Polariton Meta-Optics with Phase-Change Materials

Surface phonon polaritons (SPhPs) and surface plasmon polaritons (SPPs), evanescent modes supported by media with negative permittivity, are a fundamental building block of nanophotonics. These modes are unmatched in terms of field enhancement and spatial confinement, and dynamical all‐optical control can be achieved, e.g., by employing phase‐change materials. However, the excitation of surface polaritons in planar structures is intrinsically limited to p‐polarization. On the contrary, waveguide modes in high‐permittivity films can couple to both p‐ and s‐polarized light, and in thin films, their confinement can become comparable to surface polaritons. Here, it is demonstrated that the s‐polarized waveguide mode in a thin Ge3Sb2Te6 (GST) film features a similar dispersion, confinement, and electric field enhancement as the SPhP mode of the silicon carbide (SiC) substrate, while even expanding the allowed frequency range. Moreover, it is experimentally shown that switching the GST film grants nonvolatile control over the SPhP and the waveguide mode dispersions. An analytical model is provided for the description of the GST/SiC waveguide mode and it is shown that the concept is applicable to the broad variety of polar crystals throughout the infrared spectral range. As such, complementarily to the polarization‐limited surface polaritons, the s‐polarized waveguide mode constitutes a promising additional building block for nanophotonic applications.

Section: Methodsmentioning

confidence: 99%

Surface Polariton‐Like s‐Polarized Waveguide Modes in Switchable Dielectric Thin Films on Polar Crystals

Paßler

Heßler

Wuttig

et al. 2019

“…The dynamic control is unambiguously revealed in the nano‐FTIR around the two reststrahlen bands of hBN (Figure f): the in‐plane and out‐of‐the plane phonon resonances are dynamically tuned by controlling the temperature of the hBN/VO 2 vdW heterostructure. Note that in addition to VO 2 , the phonon polaritons can be tuned with other phase change materials, for example Ge 3 Sb 2 Te 6 (GST) where the dispersion of phonon polaritons were altered with photoinduced phase transition (Figure g): the erasing of the polariton dipolar modes were observed via the transition from amorphous‐GST (top) to crystalline‐GST (bottom).…”

Section: Phonon Polaritons In Low‐dimensional Materialsmentioning

confidence: 99%

Phonon Polaritons and Hyperbolic Response in van der Waals Materials

Shen

Qiu

et al. 2019

113

Phonon polaritons provide useful opportunities, complementary to those provided by plasmon polaritons, in the study of the interaction of light with matter at small scales. The focus of this review is on phonon polaritons in low‐dimensional van der Waals (vdW) materials and heterostructures. Phonon polaritons confined in vdW materials exhibit large electromagnetic localization and are easy to hybridize with other collective modes. The extreme optical anisotropy in vdW systems produces the natural hyperbolic dispersion, enabling the access to deep subdiffractional optics and often yielding improved figures of merit over hyperbolic metamaterials. These virtues hold promises for practical nanophotonic applications, including optical sensing, super‐resolution imaging, energy and emission engineering, quantum optics, and a next generation of optical circuit elements.

“…[ 26 ] Following further studies of PhPs in α‐MoO 3 , novel nanophotonic devices on α‐MoO 3 have been proposed, such as broadband absorbers, high quality factor polariton resonators and subwavelength steering and focusing devices. [ 26–29 ] However, all the research on α‐MoO 3 mentioned above has focused on infrared frequencies, while the characteristics and the application of α‐MoO 3 in the visible frequency range have seldom been described. [ 30 ] In this work, by designing metal/α‐MoO 3 /metal Fabry–Perot (FP) cavities, we study the anisotropic optical properties of α‐MoO 3 in the visible frequency range.…”

Section: Introductionmentioning

confidence: 99%

Polarization Reflector/Color Filter at Visible Frequencies via Anisotropic α‐MoO₃

Wei

Dereshgi

Song

et al. 2020

2D van der Waals materials have attracted increasing attention in recent years due to their exciting physical properties and offer new opportunities for creating devices with enhanced or novel functionalities. In particular, α‐MoO3 is an emerging member of the fast‐growing 2D family with strong natural anisotropic optical properties. However, anisotropic optical properties of ‐MoO3 in the visible frequency range remain elusive. Here, α‐MoO3 is investigated as an optical material at the visible frequency (450–750 nm), which exhibits a polarization‐dependent complex refractive index due to the anisotropic crystal structure. As a proof of concept, polarization‐sensitive photonic devices including polarization reflectors and polarization color filters are designed and realized by constructing metal–insulator–metal Fabry–Perot cavities. It is observed that resonance frequencies for designed transmission and reflection filters change up to 25 nm with incident polarization which stems from the polarization‐dependent complex refractive indices of α‐MoO3. The largest contrasts are observed for two orthogonal polarization states parallel to the two orthogonal in‐plane crystal directions. The approach in this study offers new directions for potential applications in the development of polarization‐dependent devices based on 2D van der Waals materials for visible frequencies.