Tunable Mid‐Infrared Phase‐Change Metasurface

Abstract

reduce the size of these sensors, [4][5][6][7][8][9][10][11][12] since it exhibits a unique surface condition with tailored spectral properties and strong electric field enhancement, which results in a high sensitivity to the surroundings. [13][14][15][16][17][18][19][20][21] To date, most approaches toward metamaterial inspired sensors are based on perfect light absorption. [17,19,22,23] However, the measurement of their reflectance makes both optical alignment and chip integration challenging. [24] Furthermore, metamaterial sensors that are designed for the M-IR are rarely discussed because robust sources, detectors, and efficient components are limited. [25] In addition, despite metamaterial sensors exhibiting excellent sensitivity at their designed frequency, demonstrations of wideband or frequency-swept detection are uncommon. This is because the metamaterial optical response is usually fixed by its dimensions and dielectric properties. [26] Consequently, measurements at different wavelengths using a single metamaterial device are impossible. Recently, metamaterials that are tuned by integrating graphene, [27] vanadium dioxide, [28] liquid crystals, [29] and metal hydrides [30] were investigated. Particularly, the graphene [27] and vanadium dioxide [28] based metasurfaces are promising for dynamically tuning plasmonic induced transparency.Note, these tuning mechanisms tend to be impractical in the M-IR region because the materials involved have a strong Drude contribution to the dielectric function. The M-IR region is, however, an important spectral band where there exists an atmospheric transparency window and molecular vibrational fingerprints. [31][32][33] Chalcogenide phase change materials (PCMs) have a remarkable portfolio of properties. [34][35][36] In particular, unlike silica glasses, the low phonon energies of chalcogenides allow them to be transparent in the M-IR. [37] The fast switching between two structural states of the phase change data storage material, Ge 2 Sb 2 Te 5 (GST), make it ideal for active photonic devices. [34,[38][39][40][41][42][43][44][45][46][47][48] Notably, in the M-IR region GST exhibits a pronounced contrast in the real part of the permittivity (ε r ), and a negligibly small ratio of the imaginary (ε i ) to the ε r , indicating low absorptive losses. [49,50] In addition, it is now possible to design the nanostructure of GST to achieve specific switching characteristics. [51,52] Thus, there is evidence that chalcogenide PCMs can enable practical spectroscopically programmable M-IR metamaterials.In this work, we demonstrate a phase change material tuned transmissive M-IR metasurface. The metasurface consists of an array of Au square pillars stacked above a GST switchable layer. Contrary to other metal-dielectric-metal trilayer reflective metamaterials, our design works in transmission mode by avoidingThe intense light-matter interaction of plasmonic metasurfaces provides an appealing platform for optical sensing. To date, most metasurface sensors are not spectrally tuned. Mo...

Advanced Optical Programming of Individual Meta‐Atoms Beyond the Effective Medium Approach

“…Commonly, active infrared MSs based on PCMs exhibit different operation states by switching the entire MS via heating and short electrical or optical pulses . Intermediate states of the PCM crystallization have also been exploited to obtain partial resonance shifts by adjusting the annealing conditions.…”

A Stretchable Terahertz Parabolic‐Shaped Metamaterial

“…It can be observed that the trend of the Q ‐factor at ω 1 shows a linear increase with a maximum value of 50. The abovementioned electromagnetic performance is better than that obtained for other THz‐metamaterial devices reported in the literature . This result can be explained by the field distributions for the PSM in the TE and TM modes, as shown in Figure c.…”

“…There have been many novel inventions that have been greatly improved by using a THz metamaterial to replace classic devices, such as waveguides, resonators, filters, polarizers, and switches . To make a THz metamaterial more flexible and applicable, some progress has been made in the realization of controlling THz waves by using optical, electrical, magnetic, and thermal approaches. Among these approaches, a reconfigurable metamaterial becomes feasible in the active manipulation of THz wave applications.…”

Recent Progress in Active Optical Metasurfaces

“…Compared with other phase change materials, the well‐established technique of GST fabrication is already amenable to hybridization due to the high quality GST thin films which can currently be obtained through magnetron sputtering using argon as the sputtering gas. Although optically triggered phase transition was reported in an early study, tuning of GST‐hybrid metasurfaces has been primarily achieved through direct thermal control . In particular, the large change in refractive index of GST has been used to tune a variety of metasurface properties, including nanoantenna resonance characteristics, absorption/emission properties, chirality, and phase discontinuities among others.…”