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We experimentally investigate mid-infrared (MIR) supercontinuum (SC) generation in chalcogenide step-index optical fibers. The pump source is generated by the difference frequency generation with a pulse width of ~170 fs, a repetition rate of ~1000 Hz, and a wavelength range tunable from 2.5 to 11 μm. The wide MIR SC will be applied in sensing, medical and biological imaging areas.

We successfully synthesized Er3+-Yb3+ doped cubic phase NaYF4 nanocrystals by a facile solvethermal method. The average size of the as-prepared nanocrystals was about 12 nm based on the observation of scanning electron microscope and transmission electron microscope. NaYF4/SiO2 nanoparticles were prepared. The thickness of shell layer was about 7 nm. The as-prepared samples were annealed at different temperature. The cubic phase NaYF4 did not transit to hexagonal phase, but to amorphous phase as the annealing temperature increased to 700 °C. When temperature further increased to 1100 °C, the amorphous NaYF4 reacted with SiO2 shell and formed a new phase, NaYSiO4. Under the excitation by a 976 nm laser, the Er3+-Yb3+ doped NaYF4, NaYF4/SiO2, and NaYSiO4 nanoparticles showed intense visible upconversion emissions. Since the host materials changed from fluoride crystals to amorphous fluoride, then to silicate crystals, the spectral profiles were different. Fluorescent lifetimes obtained from decay curves were applied to analyze the multi-phonon relaxation processes in different hosts. The Er3+-doped upconversion phosphors will be useful for light converting in solar cell applications in the future.

We experimentally demonstrate mid-infrared supercontinuum (SC) generation in chalcogenide multi-step index fibers (MSIF) pumped by a femtosecond laser. The fabricated chalcogenide MSIF is composed of a high refractive index core (C1) in the center, which is enclosed by a lower refractive index core layer (C2) and an outer cladding. This fiber structure is advantageous to tailor the chromatic dispersion with higher freedom and to keep the effective mode area small at long wavelengths. The high refractive index core, low refractive index core, and the outer cladding materials are As 2 Se 3 , AsSe 2 and As 2 S 5 , respectively. When the diameter of C1 and C2 are 7.8 and 30 μm, respectively, the zerodispersion wavelength (ZDW) of the fiber is 12.5 μm. The chromatic dispersion profile is near-zero and flattened within the range of ±20 ps/km/nm in the wavelength range from 4 to 17 μm and a broad normal dispersion region is obtained in the wavelength range shorter than the ZDW. In practice, a 2.8 cm long fiber is pumped at 10 μm by using a femtosecond laser whose pulse width is ~200 fs. The SC generation extending from 2 to 14 μm is obtained. Most of its spectrum is in the normal dispersion region of the fiber. These results are promising for the highly coherent mid-infrared SC generation.

We report here the design of a new chalcogenide hybrid microstructured optical fiber (HMOF) with a buffer layer around the core and its potential performance of tailoring chromatic dispersion and supercontinuum (SC) generation. The new chalcogenide HMOF has an AsSe 2 core. The refractive index difference Δn between the AsSe 2 core and cladding material is supposed to be 0.3. The fiber microstructure and the Δn between the core and buffer materials are designed in order to obtain broad anomalous dispersion regimes with near-zero and flattened chromatic dispersion profiles for broadband SC generation. Moreover, the suppression of chromatic dispersion fluctuation caused by fiber transverse geometry variation is investigated. By using the proposed chalcogenide buffer-embed HMOFs, the calculation shows that near-zero and flattened anomalous chromatic dispersion regimes from 4.5 μm can be obtained. When the variation of fiber structure occurs for ±1, ±5 and ±10 %, the chromatic dispersion fluctuation can be greatly suppressed. In addition, the calculation shows that a broad SC spectrum from 2.5 to more than 16.0 μm can be obtained when a 0.9-cmlong section of the new chalcogenide buffer-embed HMOF is pumped at 5.0 μm by a femtosecond laser with 1-kW peak power.

We demonstrate the effects of stimulated Raman scattering (SRS) in the all-solid-core chalcogenide microstructured optical fibers (MOFs) with AsSe2 core and As2S5 cladding, which are fabricated by the rod-in-tube drawing technique. The core diameters of the MOFs are ~6.3 (Fiber I), 3.0 (Fiber II), 2.6 (Fiber III) and 2.2 (Fiber IV) μm, respectively. The chromatic dispersion of the fundamental mode in Fibers I-IV is simulated by the full-vectorial mode solver technique. The first-order Stokes wave is investigated in the fibers with different core diameters pumped by the picosecond pulses at 1958 nm. In Fiber I, no obvious Raman peak is observed with the pump power increasing, because the effective nonlinearity is not high. In Fiber II, a Raman Stokes peak at ~2065 nm begins to emerge at the pump power of 110 mW. The conversion efficiency is as weak as -36.6 dB at 150 mW pumping. In Fiber III, the first-order Raman peak at ~2060 nm begins to emerge at 40 mW pumping. The conversion efficiency is -15.0 dB, which is 21.6 dB higher than that in Fiber II. In Fiber IV, the Stokes peak at 2070 nm begins to appear at 56 mW pumping. The maximum conversion efficiency of the first-order Stokes wave is obtained in the MOF with the core diameter of 2.6 μm. The evolution of the first-order Stokes wave with pump power and fiber length is investigated. This is the first demonstration of Raman effects in the AsSe2-As2S5 MOF, to the best of our knowledge.

Stimulated Raman scattering is an attractive nonlinear optical process that produces the power transfer from a given frequency to one or several down-shifted Stokes beams [1-4]. It is becoming an exciting issue because of the wide application, ranging from sensors, slow light generation to Raman amplifiers and lasers [5-11]. Ever since Stolen et al. first reported it in 1972[3], SRS has been successfully demonstrated based on various fiber structures and fiber materials [12-24]. Moreover, in optical fibers with sufficiently high Raman gain and pump power, multiple-order cascaded Raman shift can be generated, which has already been observed in silica, tellurite and chalcogenide optical fibers [18, 25-28]. However, relatively few researches concerning this have been carried out on fluoride fibers, although they have high transparency from the ultraviolet (UV) region to the mid-infrared (MIR) region up to ~8 μm. In this work, we demonstrated fourth-order cascaded Raman shift in a birefringence ZrF4‒BaF2‒LaF3‒AlF3‒NaF (ZBLAN) fluoride fiber. To the best of our knowledge, this is the first demonstration of fourth-order cascaded Raman shift in fluoride fibers. The pump source was a picosecond laser with the center wavelength of 1064 nm. At the average pump power of ~7W, fourth-order cascaded Raman shift was observed if the pump pulse was polarized to the slow axis, and only third-order cascaded Raman shift was obtained if the pump pulse was polarized to the fast axis. Furthermore, the generalized nonlinear Schrodinger equation (GNLSE) was used to simulate the cascaded Raman shift generation process, and the results were in good agreement with the experiments.

The supercontinuum generation and rogue wave generation in a step-index chalcogenide fiber are numerically investigated by solving the generalized nonlinear Schrodinger equation. Two noise models have been used to model the noise of the pump laser pulses to investigate the consistency of the noise modeling in rogue wave generation. First noise model is 0.1% amplitude noise which has been used in the report of rogue wave generation. Second noise model is the widely used one-photon-per-mode-noise and phase diffusion-noise. The results show that these two commonly used noise models have a good consistency in the simulations of rogue wave generation. The results also show that if the pump laser pulses carry more noise, the chance of a rogue wave with a high peak power becomes higher. This is harmful to the SC generation by using picosecond lasers in the chalcogenide fibers.

Based on a suspended core birefringent tellurite microstructured optical fiber (BTMOF), the supercontinuum (SC) spectra are generated by pumping near the zero dispersion wavelengths (ZDWs) in the telecommunication band with a tunable picosecond fiber laser. The ZDWs of the suspended core BTMOF are calculated to be 1560 nm and 1532 nm for the X-axis and Y-axis, respectively. When the pump is polarized along the X-axis, the SC broadening is governed by the nonlinear effects of four-wave mixing (FWM), cross-phase modulation (XPM) and stimulated Raman scattering (SRS). When the pump is polarized along the Y-axis, the SC generation is governed by the nonlinear effects of SRS.

The novel property of the mid-infrared (MIR) higher-order soliton fission in a tapered tellurite microstructured optical fiber (TMOF) is experimentally investigated. The TMOF is tapered to offer an ideal environment for the formation of optical solitons. From ∼30 to 80 mW, the redshift of the first fundamental soliton (SSFS) is obvious. From ∼80 to 120 mW, two fundamental solitons are obtained by the fission of the higher-order solitons. The redshift of the first fundamental soliton almost stops because the increased pump power is preferentially distributed to the second fundamental soliton. From ∼120 to 180 mW, obvious redshift of the first fundamental soliton is observed again, and a third fundamental soliton is obtained at ∼180 mW. With the average pump power increasing to ∼220 mW, five fundamental solitons are observed.

We report here the potential of fiber optical parametric amplification (FOPA) by using highly nonlinear chalcogenide double-cladding fibers. The fibers are designed with an AsSe 2 -based core layer surrounded by two cladding layers. The size and the refractive index differences (dn) between the core and cladding are investigated to obtain flattened chromatic dispersion spectra over a wide wavelength range up to the mid-infrared window. The inner cladding with dn 2 is added to suppress the variation of the chromatic dispersion caused by the fluctuation of the core diameter. Our numerical calculations shows that very broad anomalous dispersion ranges from 5.0 μm up to 11.0 μm where the chromatic dispersion is less than 10 ps/km-nm can be obtained when the core diameter varies from 2.0 to 9.0 μm and the inner cladding diameter is kept at 9.0 μm. The dn 1 and dn 2 are 0.30 and 0.02, respectively. The FOPA calculation is carried out using a 3-cm-long fiber whose core diameter is 3 μm. When the pump power is 3 W at 5320 nm, a very broad gain bandwidth is obtained from 3.3 up to 11 μm. Moreover, the gain spectrum is flattened (about 32 ± 1 dB) in the ranges from 3.3 to 4.1 μm and from 7.5 up to 11.0 μm. When the core diameter fluctuates from 2.0 to 5.0 μm, the FOPA gain spectra can be maintained.

We successfully synthesized Er 3+ /Yb 3+ co-doped KY 3 F 10 nanocrystals by a facile hydrothermal method. The average size of the as-prepared nanocrystals was about 60 nm based on the observation of scanning electron microscope. Under the excitation of a 976 nm laser, the Er 3+ /Yb 3+ doped KY 3 F 10 nanocrystals showed intense near-infrared emission band centered at 1539 nm. The optimal concentrations of Er 3+ were carefully selected according to the quantum yield measurement for a stronger emission in the C-band. The as-prepared nanocrystals were dispersed into a monomer, bisphenol A ethoxylate diacrylates, in which self-written waveguides can be fabricated under the irradiation of an induced laser at 450 nm. The KY 3 F 10 : Er 3+ /Yb 3+ nanocrystals embedded polymer waveguide were fabricated by laser-induced self-written technique. Two pieces of single mode fiber were well connected with the waveguide in the fabrication procedure. Under a 976 nm laser pumping, amplified spontaneous emission at 1539 nm was observed in the KY 3 F 10 : Er 3+ /Yb 3+ nanocrystals doped waveguide.

We report the coherent mid-infrared supercontinuum generation in an all-solid chalcogenide microstructured fiber with all-normal dispersion. The chalcogenide microstructured fiber is four-hole structure with core material of AsSe2 and air holes are replaced by As2S5 glass rods. Coherent mid-infrared supercontinuum light is generated in a 2-cm-long chalcogenide microstructured fiber pumped by a 2.7 μm laser. The simulated and experimental results have a good match and the coherence property of supercontinuum light in the chalcogenide microstructured fiber has been studied by using the complex degree of coherence theory. Coherent mid-infrared supercontinuum generation is extended to 3.3 μm in this work.

We report here flattened supercontinuum (SC) generated in tellurite-phosphate and chalcogenide-tellurite hybrid microstructured optical fibers (HMOFs) whose chromatic dispersion spectra are tailored with high freedom due to large refractive index difference (∆n) between the core and cladding glasses. It is shown in the simulation that the tellurite-phosphate HMOF whose chromatic dispersion spectrum is near-zero and flattened with three zero-dispersion wavelengths (ZDWs) over a wide wavelength range from 1000 to 4000 nm is beneficial to obtain broad and flattened SC spectra. By using a large ∆n of 0.49, the tellurite-phosphate HMOF which has flattened chromatic dispersion and three ZDWs is successfully fabricated. When a 20-cm-long tellurite-phosphate HMOF is pumped at 1550 nm with a 1560-W peak power, an SC extended from ~800 to 2400 nm where ~5-dB spectral flatness in the wavelength ranges from 890 to 1425 nm and from 1875 to 2400 nm (~1060-nm bandwidth in total) is observed. In addition, a flattened SC spectrum with ~6-dB spectral flatness over a broad wavelength range from 950 to 3350 nm (2400-nm bandwidth in total) is generated by pumping a 1-cm-long chalcogenide-tellurite HMOF at 2300 nm with a 40-MW peak power.

We present the broad and ultra-flat optical parametric gain in the highly nonlinear tellurite fibers with tailored chromatic dispersion. The effect of pump wavelengths and powers on dual-pump configuration of four-wave mixing (FWM) are investigated. It is clarified that an ultra-flat gain bandwidth with 658 nm and ±0.01 dB fluctuation can be achieved at the dual-pumping power of 1.25 W. Moreover, a gain bandwidth with 1524 nm and 60 dB signal gain with gain ripples can be obtained at the dual-pumping power of 3.0 W in 25 cm-long hybrid tellurite microstructured optical fiber.

Nonlinear optical polymers show promising potential applications in photonics, for example, electro-optical devices. Poly (methyl methacrylate) (PMMA) is widely used in optical waveguides, integrated optics and optical fibers. However, PMMA has not been used for nonlinear optical waveguides since it has a low nonlinear refractive index. We successfully prepared chalcogenide amorphous nanoparticles doped PMMA that had a high nonlinearity. The As3S7 bulk glass was dissolved in propylamine to form a cluster solution. Then the As3S7/propylamine solution was added into methyl methacrylate (MMA) containing photoinitiator Irgacure 184 about 0.5 wt%. After well mixing the As3S7 nanoparticle doped MMA was transparent. Under the irradiation by a 365 nm UV lamp, As3S7 nanoparticles doped PMMA was obtained with yellow color. The third-order nonlinear optical susceptibility of As3S7 nanoparticles doped PMMA was investigated. An optical waveguide array based on the As3S7 nanoparticles doped PMMA composite of high nonlinearity was fabricated.

Widely wavelength tunable soliton self-frequency shift (SSFS) from 1.58 μm to 2.07 μm was experimentally demonstrated in a highly nonlinear fiber pumped with a mode-locked sub-100 fs Er-doped fiber laser. The maximum output spectrum (full width at half maximum, FWHM) around 2 μm is 143 nm. Although the pulse width of SSFS was measured to be a few picoseconds, the large FWHM bandwidth of SSFS spectrum shows that soliton with sub-50 fs could be achieved if the giant chirped pulse is efficiently re-compressed to be transforms limited. Dispersive wave with a minimum pulse width of 50 fs was also observed.

Chalcogenide microstructured fibers (MOFs) have great advantages for supercontinuum (SC) generation in mid-infrared (MIR) region, because they possess the properties of high nonlinearity and wide transmission window, simultaneously. The nonlinear parameters of chalcogenide MOFs can be higher by several tens or hundreds than those of silica, fluoride and tellurite fibers depending on the material components and fiber structures. Chalcogenide MOF can be transparent from visible up to the infrared region of 12 or 15 μm depending on the compositions. In this paper, we demonstrate the SC generation in two kinds of suspended-core chalcogenide MOFs with different material components and fiber structures. One is an As 2 S 3 MOF with three-hole structure (Fiber I). The other is an As 2 S 5 MOF with four-hole structure (Fiber II). For Fiber I, the SC range of 3020 nm (from 1510 to 4530 nm) were obtained in a 2.4 cm fiber, when pumped by the wavelength at 2500 nm. The SC extends to the wavelengths longer than 4 μm. For Fiber II, the SC range of 4280 nm (from 1370 to 5650 nm) is generated in a 4.8 cm fiber when pumped by the wavelength at 2300 nm, which covers more than two octaves. Compared to the SC generated in Fiber I, the SC spectral range in Fiber II has been increased by more than 1200 nm due to the better transmission property of the As 2 S 5 glass; the SC extends to the wavelengths longer than 5 μm.

Superluminal propagation at negative group velocity was demonstrated in a highly nonlinear fiber embedded in a Brillouin laser ring cavity. A maximum advancement of 369 ns and strong Stokes lasing power of 482 mW were achieved when the cavity was pumped with a 1 MHz sinusoidal wave modulated signal at power level of 1 W. The frequency dependence of fast light in this fiber ring cavity was examined with modulation frequencies of 1 kHz to 15 MHz. a maximum fractional advancement of 0.54 was achieved at 10 kHz and a maximum negative group index of - 9480 was demonstrated at 1 kHz.

We successfully synthesized Er 3+ /Yb 3+ /Ce 3+ -codoped cubic phase NaYF 4 nanocrystals with the size of ∼14 nm by a solvothermal method. Under the excitation of a 976 nm laser diode, the as-prepared nanocrystals showed strong 1530 nm emissions and weak visible emissions. With the addition of Yb 3+ ions, both visible and near-infrared emissions of Er 3+ were enhanced. The addition of Ce 3+ ions can effectively quench the visible emissions and increase the population of electrons on the 4 I 13/2 of Er 3+ ions, further enhance the 1530 nm near-infrared emissions. The doping concentrations of lanthanide ions were carefully adjusted. It was found that the NaYF 4 nanocrystals doped with 1% Er 3+ , 10%Yb 3+ , and 10%Ce 3+ showed the most intense 1530 nm emissions. By dispersing the as-prepared nanocrystals in bisphenol A ethoxylate diacrylates (BPAEDA), the transparent nanocrystals doped polymer composite materials were prepared. By using the technique of light-induced self-written waveguide fabrication, NaYF 4 nanocrystals doped waveguides with the length of 20 mm were prepared. Under the excitation of a 976 nm laser, the green visible light was observed from the waveguide devices.

Fiber-optical parametric amplification (FOPA) has been intensively studied and exploited for various interesting applications such as wavelength conversion, wavelength division multiplexing, optical signal processing and so on. However, its efficiency is governed by the fiber nonlinearity and chromatic dispersion. By employing tellurite glass we propose novel highly nonlinear tellurite hybrid microstructured optical fibers (HMOFs) which have nonlinearity of 6642 W -1 km -1 and near-zero flattened dispersion profiles from 1.3 to 2.3 μm with four zero dispersion wavelengths for FOPA applications. The linear phase-mismatch, optical signal gain and gain bandwidth are precisely calculated by using a full propagation constant which includes the contribution of all high-order dispersion parameters. In contrast with silica fibers, the signal gain is shown to be generated in the wavelength regions where Δβ and the parametric gain coefficient g is imaginary. It is shown that the proposed tellurite HMOFs with short fiber length L

A novel highly nonlinear three-core chalcogenide-tellurite fiber is proposed and fabricated in the paper. Each core with high index is made of chalcogenide glass (Ge 15 Ga 3 Sb 13 S 69 ). The background with low index is made of TeO 2 –ZnO–Li 2 O–Bi 2 O 3 (TZLB) glass. Each core of this fiber can be considered as a single core. And it can be used for the high power transmission. The effective modal refractive index and th e chromatic dispersion are calculated with the light beam coupled in one core of the fiber, respectively. Supercontinuum generation from 1400 nm to 3536 nm in this fiber is investigated under the pump of a 2200 nm femtosecond fiber laser. Keywords: chalcogenide-tellurite fiber, high nonlinearity, chromatic dispersion, supercontinuum generation 1. INTRODUCTION Multicore fibers (MCFs) have been attractive during the last decade [1, 2]. They have been widely applied to the fiber lasers and amplifiers [3], the spatial division multiplexing [4], the passive optical network (PON) [5], microwave photonics (MWP) and sensing elements [6], etc. With the development of MCFs, the coupled-mode theory, phase locking and mode shaping technology have also been widely studied [7]. Compared with the single-core fibers, MCFs have a lot of advantages. For example, they can overcome the capacity limit and offer solutions for high-power transmission. However, most of the MCFs reported are based on the silica glass and cannot apply in the mid-infrared (mid-IR) wavelength range. A variety of soft glasses, such as tellurite and chalcogenide glass, are transparent at wavelengths substantially beyond that of silica glass and possess wide transmission regions in the mid-IR, and highly nonlinear refractive indices. If the tellurite and chalcogenide glasses are used for the MCF structure, it could lead to applications of great interest, such as the stress and temperature sensing, the high power laser or amplifier and high capacity signal transmission. In the paper, we design and fabricate a highly nonlinear three-core chalcogenide-tellurite fiber with three cores arranged in a trigonal array. The three cores with the high index are made of the Ge

We present here, the extensive study of broadband and high parametric gain in highly nonlinear tellurite optical fiber. The chromatic dispersion has been designed to achieve broad gain bandwidth and phase-matching over broad spectral range. The optical parametric gain under pulse repetition rate dependence and with no influence of group velocity gain spectrum has been calculated for different fiber lengths. When the parametric gain was calculated, with dependence on group velocity and repetition rate of pulse, the gain bandwidth was found to be shrinking abruptly due to lessening of pump power. The pulse repetition rate was assumed to be 20 GHz, with fiber core diameter of 0.895 μm and calculated nonlinearity coefficient γ was 6642 W -1 km -1 . The study has been extended to realize the impact of pump power variation over supercontinuum generation with fiber length of 75 cm.

Alternative materials to silica glass are necessary for supercontinuum (SC) generation at longer wavelengths in the midinfrared (MIR) region. The alternative materials should possess the properties of wide transmission window and high nonlinearity, simultaneously. Chalcogenide glass is the suitable candidate due to its excellent properties of transmission and nonlinearity in MIR region. In this paper, we demonstrate the SC generation in a suspended-core As 2 S 3 chalcogenide microstructured optical fiber (MOF). The variation of SC is investigated by changing the fiber length, pump peak power and pump wavelength. In the case of long fibers (20 and 40 cm), the SC ranges are discontinuous and stop at the wavelengths shorter than 3500 nm, due to fiber absorption. In the case of short fiber as 2.4 cm, the SC range is continuous and can extend to the wavelengths longer than 4 μm. The process of SC broadening is observed when the pump peak power increases from 0.24 to 1.32 kW at 2500 nm in the 2.4 cm long fiber. The variation of SC range with the pump wavelength changing from 2200 to 2600 nm is studied. The selected wavelengths correspond to the dispersion of As 2 S 3 MOF from the normal to anomalous region. The SC generation is simulated by the generalized nonlinear Schrodinger equation. The simulation includes the SC difference between 1.3 and 2.4 cm long fiber at 2500 nm pumping and the variation of SC with pump peak power in 2.4 cm long fiber. The simulation agrees well with the experiment.

We present here the broadband and parametric gain for tellurite/phospho-tellurite optical fiber by carefully engineering the chromatic dispersion for optical parametric amplifier. This optical parametric amplification with broad bandwidth promises significant solutions for wavelength division multiplexing (WDM) and advanced ultrafast optical telecommunication systems. The parametric gain has been obtained with inclusion of higher and even order dispersion parameters in phase-mismatching factor (Δβ). The results have been obtained for step index fiber (SI) and hybrid microstructured optical fiber (HMOF) with engineered chromatic dispersion, having one zero dispersion wavelength (ZDW) and two ZDWs. The HMOF with a core diameter of 1.1 μm and chromatic dispersions having two ZDWs at 1262 and 1559 nm provides broadest parametric gain bandwidth (280 nm). This broad bandwidth advents due to the high nonlinear coefficient of tellurite/phospho-tellurite hybrid microstructured optical fiber. The paper explores variation in dispersion parameters, supercontinuum spectra and bandwidth of the parametric gains for these fibers.

The hybrid microstructured optical fibers (HMOFs) are emerging due to their capability of tailoring the dispersion. The chromatic dispersion and other related optical properties, such as optical mode confinement and effective index, have been calculated using the finite element method. We have realized four zero dispersion wavelengths (ZDWs) of 1566, 1605, 1726 and 1790 nm. The signal and idler wavelength dependent on pump wavelength is calculated. The gain bandwidth is 134 nm for the pump wavelength of 1761 nm between third and fourth ZDW. The supercontinuum generation is studied for the pump wavelength 1761 nm.

We present an all-solid tellurite-phosphate photonic bandgap fiber (PBGF) with high-index rods in the cladding. The low-index background material is phosphate glass (PZNK) and the high-index rods are made of tellurite glass (TZLB). The all-solid tellurite-phosphate PBGF has three bandgaps and the first one is wide in frequency. It is easier to draw than the silicon PBGF due to the phosphate glass has lower fiber-drawing temperature. It can be widely used in the photoelectron field, compact nonlinear devices and devices which work in the mid-infrared range, such as wavelength filter, phase-locked high-power lasers, fiber sensors in the mid-infrared for gases detecting, etc.

Quantum efficiencies of Er 3+ -doped silicate, phosphate, tellurite and fluoride glasses have been examined under simulated sunlight excitation. The quantum efficiency of the whole emission bands was obtained as about 75 % for fluoride glass and about 2 % for silicate glass. The maximum quantum efficiency of the emission band at 1530 nm was about 35 % for fluoride glass and about 17 % for silicate glass. The product of the stimulated emission cross-section and the emission lifetime σ st τ f was about 46×10 -24 cm 2 sec for fluoride glass and about 54×10 -24 cm for silicate glass. These values are about 2–4 times larger than that of Nd-doped glasses.

We demonstrate the square-pulse operation in a ring cavity with a 207 m single-mode tellurite fiber. The high nonlinearity and birefringence of the tellurite fiber play the key role during the square-pulse formation. The CW operation is obtained when pump power exceeds 80 mW. When the pump power is increased to 140 mW, the single pulse operation with the repetition rate of 689 kHz corresponding to the cavity fundamental frequency is initiated from the ASE noise by the nonlinear polarization rotation (NPR) process. Keeping the pump power at 140 mW and rotating one of the paddles of the polarization controller (PC) toward one direction in a small scale, the pulse number in one packet increases monotonically from 1 to 11. This process continues until the stable square pulse is formed at last. The stable square pulse has the FWHM of 118 ns and the repetition rate of 689 kHz. It is formed by the nonlinear polarization switching. In our cavity, the tellurite fiber is long enough to make the laser operate in the multibeat-length regime, which could lower the threshold for nonlinear polarization switching and clamp the peak power at a low level. This is advantageous for increasing the pulse width because the pulse duration is determined by the intra-cavity energy and the clamped peak power. When the linear phase delay bias in the cavity is set close to the polarization switching point, the third-order harmonic pulses and multiple packets are also observed under different pump levels.

Supercontinuum (SC) generation from a highly nonlinear tellurite microstructured fiber with multi-ring holes was demonstrated by pumping with a 2 μm high power mode-locked fiber laser. The chromatic dispersion of the fiber was measured with a homemade white-light spectral interferometer on a wide wavelength range and matched very well with the theoretical calculation. The zero dispersion wavelength (ZDW) of the fiber was measured to be 1358 nm and calculated to be 1390 nm. Although the pumped wavelength was far away from ZDW, with flat dispersion profile of the fiber on the anomalous dispersion, the SC could be expanded from 650 nm to 2850 nm with launched pulse energy of several hundred picojoules. Simulations of SC generation were performed and showed fair agreement with the experimental results.

The compositional dependences of glass formation, thermal properties and optical properties are investigated for TeO 2 -ZnO-Na 2 O-P 2 O 5 system for hybrid microstructured optical fibers. The refractive indexes at 1.55 μm and glass transition temperature vary in a wide range from 1.513 to 2.036 and from 265°C to 376°C by controlling of the TeO 2 /P 2 O 5 and ZnO/Na 2 O content, respectively. These properties endow tellurite-phosphate glasses with large freedom in the hybrid microstructured optical fiber design. The structures of glasses are investigated by Raman spectra to understand the structural dependence on composition. Using the present glasses, some microstructured optical hybrid fibers with particular dispersion profiles are designed and demonstrated.

Though soft glass such as tellurite or chalcogenide glass is transparent in the range of 3 - P ILEHUP DGHRILWLVGL IILFXOWto generate supercontinuum (SC) to that range because of the high loss, the wavelength limit of pump source, and the challenges i n light -coupling. To circumvent these problems, we developed SC light source by using tellurite bulk glass through filamentation. For this scheme, the optical path length in the glass is very short due to the adopted high pump power, so the negative influe nce of material loss is reduced greatly. The light -coupling is straightforward, and the coupling efficiency is high. The bulk glass for SC generation is cheap, and can be fabricated easily. We adopted a pump wavelength of 1600 nm which is comparatively lon g. Such a long pump wavelength ensures a large energy ratio of the JODVV¶VEDQGJDSWRWKHLQFLGHQWSKRWRQ VRWKHGLVDGYDQWDJHRIVPDOOEDQGJDSRIWHOOXULWHJODVVLVUHGXFHG DQGWKHWZR -photon absorption is avoided as well. We have shown that under suitab le pump condition, the SC generation by ILODPHQWDWLRQFDQFRYHUIURPYLVLEOHWR P ,WLVWKHEURDGHVW6&JHQHUDWLRQE\WHOOXULWH LQFOXGLQJJODVVDQGILEHU )RUthe suitable pump condition, the glass was free of optical breakdown. If the interface refl ections were deducted, the SC conversion efficiency was 87%. The SC conversion efficiency was stable. To the best of our knowledge, this is the first report on filamentation in tellurite glass which has a comparatively small bandgap. Keywords: tellurite g lass, filamentation, supercontinuum generation

We demonstrate an all-fiber broadband supercontinuum (SC) source with high efficiency in a single-mode high nonlinear silica fiber. The SC is pumped by the 1557 nm sub-picosecond pulse, which is generated by a homemade passively mode-locked fiber laser, amplified by an EDFA and compressed to 600 fs. The high nonlinear fiber used in experiments has the zero-dispersion wavelength of 1584 nm with low dispersion slope. The pump pulse is in the normal dispersion region and the SC generation is initiated by the SPM effect. When the long-wave band of the spectrum is extended to the anomalous dispersion region, the soliton effects and intra-pulse Raman effects extend the spectrum further. Meanwhile, the dispersive waves shorter than 1100 nm begin to emerge because the phase matching condition is satisfied and the intensity increases with increasing the pump intensity. The broad SC spectrum with the spectral range from 840 to 2390 nm is obtained at the pump peak power of 46.71 kW, and the 10 dB bandwidth from 1120 nm to 2245 nm of the SC covers one octave assuming the peak near 1550 nm is filtered. The temporal trace of the SC has the repetition rate of 16.7 MHz, and some satellite pulses are generated during the nonlinear process. The SC source system is constructed by all-fiber components, which can be fusion spliced together directly with low loss less than 0.1 dB and improves the energy transfer efficiency from the pump source to the SC greatly. The maximum SC average power of 332 mW is obtained for the total spectral range, and the slop efficiency to the pump source is about 70.3%, which will be lower when the peaks near 1550 nm are filtered, but is higher than those in PCFs. The spectral density for the 10 dB bandwidth is in the range from -17.3 to -7.3 dBm/nm.

We report the fabrication of tellurite composite microstructured optical fiber (CMOF) with ultra-flattened zero dispersion (±3 ps/nm/Km) over 200nm band. To obtain this dispersion profile together with high nonlinearity, one ring of air holes and two layers of glass cladding are employed in the tellurite CMOF. The core of fiber is made of TeO 2 -Li 2 O-WO 3 -MoO 3 -Nb 2 O 5 (TLWMN) tellurite glass which possesses high linear and nonlinear refractive indices. The refractive index (n) at 1544nm and nonlinear refractive index (n2) of TLWMN glass is 2.08 and 3.78×10 -11 esu, respectively. TeO 2 -ZnO-Na 2 O-La 2 O 3 (TZNL) glass with n of 1.96 at 1544 nm and TeO 2 -ZnO-Li 2 O-Na 2 O-P 2 O 5 (TZLNP) glass with low refractive index n of 1.63 at 1544 nm are used as the first cladding and the second cladding, respectively. Six small air holes are located between the core and the first glass cladding. Such kind of fiber with ~1.7 μm core and ~0.6 μm air holes are fabricated by a rod-in-tube method. The chromatic dispersion of the fiber is calculated by the fully vectorial finite difference method (FV-FDM) and becomes (±3 ps/nm/Km) in the wide range from 1.53 μm to 1.72 μm. And the nonlinear coefficient of present fiber is about 3.47 m -1 W -1 which is much higher than that of silica MOFs. Furthermore, broad and flattened supercontinuum generation is demonstrated in 30-cm-long fiber with femtosecond laser pumping at 1557 nm. This kind of fiber has promising potential in nonlinear applications owing to the high nonlinearity and flattened dispersion profile.

We investigated the spectroscopic properties of borosilicate glass co-doped with Tb 3+ and Yb 3+ , focusing our attention on studying the possibility of the cooperative up-conversion process in the Tb 3+ -Yb 3+ co-doped system as a pumping scheme for Tb 3+ . A rate equation model for the Tb 3+ -Yb 3+ co-doped system were analyzed. The model could reproduce the up-conversion emission dynamics well for all the samples co-doped with different Tb 3+ number densities.

The microstructured optical fibers have been considered in this paper due to their unique nonlinear properties. These optical fibers have enormous potential and they are also unrestraint to tailor the design for obtaining promising dispersion properties. It has been observed that conversion efficiency significantly increases when nonlinear contribution to propagation constant is considered for phase matching. The phase matching have been obtained for even and higher order dispersion with the optical pump pulse conditions. The coupled mode theory along with nonlinear Schrodinger equation has been used to reveal the optical properties of telluride/phospho-tellurite hybrid microstructured optical fiber. The paper has been focused to investigate the effective index, pulse propagation intensity and quasi phase matching.

For a suspended nanowire, the holes surrounding the core are expected to be as large as possible to propagate the light at wavelengths as long as possible. However, the fabrication of nanowire surrounded with large holes is still a challenge so far. In this paper, a method which involves pumping positive pressure of nitrogen gas in both the cane fabrication and fiber-drawing processes, is proposed. A suspended nanowire, with a core diameter of 480 nm and an unprecedented large diameter ratio of holey region to core (DRHC) of at least 62, is fabricated in the length of several hundred meters. Owing to the large holes, the confinement loss of the suspended nanowire is insignificant when the wavelength of light propagated in it is 1700 nm. Additionally, the tube-shaped glass cladding of the suspended nanowire shifts the singlemode cutoff wavelength to 810 nm, which is much shorter than the cutoff wavelength, 1070 nm, of a naked nanowire with the same diameter. A single-mode supercontinuum (SC) generation covering a wavelength range of 900-1600 nm is obtained under 1064 nm pump pulse with the peak power as low as 24 W. A single-mode third harmonic generation (THG) is observed by this nanowire under the pump of a 1557 nm femtosecond fiber laser. This work indicates that the suspended nanowire with large holes can provide high nonlinearity together with single-mode propagation, which leads to interesting applications in compact nonlinear devices.

We propose a tellurite core phosphate cladding composite microstructured optical fiber (MOF) with high nonlinearity and flattened dispersion for parametric amplification. To rea lize flattened dispersion, the structure parameters such as the tellurite core diameter, the air hole diameter and the distance between the centers of the two neighboring air holes are optimized. The ultraflat dispersion curve is obtained for tellurite core of 1.1 m, pitch of 1.2 m and air hole diameter of 0.5 m. In this case, the flattened dispersion with value between -4 and 0.5 ps/nm/km is obtained ranging from 1400 to 1600 nm. The nonlinear coefficient J is as high as 2.5 m -1 W -1 at 1.5 m. The optical parametric gain bandwidth of nearly 200 nm can be achieved in composite tellurite/phospha te MOF with the length of 2.5 m and the pump power of 0.4 W. 1. INTRODUCTION Four-wave mixing (FWM) is one of the basic nonlinear opti cal phenomena observed in opti cal fibers and lead to many applications such as parametric amplification, wavelength conversion, and oscillators

We demonstrate four-wave mixing based broadband (>68 nm) wavelength conversion and flattened supercontinuum generation spanning from 900 to 2800 nm in a 36-cm long tellurite microstructured fiber which has a high nonlinearity. By reducing the size of air holes of the tellurite microstructured fibers, single mode propagation and small dispersion slope are obtained without the propagation loss enhancement. Our results show that chromatic-dispersion controlled tellurite microstructured fibers are promising candidates for nonlinear applications.

Supercontinuum (SC) generation has the important applications such as broadband light source, optical coherence tomography, ultra-short pulse compression, and optical frequency metrology, etc. Tellurite glass is transparent in the mid-infrared range, and has a higher n 2 than silica glass by at least one order of magnitude. We have fabricated the hexagonally shaped tellurite air-clad fiber with a core diameter of around 1 μm through controlling the temperature field exactly in the process of fiber-drawing. Since the SC generation strongly depends on the chromatic dispersion, which is determined by the microstructure of fiber, it is interesting to investigate and demonstrate such dependence for such a small core fiber in detail. In this work by pumping a positive pressure of nitrogen gas into the holes of preform, we obtained 1 μm core fibers with diameter ratio of holey region to core (DRHC) varied from 3.5 to 20. The dispersion was tailored effectively by the variation of DRHC. Dependences of SC on the microstructure and dispersion were demonstrated. The pump lasers were picosecond and femtosecond fiber lasers. One octave flattened SC generation was obtained for the fibers pumped by 1064 nm picosecond fiber laser with the pulse energy of several hundred pJ. Intense second and third harmonic generations were obtained under the pump of a 1557 nm femtosecond fiber laser. The correlation of dispersion and SC spectra was analyzed. Such tellurite microstructured optical fibers (MOFs) with high nonlinearity and controlled dispersion are significant in nonlinear applications.

Silicate based transparent glass-ceramics containing YLiF 4 (YLF) nanocrsystals have synthesized by conventional melt quenching of glass followed by controlled heat treatment of the precursor glass. X-ray diffraction powder pattern of the glass-ceramic revealed that precipitated crystalline phase was solely YLF. The averaged diameter of primary crystallites was roughly about 8 nm. It was confirmed by comparison of the fluorescent properties of rare-earth ions-doped precursor glass and glass-ceramic that rare-earth ions could be successfully incorporated into YLF nano-crystals in the glass-ceramics. This transparent glass-ceramic containing YLF nano-crystals is promising as a gain medium in rare earth-doped fiber lasers and amplifiers.

We report emission from a bismuth doped chalcogenide glass with a full width half maximum of 850 nm. The quantum efficiency and lifetime were 32% and 175 µs. We report two new bismuth emission bands at 2000 and 2600 nm.

We report broad near-infrared soliton source generation in a TeO 2 -Bi 2 O 3 -ZnO-Na 2 O tellurite microstructured optical fiber pumped by a 1557 nm femtosecond fiber laser. A continuous soliton wavelength shift from 1582 nm to 1851 nm was realized through a tellurite microstructured optical fiber as short as 6.5 cm. Experimental results are in good agreement with the numerical simulations using a generalized nonlinear Schrodinger equation. In addition, an analytical description of the Raman response function of tellurite glass is provided, and a Raman contribution factor of 0.51 is obtained from the actual Raman gain spectrum.

The absorption and fluorescence characteristics of Er doped and Nd, Er codoped fluoride glasses were investigated under illumination of the simulated sunlight, laser or a monochromatic light filtered from a Xe lamp. Er was used as a sensitizing agent enhancing the energy conversion and the emission efficiency of Nd ions in fluoride glass intended for the sunlight excitation. Er doped fluoride glasses showed four emission peaks under simulated sunlight illumination at the wavelengths of 550, 848, 980, and 1530 nm attributed to the electronic transitions of Er 3+ ions. The quantum efficiency of the emission from all of the bands had a peak at x = 0.5 mol. % Er and with the maximum of 73 %. The intensity of each emission band showed different ratios for various ErF 3 contents. It is expected that concentration quenching of 4 S 3/2 state is easy to occur with high concentration of ErF 3 compared to the other states. The energy transfer from Er to Nd was studied using a monochromatic light illumination which is absorbed by Er 3+ ions only. Strong contribution of Er absorption to the 1.05 μm emission of Nd, Er co-doped fluoride glass was observed. Er was confirmed as a suitable sensitizer for the enhanced energy conversion and emission efficiency of Nd ions in ZBLAN glasses which are proposed for highly efficient solar pumped fiber lasers.

Transparent glass-ceramics containing nano-crystals were prepared by controlled heat-treatment of conventionally melt-quenched NaF-YF 3 -Al 2 O 3 -SiO 2 oxyfluoride glass. The precipitated crystallites were composed of only cubic NaYF 4 and the average diameter was estimated as less than 10 nm from the X-ray diffraction analysis. The crystallites were so small that the transparency of the glass was kept after crystallization. NaYF 4 has a crystal structure of a fluorite type that cation sites were randomly occupied by Na + and Y 3+ . It is expected that the Y 3+ sites can be substituted to other rare-earth ions which have the similar ionic radii. We have been prepared Tb 3+ and Yb 3+ co-doped glass and glass-ceramics. Green fluorescence was observed when the glass and glass-ceramics were excited by a 974 nm laser. The up-conversion intensity was enhanced by the crystallization.

Tellurite highly nonlinear microstructured fibers were fabricated by pumping a positive pressure of nitrogen gas into the holes of cane in the fiber drawing process. By adjusting the pump pressure to inflate the holes of the fiber, the microstructures were reshaped, and the chromatic dispersions were tailored. Two kinds of fiber were fabricated. One is an air-clad fiber with a 1 μm hexagonal core, which is the smallest core in this shape for the air-clad fiber. By changing the inflation pressure, the diameter ratio of holey region to core (DRHC) was changed in the range of 1-20. Fibers with DRHC of 3.5, 10, 20 were demonstrated. By increasing the DRHC, the zero dispersion wavelengths were shifted to the short wavelength and the confinement loss were decreased. Another is a complex microstructure fiber with a 1.8 μm core surrounded by four ring holes. The shape of the microstructure was reshaped so heavily by the inflation pressure that it is obviously different from the original shape in the cane. The correlations among pump pressure, hole size, surface tension and temperature gradient were investigated. The temperature gradient at the bottom of the preform's neck region was evaluated quantitatively. The chromatic dispersion of this fiber was compared with that of a step-index air-clad fiber. It was found that this fiber had a much more flattened chromatic dispersion. Supercontinuum generations were investigated by the pump of a 1557 nm femtosecond fiber laser. Intense third harmonic generations were obtained from the 1μm haxgonal core fiber. Broad and flattened spectrum was obtained from the complex microstructure fiber. This investigations show that, by using a positive pressure to reshape the microstructure and by controlling the fabrication conditions exactly, highly nonlinear soft glass fibers with desirable chromatic dispersion can be fabricated, and such fibers have interesting applications in highly nonlinear field such as THG and SC generation.

We present the simulation results of the optical parametric amplification in the composite chalcogenide-tellurite microstructured fiber driven by a single wavelength. Further, by applying dual pumping scheme, with two equal power pumps with different wavelengths, lying on opposite sides of the zero dispersion wavelength (ZDWL), we achieve a relatively flat gain spectrum over a wider bandwidth than that possible for single pump. The two pumps in the dual pumping scheme have the power half that of the pump power in single pumping scheme. The composite microstructured fiber designed here not only shows zero dispersion in the telecommunication band but also has two ZDWLs (one in the telecommunication band at 1.51 μm and the other at 2.19 μm) with anomalous dispersion between the two ZDWLs. In addition, the composite fiber has high nonlinearity (of the order of 16 W -1 m -1 ). With a single pump at the first ZDWL, 1.51 μm, the parametric gain over more than 1000 nm wide wavelength band, starting from 1.14 to 2.21 μm, is achieved with a 11.13 dB gain difference between the gains near the pump and optimal wavelengths. In the dual pumping scheme, the difference between the gains at optimal wavelengths and pump wavelength is only 2.45 dB; while the difference between the maximum and minimum gain is 3.43 dB. The maximum value of the gain at the optimal wavelengths, in both single pumping and dual pumping schemes are same. We further show that by selecting proper pump wavelengths ultra-broadband gain can be achieved.

We propose a chalcogenide (As 2 S 3 ) core tellurite cladding microstructured fiber with flattened normal dispersion for ultraflat supercontinuum (SC) generation. To realize flattened normal dispersion, the structure parameters are optimized such as the chalcogenide core diameter, the air hole diameter and the distance between the centers of the two neighboring air holes. The ultraflat normal dispersion curve is obtained and the pulse propagation is investigated using a nonlinear Schrodinger equation. It is shown that an ultraflat SC spectrum with deviations less than 4 dB over an octave (from 1400 nm to 3000 nm) can be achieved by the illumination of a pulsed light with a pulse width of 200 fs, central wavelength of 2000 nm and peak power of 1000 W.

The efficiency of energy transfer from Cr to Nd in silicate glasses has been examined in order to develop a gain medium for high-efficiency solar pumped fiber lasers (SPFLs). The internal quantum efficiency (QE) of the emission from the 4 T2 state of Cr in Cr-doped glasses and from the 4 F3/2 state of Nd in Nd-doped and Nd,Cr codoped glasses was measured using an integrating sphere. For Cr-doped and Nd,Cr codoped glasses, 650 nm excitation was used. For Nd-doped glasses, 808 nm excitation was used. The QE of Cr-doped glass (ηCr) was 7.5 % for 0.05 mol.% Cr2O3, the QE decreased monotonically with increasing Cr2O3 content. The QE of the Nd-doped glass (ηNd) has a maximum of 43 % at 0.2 mol.% Nd2O3. We suggest that absorption of host glass could lower the QE at the low content side of the maximum. The QE of Nd emission in Nd,Cr codoped glass (ηNd,Cr) excited at 650 nm, which excites the 4 A2→ 4 T2 transition of Cr was 5.7 % for 0.05 mol.% Cr2O3 and 0.2 mol.% Nd2O3 content. The energy transfer quantum efficiency, ηtr, from Cr to Nd which is defined as the ratio of the ηCr and the ηNd,Cr was calculated from the obtained QEs. The largest ηtr was 13.4 % at 0.01 mol.% Cr2O3, and decreased with increasing Cr2O3 when content of Nd2O3 was fixed by 0.2 mol.%. This tendency is quite similar to the QEs of the Cr emission in Cr-doped glasses. Thus an increase in the QE of Cr maybe essential to increase the ηtr.

The quantum efficiencies of the emission from the 4 F 3/2 (R) level of Nd doped in tellurite glass were measured with an integrating sphere using natural sunlight(η ns ), simulated sunlight (η ns ), and 808 nm laser light (η 808 ), respectively. The radiative quantum efficiency (η r ) was estimated from the fluorescence lifetime (τ f ) and the radiative lifetime calculated by Judd-Ofelt analysis (τ r ). η r was almost 100 % for χ ≤ 0.5 mol.%. η 808 was 86 % for χ=0.05 mol.% and decreased monotonically with increasing in χ. η ns had a peak at χ=0.5 mol.% and the maximum was 33 %. It is thought absorption of the excitation light by the host glass limits the quantum efficiency of the tellurite glass under sunlight excitation. Therefore, it is important to reduce absorption of the tellurite glass host in order to realize efficient solar-pumped tellurite fiber lasers.

We present the design, dispersion calculations and tailoring, and simulation of the parametric gain in the composite tellurite-fluorophosphate glass fiber. The fiber has the tellurite core subsequently surrounded by fluorophosphate and tellurite claddings. Thermal properties of the tellurite and fluorophosphate glasses match, depicting the feasibility of the fabrication of the fiber under controlled environment. The composite fiber introduced here has the advantage of easy handling over the fiber tapers or the air cladding tellurite nanofibers. With our analysis we observe that the fluorophosphate and the tellurite cladding thickness along-with the fiber core diameter, have control on the dispersion and the parametric gain. The wavelength band, over which the dispersion is anomalous, increases with increasing tellurite core diameter. For longer wavelengths, increasing the fluorophosphate cladding thickness causes increase in the anomalous dispersion bandwidth and further flattening of the dispersion curve. The slope of the dispersion curve near the zero dispersion wavelength (ZDWL) is greatly reduced for thicker outer tellurite ring claddings. It is possible to design zero flattened dispersion fiber or the fiber providing two ZDWLs in the communication band, which can generate broadband parametric amplification. The gain obtained has strong bandwidth dependence on the dispersion slope. We study the effects of the fiber length, pump power, and pump detuning from the ZDWL, on the parametric amplification. With multiple pumping with proper selection of the pump wavelengths, the parametric amplification process can generate ultra flat, broadband amplifiers as the dispersion provided by the composite fiber is anomalous over a wide bandwidth.