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We have prepared a novel fiber consisting of three different glasses with W-type double-cladding structure and constant core-to-cladding ratio by the extrusion method. An ultra-high numerical aperture (NA ≥ 2.17) indicates that this fiber has a good capability of collecting and confining light in a wide wavelength range. The lowest fiber loss is approximately 1.7 dB/m at 6.1 μm. Supercontinuum spectrum covering 1.6 μm to 10.85 μm at a bandwidth of −30 dB has been demonstrated in a 21 cm long fiber pumped by 5 μm laser. This chalcogenide fiber has high-NA and W-type double-cladding structure, and thus shows great potentials in the field of high power laser delivery, high efficiency imaging and high-capacity signal transmission in the mid-infrared. [ABSTRACT FROM AUTHOR]

We have developed an innovative extrusion with double peeling-off process to fabricate chalcogenide (GhG) preform, with an aim to remove the defects, such as bubbles, oxidation, and particles that always induce large optical losses in ChG glass fibers. As a result, none of the defects is found in the core-cladding interface of the fiber. The loss in a wavelength range of 5.5–8.2 μm is generally lower than 1 dB/m, with a minimum value of 0.2 dB/m at 6.3 μm. Moreover, a flat mid-infrared (MIR) supercontinuum (SC) spectrum spanning from 1.4 μm to 13.7 μm is generated in an 18 cm-long Ge-As-Se ChG fiber, accompanied with a highest spectrum flatten ratio of 72.4%. [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]

A combined infrared suspended-core fiber (SCF) is fabricated using a stacked glass extrusion method. As2S 3 glass is used as the center core host material, and Ge20As20Se15Te45 glass is used to form supporting bridges and act as the ring host material. In this paper, a continuous and robust extrusion process was used to fabricate the SCFs on stacked chalcogenide glass substrates. Glass flow disruption and shear band formation at the interfaces between the different glasses were avoided while the suspended core was formed directly from the core glass. The near-field optical energy distribution image of the resulting multimaterial SCF shows that light propagates effectively in the core. The losses of the multimaterial SCF were also measured at wavelengths ranging between 2.5 and 7 μm, and the lowest transmission loss was 1.86 dB/m at 4.8 μm. The spectral behavior of the supercontinuum (SC) in the SCF is investigated by varying the pump wavelength and the pump power. A mid-infrared SC spanning a wavelength range from 2.05 to 6.95 μm is generated in a 19-cm-long combined chalcogenide SCF that is pumped at 4.5 μm using an optical parametric amplifier laser system. [ABSTRACT FROM AUTHOR]

Chalcogenide glasses have the advantages of a wide transparency window (over 20 μm) and high optical nonlinearity (up to a thousand times greater than that of silica glasses), making them good candidates for mid-infrared supercontinuum generation. In this review, we describe both the history and recent developments in mid-infrared supercontinuum generation from chalcogenide fibers according to three kinds of fiber structures: step-index, microstructured and tapered fibers. We also review the coherence properties of mid-infrared supercontinuum generation and all-fiber supercontinuum sources based on chalcogenide fibers. [ABSTRACT FROM AUTHOR]

We conducted a numerical study of mid-infrared (MIR) supercontinuum (SC) generation with femtosecond pulses in Ge 23 Sb 12 S 65 chalcogenide photonic crystal fiber (PCF). This PCF has multilayer air holes in the cladding region, which renders its flexibility for controlling the dispersion and confinement loss of the fiber. The broad and flat dispersion profiles and the low confinement loss of the designed PCF combined with the wide MIR transparent window of Ge 23 Sb 12 S 65 chalcogenide glass largely contributed to the broadband MIR SC generation. Owing to the ultra-high nonlinearity of the designed Ge 23 Sb 12 S 65 PCF, an ultra-broadband SC ranging from 1.9 μm to 9.3 μm was obtained in a 15 cm fiber by applying a very low pump power of 165 W at 3.3 μm wavelength. [ABSTRACT FROM AUTHOR]

Fibers exhibiting flattened and decreasing dispersion are important in nonlinear applications. Such fibers are difficult to design, particularly in soft glass. In this work, we develop a preliminary design of a highly nonlinear tapered hybrid microstructured optical fiber (TH-MOF) with chalcogenide glass core and tellurite glass microstructure cladding. We then numerically studied its dispersion, loss, and nonlinearity-related optical properties under fundamental mode systematically using the infinitesimal method. The designed TH-MOF exhibits low chromatic dispersion that is similar to a convex function with two zero-dispersion wavelengths and decreases with fiber length from 2 to 5 μm band. The potential use of the TH-MOF in nonlinear applications is demonstrated numerically by a supercontinuum spectrum of 20 dB bandwidth covering 1.96–4.76 μm generated in 2-cm-long TH-MOF using near 3.25-μm fs-laser pump. [ABSTRACT FROM PUBLISHER]

Two kinds of step-index As-S fibers have been fabricated by an isolated extrusion method with a numerical aperture (NA) of 0.52, but with different core size of 10 or 50 µm. With a femtosecond laser pumping, their supercontinnum (SC) generation spectra were recorded in order to testify the effect of high-order modes on SC generation. The spectra spanning from 1.0 to 6.7 µm and from 1.5 to 8.6 µm can be obtained in a 16-cm-long fiber with 10 µm-core diameter pumping by central wavelength of 2.9 and 4.0 µm, respectively. The results show that high-order modes would deplete the spectra spanning in red-shifting part. The SC generation in small-core fiber is much more efficient than that in large-core fiber. This is the first comparative investigation on the SC generation from the quasi single- and multi-mode ChG fibers under the same conditions. [ABSTRACT FROM AUTHOR]

Compared with the traditional fluoride fibers and tellurite fibers that can work in the near-infrared region, suspended-core fibers based on chalcogenide glasses have wider transmitting regions and higher nonlinear coefficients, thus the mid-infrared supercontinuum generations can be achieved easily. Rather than adopting the traditional fabrication technique of hole-drilling and air filling, we adopted a totally novel extrusion technique to fabricate As2S3 suspended-core fibers with four holes, and its mid-infrared supercontinuum generation was investigated systematically by integrating theoretical simulation and empirical results. The generalized nonlinear SchrÖdinger equation was used to simulate the supercontinuum generation in the As2S3 suspended-core fibers. The simulated supercontinuum generation in the As2S3 suspended-core fibers with different pump wavelengths (2-5 µm), increasing powers (0.3-4 kW), and various fiber lengths (1-50 cm) was obtained by a simulative software, MATLAB. The experimental results of supercontinuum generation via femtosecond optical parametric amplification (OPA) were recorded by changing fiber lengths (5-25 cm), pump wavelengths (2.9-5 µm), and pump powers (10-200 kW). The simulated consulting spectra are consistent with the experimental results of supercontinuum generation only if the fiber loss is sufficiently low. [ABSTRACT FROM AUTHOR]

A mid‐infrared (MIR) supercontinuum (2–16 μm @40 dB) has been generated in a telluride glass fiber, which covers the whole MIR molecular fringerprint region, as this is of key importance for extensive applications in diagnostics, gas sensing, and greenhouse CO2 detection. It is also a fresh demonstration of the single‐mode telluride glass fiber for its merits of ultra‐high nonlinearity and low‐loss. (Picture: Zheming Zhao et al., article number 1700005, in this issue) [ABSTRACT FROM AUTHOR]

• Direct femtosecond laser writing chalcogenide glass infrared fiber Bragg gratings of high reflectivity and narrow bandwidth. • Discussions and solutions to current problems in chalcogenide glass fiber's fabrication using direct femtosecond laser writing. • Foundation for fabricating FBG with arbitrary periods in ChG fibers obtained. Chalcogenide glass (ChG) fiber Bragg grating (FBG) is one of the key components in monolithic infrared fiber lasers and sensors. However, its effective fabrication using direct femtosecond laser writing is still seldom reported, owing to complications attributable to ChG. In this study, a double-D shaped ChG fiber was used to fabricate FBGs with high reflectivity (a 20.5 dB dip in the transmittance) and narrow 3-dB bandwidth (164 pm) using direct femtosecond laser writing. The high sensitivity to laser powers of the direct writing of the ChG FBG was revealed and understood from the perspective of the low laser-induced damage threshold of ChGs. Lower-order reflectance of the directly written FBGs at the mid-infrared wavelength region were quantitively predicted to have higher reflectivity. These results provide a robust method of writing FBGs with arbitrary periods in ChG fibers, establishing a solid foundation for the development of infrared fiber lasers and fiber sensors. [ABSTRACT FROM AUTHOR]

• Thermal and basic properties of Te–As–Se glasses were collected systematically. • Damage thresholds of Te–As–Se glasses was determined. • Femtosecond laser irradiation on the structural evolutions was studied. Te–As–Se (TAS) chalcogenide (ChG) glasses have broad transmission range of up to 18 μm and are suitable candidates for mid-infrared (MIR) applications. In this work, TAS glasses were synthesized via melt-quenching technique. Glass-forming domain was determined by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). Optical properties and structural information were recorded. A series of glasses with compositions of Te x As 40 Se 60- x (x == 0, 10, 20, 30, 40, 50, in mol%) was irradiated by 3 μm femtosecond (fs) laser with different powers. The morphology and structural information after laser ablation were then studied via scanning electron microscopy (SEM) and Raman technique. The laser damage threshold decreased from 29.45 mJ/cm2 to 21.93 mJ/cm2 with the increase in Te contents in the Te x As 40 Se 60- x glasses. This study is of great importance in supercontinuum (SC) generation and infrared laser transmission based on TAS fibers in the MIR range. [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]

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]

We experimentally demonstrate the mid-infrared supercontinuum generation in a chalcogenide step-index fiber consisting of an As 2 Se 3 core and an As 2 Se 2 S cladding. The fiber with the core diameter of 21 μ m was fabricated through the rod-in-tube technique and fiber-drawing process. The effect of pump wavelength, fiber length, and pump power on the spectral bandwidth and output power of the supercontinuum spectra generated from the fiber pumped by the ultrashort pulses of ∼ 150 fs with a repetition rate of 1000 Hz was systematically investigated. When pumping a 12-cm-long fiber at a wavelength of 6 . 5 μ m with 14 mW pump laser power, a broadband supercontinuum spanning from 2 . 0 μ m to 12 . 7 μ m with an output power of 300 μ W was obtained. [ABSTRACT FROM AUTHOR]

We report a broadband supercontinuum generation in a chalcogenide fiber taper with an ultra-high numerical aperture. The chalcogenide step-index fiber consisting of As 2 Se 3 core and As 2 S 3 cladding was fabricated by using the isolated stacked extrusion method. The fiber taper with a core diameter of 1.75 μm was prepared by employing a homemade tapering setup. By pumping the fiber taper with a femtosecond laser pulses at 3.3 μm, a broadband supercontinuum generation spanning from 1.9 to 5.7 μm was achieved. [ABSTRACT FROM AUTHOR]

This work experimentally demonstrates the supercontinuum (SC) generation in a three-hole arsenic free Ge 20 Sb 15 Se 65 chalcogenide suspended-core fiber. Mechanical drilling was used to prepare the chalcogenide glass preform, which was drawn into suspended-core fibers. The zero-dispersion wavelength of the fiber is moved toward the shorter wavelength of about 3.2 μm through changing the fiber core diameter by controlling the pressure of inert gas during fiber drawing. When a 15 cm-long fiber with a core diameter of 6 μm is pumped using 150 fs pulses at 3.3 μm, SC spanning from ∼3 μm to ∼8 μm was generated. [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]

A high-purity As 40 S 59 Se 1 /As 2 S 3 core/cladding step-index fiber for supercontinuum generation was fabricated in this study. The glass rods were obtained by using a relatively effective and inexpensive method of modified physical and chemical purification. Then, the multi-material fiber preform was fabricated through a modified laboratory using one-step co-extrusion process. Moreover, the fiber preform with a Polyether Sulfone (PES) polymer was drawn with a core diameter of ~ 22 μm. The core/cladding ratio of the fiber was approximately 1:17, and the minimum loss was approximately 1 dB/m between 4 and 6 μm. By pumping a 13 cm-long fiber with different laser powers and another two different lengths (20 cm and 50 cm, respectively) of fiber at 4.8 μm, a supercontinuum covering 1–5 μm could be recorded in all fibers. This study attained a 1–5 μm supercontinuum that covered the second atmospheric window. Result of this study can be a promising reference in the production of mid-infrared light source. [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]

• 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]

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]