利用啁啾飞秒激光脉冲调控金薄膜中传输表面等离激元的群延迟色散

Tailoring group delay dispersion of surface plasmon polaritons propagating on thin gold film by chirped femtosecond laser pulses

准确评估与灵活调控表面等离激元(surface plasmon polaritons,SPP)的传输特性对基于等离激元效应设计的高速-小型化器件具有重要意义.本文从理论上推导了SPP在不同厚度金膜表面传播的群速度色散.当金膜厚度小于40 nm时,随着膜厚度的增大,SPP的群速度色散显著减小;金膜厚度为40-60 nm时,SPP的群速度色散下降趋势变缓,并在厚度大于60 nm后保持恒定.利用时域有限差分方法,数值模拟了不同传播距离下SPP的电场时间演化.通过比较不同传输距离下SPP近场强度与入射光色散量的关系确定SPP的群速度色散,并得到接近理论推导的结果,进而提出利用负啁啾脉冲激发SPP来补偿传输中产生的群延迟色散,实现不同传输距离SPP场振幅、脉宽的调控.此外,利用定制的SPP激发金属纳米天线,通过调控入射脉冲色散量与SPP在金膜中传播产生群延迟色散的传播特性相结合的手段,实现在纳米信号接收器中热点位置的fs时间灵活时空相干控制.这对于利用等离激元效应设计和控制微型片上集成系统具有重要意义.

Understanding the propagation characteristics of surface plasmon polaritons(SPPs)is of great significance in designing and constructing on-chip integrated systems utilizing plasmonic effect.Accurately characterizing and flexibly controlling SPP on thin metal film are indispensable.Here,we theoretically derive the group velocity dispersion of SPP propagation on the surface of Au films with various thicknesses.The results obtained in this work indicate that when the thickness of the Au film is less than 40 nm,group velocity dispersion of SPP decreases significantly as the film thickness increases.The decrease of group velocity dispersion becomes mild with the thickness increasing from 40 nm to 60 nm,then the dispersion keeps a very low constant value for the film thicker than 60 nm.Using the finite-difference time-domain method,temporal evolution of localized electric field of SPP is numerically simulated for various propagation distances.By comparing the field amplitudes and the dispersions of SPP which are excited by incident light pulses with different dispersions,group velocity dispersions of SPP on the Au films are obtained,showing a good consistence with the theoretical results.Moreover,we demonstrate that by utilizing the tailored SPP to excite metal nanoantenna,selective excitations at different frequencies on a femtosecond temporal scale can be achieved through localized surface plasmonic resonant effect.Manipulating the sign and amount of the dispersion from the incident pulse,the active control of the switching sequence and switching time of electric field between the Au cylinders can be achieved.Manipulating the propagation distance of SPP,the active control of the switching time of electric field between the Au cylinders can be achieved.Therefore,those results provide a promising avenue for realizing functions such as signal propagation,reception,adjustment,and encoding in on-chip interconnect circuit systems based on SPP.This work shows that the dispersion can be used as degree of freedom for controlling the amplitude,phase and pulse width of SPP propagating on thin film,and it is of great importance in designing and controlling on-chip integrated systems through utilizing plasmonic effect,such as ultrafast frequency demodulators and nanoantennas in on-chip interconnect optical circuits.