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High-power laser delivery in infrared optical fiber has received much attention due to the urgent needs in the fields of national defense security, biomedicine, advanced manufacturing, and so on. In recent decades, there has been extensive research aimed at enhancing the capabilities of infrared laser power delivery through the purification of infrared glass or the optimization of fiber structures. This article provides an overview of common passive mid-infrared (MIR) optical fibers with numerous glasses and fiber structures, as well as their characteristics in laser power delivery. This review also highlights potential research directions and analyzes the challenges of passive mid-infrared fibers in the current applications. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As40Se40Te20 glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As40Se40Te20 glass was prepared and unclad and step‐index fibers were drawn. An unclad As40Se40Te20 glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As40Se40Te20/As40Se42Te18 step‐index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step‐index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As40Se40Te20 fiber, covered almost all the transparent range of material. [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]

Abstract In this paper, we described the fabrication and polishing characteristics of the end-faces of highly stable physical contact type chalcogenide optical fiber connectors. The effects of downforce pressure, polishing duration, and polishing fluid on the polishing process with abrasive grit size of 0.02 μm were investigated, and the final polishing parameters were determined. The surface roughness Ra was approximately 20 nm in the fiber area, and the average fiber roughness of the core region (10 μm × 10 μm) was about 3 nm, which were measured by the profilometry and atomic force microscope. Finally, the optical performance was analyzed in terms of the insertion loss of 1 dB and return loss of -18 dB. [ABSTRACT FROM AUTHOR]

• There is the first paper related to Nd3+-doped phosphate fiber laser through 888 nm direct pumping. • We have manufactured low loss Nd3+-doped phosphate fibers by the peeled-off isolated stacked extrusion method. • The optical-to-optical efficiency of our fiber laser is higher than that of the same type of laser previously reported. For the first time, we have demonstrated efficient 1054 nm laser output with low loss Nd3+-doped phosphate glass fibers at room temperature using an 888 nm laser diode as the direct pumping source. Therein, the home-made Nd3+-doped phosphate glass fiber is the key for laser performance improvement. The transmission loss of the large-core single-cladding Nd3+-doped phosphate fibers prepared by the novel peeled-off isolated stacked extrusion method is as low as 1.1 dB/m at ∼1 μm. On this basis, a low-loss Fabry-Perot cavity is constructed by precisely controlling the relative distance between the fiber end facet and the cavity mirror with a microscope. The record-breaking optical-to-optical efficiency of Nd3+-doped phosphate glass fiber lasers, 50.2% is achieved with the maximum output power of 6.71 W. During laser operation, the output laser power does not roll over, even at high pump powers. The output laser power is limited only by the available pump power. This work will lay a solid foundation to the high-power fiber laser fabrication, and will find many applications in the future. [ABSTRACT FROM AUTHOR]

In this work, we investigated a new procedure for preparation of purified As–Se glass. After drawing the fibers, an unclad fiber with minimum loss of 2.2 dB/m and a fiber coated with polyether sulfone with minimum loss of 4.2 dB/m were obtained. By pumping the unclad glass fiber in the normal dispersion region at 3 μm, the broadest supercontinuum generation spectrum, covering 1.6 μm to 11 μm with a 40 dB spectral flatness, was recorded from a 15 cm long fiber. The results showed that broadband SC covering nearly almost all transmittance of the material can be achieved with a pump laser in the normal dispersion region. [ABSTRACT FROM AUTHOR]

As 2 Se 3 glass fibers measuring 250 μm in diameter were fabricated based on different draw processing parameters, including preform dropping temperatures (T 1 = T g + ΔT, ΔT = 20, 30, 40, 50 °C), fiber-drawing temperatures (T 2 = T g + ΔT, ΔT = 10, 20, 50 °C), and drawing speeds. Raman spectra indicated crystallization on fiber surface at high temperatures. After fiber drawing, oxygen was detected on fiber surface by energy dispersive X-ray spectra. High-quality fiber with minimum loss of 1.88 dB/m (at 9.05 µm) was achieved under optimal dropping temperature of 218.1 °C (T g + 30 °C), fiber-drawing temperature of 208.1 °C (T g + 20 °C), and drawing speed of 0.10 m/min. [ABSTRACT FROM AUTHOR]

We have investigated the optimization parameters for polishing end-surface of chalcogenide glass fiber connector in the paper. Six SiC abrasive particles of different sizes were used to polish the fiber in order of size from large to small. We analyzed the effects of polishing parameters such as particle sizes, grinding speeds and polishing durations on the quality of the fiber end surface and determined the optimized polishing parameters. We found that, high-quality fiber end surface can be achieved using only three different SiC abrasives. The surface roughness of the final ChG fiber end surface is about 48 nm without any scratches, spots and cracks. Such polishing processes could reduce the average insertion loss of the connector to about 3.4 dB. [ABSTRACT FROM AUTHOR]

• A robust tungsten tellurite glass fiber was fabricated by extrusion method. • 70TZLW glass exhibits higher T g and ΔT than those of TeO 2 -ZnO-Na 2 O glasses. • The average bending strength of 70TZLW fiber is about 570 MPa, which exceeds that of fluoride fibers by>30 %. Robust tungsten tellurite (70TZLW) glass fiber consisting of 70TeO 2 -16ZnO-4La 2 O 3 -10WO 3 core and 70TeO 2 -16ZnO-5.5La 2 O 3 -8.5WO 3 cladding (in mol.%) was prepared by extrusion method. Due to the adding of La 2 O 3 and WO 3 , 70TZLW glass exhibits higher glass transition temperature (385–395 °C) and thermal stability (>145 °C) than those of TeO 2 -ZnO-Na 2 O glasses, which is beneficial to the drawing of optical fiber. In addition, the mean optical losses of the bare wires drawn by the core and cladding glass preform are about 1.19 dB/m and 1.16 dB/m, while that is about 1.04 dB/m for the fiber drawn from the accordingly extruded preform at the wavelength of 1310 nm. Moreover, the average mechanical bending strength of the fiber reaches to about 570 MPa with a Weibull slope of 67.4. These results show the improvement in work ability and the greater practical potential of the 70TZLW extruded fiber compared to TeO 2 -ZnO-Na 2 O fibers for infrared application. [ABSTRACT FROM AUTHOR]

In this work, Ge 15 Sb 20 Se 65 bare glass fiber with a diameter of 500 μm was fabricated, and then tapered with different tapering parameters. The analysis of Raman and energy dispersive X-ray spectra (EDS) indicated that, a slight change in the chemical composition of the glass, fiber and tapering fiber has negligible effect on the glass structure. It was found that, the waist diameter decreases exponentially with increasing tapering length and speed, and high quality taper fiber with the cone diameter of 2.65 μm can be achieved under the optimal tapering conditions. Finally, the simulated and experimental results of the output transmission under different waist length and taper ratio show that the transmission decreases with increasing waist length and taper ratio. [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 RCF with excellent efficiency on optical mode controlling and dispersion tuning. • The first order vortex light OAM 0,1 can be stably transmitted in the RCF. • The lowest loss of the RCF is 0.28 dB/m at 8.1 μm. • SC spectra form 1 to 14.4 µm in this RCF via pumping it near its ZDW around 4.5 µm. The efficiency of mode controlling and dispersion tunning in chalcogenide glass fiber is vital to improve the transmission capacity and spectral spanning efficiency in the mid-infrared. A solid-state ring-core fiber (RCF) is designed for mode controlling and dispersion tuning. The simulation results show that LP 01 -mode is well confined in the high-index cladding-ring, and the confinement loss (CL) analysis of other modes is performed as well. RCF can be regarded as an LP 02 -mode fiber in the center, which is different from LP 01 -mode in the step-index fiber when the wavelength is larger than 5.6 μm. Moreover, OAM 0,1 can be stably transmitted in the ring, since LP 01 -mode and OAM 0,1 have identical ring-shaped profiles. For LP 02 in the core, the zero-dispersion wavelength (ZDW) can be blue-shifted to 4.4 µm from 6.7 µm. For the first time, we have successfully fabricated a novel mid-infrared RCF based on Ge 9 As 22 Se 69 -Ge 9 As 22.5 Se 68.5 -Ge 10 As 22 Se 68 glasses. The lowest loss is 0.28 dB/m at 8.1 μm. The supercontinuum (SC) spectra can be effective broadening (1–14.4 µm) in this RCF via pumping the ZDW around 4.5 µm. In all, this RCF has great advantages in effective mode controlling and dispersion tuning, and has great potentials in developing broad SC and vortex mode controlling. [ABSTRACT FROM AUTHOR]

We report broadband supercontinuum (SC) spectra generated from low-loss single-mode fibers (SMF) based on novel Ge–As–S–Se (GASS) chalcogenide (ChGs) glasses. The step-index fibers (SIF) possess an ultra-low background loss of 0.27 dB/m at wavelength of 2.5 ∼ 7. 5 μ m were fabricated by an optimized peeled-off extrusion method. SC generation was studied by pumping the fiber with 15 cm and 100 cm at same condition (5 μ m, ∼ 150 fs, 1 kHz, 25 mW), respectively. Output SC covering 1.46 ∼ 9. 32 μ m was obtained in this 15-cm fiber, while a relatively wide output SC spanning from 1.68 to 8. 28 μ m was observed in 100-cm fiber. Due to simulated numerical model does not account for higher-order modes at shorter wavelengths, cladding modes, polarization effects etc. Experimental SC spectral profile in the short and long S/Se fibers is slightly different with the simulation analysis. To the best of our knowledge, this is the first report on the performance of GASS fiber. • The fiber with an ultra-low background loss of 0.27 dB/m in 2.5 ∼ 7. 5 μ m. • SC spectrum covering 1.46–9.32 μ m was obtained in a 15 cm fiber, 1.68–8.28 μ m for 100 cm. • This fiber was better than As 2 S 3 fiber in operating window and higher damage than As 2 Se 3. [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]

• High quality Ge-As-S glass and low loss fibers were prepared. • FZP working in visible and near infrared bands was fabricated on Ge-As-S glasses surface by laser direct writing. • With a well-designed FZP on the fiber end face, ChG fiber can achieve excellent self-focusing effect without the collimating and focusing lens. Chalcogenide glass (ChG) has excellent optical properties in the mid-infrared range. The micro-optical fiber devices made of ChG play a strong part in various infrared sensing and detection fields. In this work, Fresnel zone plate (FZP) was fabricated on the Ge-As-S ChG surface and the end face of ChG fiber through femtosecond laser direct writing. FZP with high optical quality was obtained by optimizing the laser writing parameters. Clear focusing pattern can be observed in the visible and infrared bands with the prepared FZP. The full width at half maximum (FWHM) of laser beam with wavelength of 1550 nm is recorded to be 10.39 μm at the focus of FZP, and the numerical aperture (NA) is 0.122. With a well-designed FZP on the fiber end face, the ChG fiber can achieve a self-focusing effect without the collimating and focusing lens. The FWHM of the 1550 nm laser beam at the focus is measured to be 7.46 μm, and NA is 0.162. The combination of FZP and ChG fiber can make the structure of the optical fiber more compact and has potential application value in enhancing the interaction between light and material in the infrared band. [ABSTRACT FROM AUTHOR]

• Two kinds of fibers based on S-rich and S-poor have been fabricated successfully. • As-S-Se system has a transmission varied range between full S-based and full Se-based. • S-rich fiber shows a lower loss, the of S-poor fiber shows a better SC results. Two kinds of single-mode (SMF) step-index(SIF) chalcogenide fibers based on S-rich and S-poor As-S-Se glass have been fabricated successfully by an isolated extrusion method. We experimentally explored the effects of S and Se weights on the IR light transmission in the infrared area of the waveguide medium. By exploring the infrared transmission. It is found that the As-S-Se system has a transmission varied range between full S-based (As 2 S 3) and full Se-based (As 2 Se 3) glasses. The results show that with the addition of selenium, the red-shift is observed in both the short-wavelength absorption edge and long-wave cut-off wavelength. This phenomenon can be sourced from the varying of optical band gaps and phonon energies. Simultaneously, single-mode fibers was employed to evaluate the attenuation and supercontinuum(SC). We found that S-rich fiber shows a lower optical loss of 0.67–1.5 dB/m in 4.1–5.9 μm region, with a minimum value of 0.67 dB/m at 4.6 μm than that of S-poor fiber does. Yet, the SC results of S-poor fiber shows a flatter and broader spectrum region than that of S-rich fiber does. [ABSTRACT FROM AUTHOR]

• Arsenic-free low-loss fiber was fabricated by a process of peeled-off extrusion. • The fiber exhibits a minimum optical loss of 0.87 dB/m at 5.1 μm. • The broadest spectrum from 1.56 to 7.59 μm at −30 dB was achieved successfully. A low-loss and Arsenic-free sulfur-based chalcogenide fiber(Ge-Sb-S) was fabricated by a novel process of peeled-off extrusion. The fiber has an optical loss of <2 dB/m in a range from 5 to 6 μm with a minimum loss of 0.87 dB/m at 5.1 μm. A mid-infrared (MIR) supercontinuum (SC) spectrum covering 1.56–7.59 μm was generated from a 22-cm long fiber pumped with a femtosecond laser at 4 μm (−150 fs, 1 kHz). Simultaneously, we demonstrated that the optical fiber has a transmission efficiency of 53% at 4 μm, which is the key significance for applications such as IR night vision, bio-photonics, military defense and environmentally friendly industry. [ABSTRACT FROM AUTHOR]

A chemically stoichiometric chalcogenide (ChG) glass fiber with ultra-high germanium-containing has been realized for the first time. Here, an isolated extrusion (ISE) with a peeled-off method was carried out for the fiber fabrication with glasses of core Ge 33 As 12.5 Se 54.5 and cladding Ge 33 As 12 Se 55. The fiber exhibits an optical loss of < 3 dB/m in a range of 5.1–7.9 μm, and the minimum loss of 2.11 dB/m was obtained at 6.61 μm. For SC generation, The broadest spectrum from 1.66 to 11.40 μm at − 30 dB was achieved in the 13 cm-long fiber pumped by 5 μm laser with pump power of 25 mW. This fiber possesses the potential applications of high power laser generation and transmission. [ABSTRACT FROM AUTHOR]

• Morphologies of damage craters were inequable with an increasing laser fluence. • Damage threshold on surface of As 2 S 3 fiber is slightly larger that of As 2 S 3 glass. • Morphologies of damage craters on surface of As 2 S 3 fiber and glass were similar. • Compared with damage in MIR region, damage threshold decreased under 800 nm laser. In this study, we investigated femtosecond laser-induced damage on the end face of an As 2 S 3 chalcogenide (ChG) glass fiber by repeatedly inducing 1 kHz ultrashort pulses with 150 fs duration at 800 nm wavelength in comparison with the bulk As 2 S 3 glass. The damage size, geometries, and morphology changes under different laser powers were measured and analyzed with optical, and scanning electron microscopes (SEM). The laser-induced damage threshold on the end face of three As 2 S 3 fibers calculated using the linear regression method was 32.15 mJ/cm2, whereas that of As 2 S 3 bulk glass was approximately 24.32 mJ/cm2. The femtosecond laser-induced damage on the As 2 S 3 bulk glass at 800 nm wavelength was also compared with that in the mid-infrared (MIR) region, which indicates a decrease in the damage threshold and an aggravation in the morphologies of damage craters under an irradiation of 800 nm femtosecond pulsed laser. To the best of our knowledge, this study is the first to investigate the interaction of femtosecond laser with the end face of ChG glass fiber. This work provides scientific guidance for the fabrication of novel photonic devices based on ChG glass fibers. [ABSTRACT FROM AUTHOR]