Hybrid slot-waveguide fed antenna using hexagonal boron nitride D'yakonov polaritons.

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.

Hybrid long-range hyperbolic phonon polariton waveguide using hexagonal boron nitride for mid-infrared subwavelength confinement.

Long propagation waveguides are critical for any photonic-on-chip applications. There has been an extensive investigation in using plasmon polaritons for near-infrared and optical networks, however, for mid- to long-wave IR applications phonon polaritons are required given that plasmonic polaritonic effects are negligible. In recent years, extensive research has been conducted on hexagonal boron nitride (h-BN), which has shown h-BN to have naturally occurring subwavelength, volumetrically confined hyperbolic phonon polaritons (HPhPs). This work presents numerical results for both long- and short-range phononic volumetric polariton modes in a slab of h-BN. A hybrid long-range phononic waveguide consisting of two identical dielectric cylinder wires symmetrically placed on each side of the h-BN slab is coupled to the long-range HPhP mode. Based on analytical coupled-mode theory and computational finite element analysis, we have investigated the modal characteristics of the hybrid long-range phonon polaritonic waveguide. Due to the strong coupling between the high index cylindrical-waveguide mode and the HPhPs in the h-BN thin film, subwavelength confinement can be achieved (modal area ranging from  10-2λo2 to  10-1λo2) while enabling long propagation distances (7λ0-370λ0).

Hybrid surface phononic waveguide using hyperbolic boron nitride.

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 analysis of 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 λo 2 (λo is free-space wavelength) and enables propagation distances up to 100 λo. Our work is fully compatible with integrated polaritonic devices in the mid-IR and provides a systematic approach to design hybrid phononic waveguides.

Phase resolved near-field mode imaging for the design of frequency-selective surfaces.

Frequency-selective surfaces (FSS) are a class of metasurfaces with engineered reflectance, absorbance, and transmittance behavior. We study an array of metallic crossed dipole FSS elements in the infrared using interferometric scattering-type scanning near-field optical microscopy (s-SNOM). We resolve the dependence of the near-field phase on the dimensions of the elements and compare with numerical models. The combined phase and amplitude information of the underlying near-field mode distribution compared to conventional far-field absorption spectroscopy greatly improves the targeted design of frequency-selective surfaces.

Near-field measurement of infrared coplanar strip transmission line attenuation and propagation constants.

Impedance matched and low loss transmission lines are essential for optimal energy delivery through an integrated optical or plasmonic nanocircuit. A novel method for the measurement of the attenuation and propagation constants of an antenna-coupled coplanar strip (CPS) transmission line is demonstrated at 28.3 THz using scattering-type scanning near-field optical microscopy. Reflection of the propagating optical wave upon an open-circuit or short-circuit load at the terminal of the CPS provides a standing voltage wave, which is mapped through the associated surface-normal E(z) electric near-field component at the metal-air interface. By fitting the analytical standing wave expression to the near-field data, the transmission line properties are determined. Full-wave models and measured results are presented and are in excellent agreement.

Determination of electric-field, magnetic-field, and electric-current distributions of infrared optical antennas: a near-field optical vector network analyzer.

In addition to the electric field E(r), the associated magnetic field H(r) and current density J(r) characterize any electromagnetic device, providing insight into antenna coupling and mutual impedance. We demonstrate the optical analogue of the radio frequency vector network analyzer implemented in interferometric homodyne scattering-type scanning near-field optical microscopy for obtaining E(r), H(r), and J(r). The approach is generally applicable and demonstrated for the case of a linear coupled-dipole antenna in the midinfrared spectral region. The determination of the underlying 3D vector electric near-field distribution E(r) with nanometer spatial resolution and full phase and amplitude information is enabled by the design of probe tips with selectivity with respect to E(∥) and E(⊥) fabricated by focused ion-beam milling and nano-chemical-vapor-deposition methods.

Demonstration of a single-layer meanderline phase retarder at infrared.

Meanderline wave plates are in common use at radio frequencies as polarization retarders. We present initial results of a gold meanderline structure on a silicon substrate that functions at a wavelength of 10.6 microm in the IR. The measured results show a distinct change in the polarization state of the incident beam after passing through the device, inducing a 74 degrees phase retardance between horizontal and vertical components. A high degree of polarization (88%) is maintained in the transmitted beam with an overall power transmittance of 38% and a beam profile that remains essentially unchanged.