Reversible optical tuning of GeSbTe phase-change metasurface spectral filters for mid-wave infrared imaging.

Matthew N Julian,Hyun Jung Kim,Scott Bartram,Calum Williams,Stephen Borg

doi:10.1364/optica.392878

Abstract

Tunable narrowband spectral filtering across arbitrary optical wavebands is highly desirable in a plethora of applications, from chemical sensing and hyperspectral imaging to infrared astronomy. Yet, the ability to reconfigure the optical properties, with full reversibility, of a solid-state large-area narrowband filter remains elusive. Existing solutions require either moving parts, have slow response times, or provide limited spectral coverage. Here, we demonstrate a 1-inch diameter continuously tunable, fully reversible, all-solid-state, narrowband phase-change metasurface filter based on a GeSbTe-225 (GST)-embedded plasmonic nanohole array. The passband of the presented device is with transmittance and operates across the 3–5 µm thermal imaging waveband. Continuous, reconfigurable tuning is achieved by exploiting intermediate GST phases via optical switching with a single nanosecond laser pulse, and material stability is verified through multiple switching cycles. We further demonstrate multispectral thermal imaging in the mid-wave infrared using our active phase-change metasurfaces. Our results pave the way for highly functional, reduced power, compact hyperspectral imaging systems and customizable optical filters for real-world system integration.

Highlights

Narrowband spectral filtering is integral in applications ranging from chemical spectroscopy and hyperspectral imaging to infrared (IR) astronomy [1,2]
In comparison to other popular GST stoichiometries, such as GST-326, GST-629, and GST-8211 [44,47], GST-225 was selected for the mid-wave IR (MWIR) spectral filters in this work due to its ubiquity in commercial rewritable optical storage media; low power switching; fast-tuning speed; relative ease of conformal deposition; large n/ k across the MWIR; and optimized process parameters established in our laboratory
Co.) in the spectral range from 1–10 μm. Results of both the x-ray diffraction (XRD) and ellipsometry measurements of as-deposited GST-225 are shown in Fig. 1 for amorphous GST (a-GST) and both hexagonal-centered cubic (HCC) and face-centered cubic (FCC) crystalline GST (c-GST)

Summary

INTRODUCTION

Narrowband spectral filtering is integral in applications ranging from chemical spectroscopy and hyperspectral imaging to infrared (IR) astronomy [1,2]. PCMs based on transition metal chalcogenide alloys such as GeSbTe (GST) are largely transparent across various spectral imaging wavebands and exhibit significantly large, reversible refractive index modulation upon crystallization, making them ideal candidates for use in such spectrally robust filter designs [36] Such “exotic” optical materials have been utilized recently as the tunable medium for absorptive color filters [37,38,39,40], thermal emission switches [18,19], MWIR absorptive pixel arrays [41], programmable metasurface phase and amplitude modulators [42,43], and tunable metalenses [22,23]. The results presented represent a significant step toward robust, tunable spectral filters, with applications in compact, fast-switching, and all-solid-state tunable filter systems for imaging in a wide variety of fields, from astronomy to remote Earth sensing

GST Thin-Film Morphology

Phase-Change Plasmonic Metasurface

Reversible All-Optical Continuous Tuning

Mid-Wave Infrared Imaging

DISCUSSION AND CONCLUSION