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Extinction ratio (ER) is one of the important parameters to characterize the polarization‐maintaining (PM) performance of the fiber. In this paper, we report the preparation and properties of a novel chalcogenide microstructure fiber with a high ER. We fabricate a preform using a peeled‐off extrusion method. The core and cladding material of the fiber are Ge9As23Se68 and Ge10As22Se68. The preform was drawn into a fiber with an average ER of −17.08 dB. The loss of the fiber is less than 2 dB over 5.20–8.55 μm, and the minimum loss of the fiber is 0.57 dB/m at 6.2 μm. Moreover, a flat mid‐infrared supercontinuum spectrum spanning from 1.53 to 12.50 μm is generated by pumping an 18‐cm‐long PM fiber for the first time. [ABSTRACT FROM AUTHOR]

We have prepared an ultra‐large core, high numerical aperture (NA) chalcogenide (ChG) step‐index fiber (SIF) with a mode area of >43 600 μm2 at the wavelength of 5.5 μm by an improved extrusion method. The fiber based on two ChG glasses with similar softening temperature has a core diameter of 339.0 μm and ultra‐thin cladding. The fiber exhibits a minimum loss of 1.75 dB/m at 9.74 μm and an optical loss of <5.0 dB/m from 5.3 to 10.8 μm. Broadband supercontinuum (SC) covering from 1.2 μm to 13.7 μm has been generated in a 17‐cm‐long ultra‐large mode area fiber with large core and high NA. All these show that, the fiber possesses the potential for high‐power infrared laser transmission. [ABSTRACT FROM AUTHOR]

By conventional melt‐quenching techniques, a series of Dy3+‐doped (0.1 to 1.0 wt%) Ga5Ge20Sb15S60 bulk glasses were fabricated and their potential for developing mid‐infrared fiber laser beyond 4 μm were evaluated, in which the optimal Dy3+ doping concentration was found to be 0.3 wt% and the largest laser quality factor value (σe × τmea = 2.62 × 10−23 cm2 s) among all of the Dy3+‐doped chalcogenide glass was obtained. On this basis, through using the chemical purification methods with chlorine gas combined with the dynamic distillation process, the high‐purity GGSS glasses with low O–H and S–H absorptions were successfully fabricated, which was confirmed by the optimized mid‐infrared linear transmittance and improved fluorescent lifetimes of Dy3+: 6H13/2, 6H11/2 levels. Furthermore, for the first time to the best of our knowledge, the Dy3+‐doped, single‐mode, and double‐cladding chalcogenide fibers with the core/cladding ratios of 125:60:11 and 125:66:11.5 were achieved by a multistage rod‐in‐tube fiber drawing process and extrusion methods, respectively. The GeS2‐based fiber exhibits excellent transmission performance at 1.0‐5.0 μm: 3.0 dB/m at 2.9 μm (O–H), 2.4 dB/m at 4.1 μm (S–H). Combining the advantages of high‐purity, high doping concentration and single‐mode double‐cladding structure, the optimized active fiber should be an ideal efficient and low‐threshold medium toward mid‐infrared fiber laser beyond 4 μm. [ABSTRACT FROM AUTHOR]

High nonlinear fibers with low zero‐dispersion wavelength (ZDW), high laser power tolerance and large band‐gap are urgent for all‐optical‐band supercontinuum (SC) generations. Widely used chalcogenide fibers usually have a large ZDW and low laser power tolerance, and thus are not ideal for such purpose. Here, an ultra‐low material ZDW chalcohalide (ChH) glass fiber with high nonlinearity as well as high laser power tolerance has been fabricated successfully via a novel peeling‐off‐extrusion method. The step‐index fiber has double‐cladding structure, the inner cladding is GeGaSe‐CsI glass and the outer one is GeSbS jacket. The core glass has an ultra‐low material ZDW of 3.5 μm and large absorption edge of 2.0 eV. The nonlinear refractive index is 6.67 × 10−18 m2/W @1.55 μm. Broadband SC generation covering 1.05‐13.0 μm is demonstrated in this novel ChH fiber. Such glass fiber with high nonlinearity, wide transparent range, low ZDW and high laser damage threshold is promising for the applications in the mid‐infrared. [ABSTRACT FROM AUTHOR]

The fabrication and characterization of IR chalcogenide polarization-maintaining (PM) step-index optical fibers with elliptical-core and 1-in-line-core have been reported for the first time. An improved isolated co-extrusion method was used to fabricate these core-shaped PM fibers. The elliptical core had a horizontal radius of a = 3.66 μm, vertical radius of b = 1.83 μm and the 1-in-line core of a = 4.83 μm, b = 1.42 μm, respectively. Single-mode PM beam spots were observed for the elliptical-core and 1-in-line-core fibers in the near-field energy distributions. The highest values of birefringence of the elliptical-core and 1-in-line-core fibers are 2.09 × 10 −4 at 2.7 μm and 3.272 × 10 −4 at 2.8 μm, respectively. The extinction ratios of −3.7 dB and −2 dB were achieved in fibers of 0.5 m long with elliptical-core and 1-in-line-core, respectively. [ABSTRACT FROM AUTHOR]

Highly nonlinear suspended-core fibers (SCFs) with tunable dispersion have attracted much attention in the fields of Raman amplification, optical frequency combs, broadband and flat supercontinuum generation (SCG). To address the limitation of applications due to its fragile suspension arms, this study proposes the design of a fiber structure with three parabolic air holes. Numerical simulations are performed to optimize an arsenic sulfide SCF in terms of dispersion management and SCG in the wavelength range from 0.6 µm to 11.6 µm. Results show that the proposed SCF has dual zero-dispersion wavelengths (ZDWs) that can be shifted by adjusting the parabolic coefficient of the air-hole and the equivalent diameter of the suspended core. By means of structural optimization, an SCF with 1 μm equivalent diameter and a parabolic coefficient of 0.18 μm−1 is proposed. The first ZDW of the SCF is blue-shifted to 1.541 μm, which makes it possible to use a commercial light source with a cheaper price, more mature technology and smaller volume as the pump source. SCG is studied by solving the generalized nonlinear Schrödinger equation using the split-step Fourier method, and a 0.6–5.0 μm supercontinuum spectrum is obtained at a pump source peak power of 40 kW. [ABSTRACT FROM AUTHOR]

A highly sensitive mid-infrared evanescent wave sensor based on side-polished (SPF) chalcogenide fiber (ChG) was proposed in this work. The optimum optical fiber parameters were determined via numerical simulation by detecting the leakage intensity of evanescent waves from the optical fiber of different polish depths. The SPF remarkably enhanced the evanescent wave sensing while maintaining fiber loss and strength. Graphene oxide (GO) was coated on the fiber to enhance the sensitivity of SPF sensor for butane (C 4 H 10). GO has a great specific surface area and abundant oxygen-containing functional groups, which enlarges the contact area of GO with gas molecules and enables to adsorb gas. Results show that the GO-SPF sensor can be three and five times more sensitive than the original fiber optic sensor and SPF sensor for butane gas detection, and has a fast response time and good repeatability. [ABSTRACT FROM AUTHOR]

• • A low scattering-loss tellurite fiber(Te-Zn-La-W) was fabricated by an effective process of air-exhausting extrusion based on ceramics die. • • The results demonstrate that the tellurite glass was well-preserved during the extrusion, and no visible particle defects were found at the core-cladding fiber interface. • • The TZLW fiber shows a low optical loss a minimum value of 0.67 dB/m at 1.31 μm, which is approximately 77 % lower than that of fibers prepared using a stainless-steel die. During the preparation of tellurite fiber preforms, defects such as air bubbles and contaminated particles at the core-clad interface can significantly increase fiber loss. In this paper, we have proposed an effective method to solve these defects. Firstly, zirconia (ZrO 2) ceramics were used as the die material due to their low contamination and high chemical stability, avoiding the surface reduction of TeO 2 glass associated with metal-based die. Furthermore, the die was designed with an air-exhausting channel between the interface of the core and cladding glasses. The results demonstrate that the tellurite glass was well-preserved during the extrusion, and no visible particle defects were found at the core-cladding fiber interface. The fabricated fiber exhibits an optical loss as low as 0.67 dB/m at 1.31 μm, which is approximately 77 % lower than that of fibers prepared using a stainless-steel die. This air-exhausting extrusion based on ceramic die, proves to be an effective method for the fabrication of low loss tellurite fibers for mid-infrared. [ABSTRACT FROM AUTHOR]

Abstract High quality large-core As Se chalcogenide fiber was fabricated via a novel extrusion method to peel off the out-layer of the core glass, and thus all the defects, such as deformations, interface bubbles between the core and cladding can be eliminated effectively. The raw materials were purified by the dynamic distilling and the glasses were prepared by the melt-quenching method. The preform was prepared by an improved isolated stacked homemade extrusion (ISE) machine. The fibers coated with polymer protection were drawn out with a core diameter of ∼240 μm. The core/cladding ratio of the fiber were kept approximately 1:2, and the optical loss was generally lower than 1.5 dB/m in a wavelength range of 5.6–9.7 μm, with a minimum value of 0.6 dB/m at 8.3 μm. The calculated fiber numerical aperture was approximately 0.55. Supercontinuum (SC) generation experiments of fiber at different wavelengths and pump powers were performed. A flattened SC spectrum can be obtained in this large-core fiber with femtosecond pumping. Highlights • A peeled-off extrusion technique was presented for chalcogenide glass fiber. • This step-index As-Se fiber shows a low optical loss in midinfrared with a minimum value of 0.6 dB/m at 8.3 μm. • A flatness supercontinuum spectrum covering 1.5-13.3 μm can be obtained in this As-Se fiber pumped with a femtosecond laser. [ABSTRACT FROM AUTHOR]

• The –OH absorption coefficients were drastically reduced from 0.21 cm−1 (0.09 ppm) to 0.023 cm−1 (0.01 ppm). And the 4I 11/2 lifetime was significantly improved from 2.3 ms to 4.8 ms. • A perfect S-DCF was designed and fabricated via a novel extrusion-stacking method for the first time. • Emission spectra of single cladding fiber, circle double cladding fiber (C-DCF) and S-DCF at 1600–1640 nm and 2500–2900 nm wavelength were compared, and all the results certificate the excellence of S-DCF in pump-absorption efficiency. High-purity chalcogenide glasses and optimal fiber structure design are essential to enhance fluorescence lifetime and pump absorption efficiency in a chalcogenide-based fiber laser. Here, Er3+-doped As 2 S 3 glasses, with a low –OH concentration of only 0.023 cm−1 (0.01 ppm), were prepared by the novel purification method, and the 4I 11/2 level lifetime of purified glasses was increased successfully from 2.3 ms in unpurified glass to 4.8 ms in the purified glass. Furthermore, a special chalcogenide preform with square inner double cladding (S-DCF) was designed and fabricated via a novel extrusion-stacking method for the first time. Compared with circle inner double cladding fiber and single cladding fiber, the pump absorption efficiency is increased by 2–5 times, which fits well with the simulation result by the three-dimensional ray tracing method. All the results mentioned above demonstrated that the elimination of –OH and the optimized structure of S-DCF can improve the luminescence efficiency apparently and promote the development of mid-infrared fiber laser based on Er3+-doped chalcogenide glass. [ABSTRACT FROM AUTHOR]

Chalcogenide suspended core fibers are considered as an excellent candidates for several applications in near-and-mid IR applications because of their characteristics of higher linearity and nonlinearity. In this paper, the influence of the fiber structure and host glass on dispersion and nonlinear properties, including the core size and the width of the bridge, especially the shape of the fiber core were analyzed with the finite element method in detail. And then, the optimized structure of SCFs made of As 2 S 3 , Ge 20 Sb 5 Se 75 , As 2 Se 3 , Ge 15 As 15 Se 17 Te 5 , which stand for the typical samples of S-based, Se-based and Te-based chalcogenide glasses, have been adopted to get suitable dispersion properties and highest nonlinear optical properties in all kinds of glasses. [ABSTRACT FROM AUTHOR]

• The mechanism of impurity absorption and heterophase inclusion in Ge-As-S glass was investigated. • Heterophase inclusions in Ge-As-S glass can be effectively suppressed by dynamic distillation and melting at the optimized melting temperature. • The average loss of purified fiber and unpurified one is 1.86 dB/m and 2.87 dB/m, respectively. About 1 dB/m decrease in the loss is due to the absence of the visible heterophase inclusion particles in the glass. Strong absorption from the impurities and background scattering induced by heterophase inclusions are major issue in the applications of Ge-As-S glass in mid-infrared (MIR). Here, we report that, the absorption of impurities sourced from raw materials can be removed effectively by oxygen getters and hydrogen getters under static vacuum distillation, leading to almost disappearance of the absorption at 3.11 μm due to S H, <4.08 ppm at 4.01 μm due to S H and < 11.03 ppm at 7.5 μm due to As-O, respectively, in Ge 10 As 28 S 62. The impurities of H 2 O and CO 2 can be further eliminated to near zero by dynamic distillation. On the other hand, the heterophase inclusions, originating from raw materials of sulfur, arsenic and germanium, the silica-container and deoxidizer of Mg, can be eliminated thoroughly by dynamic distillation and optimized melting temperature. We draw the fibers using unpurified and purified glasses and found that, comparing with the fiber loss of 2.87 dB/m at unpurified glass, the optical loss can be decreased to about 1.86 dB/m in purified glass without any visible particles or heterophase inclusions. All the results pave the way of developing low loss Ge-As-S glass fiber for high power laser delivery. [ABSTRACT FROM AUTHOR]

The influence of extrusion on the properties of chalcogenide glasses and fibers was investigated systematically via measuring and analyzing their structural and physical properties of Ge 10 As 22 Se 68 and As 2 S 3. The experimental results showed that the extrusion processing has an insignificant effect on the glass network, crystallization, and compositions, but does have an influence on the glass transmission rate, refractive index and density. Meanwhile, the fiber loss after extrusion processing was greatly improved with 57.65% or 71.43%, corresponding to Ge 10 As 22 Se 68 or As 2 S 3 fiber, respectively. [ABSTRACT FROM AUTHOR]

• This is the first time to achieve a high-quality and robust fusion splicing between fluorotellurite and As 2 S 3 fibers. • The loss of fusion splicing between silica and fluorotellurite fibers is 0.5 dB, the fusion-splicing point between fluorotellurite and As 2 S 3 fibers is achieved with a splicing loss of approximately 0.55 dB. This work lays a solid foundation for building an actual all-fiber cascaded mid-infrared supercontinuum source. • The beam quality can be well maintained through the fusion splicing point between fluorotellurite and As 2 S 3 fibers. Besides, the temperature of the splicing joint has no evident increase with a 2 W pump power at 1.55 μm. We demonstrate a low-loss and high-robustness fusion splicing point between fluorotellurite fiber and arsenic sulfide-based chalcogenide fiber (As 2 S 3) by using an asymmetric fiber splicing technology. The splicing loss of point is less than 0.55 dB at the wavelength of 1.55 μm, and the monitored tension is 129 g by tuning the distance of the fusion splicing head offset in the fusion splicing process. Using an all-fiber testing system, the fusion splicing point loss between the 1.55 μm testing light source tail fiber (silica fiber) and the fluorotellurite fiber is 0.503 dB. The output power from the As 2 S 3 fiber is 0.91 W with a testing light source of 2 W, and the temperature of the splicing joint shows no evident increase. This finding indicates that the fusion splicing point offers excellent beam quality. This work lays a solid foundation for building an all-fiber cascaded system generating mid-infrared supercontinuum with high-coupling efficiency between mid-infrared soft-glass fibers. [ABSTRACT FROM AUTHOR]

Chalcogenide glass fiber usually possesses a single zero-dispersion wavelength (ZDW) that is more than 5 µm. Here, a novel W-typed double cladding chalcogenide glass fiber was designed and fabricated with optimized dispersion properties based on As 2 Se 3 -Ge 7 As 23 S 70 -Ge 10 As 23 Se 67 glasses. The results show that there are two ZDWs locating at near-infrared 2.95 µm and far-infrared 11.77 µm, and the dispersion less than 8 ps/km/nm at this range. Based on numerical simulation and viscosity analysis, a novel W-typed double-cladding fiber is fabricated via extrusion method, and the lowest loss of 1.15 dB/m is obtained at 5.68 µm. The optimized structure and dispersion distribution of the fiber ensure the excellent supercontinuum generation. When pumping at 3 µm near the first ZDW, a bandwidth supercontinuum (SC) spanning from 1 to 10.9 µm can be obtained. By pumping at 5 µm, a broad bandwidth of SC output from 1.3 to 13 µm can be obtained. This kind of low ZDW fiber has great potential for the generation of supercontinuum in the future. [ABSTRACT FROM AUTHOR]

• A dual-clad step-index chalcogenide fiber based on tellurium glasses was proposed and investigated detailedly for midinfrared coherent supercontinuum generation. • The structure of the fiber with a W-type refractive-index profile was numerically studied and optimized for all-normal dispersion profile. • Due to the large material zero dispersion wavelength, an all-normal dispersion tellurium chalcogenide fiber was realized via the waveguide chromatic engineering. • The optimized fiber was fabricated via extrusion and employed for coherent supercontinuum generation. • The result shows that a high coherent supercontinuum covering 3.5–10.5 μm can be generated in this fiber with 5 μm femtosecond laser pumping. • This is the first numerical investigation on the dispersion engineering of tellurium chalcogenide dual-clad step-index fiber. Considerable investigations have been carried out for chromatic dispersion tailoring of chalcogenide glass fiber with various structures and different material compositions. Here we proposed a tellurium-based chalcogenide glass fiber with a dual-clad structure in a W-type refractive-index profile. The structure of the fiber based on Ge-As-Se-Te glasses was numerically analyzed in detail. The simulation results indicate that an all normal dispersion profile can be realized in this tellurium glass fiber with an optimized dual-cladding structure. Then the optimized tellurium chalcogenide fiber with an all-normal dispersion profile was fabricated by multi-extrusion method. Pumping with a 5 μm ultra-short pulsed laser (150 fs, 1 kHz), abroadband supercontinuum (SC) covering 1.5–11 μm can be generated in the 19 cm-long fiber. The coherence of SC was also investigated by numerical simulation. The result shows that a high coherent SC covering 3.5–10.5 μm can be generated in this all-normal dispersion fiber. In conclusion, all-normal dispersion profile can be realized easily in this tellurium-based glass fiber due to their large materials ZDWs. [ABSTRACT FROM AUTHOR]