Wang Wenkang, Wang Qi, Sun Ronglei, Han Ya, Cheng Rui
Opt Express. 2023 Oct 23;31(22):35864-35879. doi: 10.1364/OE.502289.
It is shown that the thermo-optic (TO) coefficients of various waveguide modes of a sub-wavelength grating (SWG)-assisted strip waveguide is closely dependent on the various waveguide parameters with different dependencies, including the SWG width, strip waveguide width, duty cycle, and pitch. This offers what we believe to be new degrees of freedom in the design of TO coefficients for integrated-optic waveguides, opening the door to engineering the TO coefficients of individual spatial modes or polarization states using sub-wavelength structures. Such a capability is expected to offer new design possibilities for a variety of integrated photonic, thermo-optic devices. To demonstrate the application of the concept, a mode-insensitive switch on silicon-on-insulator using a TO coefficient-engineered SWG as a mode-independent, thermo-optic phase shifter is designed and experimentally demonstrated. The experimental results show that the switching powers of the TE0-TE2 modes are only ∼29 mW, and the maximum extinction ratios for the cross (bar) states are 38.2 dB (31 dB), 37.9 dB (37 dB), and 31.9 dB (20.5 dB) for the TE0-TE2 modes, respectively, at the wavelength of 1550 nm.
结果表明，亚波长光栅（SWG）辅助条形波导的各种波导模式的热光（TO）系数与各种波导参数密切相关，且依赖关系各不相同，这些参数包括SWG宽度、条形波导宽度、占空比和节距。这为集成光波导的TO系数设计提供了我们认为的新自由度，为利用亚波长结构设计单个空间模式或偏振态的TO系数打开了大门。这种能力有望为各种集成光子热光器件提供新的设计可能性。为了演示该概念的应用，设计并通过实验展示了一种基于绝缘体上硅的模式不敏感开关，该开关使用经过TO系数工程设计的SWG作为与模式无关的热光相移器。实验结果表明，在1550 nm波长下，TE0 - TE2模式的开关功率仅约为29 mW，TE0 - TE2模式的交叉（条形）状态的最大消光比分别为38.2 dB（31 dB）、37.9 dB（37 dB）和31.9 dB（20.5 dB）。
