Recently, Ma Shunbao (first author), a master's student in our laboratory, and Researcher Dai Shixun (corresponding author) published a paper titled "Low-power fiber-coupled acousto-optic modulator with high diffraction efficiency based on novel Ge-Sb-S glass featuring enhanced laser-induced damage threshold" in the Journal of Alloys and Compounds (IF=6.2) [1050 (2026) 185671]. The paper is available at: https://doi.org/10.1016/j.jallcom.2025.185671

       As core components in beam steering, optical scanning, and Q-switching applications, acousto-optic modulators (AOMs) directly determine the overall performance of optoelectronic systems. Conventional acousto-optic materials such as TeO₂ crystals and fused silica exhibit inherent limitations in practical applications. Although TeO₂ possesses excellent acousto-optic coefficients, its strong anisotropy and thermal expansion mismatch often lead to structural cracking under high-power laser irradiation. Fused silica, despite its good thermal stability, suffers from a low acousto-optic figure of merit            (M² = 1.51 × 10^-18 s³/g), limiting its applicability in high-efficiency, low-power modulation scenarios. Chalcogenide glasses (ChGs) have emerged as promising candidates for novel infrared acousto-optic materials due to their high refractive indices, broad infrared transparency, and excellent acousto-optic properties. However, traditional arsenic-based chalcogenide glasses (such as As₂S₃ and As₂Se₃) pose environmental and health concerns, and their relatively low glass transition temperatures (Tg < 190 ℃) and poor mechanical durability render them unsuitable for high-power applications.

       To address the above challenges, this study systematically investigated the thermomechanical, optical, acoustic, and acousto-optic properties, as well as the laser-induced damage threshold, of Ge39-xSbxS61 (x = 5, 15, 24, 34 mol%) glasses. By precisely tailoring the Ge/Sb ratio, the intrinsic composition-structure-property relationships were elucidated. Experimental results demonstrate that Ge15Sb24S61 glass exhibits the most excellent comprehensive performance: an acousto-optic figure of merit of 251.2 × 10-18 s3/g (approximately 166 times that of fused silica), a high laser-induced damage threshold of 3.92 J/cm2 under 1550 nm nanosecond laser irradiation (2.2 times that of Ge20Sb15Se65), low ultrasonic attenuation of 5.3 dB/cm at 100 MHz, and a moderate thermo-optic coefficient of 26.5 × 10-6/℃. Furthermore, this composition lies near the center of the Ge-Sb-S ternary glass-forming region, favoring compositional stability and reproducibility for large-scale fabrication.

Based on the optimized Ge15Sb24S61 glass, the research team, in collaboration with the 26th Research Institute of China Electronics Technology Group Corporation, successfully developed a fiber-coupled acousto-optic modulator operating in the 1550 nm band (as shown in Fig. 1). After applying a double-layer ZrO2 anti-reflective coating, the glass transmittance increased from 68.2% to 99.5% (as shown in Fig. 2). The device employs a LiNbO3 piezoelectric transducer with a Cr/Au/Sn multilayer electrode layer to achieve acoustic impedance matching with the glass medium, ensuring efficient coupling of ultrasonic energy. Performance characterization demonstrates that the modulator achieves a diffraction efficiency of 78.88% at an ultra-low RF driving power of 0.35 W, with rise and fall times of 43 ns and 47 ns, respectively, an insertion loss of 2.42 dB, and an extinction ratio as high as 59 dB (as shown in Fig. 3). The overall performance is comparable to common commercial AOMs, with significant advantages in power consumption.

To further validate the practicality and stability of the device, the research team constructed an actively Q-switched fiber laser system based on this modulator (as shown in Fig. 4). Experimental results show that as the repetition rate increases from 10 kHz to 30 kHz, the pulse width increases from 460 ns to 1024 ns, with stable pulse trains and energy fluctuation less than 0.5%. After introducing the modulator, the beam quality M² exhibits minimal degradation (M_x²: 1.020 → 1.029, M_y²: 1.031 → 1.035), demonstrating that the modulator introduces negligible wavefront distortion during dynamic modulation (as shown in Fig. 5).

This study successfully developed a novel arsenic-free chalcogenide glass combining high acousto-optic figure of merit, high laser-induced damage threshold, and low acoustic attenuation. Based on this material, a low-power, high-efficiency, high-stability fiber-coupled acousto-optic modulator was fabricated, providing a new material platform for next-generation high-performance acousto-optic devices with significant application prospects in fiber-optic communications, laser modulation, and high-power laser applications.

Fig. 1. Ge₁₅Sb₂₄S₆₁ glass-based fiber-coupled AOM: (a) Photograph of the device (inset: RF driver); (b) Internal structural diagram; (c) Structural diagram of the transducer bonding process.

Fig. 2. Transmittance spectra of Ge₁₅Sb₂₄S₆₁ glass before and after coating.

Fig. 3. Ge₁₅Sb₂₄S₆₁ glass-based fiber-coupled AOM: (a) variation curve of diffraction efficiency with RF power; (b) Time-resolved optical response; (c) Optical pulse rise/fall time.

Fig. 4. Q-switching verification setup for fiber-coupled AOM based on Ge₁₅Sb₂₄S₆₁ glass.

Fig. 5. (a) Pulse width variation under different pump powers; (b) Pulse sequence at 10, 20, and 30 kHz repetition rates; (c) Single-pulse profiles at 10, 20, and 30 kHz repetition rates; (d) M² measurement and beam profile.