Large mode-area all-solid anti-resonant fiber based on chalcogenide glass for mid-infrared transmission.

A large mode-area chalcogenide all-solid anti-resonant fiber has been designed and successfully prepared for the first time. The numerical results show that the high-order mode extinction ratio of the designed fiber can reach 6000, and the maximum mode-area is 1500 um2. The fiber possesses a calculated low bending loss of less than 10-2 dB/m as the bending radius is larger than 15 cm. In addition, there is a low normal dispersion of -3 ps/nm/km at 5 µm, which is beneficial for the transmission of high power mid-infrared laser. Finally, a completely structured all-solid fiber was prepared by the precision drilling and two-stage rod-in-tube methods. The fabricated fibers transmit in the mid-infrared spectral range from 4.5 to 7.5 µm with the lowest loss of 7 dB/m @ 4.8 µm. Modeling suggests that the theoretical loss of the optimized structure is consistent with that of the prepared structure in the long wavelength band.

Low-loss chalcogenide microstructured optical fibers prepared by eliminating interfaces defects.

The loss of chalcogenide microstructured optical fibers (ChG-MOFs) is generally higher than that of step fibers, mainly due to the immature fiber preform preparation method and strong waveguide defect scattering. Chemical polishing is used to polish mechanically drilled preforms to prepare ChG-MOFs with low defect scattering. Firstly, the scattering loss caused by the defective layer of ChG-MOFs is studied theoretically and experimentally. Then, a single-mode photonic crystal fiber (PCF) was prepared to verify the effect of chemical polishing on reducing fiber loss. The experimental results show that the PCF average loss is reduced from more than 8 dB/m to less than 2 dB/m, and the minimum loss reaches 0.8 dB/m @ 2.7 µm. At the same time, the bending strength of the PCF after chemical polishing is also significantly improved.

Chalcogenide GRIN glasses with high refractive index and large refractive index difference for LWIR imaging.

Gradient refractive index (GRIN) materials utilize an internally tailored refractive index in combination with the designed curvature of the optical element surface, providing the optical designer with additional freedom for correcting chromatic and spherical aberrations. In this paper, new GRIN materials suitable for the second (3-5 µm) and third (8-12 µm) atmospheric windows were successfully developed by the thermal diffusion method based on Ge20As20Se60-xTex series high refractive index glasses, where the maximum refractive index difference (Δn) at 4 µm and 10.6 µm were 0.281 and 0.277, respectively. The diffusion characteristics and refractive index distribution of the GRIN glass were analyzed by Raman characterization. Furthermore, the performance of GRIN singlet and homogeneous singlet in the LWIR band (8 µm, 10.6 µm (primary wavelength), 12 µm) was compared, and the results showed that the GRIN singlet had better chromatic aberration correction and unique dispersion characteristics.

Development and characteristics of infrared gradient refractive index chalcogenide glasses by hot pressing.

Compared with ordinary uniform lenses, the length and refractive index distribution of gradient refractive index (GRIN) lenses can effectively correct aberration and chromatic aberration. This advantage makes the miniaturization, integration, and lens lightweight possible. Although the visible GRIN lenses based on silicate glass are widely used, the infrared GRIN lenses based on chalcogenide glass are still elusive. This paper introduces a new method for preparing this kind of lens by hot pressing sintering diffusion of chalcogenide glasses. A series of chalcogenide glasses Ge10As22Se68-xSx (x = 4, 7, 10, 14, 24, 28, 34 mol%) with refractive index range from 2.37 to 2.57 (n@8 µm) and similar glass transition temperature (ΔTg < 10℃) were prepared by melt quenching. The relationship between Raman peaks and the refractive index of glasses was studied. Furthermore, the refractive index profile formed by elemental diffusion was characterized by Raman signals. The results show that the diffusion length reaches more than 290 µm, and larger diffusion distances can be achieved by stacking multiple layers. The obtained GRIN glass maintains good transmittance in the whole atmospheric window of 2 ∼ 12 µm.

Characteristics and preparation of a polarization beam splitter based on a chalcogenide dual-core photonic crystal fiber.

We reported on a polarization beam splitter based on a novel chalcogenide dual-core photonic crystal fiber. The glass matrix of the optical fiber is Ge10As22Se68. We used computerized numerical control precision drilling methods to manufacture preforms. Then the preform was drawn into an optical fiber with a regular hole structure. The maximum extinction ratio reached -32.76 dB with a 26.27 mm-long optical fiber. Numerical results show that the shortest working length of the designed polarization beam splitter is 636 µm. In addition, the modeling analysis based on the actual structure shows that the theoretical value is consistent with the measured value.

Role and application of iron in water treatment for nitrogen removal: A review.

It is crucial to have a review on the role of iron in water treatment for the guidance towards the selection of appropriate processes, content of iron, and application conditions, as there are few reviews available at present and the systematic information is lacking for both researchers and engineers. The objectives of this review are to summarize the state of arts with respect to iron applied in nitrogen removal, discuss chemical and biological or bio-chemical combined nitrogen removal pathways and processes coupled with iron, and to reveal reaction mechanisms as well as providing references or even solutions to pertinent the practical engineering application of nitrate removal coupling with iron. The following information have been summarized and discussed in details: (1) iron based materials with varieties of preparations and forms, (2) major coupling ways of nitrogen removal methods or processes with iron application, (3) chemical reaction equations about a variety of chemical and biological or bio-chemical combined processes and the main mechanisms. In addition, challenges and/or drawbacks during the nitrogen removal processes will also be discussed in this paper, which is aimed to seek better practical engineering applications of nitrate removal coupling with iron.

Role of illumination intensity in microcystin development using Microcystis aeruginosa as the model algae.

Microcystis aeruginosa (M. aeruginosa) is one of the most common genera of cyanobacteria in algal blooms. In the present work, the impact of the illumination intensity on the growth of M. aeruginosa has been studied and a grinding method for the extraction of intracellular microcystins (MCs) was developed. The variations of algal density, pH, total phosphorus (TP), and total nitrogen (TN) have been investigated during MCs' culturing period. Results showed that the extraction efficiency of MC-YR by the grinding method was 275% higher than the sonication method, and the extraction efficiencies of MC-RR and MC-LR by the grinding method were similar to the sonication method. The optimal illumination intensity for M. aeruginosa was found to be 19-38 µmol m-2 s-1 with suitable pH range of 7.5-10.5. Active release of extracellular MCs was not significantly observed when illumination intensities were ≤ 38 µmol m-2 s-1. Furthermore, the intracellular MC yields under different illumination intensities were found to be a relatively stable level. However, excess illumination intensity (≥ 47 µmol m-2 s-1) led to the lysis of algal cell and increased the concentrations of extracellular MCs, with MC-RR as the dominant compound. The calculated intracellular/extracellular MCs ratios for MC-RR, MC-LR, and MC-YR were 2.38 (N = 100, SD = 2.44), 2.68 (N = 64, SD = 3.48), and 1.25 (N = 30, SD = 1.64), respectively. Strong illumination intensity and cell lysis were found to be the two major factors influencing the release of extracellular MCs.