Abstract
We propose a novel SPP coupling scheme capable of high SPP throughput and high SPP coupling efficiency based on a slit of width greater than the wavelength, immersed in a uniform dielectric. The dispersive properties of the slit are engineered such that the slit sustains a low-loss higher-order waveguide mode just above cutoff, which is shown to be amenable to wavevector matching to the SPP mode at the slit exit. The SPP throughput and SPP coupling efficiency are quantified by numerical simulations of visible light propagation through the slit for varying width and dielectric refractive index. An optimal SPP coupling configuration satisfying wavevector matching is shown to yield an order-of-magnitude greater SPP throughput than a comparable slit of sub-wavelength width and a peak SPP coupling efficiency ≃ 68%. To our knowledge, this is the first investigation of coupling between higher-order waveguide modes in slits of super-wavelength width and SPP modes.
Highlights
Surface-plasmon-polariton (SPP) modes, transverse-magnetic (TM) electromagnetic waves that exist at a metal-dielectric interface, hold promise for the miniaturization of optical devices [1, 2]
We show that the TM1 mode just above cutoff is advantageous for SPP coupling because it possesses a transverse wavevector component that is larger than that achievable with a TM0 in a slit of sub-wavelength width
The numerical simulations provide evidence of high-throughput and high-efficiency SPP coupling from a slit of super-wavelength width
Summary
Surface-plasmon-polariton (SPP) modes, transverse-magnetic (TM) electromagnetic waves that exist at a metal-dielectric interface, hold promise for the miniaturization of optical devices [1, 2]. Plane-wave modes directly incident onto a metal-dielectric interface cannot efficiently couple into SPP modes due to a mismatch between the SPP wavevector and the component of the plane-wave wavevector along the interface. Scatterers have been used to bridge the wavevector mismatch between plane-wave and SPP modes. When a scatterer is illuminated, enhancement of the incident plane-wave wavevector along the metal-dielectric interface by the Fourier spatial frequency components of the scatterer geometry in the plane of the interface enables wavevector matching between the incident light and the SPP mode. When a slit is illuminated by a TM-polarized plane wave, a small portion of the incident wave excites a guided mode in the slit. The throughput and efficiency of a slit are highly dependent on the width of the slit relative to the wavelength of the incident plane wave. We showed in our previous work [3] that the SPP coupling efficiency of a sub-wavelength slit is increased up to
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