Very sharp 90° micro-bends for adiabatic optical wave propagation in multimode waveguides are demonstrated by an inverse design method, and the devices are fabricated on a silicon-on-insulator platform. The compact bending structures are based on digital waveguide metastructures with footprints as small as $2.6\mathrm{\mu m}\times 2.6\mathrm{\mu m}$. For waveguides with widths of 2 μm and bending radii of only 1 μm, the ${\mathrm{TE}}_{00}$ mode is able to turn around the sharp corner with 1 dB loss and $>20\mathrm{dB}$ suppression ratio to higher-order modes. The transmission spectra of the devices are measured with $\sim 1\mathrm{dB}$ loss over a 40 nm bandwidth which are consistent with the numerical simulations.

中文翻译：

---

基于逆向设计的绝热绝热弯头

通过逆向设计方法展示了用于绝热光波在绝热光波中传播的非常尖锐的90°微弯，并在绝缘体上硅平台上制造了这些器件。紧凑的弯曲结构基于数字波导元结构，其占地面积小至$2.6\mathrm{微米}\times 2.6\mathrm{微米}$。对于宽度为2μm，弯曲半径仅为1μm的波导，${\mathrm{TE}}_{00}$ 模式能够以1 dB的损耗转过尖角，并且 $>20\mathrm{D\; b}$高阶模式的抑制比。器件的透射光谱用$〜\mathrm{1个}\mathrm{D\; b}$ 在40 nm带宽上的损耗与数值模拟一致。