Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Abstract

Anisotropy has been a key property employed in the design of optical components for hundreds of years. However, in recent years there has been growing interest in polaritons supported within anisotropic (low crystal symmetry) materials for their ability to compress light to smaller, deeply subwavelength dimensions. While historically the first anisotropic polaritons probed were hyperbolic modes, research into anisotropic materials has recently turned toward hybrid materials and optical modes, employing phenomena such as phonon confinement, polaritonic strong coupling, and Moiré structures to design the optical properties. In this Perspective, we will briefly introduce the physics and theories of polariton anisotropy, review recently investigated anisotropic and two-dimensional materials, and then move on to a discussion of approaches toward realizing hybrid modes and identifying new materials. Based on the results from the past few years, we extend these discussions to highlight outstanding challenges and outline what we perceive as promising paths to further explore the potential for polariton anisotropy and hybrid systems in future nanophotonic optical devices.

Two-dimensional natural hyperbolic materials: from polaritons modulation to applications

“…These applications have been reviewed by some groups. 7,43,44,47 To avoid repetition, several recently proposed and improved promising directions are exemplified as follows.…”

“…7,15,[24][25][26]46 Although some reviews about natural HMs have been also published, they are restricted to either only reviewing hyperbolic phonon polaritons in materials (e.g., hBN, α-MoO 3 , α-V 2 O 5 , and β-Ga 2 O 3 ) or solely introducing hyperbolic plasmon polaritons in black phosphorus (BP) and WTe 2 . 7,[42][43][44]47 Comparisons and discussions of phonon polaritons, plasmon polaritons, and exciton polaritons have been also made by W. Ma et al and Y. Wu et al 48,49 However, their reviews focus on either in-plane anisotropic polaritons or manipulation strategies for polaritons in vdW materials, from which many recently reported 2D natural HMs (e.g., ZrSiSe, β-Ga 2 O 3 , perovskites and tetradymites) along with the related hyperbolic properties are missing. 48,49 In particular, hyperbolic exciton and shear polaritons have recently been experimentally identified in tetradymites and β-Ga 2 O 3 , respectively.…”

Near-Field Retrieval of the Surface Phonon Polariton Dispersion in Free-Standing Silicon Carbide Thin Films

“…An intriguing feature of phonon polaritons is the possibility of anisotropic propagation due to the complex crystal structure of polar dielectrics, related to the simultaneous presence (i.e., at fixed frequency) of both positive and negative terms in the dielectric tensor. − Thin films of layered van der Waals (vdW) materials have attracted considerable attention as they support highly anisotropic hyperbolic and elliptical phonon polaritons, combined with extreme subdiffractional confinement. − More recently, the possibility of twisting one layer with respect to the other has increased the dispersion engineering possibilities in these novel vdW materials. − …”

Mid-infrared dual-comb polarimetry of anisotropic samples

“…The anisotropy of materials is associated, for example, with direction dependent optical, mechanical, physical and chemical properties [1][2][3][4][5][6][7] . Anisotropy plays a key role in optoelectronic, photonic, polymer, catalytic and bio-related research and applications.…”

“…Anisotropy plays a key role in optoelectronic, photonic, polymer, catalytic and bio-related research and applications. Specific examples are the design and engineering of optical devices [1][2][3][4] , two-dimensional (2D) materials 3 , and touch-spun nanofibers for nerve regeneration 7 , the latter of which are studied in this work. For the analysis of anisotropic material properties, infrared (IR) methods are prominently used, as these probe material and structural properties in a contact-less manner in various environments with high sensitivity.…”