基于周期性光栅结构的表面等离激元探测

表面等离激元具有突破光学衍射极限、局域场增强等特点,有望代替电子和光子作为信号载体,综合光学系统的高带宽特性与电子系统的紧凑性,构建新一代高速、高集成化的光电集成电路。为了有效探测表面等离激元,基于时域有限差分法提出一种基于周期性光栅的平面型表面等离激元探测结构模型,其中包括耦合光栅、条形波导以及探测光栅。首先简要阐述了探测结构的工作原理,并建立了工作在670,1310和1550 nm波段的仿真模型;同时研究等离激元耦合效率随入射光偏振角度的变化以及等离激元吸收率与波导长度的关系;最后实验制备了相应的表面等离激元探测结构。结果表明:表面等离激元的耦合效率与偏振角度成余弦平方关系;在670 nm波段,吸收率在波导长度为5μm的条件下为4.3%,衰减长度为17.1μm,与表面等离激元传播长度的理论值17.5μm基本吻合;实验测得的光电流随偏振角度的变化趋势与仿真的吸收率变化趋势一致,证实了上述模型能够实现对表面等离激元的有效探测。所提出的表面等离激元探测结构模型为将来高速、集成化的新型光电集成电路提供了理论和实验基础。

Detection of surface plasmons based on periodic grating structure

Owing to the ability of surface plasmons to circumvent the optical diffraction limit and ultra-fast transmission speed, they are expected to replace electrons and photons as signal carriers in the construction of next-generation high-speed, highly integrated optoelectronic integrated circuits. They can integrate the high bandwidth characteristics of the optical system with the compactness of the electronic system. However, the detection of surface plasmons is difficult. In this study, a simulation model that includes a grating coupler, strip waveguide, and detecting grating was established based on the finite-difference time-domain method for detection surface plasmons both in the visible and optical-communication bands. We first analyzed the operation principle of the proposed detection structure and established three simulation models operating at 670, 1310, and 1 550 nm. Next, the relationship between the coupling efficiency and polarization angle of the incident light was analyzed along with that between the absorption efficiency and waveguide length. Finally, the detection structure was experimentally prepared according to the simulation models. The results reveal that the coupling efficiency exhibits a cosine squared relation with the polarization angle. In the case of a 5-μm waveguide, the absorption efficiency is 4.3% at 670 nm and its attenuation length is calculated as 17.1 μm, which is consistent with the theoretical value of the propagation length(17.5 μm). Furthermore, the variation trend of the photocurrent with polarization angle obtained through experiments matched with the absorption efficiency in simulations. The detection structure is proved to effectively detect the surface plasmons. The proposed models for detecting surface plasmons provide theoretical and experimental bases for future high-speed and integrated plasmonic interconnect circuits.