A multilayer metal-insulator (MMI) stack system is viewed as an anisotropic metamaterial to exhibit plasmonic behavior
and a candidate of "metametal". The dispersion of the fundamental super mode propagating along the boundary between
an MMI stack and a dielectric coating is theoretically studied and compared to that of surface waves on a single metalinsulator
boundary. The conditions to obtain artificial surface plasmon frequency are thoroughly investigated, and the
tuning of effective surface plasmon frequency is verified by electromagnetic modeling. The design rules would bring
important insights into layer-by-layer metamaterial development related to superlenses, optical lithography, nanosensing
and imaging.
We demonstrate integrated plasmonic devices on silicon-on-insulator (SOI) substrate for photon-plasmon conversion
and plasmonic mode transformation at near-infrared frequency. The plasmonic junction converts photons to surface
plasmons and then back to photons with 7.35 dB conversion loss, and has successfully focused multimode plasmonic
propagation to deep subwavelength (80 nm by 50 nm) single mode propagation with 2.28 dB/μm propagation loss. The
integration approach leads to a robust and versatile platform for 3D nanoplasmonic gauges potentially functional in
ultra-fast communications and optical sensing.
Due to the large transverse mode size in the frequency regime far below plasma frequency, some important applications
of surface plasmons in the THz or microwave frequency regime have been limited where deep subwavelength optical
devices are a critical technique. Here we experimentally demonstrated focusing and guiding electromagnetic (EM) waves
in a 3D spoof surface plasmonic waveguide, which is a row of rectangular rods patterned on an aluminum slab. The
maximum of the mode size can be mapped in the middle plane of two neighboring rods. The mode size slightly varies
with different frequencies and minimizes at 0.04λ-by-0.03λ at 2.25 GHz. Moreover, due to the tight binding of surface
waves, the decrease of the waveguide width does not significantly affect the dispersion of the guided modes. This fact
enables the mode tapering in the transverse direction from a wide waveguide into deep subwavelength waveguide with
high efficiency. To this end, a tapered spoof surface plasmonic waveguide was fabricated as the input is the uniform
spoof surface plasmonic waveguide and its performance was investigated in experiments. From the experimental results,
as the EM waves propagate in the taper, the mode size becomes smaller and smaller with the intensity gradually
increasing, and eventually EM waves are coupled into the deep subwavelength mode.
We propose integrated waveguides for terahertz (THz) and mid-infrared (MIR) applications on wafer platform. Based on
the prototype of spoof plasmonic waveguides consisting of textured metallic surface, we explore the possibility of
coating periodic metallic pattern with silicon (at 0.6 THz) or germanium (at MIR region of 30 THz) to further shrink the
relative mode size of propagation spoof plasmonic waves. Numerical modeling via 3D finite-difference time-domain
(FDTD) has shown deep sub-wavelength mode confinement in transverse directions to smaller than λ/50 by λ/50, with an
estimated propagation loss of less than 0.1 dB for each repetitive unit.
We propose a "slot-to-slot" coupler to convert power between optical and metal-insulator-metal (MIM) plasmonic
modes. Coupling efficiency of larger than 60% is obtained from 2D FDTD simulation. Based on this prototype, a quasi-MIM plasmonic junction is demonstrated using e-beam lithography onto an SOI substrate. The junction is formed by
depositing a thin layer of gold (~20 nm) on part of a dielectric slot. When probed by 1520-nm laser, coupling efficiency
of 36% is achieved for a 500-nm long quasi-MIM junction. Optical modulation is under investigation by pumping the
device using visible light to change the optical property of gold.
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