Optical nanoantenna impedance matching and duality and hybrid surface phononic waveguide
This work contributes to critical requirements for optical and infrared nanoantenna and waveguide applications; 1) the impedance of an optical nanoantenna is addressed, and 2) long propagation lengths and high confinement waveguide is designed. Optical nanoantennas have been studied as a means to manipulate nanoscale fields, local field enhancements, radiative rates, and emissive directional control. However, a fundamental function of antennas, the transfer of power between a coupled load and far-field radiation, has seen limited development in optical antennas owing largely to the inherent challenges of extracting impedance parameters from fabricated designs. As the transitional element between radiating fields and loads, the impedance is the requisite information for describing, and designing optimally, both emissive (transmitting) and absorptive (receiving) nanoantennas. Here we present the first measurement of an optical nanoantenna input impedance, demonstrating impedance multiplication in folded dipoles at infrared frequencies. This quantification of optical antenna impedance provides the long sought enabling step for a systematic approach to improve collection efficiencies and control of the overall antenna response. Sub-diffraction limited waveguides have been studied as a means to manipulate light into nanoscale regions. Hybrid waveguides are popular candidates in optical regimes for subwavelength confinement and long range propagation. However, advances in the mid-IR are lacking due to high propagation losses and limited confinement. Here we present the first hybrid phononic waveguide using a hyperbolic material h-BN to generate surface phonon polaritons. The strong coupling between the photonic cylinder and phononic surface enhances the confined field up to 10-³ λ² and enables propagation distances up to more than two orders of magnitude above the operational wavelength. Our work is fully compatible with integrated polaritonic devices in the mid-IR and provides a systematic approach to design hybrid phononic waveguides.