# Ultra-low-loss Polaritons in Isotopically Pure Materials: A New Approach

## TL;DR

This paper demonstrates that isotopic enrichment of hexagonal boron nitride significantly enhances phonon polariton lifetimes and propagation lengths, advancing the development of low-loss nanophotonic devices.

## Contribution

It introduces a novel isotopic enrichment method to substantially reduce optical losses in phonon polariton materials, improving their performance for nanophotonics.

## Key findings

- Three-fold increase in polariton lifetime with isotopic enrichment
- Direct imaging shows longer polariton propagation lengths
- Provides a pathway for low-loss PhP nanophotonic devices

## Abstract

Conventional optical components are limited to size-scales much larger than the wavelength of light, as changes in the amplitude, phase and polarization of the electromagnetic fields are accrued gradually along an optical path. However, advances in nanophotonics have produced ultra-thin, co-called "flat" optical components that beget abrupt changes in these properties over distances significantly shorter than the free space wavelength. While high optical losses still plague many approaches, phonon polariton (PhP) materials have demonstrated long lifetimes for sub-diffractional modes in comparison to plasmon-polariton-based nanophotonics. We experimentally observe a three-fold improvement in polariton lifetime through isotopic enrichment of hexagonal boron nitride (hBN). Commensurate increases in the polariton propagation length are demonstrated via direct imaging of polaritonic standing waves by means of infrared nano-optics. Our results provide the foundation for a materials-growth-directed approach towards realizing the loss control necessary for the development of PhP-based nanophotonic devices.

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Source: https://tomesphere.com/paper/1705.05971