Abstract
Abstract Exploiting multiple near-field optical eigenmodes is an effective means of designing, engineering, and extending the functionalities of optical devices. However, the near-field optical eigenmodes of subwavelength plasmonic nanostructures are often highly multiplexed in both spectral and spatial distributions, making it extremely difficult to extract individual eigenmodes. We propose a novel mode analysis method that can resolve individual eigenmodes of subwavelength nanostructures, which are superimposed in conventional methods. A transmission matrix is constructed for each excitation wavelength by obtaining the near-field distributions for various incident angles, and through singular value decomposition, near-field profiles and energy spectra of individual eigenmodes are effectively resolved. By applying transmission matrix analysis to conventional electromagnetic simulations, we clearly resolved a set of orthogonal eigenmodes of single- and double-slot nanoantennas with a slot width of 20 nm. In addition, transmission matrix analysis leads to solutions that can selectively excite specific eigenmodes of nanostructures, allowing selective use of individual eigenmodes.
Highlights
Optical nanocavities have provided effective channels for strong interaction between light and matter in small spaces owing to their excellent ability to confine light energy in nanometer-scale space
Metal-based plasmonic nanocavities allow the realization of subwavelength nanocavities beyond the diffraction limit by utilizing surface plasmon polaritons (SPPs)
We provide a theoretical framework for the energy spectrum and near-field profile of each eigenmode superimposed by the other eigenmodes to be resolved through singular value decomposition (SVD) of the T-matrix
Summary
Optical nanocavities have provided effective channels for strong interaction between light and matter in small spaces owing to their excellent ability to confine light energy in nanometer-scale space. We constructed a fully phase-referenced far-to-near-field transmission matrix (T-matrix) at a single wavelength and observed the decomposed near-field eigenmodes through singular value decomposition (SVD) of the measured matrix These experimental observations indicated the potential to develop a novel mode decomposition method that can effectively resolve the spatio-spectrally complex eigenmodes of subwavelength nanostructures experimentally and through simulations. We developed a new mode analysis method based on a T-matrix, which can effectively resolve spatio-spectrally multiplexed eigenmodes of subwavelength nanostructures. By applying the T-matrix-based mode analysis method to a finite-difference time-domain (FDTD) simulation, we achieved a clear decomposition of energy spectra and near-field profiles of high-order eigenmodes of single- and double-slot nanoantennas with a slot width of 20 nm. The T-matrix-based mode analysis method leads to solutions of incident beam wavefronts that can selectively excite specific eigenmodes of nanostructures, allowing us to selectively use individual eigenmodes of subwavelength nanostructures
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