二维硒化镓晶体辅助氮化硅波导的二阶非线性效应及器件

Relying on high transparency in a wide spectral range, capability of constructing multi-layer photonic structures, and compatibility with CMOS-processes, silicon nitride has great potentials to fabricate high-quality passive devices for photonic integrated chips. However, silicon nitride is a dielectric material, making it a challenge to realize active devices. This project proposes to integrate two-dimensional gallium selenide crystals onto silicon nitride waveguides to form hybrid waveguides, which could facilitate the achievements of second-order nonlinear effects and electro-optic devices. To achieve these, following major studies will be carried out: (1) Investigating linear and nonlinear coupling mechanisms of mode fields in the hybrid waveguides; (2) Realizing the double-frequency, sum-frequency, and difference-frequency parametric processes in the hybrid waveguides and studying the physical mechanisms; (3) Constructing hybrid waveguide-integrated electro-optic modulators and characterizing their performances. Three key scientific problems are required to be solved: (1) How to design the hybrid waveguides to achieve effective nonlinear interactions and couplings between the waveguiding modes and the integrated gallium selenide crystals; (2) How to satisfy phase-matchings in the optical parametric processes; (3) How to build the external electrical fields for the electro-optic modulators. The novelties of this proposal include: (1) Achieving the second order nonlinearity in silicon nitride waveguides based on the ultrahigh second order nonlinear coefficient of the two-dimensional gallium selenide crystal and its easy integration with optical waveguides; (2) Constructing electro-optic modulators on the silicon nitride waveguides with assistance of the linear electro-optic effect in gallium selenide; (3) Realizing optical parametric processes in two-dimensional crystals with low pump power, which is enhanced by the strongly confined optical field and long interaction distance of the waveguide. The results obtained from above studies are expected to not only provide a new routing for realizing active devices in silicon nitride, but also present possibilities to develop nonlinear optoelectronic applications in two-dimensional crystals.

氮化硅具有宽波段高透明度、支持多层光子结构且与CMOS工艺兼容等优点，可为光子集成芯片提供高质量被动器件，但其电介质性使主动器件的实现存在挑战。本项目提出在氮化硅波导上集成二维硒化镓晶体形成混合波导，使之引入强二阶非线性效应并实现电光器件。主要研究：①混合波导中模场线性和非线性耦合规律；②倍频、和频、差频过程的实现机制及物理规律；③集成的电光调制器构筑及性能。拟解决关键问题为：①支持模场与硒化镓高效非线性相互作用和耦合的波导结构设计；②参量过程的相位匹配；③电光调制器的外加电场构建。创新点有：①基于二维硒化镓晶体超高二阶非线性系数及与波导易集成性，辅助氮化硅波导的二阶非线性效应；②借助硒化镓的线性电光效应，构建混合波导电光调制器；③利用波导的强局域光场和长作用距离，实现二维晶体中低泵浦功率的光参量过程。研究成果有望为实现氮化硅主动器件提供新途径，也为开发二维晶体的非线性电光应用提供新思路。

氮化硅具有宽波段高透明度、支持多层光子结构且与CMOS工艺兼容等优点，可为光子集成芯片提供高质量无源器件，但其电介质性使其有源器件的实现存在挑战。本项目提出在氮化硅光子结构上集成二维晶体，引入强二阶非线性效应并实现光电器件。项目从二维晶体的新颖二阶非线性揭示、新型光子结构设计、二维晶体辅助光子结构实现二阶非线性响应以及有源光电器件等方面均取得进展，达到了预期的研究目标。. 取得结果有：①为选择合适的二维晶体，深入研究了几种二维晶体的二阶非线性响应；实验观测到少层二硫化铼、二碲化钼、碲纳米线中独特层数依赖的二阶非线性效应，并测得其二阶非线性系数分别高达900、2500 、12500 pm/V，并在中心反演对称的二硫化钼中掺杂钒实现层数无关的二阶非线性；②为克服原子层厚度的二维晶体和光相互作用弱、非线性转换效率低的问题，设计了几种新型共振腔，包括：设计并制备出品质因子高达105的光子晶体纳腔、基于两种不同的光子晶体纳腔交替耦合的SSH结构、具有准连续域束缚态的超表面结构，并验证了这些共振腔中共振模式对硅等材料二次谐波和三次谐波超三个数量级的强烈增强；③进一步，将二维晶体集成于光子结构上实现了多种仅需毫瓦级连续激光即可泵浦出的强烈二阶非线性参量过程；在氮化硅微环上集成少层硒化镓实现了最高849%/W（123%/W）的二次谐波（和频）转换效率；将少层硒化镓集成于光子晶体共振腔上，实现了高效率的二次谐波、和频、级联和频等；在准连续域束缚态的超表面上集成少层硒化镓，获得增强因子超600的二次谐波及和频；④在以上基础上，开展了有源光电器件研究，实现了集成于氮化硅波导且可以工作在通信波段的二硫化钼光电探测器、光子晶体微腔增强的黑磷、碲化钼光电探测器，集成于微光纤的石墨烯全光开关等。. 研究成果有望为实现氮化硅光子平台上有源器件提供新途径，也为开发二维晶体的非线性电光应用提供新思路。

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