Peiqing Zhang

Ultrabroad supercontinuum generated from a highly nonlinear Ge–Sb–Se fiber

We report the fabrication of a novel high nonlinear fiber made of Ge-Sb-Se chalcogenide glasses with high numerical aperture (∼1.0), where the core and the cladding glasses consist of Ge₁₅Sb₂₅Se₆₀ and Ge₁₅Sb₂₀Se₆₅ (mol. %), respectively. The nonlinear refractive index (n₂) of the core glass is 19×10^-18  m²/W at 1.55 μm, and its laser-induced damage threshold under irradiation of 3.0 μm fs laser is approximately 3674  GW/cm². By pumping a 20-cm-long fiber with a core diameter of 23 μm using 150 fs pulses at 6.0 μm, supercontinuum spanning from ∼1.8 to ∼14  μm was generated.

Fabrication and characterization of multimaterial chalcogenide glass fiber tapers with high numerical apertures

This paper reports on the fabrication and characterization of multimaterial chalcogenide fiber tapers that have high numerical apertures (NAs). We first fabricated multimaterial As(2)Se(3)-As(2)S(3) chalcogenide fiber preforms via a modified one-step coextrusion process. The preforms were drawn into multi- and single-mode fibers with high NAs (≈1.45), whose core/cladding diameters were 103/207 and 11/246 μm, respectively. The outer diameter of the fiber was tapered from a few hundred microns to approximately two microns through a self-developed automatic tapering process. Simulation results showed that the zero-dispersion wavelengths (ZDWs) of the tapers were shorter than 2 μm, indicating that the tapers can be conveniently pumped by commercial short wavelength infrared lasers. We also experimentally demonstrated the supercontinuum generation (SCG) in a 15-cm-long multimaterial As(2)Se(3)-As(2)S(3) chalcogenide taper with 1.9 μm core diameter and the ZDW was shifted to 3.3 μm. When pumping the taper with 100 fs short pulses at 3.4 µm, a 20 dB spectral of the generated supercontinuum spans from 1.5 μm to longer than 4.8 μm.

Third-order optical nonlinearities of chalcogenide glasses within Ge-Sn-Se ternary system at a mid-infrared window

Experimental results of third-order optical nonlinearities of chalcogenide glasses (ChGs) within Ge–Sn–Se ternary system at a mid-infrared window of 3 and 3.5 μm are presented in this study. Using femtosecond Z-scan technique, positive nonlinear refractive indexes (n2) of the ChGs were obtained at the mid-infrared wavelengths, with no nonlinear absorption observed. The n2 values at 3 μm were lower than those at 3.5 μm because of the presence of hydroxyl (–OH) group. The maximum n2 was obtained from the Ge–Sn–Se ChGs with highest Sn content, reaching 2.43 × 10−17 m2/W at 3.5 μm, near two times that of As2Se3 glass. Thus, Ge–Sn–Se ChGs can be regarded as a good candidate for photonic devices that operated at mid-infrared window.

Nanocrystal-enhanced near-IR emission in the bismuth-doped chalcogenide glasses

Bismuth (Bi)-doped materials have attracted a great deal of attention because of their broadband nearinfrared (near-IR) emission around the wavelength utilized in telecommunications. In this study, broad near-IR emission band from 1 100 to 1 650 nm is generated in the Bi-doped 90GeS2-10Ga2S3 glass and glass-ceramics under 820 nm of light excitation. Based on the analysis of the absorption and emission spectra, the origin of this broadband emission is ascribed to the Bi2-2 dimers. The precipitation of \β-GeS2 nanocrystals drastically enhances the emission intensity and lifetime of Bi-doped chalcogenide glass.

1.5-14 μm midinfrared supercontinuum generation in a low-loss Te-based chalcogenide step-index fiber.

We have experimentally demonstrated midinfrared (MIR) supercontinuum (SC) generation in a low-loss Te-based chalcogenide (ChG) step-index fiber. The fiber, fabricated by an isolated extrusion method, has an optical loss of 2-3 dB/m at 6.2-10.3 μm and 3.2 dB/m at 10.6 μm, the lowest value reported for any Te-based ChG step-index fiber. A MIR SC spectrum (∼1.5 to 14 μm) is generated from the 23-cm fiber pumped by a 4.5 μm laser (∼150  fs, 1 kHz). To the best of our knowledge, this is the first SC experimental demonstration in Te-based ChG fiber and the broadest MIR SC generation pumped in the normal dispersion regime in the optical fibers.

Preparation of chalcogenide glass fiber using an improved extrusion method

Abstract. We developed the extrusion method to prepare arsenic-free chalcogenide glass fibers with glass cladding. By using the double nested extrusion molds and the corresponding isolated stacked extrusion method, the utilization rate of glass materials was greatly improved compared with the conventional extrusion method. Fiber preforms with optimal stability of core/cladding ratio throughout the 160 mm length were prepared using the developed extrusion method. Typical fiber structure defects between the core/cladding interface, such as bubbles, cracks, and core diameter variation, were effectively eliminated. Ge-Sb-Se/S chalcogenide glasses were used to form a core/cladding pair and fibers with core/cladding structure were prepared by thermally drawing the extruded preforms. The transmission loss, fiber bending loss, and other optical characters of the fibers were also investigated.

Raman gain and femtosecond laser induced damage of Ge-As-S chalcogenide glasses

Chemical stoichiometric Ge-As-S glasses were prepared, and their thermal properties, refractive index (n), optical bandgap, Raman gain, and femtosecond laser damage were examined. Results revealed that the n and density (ρ) of the glasses decreased as Ge concentration increased, whereas the bandgap and glass transition temperature (Tg) increased. The Raman gain coefficients (gR) of the samples were calculated on the basis of spontaneous Raman scattering spectra. gR decreased from 2.79 × 10-11 m/W for As2S3 to 1.06 × 10-11 m/W for GeS2 as Ge concentration increased. However, the smallest gR was 100 times higher than that of fused silica (0.89 × 10-13 m/W). When these glasses were irradiated by a laser with a pulse width of 150 fs and a power of 33 mW at 3 μm, the damaged area and depth decreased and the damage threshold increased gradually as Ge concentration increased. Raman spectra and composition analysis indicated that surface oxidation probably occurred and sulfur gasified at a high laser power. Although the gR decreased as Ge was added, the laser damage threshold of Ge-As-S glasses was higher than that of the As2S3 glass. Thus, these glasses are potential materials for Raman gain media.

Novel Ge–Ga–Te–CsBr glass system with ultrahigh resolvability of halide

CO2 molecule, one of the main molecules to create new life, should be probed accurately to detect the existence of life in exoplanets. The primary signature of CO2 molecule is approximately 15 μm, and traditional S- and Se-based glass fibers are unsuitable. Thus, Te-based glass is the only ideal candidate glass for far-infrared detection. In this study, a new kind of Te-based chalcohalide glass system was discovered with relatively stable and large optical band gap. A traditional melt-quenching method was adopted to prepare a series of (Ge15Ga10Te75)100-x (CsBr)x chalcogenide glass samples. Experiment results indicate that the glass-forming ability and thermal properties of glass samples were improved when CsBr was added in the host of Ge-Ga-Te glass. Ge-Ga-Te glass could remarkably dissolve CsBr content as much as 85 at.%, which is the highest halide content in all reports for Te-based chalcohalide glasses. Moreover, ΔT values of these glass samples were all above 100 °C. The glass sample (Ge15Ga10Te75)65 (CsBr)35 with ΔT of 119 °C was the largest, which was 7 °C larger than that of Ge15Ga10Te75 host glass. The infrared transmission spectra of these glasses show that the far-infrared cut-off wavelengths of (Ge15Ga10Te75)100-x (CsBr)x chalcogenide glasses were all beyond 25 μm. In conclusion, (Ge15Ga10Te75)100-x (CsBr)x chalcogenide glasses are potential materials for far-infrared optical application.

Mid-infrared femtosecond laser-induced damages in As 2 S 3 and As 2 Se 3 chalcogenide glasses

In this paper, we report the first measurements of mid-infrared (MIR) femtosecond laser-induced damage in two typical chalcogenide glasses, As2S3 and As2Se3. Damage mechanism is studied via optical microscopy, scanning electron microscopy and elemental analysis. By irradiating at 3, 4 and 5 μm with 150 fs ultrashort pulses, the evolution of crater features is presented with increasing laser fluence. The dependence of laser damage on the bandgap and wavelength is investigated and finally the laser-induced damage thresholds (LIDTs) of As2S3 and As2Se3 at 3 and 4 μm are calculated from the experimental data. The results may be a useful for chalcogenide glasses (ChGs) applied in large laser instruments to prevent optical damage.

Broadband mid-infrared supercontinuum generation in 1-meter-long As 2 S 3 -based fiber with ultra-large core diameter

In this study, the supercontinuum (SC) generation in a 1-m-long As2S3 fiber with a 200 μm core diameter was demonstrated experimentally. The high-purity As2S3 fiber we used exhibited very low optical loss with a background loss of approximately 0.1 dB/m at a wavelength of 2-5 μm. SC generation was studied by pumping the fiber at different wavelengths and different peak powers. A strong spectral broadening with a 30 dB spectral flatness spanning from 1.4 to 7.0 µm was obtained when the fiber was pumped with 150 fs short pulses at 5.0 µm. The SC generation in bent fiber was also studied. The result showed that the bending radius of the fiber will significantly affect the SC spectra bandwidth and the output power. The SC spectra in the used fiber could still be maintained when it was bent to a radius of 5 cm.