Reconfigurable Flat Optics with Programmable Reflection Amplitude Using Lithography-Free Phase-Change Materials Ultra Thin Films

TL;DR

This paper demonstrates a simple layered structure with phase-change materials that can dynamically modulate near-infrared light reflection from high reflection to near-perfect absorption, enabling programmable flat optical devices.

Contribution

It introduces a lithography-free, ultrathin layered system using phase-change materials for large, tunable optical reflection modulation in the near-infrared.

Findings

Achieved reflection modulation from >80% to >99.97% absorption.

Demonstrated intermediate reflection levels through partial crystallization.

Provided design guidelines for wavelength, angle, and crystallization control.

Abstract

We experimentally demonstrate a very large dynamic optical reflection modulation from a simple unpatterned layered stack of phase-change materials ultrathin films. Specifically, we theoretically and experimentally demonstrate that properly designed deeply subwavelength GeSbTe (GST) films on a metallic mirror produce a dynamic modulation of light in the near-infrared from very strong reflection (R>80%) to perfect absorption (A > 99,97%) by simply switching the crystalline state of the phase-change material. While the amplitude of modulation can lead to an optical contrast up to 10^6, we can also actively "write" intermediate levels of reflection in between extreme values, corresponding to partial crystallization of the GST layer. We further explore several layered system designs and provide guidelines to tailor the wavelength efficiency range, the angle of operation and the degree of crystallization leading to perfect absorption.