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Controlling the emission efficiency, direction, and polarization of optical sources with nanoantennas is of crucial importance in many nanophotonic applications. In this article, we design a subwavelength multilayer metal–dielectric nanoantenna consisting of three identical gold strips that are separated by two dielectric spacers. It is shown that a local dipole source can efficiently excite several hybridized plasmonic modes in the nanoantenna, including one electric dipole (ED) and two magnetic dipole (MD) resonances. The coherent interplay between the ED and MDs leads to unidirectional emissions in opposite directions at different wavelengths. The relative phase difference between these resonant modes determines the exact emission direction. Additionally, with a proper spacer thickness and filling medium, it is possible to control the spectral positions of the forward and backward unidirectional emissions and to exchange the wavelengths for two unidirectional emissions. An analytical dipole model is established, which yields comparable results to those from the full-wave simulation. Furthermore, we show that the wavelength of the peak forward-to-backward unidirectionality is essentially determined by the MD and is approximately predictable by the plasmonic wave dispersion in the corresponding two-dimensional multilayer structure. Our results may be useful to design dual-band unidirectional optical nanoantennas.

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A high-k dielectric conduction enhancement SOI LDMOS is proposed and investigated by simulation. The high-k dielectric pillars are located at sidewalls of the drift region. The high-k dielectric assists the self-adapted depletion in the drift region, reshapes the electric field distribution, and makes the three-dimensional RESURF effect realized in a high-voltage blocking state. Dependences of the breakdown voltage (VB) and the specific on-resistance (Ron,sp) on device parameters are exhibited using three-dimensional simulation. Simulation results show that the proposed structure increases VB by 16%–18% and decreases Ron.sp by 13%–20%, compared with the conventional super-junction SOI LDMOS. Furthermore, the charge-imbalance caused by the substrate-assisted depletion effect is alleviated.

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