Tailoring the group delay dispersion of surface plasmon polaritons propagating on thin gold film using chirped femtosecond laser pulse

Abstract

Comprehending the propagation characteristics of surface plasmon polaritons (SPP) holds paramount importance for 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 film with varying thicknesses. These results 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 become mild with the thickness increasing from 40 nm to 60 nm, then the dispersion keeps at extremely low value with a constant 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 amplitude and the dispersion of SPP that excited by incident light pulse with different dispersion, group velocity dispersion of SPP on the Au film is obtained, which get a well consistence with the theoretical result. Moreover, we have demonstrated that by utilizing the tailored SPP to excite metal nanoantenna, selective excitation at different frequencies in femtosecond temporal scale can be achieved through localized surface plasmonic resonant effect. Manipulating the sign and amount of the dispersion from the incident pulse, 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, active control of the switching time of electric field between the Au cylinders can be achieved. It provides a promising avenue for realizing functionalities such as signal propagation, reception, adjustment, and encoding in on-chip interconnect circuits systems based on SPP. This work shows that the dispersion can be as degree of freedom for controlling the amplitude, phase and pulse width of SPP propagating on thin film, and it is significant importance for the design and control of on-chip integrated systems utilizing plasmonic effect, such as ultrafast frequency demodulators as well as nanoantenna in on-chip interconnect optical circuits.