基于表面等离子体器件的非线性效应研究

Optical Nonliearity is the nonlinear response of the polarization from the electric field. Only when light is sufficiently intense to modify the optical response of a material system, the nonlinear parts of the polarization come to effect. Thus, it is of great interest to enhance the nonlinear effects so as to ease the requirement for extremely intense light source. Surface plasmons (SP) are coherent electron oscillations that exist at the interface between any two materials where the real part of the dielectric constant changes sign across the interface, e.g. a metal-dielectric interface. When SPs couple with a photon, the resulting hybridised excitation is called a surface plasmon polariton (SPP), an electromagnetic surface wave bounded to the interface and reaching its maximum at the interface. Devices based on SP excitations are called plasmonic devices. The advantages of applying plasmonic structures in the optical nonlinear system are threefold: First, the strong local electromagnetic fields can boost significantly the nonlinear responses. Second, extraordinary sensitivity to the surface can be exploited to control light with light. Third, femtosecond timescale of the responding time of plasmonic excitation allow ultrafast processing of signals. Thus, the main purpose of the present project is to ultilize plasmonic devices to enhance the nonlinear effects and exploit new functionalities of plasmonic devices. The main research contents include: (1) Establish numerical models to solve the nonlinear responses of SP devices, through combination of conventional numerical methods in the nano-photonic area. (2) In the nanometer or sub-nanometer scale, non-local effects are taken into account when analysing the nonlinear effects of the SP structures. (3) Study and optimize the third-harmonic generation enhanced by LSP excitations, implementation of this THG effect to improve the resolution in the tip-induced lithography will be studied. (4) Design all-optical switches based on LSP or SPP excitations, reduce the power consumption and the device footprint and raise the switching speed.

非线性效应通常需要在极大的功率密度下才能实现，本项目研究基于表面等离子体（SP）器件的非线性效应及其应用，通过表面场增强效应，降低功耗，提高集成度，并利用SP的高激发速度提高器件速度。研究内容主要包括：结合纳米光子学模拟手段，精确计算各种SP器件的非线性响应；在局部场束缚尺寸趋近极限时考虑非局域(Non-local)效应对金属介电常数的影响，修正受限制的场增强效果及非线性效应；研究基于局域化SP的三倍频效应，尝试将其应用于高分辨光刻；设计基于几类SP结构的集成型全光开关，优化开关速度、功耗等性能。本项目旨在利用SP的激发增强局部非线性响应，创新之处在于：在极限尺寸下引入非局域模型修正金属的极化强度，并且利用三倍频光强度正比于基频光强度三次方的关系提高光刻分辨率。本项目的开展在将SP结构应用于非线性光学方面作出一定的探索，在表面等离子体纳米光子器件上拓展更多功能与应用。

非线性效应通常需要在极大的功率密度下才能实现，本项目研究基于表面等离子体（SP）器件的非线性效应及其应用，通过表面场增强效应，降低器件功耗，提高集成度。研究内容主要包括：结合纳米光子学模拟手段，精确计算各种SP器件的非线性响应，在局部场束缚尺寸趋近极限时（如2纳米至20纳米）考虑非局域效应对金属介电常数的影响，得到了受非局域效应影响下更为精确的场增强效果及二次谐波响应，对设计非线性器件提供了有利的理论工具；研究基于局域化SP的三倍频效应，结合针尖增强效应将其应用于高分辨光刻，在使用波长1微米的基频光下可获得最小约10纳米的线宽，远高于衍射极限，对探索高分辨光刻技术具有积极的意义；优化各类型SP有源波导结构，在不严重影响模场尺寸和集成度的前提下减少了传输损耗，提高有源介质的增益效率，对设计基于SP结构的调制器、开关等有源器件提供了基础。