Abstract: An arrangement and method provide an optical thulium doped fiber amplifier utilizing a dual wavelength pumping scheme for amplifying an optical signal. The method includes the steps of: a first deposition (a) of energy into the fiber amplifier by pumping with radiation of a first wavelength; and a second deposition (b) of energy into the fiber amplifier by pumping with radiation of a second wavelength. The radiation of the first wavelength is arranged to induce, by single photon absorption, a population to the 3H4 level of the thulium dopant, and the radiation of the second wavelength primarily depopulates the 3F4 level, by excited absorption of a single photon, preferably by strong excited state absorption to the 3F2 level. The steps gives a population inversion between the 3H4 and the 3F4 levels and facilitate a power efficient high gain amplification.

Abstract: A family of tellurite glasses and optical components for telecommunication systems, the glasses consisting essentially of, as calculated in cation percent, 65-97% TeO2, and at least one additional oxide of an element having a valence greater than two and selected from the group consisting of Ta, Nb, W, Ti, La, Zr, Hf, Y, Gd, Lu, Sc, Al and Ga, that may contain a lanthanide oxide as a dopant, in particular erbium oxide, and that, when so doped, is characterized by a fluorescent emission spectrum having a relatively broad FWHM value.

Abstract: An optical amplifying glass having Er doped in an amount of from 0.01 to 10% as represented by mass percentage to a matrix glass comprising, by mol %, BiO2: 20 to 80, B2O3+SiO2: 5 to 75, Ga2O3+WO3+TeO2: 0.1 to 35, Al2O3≦10, GeO2≦30, TiO2≦30, and SnO2≦30, and containing no CeO2.

Abstract: A wide band erbium-doped fiber amplifier with a gain enhancement is provided comprising a first fiber amplifier adapted to amplify C-band components of an input optical signal, a second fiber amplifier connected to the first fiber amplifier in series while being disposed downstream from the first fiber amplifier to amplify L-band components of the input optical signal. A C/L splitter is disposed between the first and second fiber amplifiers and to split the amplified C and L-band optical signals to flow along different paths. A fiber reflector is disposed downstream from the second fiber amplifier to reflect the amplified L-band optical signal to flow backwards toward the second fiber amplifier. A circulator is disposed between the C/L splitter and the second fiber amplifier to guide the amplified L-band optical signal, reflected to flow backwards by the fiber reflector, so that the amplified L-band optical signal flows along a path different from that of optical signals applied to the circulator.

Abstract: Phosphate glass fibers are an attractive alternative to silica fibers because they can be co-doped with much higher concentrations of Yb and Er and exhibit a higher optical gain per unit length. However, in such fibers the absorption of the pump is high and heating effects caused by the pump laser can cause a significant change in refractive index. This problem is overcome with a phosphate glass composition that exhibits a temperature coefficient of refractive index &bgr;=dn/dT close to zero. This is achieved by avoiding alkali metal oxides in the glass composition and by adjusting the concentration of the network modifiers such as BaO.

Abstract: An optically active phosporus-silicate glass when pumped to directly excite Er ions, provides gain in 1565 nm to 1620 nm range and comprises in weight percent: SiO2 50 to 92%; Er2O3 0.01 to 2%; P2O5 greater than 5%; and Al2O3 0.0 to 0.3%.

Abstract: Disclosed are optical gain fibers which include an erbium-containing core and a cladding surrounding the core and which have ripple of less than about 25% over about a 40 nm wide window or ripple of less than about 15% over about a 32 nm wide window, or both. In one embodiment, the optical gain fibers are pumpable at 980 nm and at 1480 nm. In another embodiment, the optical gain fibers are fusion sliceable. In yet another embodiment, the core includes oxides erbium; the cladding includes silicon dioxide; and the optical gain fiber has a passive loss of less than about 0.5% of the peak absorption of the erbium absorption band in the vicinity of 1530 nm. The optical gain fibers of the present invention have a wider gain window, improved flatness across the gain window, and/or increased gain as compared to conventional optical gain fibers.

Abstract: An optical amplifying glass comprising a matrix glass and, added thereto, from 0.01 to 10 wt % of Er, characterized in that said matrix glass substantially comprises, as represented by mol %, 20 to 80 of Bi2O3, 0 to 74.89 of B2O3, 0 to 79.99 of SiO2, 0.01 to 10 of CeO2, 0 to 50 of Li2O, 0 to 50 of TiO2, 0 to 50 of ZrO2, 0 to 50 of SnO2, 0 to 30 of WO3, 0 to 30 of TeO2, 0 to 30 of Ga2O3 and 0 to 10 of Al2O3, with the proviso that said matrix glass contains at least one of B2O3 and SiO2.

Abstract: A compact, low-cost mid-gain Erbium Micro-Fiber Amplifier (EMFA) is provided by multi-mode pumping a micro fiber formed from a specialty multi-component glass and highly co-doped with Er:Yb. The specialty glass exhibits a much higher core absorption coefficient than standard glasses. As a result, the lower order modes are rapidly absorbed in the fiber core. The abrupt change in the mode profile perturbs the higher order modes and mode couples them into the lower order modes within a very short length of fiber, less than 20 cm. This “absorptive mode coupling” effect can double the absorption efficiency of a circular symmetric micro fiber and extend the length over which such a highly doped fiber can be efficiently inverted. The combination of multi-mode pumping with short fiber lengths reduces the form factor and cost of EMFAs.

Abstract: An optical waveguide including a core having silica, Al, a non-fluorescent rare-earth ion, Ge, Er, and Tm. The non-fluorescent rare-earth ion may be La. Exemplary compositions concentrations are Er is from 15 ppm to 3000 ppm, Al is from 0.5 mol % to 12 mol %, La is less than or equal to 2 mol %, Tm is from 15 ppm to 10,000 ppm; and the Ge is less than or equal to 15 mol %. The core may further include F. An exemplary concentration of F is less than or equal to 6 anion mol %.

Abstract: A method of making an erbium-doped optical fiber for use in optical amplifiers according to the present invention includes the step of providing a substrate tube. High purity silica-based cladding layers are deposited on the inside of the tube. A core glass that includes silica, Al, a non-fluorescent rare-earth ion, Ge, Er, and Tm is then deposited in the tube. The non-fluorescent rare-earth ion may be La and the core may further include F. The tube is then collapsed to form a preform. Finally, the preform is drawn to yield optical fiber.

Abstract: In accordance with the invention, the present invention provides for a polymer comprised of a general composition. The polymer has a first rare earth element, a second rare earth element, one of the elements of Group VIA, one of the elements of Group VA, a first fully halogenated organic group, a second fully halogenated organic group. A method of manufacturing the polymer is also disclosed.

Abstract: An optical waveguide amplifier fiber comprises a core region at least in part comprises Er2O3, Al2O3, GeO2 and Ga2O3. The amplifier fiber also comprises an inner clad surrounding the core region, and an outer clad surrounding the inner clad. The relative refractive index percentages and radii of the core region, inner clad and outer clad are chosen from the following ranges: the relative refractive index percent of the core segment within the range of from about 0.5% to about 1.2%; the relative refractive index percent of the inner clad within the range of from about 0.0% to about 0.3%; the outer radius of the core region within the range of from about 2.0 &mgr;m to about 5.0 &mgr;m; and, the outer radius of the inner clad within the range of from about 3.8 &mgr;m to about 10.2 &mgr;m.

Abstract: Method of synthesis of photonic band gap (PBG) materials. The synthesis and characterization of high quality, very large scale, face centered cubic photonic band gap (PBG) materials consisting of pure silicon, exhibiting a complete three-dimensional PBG centered on a wavelength of 1.5 &mgr;m. This is obtained by chemical vapor deposition and anchoring of disilane into a self-assembling silica opal template, wetting of a thick silicon layer on the interior surfaces of the template, and subsequent removal of the template. This achievement realizes a long standing goal in photonic materials and opens a new door for complete control of radiative emission from atoms and molecules, light localization and the integration of micron scale photonic devices into a three-dimensional all-optical micro-chip.

Abstract: An optical amplifying unit includes an input for the input optical signals and an output for the output of the optical signals. A single-mode active fiber codoped with Er and Yb is optically connected to the input and the output and adapted to amplify the optical signals. A first pump source generates a first pump radiation including an excitation wavelength for Er, and a second pump source for generates a second pump radiation including an excitation wavelength for Yb. A first optical coupler optically couples the first pump radiation into the core of the active fiber in a co-propagating direction with respect to signal direction, and a second optical coupler optically couples the second pump radiation into the core of the active fiber in a counter-propagating direction with respect to signal direction.

Abstract: A main object of the present invention is to provide a novel optical power limiting material of high performance being less susceptible to damages caused by heat occurring when an intensified laser beam is irradiated, having reversible characteristic and exhibiting a stable optical power limiting effect; production of the optical power limiting is simple and economical.

Abstract: An optical amplifier glass comprising a matrix glass containing Bi2O3 and at least one of Al2O3 and Ga2O3, and Er doped to the matrix glass, wherein from 0.01 to 10% by mass percentage of Er is doped to the matrix glass which has a total content of Al2O3 and Ga2O3 of at least 0.1 mol %, a content of Bi2O3 of at least 20 mol %, a refractive index of at least 1.8 at a wavelength of 1.55 &mgr;m, a glass transition temperature of at least 360° C. and an optical basicity of at most 0.49.

Abstract: By optimizing the refractive index profile, the absorption coefficient of a rare earth element doped optical fiber can be enlarged and nonlinear effect can be suppressed. Thus, according to the present invention, the optical fiber, which is suitable for wide band optical amplification, can be realized. Moreover, in the present invention, the optical fiber of W-shape profile comprising a core, the first cladding having a refractive index smaller than that of said core surrounding said core, and the second cladding having a refractive index smaller than that of said core and larger than that of said first cladding surrounding said first cladding is prepared and are suitable for the wide band optical amplification.

Abstract: A Tm-doped germanate glass composition comprises GeO2 having a concentration of at least 20 mole percent, Tm2O3 having a concentration of about 0.001 mole percent to about 2 mole percent, and Ga2O3, having a concentration of about 2 mole percent to about 40 mole percent. The composition can further include an alkaline earth metal compound selected from the group consisting of MgO, CaO, SrO, BaO, BaF2, MgF2, CaF2, SrF2, BaCl2, MgCl2, CaCl2, SrCl2, BaBr2, MgBr2, CaBr2, SrBr2, and combinations thereof, and having a non-zero concentration of less than about 40 mole percent. The composition can further include an alkali metal compound selected from the group consisting of Li2O, Na2O, K2O, Rb2O, Cs2O, Li2F2, Na2F2, K2F2, Rb2F2, Cs2F2, Li2Cl2, Na2Cl2, K2Cl2, Rb2Cl2, Cs2Cl2, Li2Br2, Na2Br2, K2Br2, Rb2Br2, Cs2Br2 and combinations thereof, and having a non-zero concentration of less than about 20 mole percent.

Abstract: An optical amplifier of the present invention includes a pump source for generating a pumping light, a wavelength division multiplexing (WDM) coupler for multiplexing an inputted optical signal and the pumping light and an optical fiber including a core and a clad, wherein the core has holmium ions less than 0.5 mole % and the clad has ions selected from the group consisting of transition metal ions, rare earth ions and a combination thereof. In addition, the phonon energy of a host material is less than 600 cm−1 and an absorption band at short-wavelength side is shorter than 530 nm.

Abstract: An apparatus for gating an optical signal comprising: an input stage arranged to receive and combine first and second optical control signals (ON, OFF) of first and second wavelengths, and an optical signal (SIGNAL IN) to be gated of a third wavelength. A gain medium is arranged to receive the signals SIGNAL IN, ON and OFF from the input stage. The gain medium (e.g. YAG) comprises a transition metal dopant (e.g. Cr4+) that has an excited state populatable by the first control signal and depopulatable by the second control signal to allow selective amplification of the optical signal to be gated by stimulated emission from the excited state responsive to the control signals. The amplification process has a very fast switch-on time that is several orders of magnitude faster than in prior art devices based on the rare earth dopant Er3+.

Abstract: An optical fiber for optical amplification used for 1.58 &mgr;m band signal light amplification, at least a core region thereof being doped with Er has a core region at least a part thereof made of silica glass co-doped with Ge and Al together with Er, and Er average atomic concentration in the core region is from 1000 wt-ppm to 3000 wt-ppm inclusive, and cutoff wavelength is from 1.3 &mgr;m to 1.5 &mgr;m inclusive.

Abstract: The specification describes rare earth doped fiber amplifier devices for operation in the extended L-band, i.e. at wavelengths from 1565 nm to above 1610 nm. High efficiency and flat gain spectra are obtained using a high silica based fiber codoped with Er, Al, Ge, and P and an NA of at least 0.15.

Abstract: An optical amplifying unit (100; 100′) for amplifying optical signals in an optical transmission system has an amplification wavelength band with a lower wavelength limit greater than 1570 nm and includes an input (101) for the input of optical signals, an output (102) for the output of optical signals and an optical amplifier (104) interposed between the input (101) and the output (102) to amplify the optical signals. The optical amplifier (104) includes an amplification fiber (108) co-doped with erbium and ytterbium, at least a pump source (109, 110) to generate pump radiation and at least an optical coupler (111, 112) optically coupling the pump sources (109, 110) to the amplification fiber (108). The optical amplifying unit has a power gain of at least 31 dB when the optical signals have an input power of at least −10.5 dBm and wavelengths within the amplification wavelength band.

Abstract: The specification describes rare earth doped fiber amplifier devices for operation in the extended L-band, i.e. at wavelengths from 1565 nm to above 1610 nm. High efficiency and flat gain spectra are obtained using a high silica based fiber codoped with Er, Al, Ge, and P and an NA of at least 0.15.

Abstract: An optical fiber is for optical amplification used for 1.58 &mgr;m band signal light amplification, at least a core region thereof being doped with Er. At least a part of the core region is made of silica glass co-doped with Ge and Al together with Er. The Er average atomic concentration in the core region is from 1500 wt-ppm to 3000 wt-ppm inclusive, and cutoff wavelength is from 0.8 &mgr;m to 1.1 &mgr;m inclusive.

Abstract: This invention relates to an amplification optical fiber which requires no gain equalizer and has a flat gain spectrum and high polarization extinction ratio, and the like. The amplification optical fiber has a core region included in a light propagation region through which signals having different wavelengths propagate, a cladding region around the core region, and a polarization maintaining structure for maintaining the polarized states of the signals. The amplification optical fiber is mainly comprised of silica glass, and Er and Al of 4 wt % or more are doped into at least part of the light propagation region including the core region.

Abstract: In accordance with the invention, the present invention provides for a polymer comprised of a general composition. The polymer has a first rare earth element, a second rare earth element, one of the elements of Group VIA, one of the elements of Group VA, a first fully halogenated organic group, a second fully halogenated organic group. A method of manufacturing the polymer is also disclosed.

Abstract: A device amplifies light at wavelengths in the vicinity of 1420-1530 nm, using thulium doped silica-based optical fiber. This wavelength band is of interest as it falls in the low-loss optical fiber telecommunications window, and is somewhat shorter in wavelength than the currently standard erbium doped silica fiber amplifier. The device thus extends the band of wavelengths which can be supported for long-distance telecommunications. The additional wavelength band allows the data transmission rate to be substantially increased via wavelength division multiplexing (WDM), with minimal modification to the standard equipment currently used for WDM systems. The host glass is directly compatible with standard silica-based telecommunications fiber. The invention also enables modified silicate based amplifiers and lasers on a variety of alternative transitions. Specifically, an S-band thulium doped fiber amplifier (TDFA) using a true silicate fiber host is described.

Abstract: An optical transmission system includes an optical transmitting unit (10) to transmit optical signals in a transmission wavelength band above 1570 nm; an optical receiving unit to receive the optical signals; an optical fiber link optically coupling the transmitting unit to the receiving unit, at least an optical amplifying unit (100) coupled along the link and adapted to amplify the optical signals; the optical amplifying unit (100) having an amplification wavelength band including the transmission wavelength band and comprising: an input (101) for the input of the optical signals, an output (102) for the output of the optical signals, at least an erbium-doped active fiber (103a, 103b) for the amplification of the optical signals, having a first end optically coupled to the input (101) and a second end optically coupled to the output (102), a pump source (104, 106) for generating a pump radiation having a wavelength greater than 1400 nm and lower than 1470 nm, and an optical coupler (105, 107) optically coup

Abstract: A borosilicate glass composition comprises SiO2 having a concentration of about 40 mole percent to about 60 mole percent, B2O3 having a concentration of about 10 mole percent to about 30 mole percent, and an alkaline earth and/or alkali compound having a concentration of 10 mole percent to about 40 mole percent. An optical fiber amplification device comprises a borosilicate glass material cladding. The core comprises a germanate glass material doped with Tm3+. The germanate glass material has a first surface configured to receive an optical signal having a wavelength of from about 1400 nm to about 1540 nm and a second surface configured to output an amplified optical signal. In this manner, low cost fiber amplifiers in the 1450-1530 nm wavelength region (corresponding to the S-band) can be achieved.

Abstract: A crystalline material for optically pumped solid state lasers has the chemical composition of M3RE1-x Ybx(BO3)3, where M is selected from the group Mg, Ca, Sr, Ba, and Ra, optionally replaced at least partially with another element from this group, RE is selected from the group Sc, Y, Lu, and Y partially replaced with Lu, and x is greater than or equal to 0 and less than or equal to 1. The material is useful for preparing lasers having high average initial power and short pulse duration, and has flat amplification and fluorescence spectra, high thermal conductivity and a large emission cross-section.

Abstract: The invention relates to a 1.4-1.52 &mgr;m-band optical amplifier. This optical amplifier includes (a) a first pumping source for a first pumping light in a wavelength range defined as being not less than 0.65 &mgr;m and being less than 0.77 &mgr;m; (b) a second pumping source for a second pumping light in a wavelength range of from 1.0 to 1.2 &mgr;m; (c) an optical multiplexer for combining said first and second pumping lights with a signal light, to produce a combined light; and (d) a light amplifying optical waveguide for amplifying said signal light by receiving said combined light, said optical waveguide comprising a core doped with Tm. The optical amplifier is highly efficient.

Abstract: An optical device is proposed having a rare earth doped glass composition consisting essentially of.

Abstract: An optical fiber amplifier is proposed comprising at least one pump light source (3), at least one amplifying fiber section (10), and at least one coupler (8) which establishes a connection between the input fiber (1) of the fiber type I, the pump light source (3), the amplifying fiber section (10), and the output fiber (12) of the fiber type I. The amplifying fiber section (10) consists of a fiber type II, and the the splices (2, 11) between the fiber type I and the fiber type II are arranged relative to the amplifying fiber section (10) such that light propagated in the direction opposite to the signal direction and light propagated in the signal direction passes through means absorbent of short wavelengths before it reaches the splices.

Abstract: An optical amplification system has an active fibre section having an optical fibre 10 and containment means 8, 12 containing light of a specific wavelength within the active fibre section. The specific wavelength of light is the result of the spontaneous transition of photons. The contained photons stimulate further photons emissions, which depopulates energy levels involved in the amplification process.

Abstract: In a method of amplifying optical input signals over a wide bandwidth, the optical input signals are applied to an optical waveguide made from a rare-earth-doped amorphous material (e.g., erbium-doped yttrium aluminum oxide material). The optical input signals include optical signals having wavelengths over a range of at least 80 nanometers, and, preferably, over a range of at least 160 nanometers. Pump light is applied to the optical waveguide to cause the waveguide to provide optical gain to the optical input signals. The optical gain causes the optical signals to be amplified within the waveguide to provide amplified optical signals over the extended 80-160-nanometer range, including, in particular, optical signals having wavelengths at one end of the range and optical signals having wavelengths at a second end or the range.

Abstract: An optical amplifier comprises a trivalent thulium-doped optical fiber; a first pump light emitting device optically coupled to the fiber for generating a primary pump source at a first wavelength, and a second pump light emitting device optically coupled to the fiber for generating a secondary pump source at a second wavelength. In a preferred aspect of the present invention, the amplifier also includes a third (auxiliary) pump light emitting device optically coupled to the fiber for generating a third pump source at a third wavelength. Each of the amplification signals comprise at least one pre-selected wavelength. The first amplification signal has a wavelength pre-selected to provide a reduced noise figure for the amplifier. The second amplification signal has a wavelength pre-selected to increase the optical efficiency of the amplifier. The third amplification signal can have a wavelength pre-selected to populate the 3F4 energy level of the fiber, and to minimize depletion of the 3H6 ground state.

Abstract: An optical fiber amplifier with a high conversion efficiency, which is capable of using the pump light in the wavelength band that can be emitted by the laser diode, is formed by an amplification optical fiber containing thulium at least in a core, to which a signal light is to be entered, and a pump light input unit configured to enter at least one pump light with a wavelength in a range of 1320-1520 nm, or more preferably 1320-1480 nm, into the amplification optical amplifier.

Abstract: In a method of amplifying optical input signals over a wide bandwidth, the optical input signals are applied to an optical waveguide made from a rare-earth-doped amorphous yttrium aluminum oxide material (e.g., erbium-doped yttrium aluminum oxide material). The optical input signals include optical signals having wavelengths shorter than 1,520 nanometers and optical signals having wavelengths longer than 1,610 nanometers. Preferably, the wavelengths range from as short as approximately 1,480 nanometers to as long as approximately 1,650 nanometers. Pump light is applied to the optical waveguide to cause the waveguide to provide optical gain to the optical input signals.

Abstract: A light amplification optical fiber capable of suppressing a decrease in an amplification efficiency thereof ascribed to the concentration quenching of erbium ions, and the nonlinearity thereof is provided. At least one rare earth element, for example, Yb, which is other than the erbium ions, and which has an ion radius not smaller than 70% and not larger than 130% of that of erbium ions is doped to a core portion of an erbium ion-doped light amplification optical fiber.

Abstract: The invention is related to a waveguide amplifier with an input for optical signals and an output for optical signals with at least one piece of amplifying waveguide with at least one mean for coupling pump laser modules to the amplifying waveguide which contains Tm ions. The invention is also related to a pumping scheme for waveguide amplifier feeding two different wavelengths in to the waveguide.

Abstract: A tellurite glass as a glass material of optical fiber and optical waveguide has a composition of 0<Bi2O3 ≦20 (mole %), 0≦Na2O≦35 (mole %), 0≦ZnO≦35 (mole %), and 55≦TeO2≦90 (mole %). The tellurite glass allows an optical amplifier and a laser device that have broadband and low-noise characteristics. In a splicing structure of non silica-based optical fiber (as a first fiber) and a silica-based optical fiber (as a second fiber), optical axes of the first and second optical fibers are held at different angles &thgr;1 and &thgr;2 (&thgr;1≠&thgr;2) respectively from a vertical axis of a boundary surface between their spliced ends, and a relationship between the angles &thgr;1 and &thgr;2 satisfies Snell's law represented by an equation of sin &thgr;1/sin &thgr;2=n2 /n1 (where n1 is a refractive index of the first optical fiber and n2 is a refractive index of the second optical fiber) at the time of splicing the first and second optical fibers.

Abstract: An optical amplifying glass comprising a matrix glass and from 0.001 to 10% by mass percentage of Tm doped to the matrix glass, wherein the matrix glass contains from 15 to 80 mol % of Bi2O3 and further contains at least one component selected from the group consisting of SiO2, B2O3 and GeO2.

Abstract: This invention relates to an amplification optical fiber which requires no gain equalizer and has a flat gain spectrum and high polarization extinction ratio, and the like. The amplification optical fiber has a core region included in a light propagation region through which signals having different wavelengths propagate, a cladding region around the core region, and a polarization maintaining structure for maintaining the polarized states of the signals. The amplification optical fiber is mainly comprised of silica glass, and Er and Al of 4 wt % or more are doped into at least part of the light propagation region including the core region.

Abstract: An improved highly doped waveguide is provided which comprises a waveguide employing an Er dopant and Pr sensitizer ions. The present invention also provides a method of efficient coupling from an optical source into a waveguide using a rotated optical element.

Abstract: Single- or few-moded waveguiding cladding-pumped lasers, superfluorescent sources, and amplifiers, as well as lasers, including those for high-energy pulses, are discloswed, in which the interaction between the waveguided light and a gain medium is substantially reduced. This leads to decreased losses of guided desired light as well as to decreased losses through emission of undesired light, compared to devices of the prior art. Furthermore, cross-talk and inter-symbol interference in semiconductor amplifiers can be reduced. We also disclose devices with a predetermined saturation power.

Abstract: A tellurite glass as a glass material of optical fiber and optical waveguide has a composition of 0<Bi2O3≦20 (mole %), 0≦Na2O≦35 (mole %), 0≦ZnO≦35 (mole %), and 55≦TeO2≦90 (mole %). The tellurite glass allows an optical amplifier and a laser device that have broadband and low-noise characteristics. In a splicing structure of non silica-based optical fiber (as a first fiber) and a silica-based optical fiber (as a second fiber), optical axes of the first and second optical fibers are held at different angles &thgr;1 and &thgr;2 (&thgr;1≠&thgr;2) respectively from a vertical axis of a boundary surface between their spliced ends, and a relationship between the angles &thgr;1 and &thgr;2 satisfies Snell's law represented by an equation of sin &thgr;1/sin &thgr;2=n2/n1 (where n1 is a refractive index of the first optical fiber and n2 is a refractive index of the second optical fiber) at the time of splicing the first and second optical fibers.

Abstract: An optical amplifier includes an organic luminescent free radical compound, preferably a salt of a radical cation or a salt of a radical anion, wherein an excited state of the luminescent free radical compound undergoes stimulated emission in an infrared wavelength region, such as 1500 to 1650 nm. Suitable organic luminescent free radical compounds include aminium infrared-absorbing dyes.

Abstract: A thulium doped silica based glass capable of supporting lasing activity including Tm3+as a lasing species disposed in a host composition, including oxides of germanium, silicon and tantalum. The preferred concentration of silicon in the host composition being between 15-25 weight percent. The preferred concentration of germanium in the host composition being between 0.1-1 weight percent. The preferred concentration of tantalum in the host composition is greater than 15 weight percent. The preferred concentration of thulium ions being in the range of 500-1000 parts per million by weight.