image: Figure | Concept and performance of liquid-like chalcogenide glass for high-power mid-infrared optics bonding. a, Optical and rheological properties of the liquid-like As-S(Se)-I glass. Transmission spectra and viscosity–temperature curves demonstrate excellent mid-infrared transparency (0.7-10 µm) and fluidic behavior with a steep viscosity decrease above 50 °C. Insets show the transparent glass sample and its remarkable flexibility at elevated temperature. b, Bonding process and mechanical reliability of the liquid-like glass adhesive. Schematic illustration of the bonding procedure where the preheated liquid glass is applied between optical substrates and solidifies upon cooling, forming a conformal high-index interface. The bonded assemblies exhibit strong shear and tensile strengths, confirming robust mechanical adhesion suitable for optical component integration. (c), High-power laser delivery through liquid-glass-bonded fiber endcaps. Illustration and experimental setup of fiber–lens bonding using the liquid-like glass, achieving improved delivery efficiencies of 70.5 % at 2.94 µm and 80.1 % at 4.7 µm, with a maximum output power of 11.7 W. Long-term cycling tests verify thermal and optical stability over more than 200 heating–cooling cycles.
Credit: Xunsi Wang et al.
High-power mid-infrared (MIR) laser systems have shown tremendous promise in spectroscopy, sensing, imaging, and industrial processing. However, their efficiency and reliability are still limited by the lack of robust optical interconnection technologies capable of low-loss and high-power delivery. This challenge stems primarily from the high Fresnel reflection at the interface of high-refractive-index elements and the narrow optical application range of traditional organic adhesives in mid-infrared optics. Existing approaches—such as anti-reflection coatings or fusion splicing—either suffer from low laser-damage thresholds or lack compatibility across dissimilar materials, posing significant barriers to compact integration and power scaling of MIR photonic systems.
In a new paper published in Light: Science & Applications, a research team led by Professor Shixun Dai, Xunsi Wang and Rongping Wang from Ningbo University, together with collaborators from Renmin University of China, the University of Southampton, and The Australian National University, report a breakthrough in solving this long-standing bottleneck. They have developed a liquid-like chalcogenide glass adhesive with an ultralow glass transition temperature (below 10 °C), a high refractive index (n≈2.1), and excellent MIR transparency. This unique material enables seamless bonding of lenses, fibers, and other optical components, dramatically improving transmission and power delivery while maintaining long-term thermal and mechanical stability.
The scientists demonstrate that using liquid-like glass as an optical adhesive increases transmission between As2S3 and As2Se3 lenses from 36 % to 91 %, between As2S3 and CaF2 lenses from 62 % to 83 % and between Ge and CaF2 lenses from 47 % to 83 %. The bonded systems achieve laser power delivery up to 11.7 W at 4.7 μm, representing a 167-fold enhancement compared to conventional MIR film-coated optics. More impressively, the bonded devices remain stable over more than 206 heating–cooling cycles and continuous operation for three months, confirming exceptional durability under high-power conditions. The researchers summarize their concept as follows:
“We prepared a liquid-like chalcogenide glass with tunable viscosity and refractive index, enabling it to fully fill interfacial gaps at modest temperatures and then solidify into a robust glass bond upon cooling. This process not only minimizes Fresnel losses but also significantly increases the damage threshold, achieving both optical and mechanical integrity simultaneously.”
“Compared with conventional polymer adhesives, our inorganic bonding glass uniquely combines the flexibility of a liquid with the durability of a solid, offering an ultrawide operational window that conventional optical glues cannot achieve. It enables efficient coupling of heterogeneous mid-infrared optical components, thereby realizing compact integration and reliable high-power transmission.” they added.
“This breakthrough paves the way for the compact integration of mid-infrared optical systems and may revolutionize how we connect, seal, and package high-index infrared components for next-generation photonics. We anticipate it will drive the rapid development of future high-performance infrared photonic devices and systems,” the researchers forecast.
Journal
Light Science & Applications
Article Title
Breaking the mid-infrared interconnection barrier: a robust bonding for high-power optics based on liquid-like chalcogenide glass