Brillouin lasers based on the SBS effect are widely used in fiber optic sensing, fiber optic gyro and coherent optical communication systems due to their narrow linewidth, good coherence, and stable output at multiple wavelengths. Currently, the SBS effect of various optical fiber is being used to make new types of Brillouin fiber lasers with high Brillouin gain. The Brillouin parameters of optical fiber depends on the substrate materials and fiber structure. The Brillouin frequency shift (v_B), linewidth (∆v_B) and gain coefficient (g_B) of fiber with varied material matrices are very different. CHG glass is widely used as a gain medium for Brillouin lasers because of its high refractive index, wide transparency range, high third-order nonlinear coefficient and better resistance to electromagnetic interference. However, the composition of ChG glass fiber based on SBS effect is mostly limited to As₂Se₃ and As₂S₃.The softening temperatures of these two substrate glasses are low, making it difficult for them to withstand high power laser pumping. Therefore, the selection of ChG systems and the optimization of compositions to explore novel substrate materials with high softening temperature and high Brillouin gain coefficients are of high importance.

    In this study, Two series of glasses, xGeSe₂-(100-x) As₂Se₃and Ge₃₀As_ySe_70-y were prepared. It is the first time to demonstrate that Ge-As-Se CHG glass is a promising substrate material for high Brillouin gain fibers in terms of both acousto-optical parameters and the stability of glass against crystallization. The study focuses on the estimation of Brillouin gain coefficients (g_B) based on the close relationship between known material acousto-optic parameters and Brillouin gain in Table 1. Theg_B of Ge₃₀As₂₀Se₅₀ (g_B= 33.77×10^-11m/W) was higher than that of the conventional arsenide glasses As₂Se₃ (g_B= 20.89×10^-11m/W) and As₂S₃ (g_B= 14.43×10^-11m/W). The acoustic attenuation of most glasses was lower than As₂S₃(401.6 dB/cm/GHz²) and As₂Se₃ (692.3 dB/cm/GHz²) at 100 MHz ultrasonic frequency As shown in Figure 1. All glasses had ΔT greater than 100 °C and had good stability against crystallization, providing a working basis for the next step of drawing the fiber. On the basis of Ge₃₀As₂₀Se₅₀ host glass, a high-purity chalcogenide single-refractive-index fiber was drawn with a minimum optical loss of 0.7 dB/m at 6.5 μm As shown in Figure 2. The above results provide an important reference for the further development of new ChG glass fiber with high g_B.

Table 1 Related parameters of  for glass samples.

                                    All parameters were measured at 1550 nm.

Fig. 1. Acoustic attenuation (α) and acoustic velocity (V_L) versus different content in (a) xGeSe₂-(100-x) As₂Se₃ glasses; (b) Ge₃₀As_ySe_70-y glasses.

Fig. 2. Optical loss spectrum of Ge₃₀As₂₀Se₅₀ glass fiber (inset image is the fiber cross-section)