers comprising soft primary coatings and to such primary coatings for protecting glass optical fibers having a sufficient high resistance against cavitation. In particular, the primary coatings have a cavitation strength at which a tenth cavitation appears (?10cav) of at least about 1.0 MPa as measured at a deformation rate of 0.20% min?1 and of at least about 1.4 times their storage modulus at 23° C. The coating preferably shows strain hardening in a relative Mooney plot, preferably has a strain energy release rate Go of about 20 J/m2 or more, and preferably has a low volumetric thermal expansion coefficient. The invention furthermore provides a method and apparatus for measuring the cavitation strength of a primary coating.

Abstract: This invention pertains to optical fiber transmission networks, and is particularly relevant to transmission of high volume of data and voice traffic among different locations. In particular, the improvement teaches improvements to an optical transport system to allow for efficient and flexible network evolution.

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 thermally stable chalcogenide glass, a process for making the same, and an optical fiber drawn therefrom are provided. A chalcogenide glass having the composition Ge(5?y)As(32?x)Se(59+x)Te(4+y) (0?y?1 and 0?x?2) is substantially free from crystallization when it is heated past the glass transition temperature Tg or drawn into optical fibers. A process for making the thermally stable chalcogenide glass includes purifying the components to remove oxides and scattering centers, batching the components in a preprocessed distillation ampoule, gettering oxygen impurities from the mixture, and heating the components to form a glass melt. An optical fiber formed from the chalcogenide glass is substantially free from crystallization and exhibits low signal loss in the near-infrared region, particularly at wavelengths of about 1.55 ?m.

Abstract: Provided are polymers comprising the condensation product of silicon-containing reactants. Also provided are compositions suitable for use in forming optical waveguides which include such polymers, as well as optical waveguides formed from such polymers. The polymers, compositions and optical waveguides have particular use in the formation of printed wiring boards having electrical and optical functionality.

Abstract: The invention relates to a micro-structured optical fibre (1) including at least one core (7, 7A, 7B, 7C, 7D1 7E, 7F) with a core space symmetry, characterised in that said core contains at least one doping material distributed in said core according to a dissymmetrical implantation relative to said at least one symmetry axis.

Abstract: A single mode optical transmission fiber comprises a depressed core having at least 0.41 weight percent fluorine and an index difference (|?n1|) with pure silica greater than 1.5×10?3, a depressed cladding having at least 1.2 weight percent fluorine and an index difference (|?n2|) with pure silica greater than 4.5×10?3 and an index difference (|?n2|?|?n1|) with the depressed core greater than or equal to 3×10?3.

Abstract: A rare earth-doped core optical fiber includes a core comprising a silica glass containing at least aluminum and ytterbium, a clad provided around the core and comprising a silica glass having a lower refraction index than that of the core, and a polymer layer provided on the outer circumference of the clad and having a lower refractive index than that of the clad, wherein aluminum and ytterbium are doped into the core such that a loss increase by photodarkening, TPD, satisfies the following inequality (A). By this rare earth-doped core optical fiber, it is possible to manufacture an optical fiber laser capable of maintaining a sufficient laser oscillation output even when used for a long period of time. TPD?10{?0.655*(DAl)?4.304*exp{?0.00343*(AYb)}+1.

Abstract: A polymer clad optical fiber is provided in which, if the diameter of an inner core is taken as a1, and the diameter of an outer core is taken as a2, and if a ratio X (which=a22/a12) between a cross-sectional area of the inner core and a cross-sectional area of the outer core is within a range of 1.8?X?2.2, and if a relative refractive index difference between the inner core and the outer core is taken as ?1, and if a relative refractive index difference between the outer core and a cladding is taken as ?2, then for a parameter Y which is defined as Y=?1/?2, when a high temperature is taken as Ymax and a low temperature is taken as Ymin, a relationship is established in which, when X is within a range of 1.8?X?2.0, then 0.25?Ymin?0.84X?0.68, and Ymax is 0.25?Ymax?0.84X?0.68, and, when X is within a range of 2.0?X?2.2, Ymin is 0.48X?0.71?Ymin??2/9X+13/9, and Ymax is 0.48X?0.71?Ymax??2/9X+13/9.

Abstract: An optical fiber comprising a flame retardant UV light-curable tight-buffer coating coated onto the fiber, wherein said tight-buffer coating is substantially halogen-free, and has a limiting oxygen index of at least about 22%, and wherein said tight-buffer coating is removable from said fiber with a strip-force of less than about 1800 grams when the fiber is upjacketed with said coating at a line speed of at least 300 m/min.

Abstract: Methods of fabricating optical elements that are encapsulated in monolithic matrices. The present invention is based, at least in one aspect, upon the concept of using multiphoton, multi-step photocuring to fabricate encapsulated optical element(s) within a body of a photopolymerizable composition. Imagewise, multiphoton polymerization techniques are used to form the optical element. The body surrounding the optical element is also photohardened by blanket irradiation and/or thermal curing to help form an encapsulating structure. In addition, the composition also incorporates one or more other, non-diffusing binder components that may be thermosetting or thermoplastic. The end result is an encapsulated structure with good hardness, durability, dimensional stability, resilience, and toughness.

Abstract: An index-matching gel for use with nano-engineered optical fibers is disclosed. The index-matching gel is cross-linked, which prevents the gel from wicking into the voids and down the nano-engineered optical fiber to a depth where the fiber performance and/or device performance is compromised. The formulation comprises a non-reactive constituent A, two reactive constituents B and C, and a catalyst D. The gel is pre-cured and forms a cross-linked internal network that results in a single-component gel that does not require meter mixing of an additional constituent or heat curing. The gel is suitable for use in the mechanical splicing of optical fibers when at least one of the optical fibers is a nano-engineered optical fiber. The gel is also suitable for use in fiber optic connectors wherein at least one of the optical fibers constituting the connection is a nano-engineered optical fiber.

Abstract: A POF (12) comprises a core (65) having a radius of R1, an outer shell (66) and an outermost shell (67). The core (65) includes concentric layers. A first layer (61) is at the periphery side and an nth layer (64) is at the center of the core (65). The refractive index increases from the first layer (61) to the nth layer (64). The refractive index N(r) at a position where a distance r apart in a radius direction from the center of the core (65) having a radius of R1 is satisfied following equations (1) and (2) when the center of a cross-sectional circle of the core (65) has the refractive index of N1, the outermost part of the core (65) has the refractive index of N2, and a refractive index distribution coefficient is shown as g: N(r)=N1[1?2?(r/R1)g]1/2??[Equation (1)] ?=(N12?N22)/(2N12).

Abstract: A rare earth-doped core optical fiber of the present invention includes a core comprising a silica glass containing at least aluminum and ytterbium, and a clad provided around the core and comprising a silica glass having a lower refraction index than that of the core, wherein the core has an aluminum concentration of 2% by mass or more, and ytterbium is doped into the core at such a concentration that the light absorption band which appears around a wavelength of 976 nm in the light absorption band by ytterbium contained in the core shows a peak light absorption rate of 800 dB/m or less.

Abstract: The present invention relates to a method of manufacturing an optical fiber by carrying out one or more chemical vapor deposition reactions in a substrate tube, with the optical fiber exhibiting a low sensitivity to the hydrogen-induced attenuation losses at a transmission wavelength of 1550 nm. The present invention furthermore relates to an optical fiber comprising a cladding layer and a light-conducting core, which fiber has been obtained by using the present method.

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: An optical fiber comprises a center core and a cladding located at an outer periphery of the core, wherein the core comprises at least one codoped layer made from silica glass doped with germanium and fluorine, and at least one lower-concentration codoped layer made from silica glass doped with germanium, or silica glass that is doped with germanium and fluorine wherein an amount of fluorine in the lower-concentration codoped layer is smaller than an amount of fluorine in the codoped layer.

Abstract: A silica-based multi core optical fiber and a fabrication method for the same are provided, and include two or more cores of GeO2—SiO2 glass including an fluorine concentration not less than about 15 w % and a germanium concentration about 0.05 wt % to 2 wt %, in a core. A relative refractive index difference of a cladding and a core is not less than about 3%; and a ratio of a cladding diameter to a core diameter is about 1.02 to 3.0. A silica-based single core optical fiber is also provided, and includes a core having a germanium concentration not less than about 15 wt % and an fluorine concentration about 0.05 wt % to 2 wt %.

Abstract: Disclosed is a fiber amplifier system including a gain fiber having a single-mode core containing dopant ions capable of producing stimulated emission of light at wavelength ?s when pumped with light of wavelength ?p. Absorbing ion filtering means is operatively associated with the gain fiber to alter the gain curve. If the absorbing ions are the same as the gain ions of the gain fiber, the system further includes means for preventing pump light from exciting the gain ions of the filtering means. The excitation prevention means may take the form of means for attenuating pump light. If the absorbing ions are different from the dopant ions of the gain fiber, such absorbing ions can be subjected to light at wavelength ?p, but they will remain unexcited. Such absorbing ions can be used to co-dope the gain fiber, or they can be incorporated into the core of a fiber that is in series with the gain fiber.