Abstract
We propose and investigate, both experimentally and theoretically, a novel mechanism for switching and modulating plasmonic signals based on a Fano interference process, which arises from the coupling between a narrow-band optical Fabry–Pérot cavity and a surface plasmon polariton (SPP) source. The SPP wave emitted from the cavity is actively modulated in the vicinity of the cavity resonances by altering the cavity Q-factor and/or resonant frequencies. We experimentally demonstrate dynamic SPP modulation both by mechanical control of the cavity length and all-optically by harnessing the ultrafast nonlinearity of the Au mirrors that form the cavity. An electro-optical modulation scheme is also proposed and numerically illustrated. Dynamic operation of the switch via mechanical means yields a modulation in the SPP coupling efficiency of ~80%, while the all-optical control provides an ultrafast modulation with an efficiency of 30% at a rate of ~0.6 THz. The experimental observations are supported by both analytical and numerical calculations of the mechanical, all-optical and electro-optical modulation methods.
Highlights
The implementation of energy-efficient and ultrafast functionalities for the generation and control of electromagnetic radiation in nanoscale devices represents a prerequisite for the development of ultra-integrated photonic circuits
To utilize the cavity as a modulating element for surface plasmon polariton (SPP) signals, the illuminating light can be delivered to the cavity either through a slit, which acts as the SPP source, placed in the waveguide (Figure 1b) or through the semi-transparent mirror (Figure 1c)
Without strongly affecting SPP modes at the Au/air interface, we numerically investigated a multilayer serving as the upper mirror, which consists of two gold films, acting as electrodes, separated by layers of indium tin oxide (ITO) and HfO2 (Figure 5a)
Summary
The implementation of energy-efficient and ultrafast functionalities for the generation and control of electromagnetic radiation in nanoscale devices represents a prerequisite for the development of ultra-integrated photonic circuits. Together with hybrid plasmonic–dielectric structures, enable strong light–matter interaction, thereby allowing the realization of small-footprint, low-power and high-efficiency switches and modulators of optical signals in an integrated manner[1]. Such components have been achieved by incorporating electro-optic or nonlinear materials[2], quantum dots and photochromic molecules into plasmonic structures[3,4] to increase weak refractive or absorptive changes of the functional media. Using the nonlinearity of plasmonic metals and adjacent dielectrics, several approaches to switching and modulation have been investigated, including controlling the dispersion of Bloch modes in plasmonic crystals[6,7], manipulating the coupling efficiency to surface plasmon polariton (SPP) modes[8] and optically modulating plasmonic losses of an aluminum SPP waveguide[9]
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