Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-27-6-9115
Timestamp: 2019-04-21 16:26:26+00:00

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Polaritonic slot waveguides have been explored as a means of manipulating nanoscale fields to compete in the race for the sub-diffractional confinement of light. Hexagonal boron nitride (h-BN), when incorporated into hyperbolic-insulator-hyperbolic (HIH) configurations, is a strong contender, with its naturally occurring anisotropy allowing it to strongly confine and enhance local fields. However, while the volumetric phonon polaritons of h-BN have been widely used for these means, its hyperbolic surface phonon polaritons (HSPhPs) or D’yakonov polaritons contain untapped potential and are widely unused. In this paper, we qualitatively discuss the hybridization of fundamental hyperbolic surface phonon polariton modes in an HIH slot waveguide. The resulting symmetric dark, or lower mode, is then used to design a patch antenn, which shows possibilities for applying the familiar microstrip transmission-line approach of antenna design to this HSPhP antenna.
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Fig. 1 (a) Dispersion curve of the SM0 mode of a semi-infinite h-BN slab with 0.6µm thickness. Inset shows the XY cross-sectional Re(Ey) of the waveguide which features the interaction between the two SM0 modes propagating along the Z direction on the YZ surfaces of h-BN waveguide at 1400cm−1. (b) Dispersion curve of the h-BN waveguide with 0.6µm thickness varied with the width of the waveguide from 0.1µm to 20µm at 1400cm−1.
Fig. 2 Normalized spatial distribution of the Y-component of electrical field, Re(Ey) for the fundamental (a) SM0-S and (b) SM0-A modes.
Fig. 3 Re(Ey) distribution of a slot waveguide with large separation between the h-BN waveguides (black rectangles) with (a) SM0-S lower, (b) SM0-S upper, (c) SM0-A lower and (d) SM0-A upper modes.
Fig. 4 Re(Ey) of (a) SM0-S lower, (b) SM0-S upper, (c) SM0-A lower, (d) SM0-A upper at 1400cm−1 for H = 0.6µm and W = 1.6µm. Insets show the H-field vector (red arrows) and E-field vector (blue arrows) of each hybrid mode.
Fig. 5 (a) Normalized energy density along x = 0 [dashed line in inset] for T = 50nm and H = 0.6µm shows the confinement and enhancement in the SiO2 layer. The shaded orange and blue areas represent the SiO2 and h-BN regions, respectively. (b) Re(Ey) of the hybrid SM0-S lower mode and (c) Re(Ey) of the hybrid volumetric mode with magnetic field vector (red arrows) and electric field vector (blue arrows).
Fig. 6 (a) Real index nsemi-inf of the hybrid SM0-S lower mode of a semi-infinite h-BN slot waveguide when H = 0.6µm from 1380cm−1 to 1520cm−1. Inset shows the normalized Re(Ey) distribution of the SM0-S lower mode for a semi-infinite h-BN slot waveguide at 1400cm−1. (b) Analytically fitted and simulated real effective index neff of the SM0-S lower slot-waveguide mode versus the width, W1 for different values of h-BN waveguide thickness H (colored lines) and with SiO2 thickness T = 50nm at 1400cm−1.
Fig. 7 Configuration of hybrid h-BN slot waveguide fed h-BN patch antenna. The SiO2 layer is shown in orange, while the h-BN layers are shown in blue with optical axis (OA) indicated by the red arrow. W1 and W2 are the widths of the h-BN slot waveguide and h-BN patch antenna, respectively, L is the length of h-BN patch antenna and H and T are the thicknesses of the h-BN layer and the SiO2 layer, respectively.
Fig. 8 Re[Ey(z)] and Re[Ez(z)] at the center of the SiO2 layer along the Z-axis for the hybrid SM0-S lower slot waveguide with W1 = 1µm and H = 0.6µm at 1400cm−1.
Fig. 9 Normalized Re(Ey) in the slot of the hybrid SM0-S lower slot waveguide fed h-BN patch antenna. Inset shows the electric field vectors in the SiO2 layer in the YZ plane.
Fig. 10 (a) Radiation field of the h-BN slot waveguide fed h-BN patch antenna and (b) the ratio of the reflected wave power due to the impedance mismatch to the guided wave power in the slot waveguide, S11.

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