Zhiyong Yang

Mid-infrared (MIR) lasers operating in the 2–6[Formula: see text][Formula: see text]m region are important for spectroscopy, sensing, communications, medicine, lidar, and electro-optical applications. Chalcogenide glasses and glass–ceramics are attractive MIR gain-media candidates because of their broad infrared transparency and low-phonon-energy hosts. This review focuses on recent progress in chalcogenide glasses and glass–ceramics toward practical MIR laser operation. Rare-earth-doped glasses and fibers are discussed from early MIR emission studies to recent Tb[Formula: see text]-, Ce[Formula: see text]-, and Pr[Formula: see text]-based laser demonstrations, with particular attention to low-loss fibers. For rare-earth-doped glass–ceramics, dopant partitioning among nanocrystals and glass–crystal interfaces is examined as a key factor governing spectroscopic performance. Transition-metal-doped systems, including Cr[Formula: see text]-, Co[Formula: see text]-, Fe[Formula: see text]-, and Ni[Formula: see text]-activated materials, are reviewed with emphasis on crystal-field engineering and crystallization-induced optical loss. Bulk, fiber, waveguide, and microcavity platforms are further compared in terms of gain–loss balance and their suitability for practical MIR laser operation.

The chalcogenide fiber combiner is a specialized optical device designed for the mid-infrared band. Its primary function is to merge optical signals from multiple fibers into a single output fiber efficiently. It allows high-efficiency combination of multiple laser beams to produce high-power or broadband mid-infrared sources, offering promising applications in infrared countermeasures, industrial processing, environmental monitoring, and medical diagnostics. This review first outlines the core concepts and design principles of chalcogenide fiber combiners. Subsequently, based on the operating wavelength bands, it highlights the current research status of mid-wave infrared and long-wave infrared chalcogenide fiber combiners, with particular emphasis on the challenges encountered in the long-wave infrared band and the recent research progress made by our team. Additionally, this review identifies the key challenges facing current research efforts and explores potential future trends in this domain, aiming to provide a valuable reference for further studies in the field.

High beam quality fiber combiners (FCs) operating in the mid-infrared (MIR) spectral range are highly desirable for power enhancement of MIR lasers, particularly for compact quantum cascade lasers. However, fabricating an MIR FC with both high output beam quality and robust power endurance remains challenging. In this work, the first high-beam-quality MIR FC for laser power scaling is designed and fabricated. The FC is constructed using Ge-As-S chalcogenide fibers with high laser resistance. It consists of three few-mode input fibers with core/cladding diameters of 40 μm/240 μm, and a multi-mode output fiber with core/cladding diameters of 100 μm /250 μm. The 3x1 Ge-As-S FC has a total length of 60 cm. It shows port transmission efficiencies as high as 86.0% at 4.6 μm and 87.6% at 2 μm. An output power of 9.1 W at 2 μm and an output beam quality of M² = 3.81 at 4.6 μm are achieved with this FC, representing the highest combined output power and the highest output beam quality reported for an MIR FC.

Radial graded‐index (R‐GRIN) lens, which has two flat surfaces, is a self‐focusing lens. It can precisely control the beam focusing and simplify the optical system structure, showing great potential in the fields of advanced optics such as optical communication, optical sensing, and optical imaging. Although R‐GRIN lenses working in the visible to near‐infrared waveband have been widely used in fiber optics and microimaging, those operating in the mid‐infrared spectral region have not been commercially available due to the lack of efficient production technology. In this work, mid‐infrared Ge–As–Se–Te chalcogenide GRIN lenses are fabricated by an innovative technique suitable for mass production, and their potential for mid‐infrared optics is assessed. The R‐GRIN lenses are fabricated by assembling a glass rod and a series of glass tubes with gradually changing refractive indices (RIs) into a coaxial preform, drawing it into a cane, cutting the cane into disks, and heat‐treating them. The fabricated R‐GRIN lenses have a diameter of 4.0 mm, a length of 3.86 mm, and an RI contrast of ∼0.238 at 10 µm. The measurement using a 4.6‐µm single‐mode laser as the light source shows that the lenses have a focal length of ∼1.0 mm and can focus the beam with a diameter of 3.3 mm into a spot with a diameter of 0.67 mm. It therefore demonstrates good potential of Ge–As–Se–Te R‐GRIN lenses for mid‐infrared optics and provides a solution for mass production of high‐performance R‐GRIN lenses.

Here, to regulate the PL efficiency of dopants, we developed a novel method for regulating the chemical surroundings of dopants by modulating the network structure of the glass matrix, including composition and controlled nanocrystallization.

Fiber combiner is an effective device to enhance the power level or broaden the spectral wavelengths through a single monolithic output aperture, by fusing multiple fibers together. This is particularly important in mid‐infrared (MIR) 2–5 µm range, in which the output power of a single laser is limited. Due to the high MIR transmission, chalcogenide glass is an ideal host for constructing MIR fiber combiner. In this study, we report the design, fabrication, and characterization of a homemade 3 × 1 chalcogenide glass fiber combiner. The fiber combiner includes a 3 × 1 As–S input fiber bundle and an output fiber. The input fiber bundle was made by tapering three As–S multimode fibers with a core diameter of 200 µm and a cladding diameter of 250 µm. The taper reduction ratio R was 2, and the length of the taper transition region was ∼2 cm. The output fiber with core diameter of 360 µm and cladding diameter of 570 µm was then spliced with the tapered end of the fiber bundle. The total length of the combiner was ∼53 cm. The measurement of power combination at 4.56 µm indicated that the transmission efficiency of three ports reached 80%, whereas the power combining efficiency of the combiner was measured to be ∼48%. In addition, efficient wavelength combining over one octave has been demonstrated, by launching three different lasers at 2.1, 3.39, and 4.56 µm through the 3 × 1 combiner. It proves that chalcogenide fiber combiner is promising for the applications of high‐level power combination and broadband wavelength combining in MIR 2–5 µm range.

Infrared graded‐index (GRIN) lenses are desirable for realizing miniaturization and lightweight of infrared imaging systems. Chalcogenide glasses have excellent infrared transparency, good rheological property, and large refractive index range, making them preferred materials for infrared GRIN lenses. In this work, aiming to find thermally matched chalcogenide compositions with high refractive index contrast for preparing GRIN glasses by the stacking diffusion approach, we investigated characteristic temperature, thermal expansion coefficient and refractive index of Ge‐As‐Se and Ge‐As‐Se‐Te glasses, optimized the glass compositions, and evaluated the feasibility of preparing GRIN glass using the optimized chalcogenide glass powders. It is found that Ge ₂₀ As ₂₀ Se ₂₀ Te ₄₀ and Ge ₁₂ As ₂₂ Se ₆₆ glasses have similar softening temperature (247°C vs. 249°C), reasonably difference of thermal expansion coefficient (3.8 ppm/K), and large refractive index contrast (∼.48). The glass powders with composition xGe ₂₀ As ₂₀ Se ₂₀ Te ₄₀ ‐(1‐x) Ge ₁₂ As ₂₂ Se ₆₆ can be hot‐pressed into glass disks with good transmittance at the same temperature and pressure. Graded refractive index profile is formed near the interface between the layers after the co‐pressed glass is thermally treated. These results demonstrate the prospect of the compositions for preparing infrared GRIN glasses.

The geometric decay factor, as an important part of the two-way reflection model, has an important modulating effect on the model. The integral geometric attenuation factor uses the normal distribution function of the microsurface elements for integration, which eliminates part of the unreasonable inflection point problem in the Blinn geometric attenuation factor in the curve. However, the integral geometric attenuation factor only considers the shading or shadowing effect under the same conditions, and the curve still has inflection points at the critical point between the shadowing and shading effects, especially at large incidence angles. To address these problems, under the same detection conditions, the detector detects a collection of reflected light from a large number of different microplane elements in the field of view, and the effects of masking and shadowing effects should be considered comprehensively. In the integral calculation of the reflected light from the microplane, it is necessary to assign the proportion of the incident light incident to each microplane element to the total incident light. The proposed modified integral geometric attenuation factor model, which is the product of the proportion of incident light striking the respective microplane element as a percentage of the incident light and the light intensity received by the detector from that surface as a percentage of the light intensity incident to this surface. The modified integral geometric attenuation factor model is compared with the integral geometric attenuation factor model, and the two-way reflection function curve of the modified integral geometric attenuation factor is compared with the measured two-way reflection function data by numerical simulation. The numerical simulation results show that the modified integral geometric attenuation factor model fits better with the measured two-way reflection function data, and can suppress the divergence trend of the integral model at large reflection angles.

Silver (Ag) thin films have garnered significant attention due to their unique optical properties. This paper systematically investigates the optical characteristics of Ag films prepared using the electron beam evaporation method. The investigation was conducted using spectroscopic ellipsometry and covers a broad wavelength range of 1679 nm to 36 µm (0.738–0.034 eV), spanning from near-infrared to far-infrared regions. Optical and dispersion models were developed to analyze the impacts of Ag nanostructures on the complex refractive indices, dielectric functions, and reflectance. The results indicate that Ag particles and coalescence films exhibit non-metallic and low absorption properties, while Ag percolation and continuous films present a typical Drude model. The reflectance of Ag films increases as the film coverage ratio increases, and it can reach close to 100% in continuous film. Additionally, a non-destructive, non-contact, and vacuum-free means of confirming the percolation threshold of Ag films was proposed based on the slope of the imaginary part curve. This work is useful to guide simulations and provide a basis for the applications of Ag films in different fields.