We present a planar subwavelength spectral light separator, which sorts light by separating different spectral and polarimetric components into different channels in a snapshot, efficient, and angularly robust way. The device is composed of subwavelength-size rectangular aperture pairs, where each aperture pair consists of two perpendicularly-oriented identical apertures, in a metal film having deep-subwavelength-size thickness. The device is planar and ultrathin. It has subwavelength-size cross-section and deep-subwavelength-size thickness. Different aperture pairs simultaneously collect different spectral components of light, and different apertures of aperture pairs simultaneously collect different linear polarization components of light. The device operation is based on Fabry-Pérot-like localized resonances in the apertures and it does not rely on any periodicity or grating effect. Hence, the device can be used in an individual, nonperiodic, subwavelength-size configuration as well as in an array configuration composed of subwavelength-size unit cells. When aperture pairs are used as detecting elements, different spectral components of light can be detected independent of the polarization of light. When apertures instead of aperture pairs are used as detecting elements, different linear polarization components of light can be detected in addition to different spectral components. The operation of the device is largely independent of the incidence angle of light, which results in an angularly robust, wide-angle device. All these features are attractive for efficient, compact, snapshot spectral imaging systems, especially for multispectral imaging purposes. We show the operation of the device by examining its interaction with electromagnetic waves with the finite-difference frequency-domain (FDFD) method.
We design a non-parity-time-symmetric plasmonic waveguide-cavity system, consisting of two metal-dielectric-metal stub resonators side coupled to a metal-dielectric-metal waveguide, to form an exceptional point, and realize unidirectional reflectionless propagation at the optical communication wavelength. We also show that slow-light-enhanced ultra-compact plasmonic Mach-Zehnder interferometer sensors, in which the sensing arm consists of a waveguide system based on a plasmonic analogue of electromagnetically induced transparency, lead to an order of magnitude enhancement in the refractive index sensitivity compared to a conventional metal-dielectric-metal plasmonic waveguide sensor. Finally, we show that plasmonic coaxial waveguides offer a platform for practical implementation of plasmonic waveguide-cavity systems.
Waveguide-resonator systems are particularly useful for the development of several integrated photonic devices, such as
tunable filters, optical switches, channel drop filters, reflectors, and impedance matching elements. In this paper, we
introduce nanoscale devices based on plasmonic coaxial waveguide resonators. In particular, we investigate threedimensional
nanostructures consisting of plasmonic coaxial stub resonators side-coupled to a plasmonic coaxial
waveguide. We use coaxial waveguides with square cross sections, which can be fabricated using lithography-based
techniques. The waveguides are placed on top of a silicon substrate, and the space between inner and outer coaxial
metals is filled with silica. We use silver as the metal. We investigate structures consisting of a single plasmonic coaxial
resonator, which is terminated either in a short or an open circuit, side-coupled to a coaxial waveguide. We show that the
incident waveguide mode is almost completely reflected on resonance, while far from the resonance the waveguide mode
is almost completely transmitted. We also show that the properties of the waveguide systems can be accurately described
using a single-mode scattering matrix theory. The transmission and reflection coefficients at waveguide junctions are
either calculated using the concept of the characteristic impedance or are directly numerically extracted using full-wave
three-dimensional finite-difference frequency-domain simulations.
We show that the performance of iterative solvers of the frequency-domain Maxwell's equations is greatly affected
by the kind of the perfectly matched layer (PML) used. In particular, we demonstrate that using the stretchedcoordinate
PML (SC-PML) results in significantly faster convergence speed as compared with using the uniaxial
PML (UPML). Such a difference in convergence behavior is explained by an analysis of the condition number of
the coefficient matrices. Additionally, we develop a diagonal preconditioning scheme that significantly improves
solver performance when UPML is used.
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