Abstract
As is well known, the on-chip waveguide with high Brillouin gain has many applications in the field of photonics. Brillouin lasers on silicon substrates are widely used in frequency tunable laser emission, mode-locked pulsed lasers, low-noise oscillators and optical gyroscopes. However, in a silicon-based Brillouin laser, a long waveguide length is still used to achieve Brillouin laser output, which is not conducive to on-chip integration. In this work is proposed a new type of waveguide structure consisting of chalcogenide As<sub>2</sub>S<sub>3</sub> rectangles and an air slit. Owing to the existence of the air gap, the radiation pressure makes the enhancement of Brillouin nonlinearity much higher than the enhancement caused only by the material nonlinearity. This makes the Brillouin gain reach 1.78 × 10<sup>5</sup> W<sup>–1</sup>·m<sup>–1</sup>, which is nearly 10 times larger than the previously reported backward SBS gain of 2.88 × 10<sup>4</sup> W<sup>–1</sup>·m<sup>–1</sup>, resulting in phonon frequency tuning in a 4.2–7.0 GHz range. This method provides a new idea for designing nano-scaled optical waveguides for forward stimulated Brillouin scattering, and at the same time, this enhanced broadband coherent phonon emission paves the way for improving the hybrid on-chip CMOS signal processing technology.
Highlights
图 1 (a) 悬浮波导系统的结构示意图; (b) 悬浮波导设计 图, t= 215 nm, w= 800 nm, 空气细缝长度s = 2 nm, 高 度 h = 213 nm; (c) 光学色散图示意图, 光共振由沿着整体色 散曲线 (实线) 的离散点 (红色和蓝色) 表示; (d) 泵浦光转 换为 Stokes 光和声子示意图. 图中 ks 和 kp 分别代表 Stoke 光和泵浦光的波矢 ; ws, wp, W分别代表 Stokes 光 、 泵 浦 光 以及产生的声子频率 Fig. 1. (a) Schematic diagram of the structure of the suspended waveguide system; (b) design drawing of floating waveguide, t = 215 nm, w = 800 m, air slit length s = 2 nm, height h=213 nm; (b) schematic diagram of optical dispersion diagram, optical resonance is represented by discrete points along the overall dispersion curve; (d) schematic diagram of pump light conversion to stokes light and phonons
了一种带有空气细缝的悬浮波导结构, 利用了空 气细缝所产生的巨大的 MB 效 应 (移动边界效应) 驱动前向 SBS 效应, 从而产生了高达 1.78 × 105 W–1·m–11 的巨大增益, 实现了 4.2—7.0 GHz 频 率可调谐
Summary
使得布里渊增益达到了 1.78 × 105 W–1·m–1, 相比之前报道的后向受激布里 渊散射 (SBS) 增益 (2.88 × 104 W–1·m–1) 扩大了将近 10 倍, 产生了 4.2—7.0 GHz 范围的声子频率调谐, 该方 法为设计用于前向 SBS 的纳米级光波导提供了新的思路, 同时这种增强的宽带相干声子发射为片上 CMOS 信号处理技术的混合铺平了道路. 2018 年, e Jouybari [12] 采用了带衬底的狭缝波导, 实现了 r 12127 W–1·m–1 的布里渊增益. 因此本文设计了一种特殊的悬浮波导, 通过正 向布里渊散射 (受激多模态布里渊散射), 将光场以 不同的光学空间模式进行耦合, 由于该波导结构的 特殊性, 使得 As2S3 的外表面全是空气层, 较大的 折射率差距将光场更好地限制在空气细缝中内, 实 现了较大的布里渊增益, 达到 1.78 × 105 W–1·m–1.
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