Polariton nanophotonics using phase-change materials

Kundan Chaudhary,Takashi Taniguchi,Ruoping Li,Matthias Wuttig,Noah A Rubin,Christina M Spägele,Xinghui Yin,James H Edgar,Luis A Jauregui,Stefano L Oscurato,Antonio Ambrosio,Michele Tamagnone,Philip Kim,Christoph Persch,Kenji Watanabe,Jiahan Li,Federico Capasso

doi:10.1038/s41467-019-12439-4

Abstract

Polaritons formed by the coupling of light and material excitations enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics. However, novel techniques are required to control the propagation of polaritons at the nanoscale and to implement the first practical devices. Here we report the experimental realization of polariton refractive and meta-optics in the mid-infrared by exploiting the properties of low-loss phonon polaritons in isotopically pure hexagonal boron nitride interacting with the surrounding dielectric environment comprising the low-loss phase change material Ge3Sb2Te6. We demonstrate rewritable waveguides, refractive optical elements such as lenses, prisms, and metalenses, which allow for polariton wavefront engineering and sub-wavelength focusing. This method will enable the realization of programmable miniaturized integrated optoelectronic devices and on-demand biosensors based on high quality phonon resonators.

Highlights

Polaritons formed by the coupling of light and material excitations enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics
We use low-loss phonon polaritons (PhPs) in isotopically pure hexagonal boron nitride (hBN) (11B isotopes with >99% purity5) with longer propagation lengths, which we combine with Ge3Sb2Te6, a stoichiometry with low absorption in the mid-infrared[29]
In summary, our results clearly establish that the hBN-GST heterostructure used in this work can serve as a versatile platform to arbitrarily control polaritons at the nanoscale to achieve freeform, transformation, and meta-optics[19]

Summary

Introduction

Polaritons formed by the coupling of light and material excitations enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics. Refractive optical elements such as lenses, prisms, and metalenses, which allow for polariton wavefront engineering and sub-wavelength focusing This method will enable the realization of programmable miniaturized integrated optoelectronic devices and on-demand biosensors based on high quality phonon resonators. A heterostructure comprising the phase-change material Ge3Sb2Te6 (GST) and isotopically pure h11BN (referred to hBN hereinafter) is the ideal system for a proof-of-concept demonstration of substrate-engineered polariton optics: hBN possesses low-loss polaritons with long propagation lengths[5] and GST can support two vastly different refractive indices in its amorphous and crystalline phases (na = 4.2 and nc = 6.1), which can co-exist at room temperature[20–29]. We show an hBN-GST heterostructure in which arbitrary patterns can be written, erased, and re-written to control the PhP propagation We achieve this by defining several structures, ranging from waveguides[30,31] to diffraction-limited focusing metalenses. We work in the second Reststrahlen band (from 1361–1610 cm−1), which is associated with in-plane optical phonons[5,6]

Methods

Results

Conclusion