April 22 - 26, 2024
Seattle, Washington
May 7 - 9, 2024 (Virtual)

Event Supporters

2024 MRS Spring Meeting
EL08.15.02

Manipulating Confined Infrared Light via Polaritonic Design of Sub-Diffractional α-MoO3 Wedges

When and Where

Apr 25, 2024
5:00pm - 7:00pm
Flex Hall C, Level 2, Summit

Presenter(s)

Co-Author(s)

Ethan Ray1,2,Mingze He2,John Buchner2,Saurabh Dixit2,Joshua Caldwell2

Georgia Institute of Technology1,Vanderbilt University2

Abstract

Ethan Ray1,2,Mingze He2,John Buchner2,Saurabh Dixit2,Joshua Caldwell2

Georgia Institute of Technology1,Vanderbilt University2
The Mid-infrared (mid-IR) spectrum of light is crucial for various applications, including thermal imaging, molecular sensing, and free-space communication. However, the application of long free-space wavelengths of mid-IR light is limited in chip-scale devices due to the diffraction limit. This problem can be circumvented by using hyperbolic materials where the dielectric permittivities along the principal crystal directions exhibit opposite signs in the mid-IR spectral region. It has been well-demonstrated that hyperbolic materials (e.g. h-BN, α-MoO<sub>3</sub>, α-V<sub>2</sub>O<sub>5</sub>) can confine high-momentum (short wavelength) electromagnetic waves in the form of hyperbolic phonon polaritons (HPhPs)- quasi-particles made from the hybridization of charged dipoles (phonons) and photons (an external light source). The propagation behavior of these HPhPs can be tuned and confined in deep sub-diffraction volumes using sub-wavelength structures, which offer distinct opportunities in the form of chip-scale nano-photonics devices for integrated optics and photonics applications.<br/><br/>In this work, we investigate sub-wavelength wedges of a hyperbolic material (α-MoO<sub>3</sub>) to demonstrate in-plane focusing of electromagnetic waves beyond the diffraction limit and a transition of polaritonic propagation in the forbidden direction of the α-MoO<sub>3</sub> crystal. We design our wedges by optimizing lateral dimensions and wedge thickness using 3D numerical simulations via COMSOL Multiphysics. Numerically, we observed transitions from adiabatic compression to standing wave in polaritonic modes through changing wedge vertex angles (θ<sub>v</sub>). For 10°&lt;θ<sub>v</sub>&lt;30°, we observe a compression factor (i.e. ratio of wavelength in standing wave region to the adiabatically compressed region in the wedge) of 2.89 (at 700 cm-1) and 1.42 (at 900 cm-1) that converge to 1 upon increasing vertex angle. Further, we investigate the effect of geometrical confinement at vertex angles 120°&lt; θ<sub>v</sub> &lt;150° on propagation direction and found that a high vertex angle of wedge enables the propagation of HPhPs in the forbidden direction. After establishing these theoretical foundations, we fabricated such wedges and characterized them with scattering-type Scanning Near-field Optical Microscopy (s-SNOM). Through s-SNOM, we found the presence of adiabatically compressed waves confined at the tip of the wedge at lower vertex angles and node formation along the forbidden propagation direction at high vertex angles. This work offers a novel tunable parameter for manipulating mid-IR light propagation in α-MoO<sub>3</sub> sub-wavelength structures. Further, these findings open avenues for chip-scale mid-IR nanophotonic devices and optical components with the ease of van der Waals integration for integrated optics and photonics applications.

Keywords

metamaterial | nanostructure

Symposium Organizers

Yao-Wei Huang, National Yang Ming Chiao Tung University
Min Seok Jang, Korea Advanced Institute of Science and Technology
Ho Wai (Howard) Lee, University of California, Irvine
Pin Chieh Wu, National Cheng Kung University

Symposium Support

Bronze
APL Quantum
Kao Duen Technology Corporation
Nanophotonics Journal

Session Chairs

Ho Wai (Howard) Lee
Pin Chieh Wu

In this Session