Ultrathin and Electrically Tunable Metamaterial with Nearly Perfect Absorption in Mid-Infrared

Abstract

Metamaterials integrated with graphene exhibit tremendous freedom in tailoring their optical properties, particularly in the infrared region, and are desired for a wide range of applications, such as thermal imaging, cloaking, and biosensing. In this article, we numerically and experimentally demonstrate an ultrathin (total thickness < λ 0 / 15 ) and electrically tunable mid-infrared perfect absorber based on metal–insulator–metal (MIM) structured metamaterials. The Q-values of the absorber can be tuned through two rather independent parameters, with geometrical structures of metamaterials tuning radiation loss (Qr) of the system and the material loss (tanδ) to further change mainly the intrinsic loss (Qa). This concise mapping of the structural and material properties to resonant mode loss channels enables a two-stage optimization for real applications: geometrical design before fabrication and then electrical tuning as a post-fabrication and fine adjustment knob. As an example, our device demonstrates an electrical and on-site tuning of ~5 dB change in absorption near the perfect absorption region. Our work provides a general guideline for designing and realizing tunable infrared devices and may expand the applications of perfect absorbers for mid-infrared sensors, absorbers, and detectors in extreme spatial-limited circumstances.

A Narrow Dual-Band Monolayer Unpatterned Graphene-Based Perfect Absorber with Critical Coupling in the Near Infrared

“…In recent years, scholars have proposed various measures to improve the absorption of graphene in the visible and near-infrared range, commonly by coupling graphene with some resonance structures [30][31][32]. For instance, a polarization-dependent graphene absorber with a one-dimensional, sub-wavelength dielectric grating has been theoretically proved to be capable of attaining perfect absorption [33].…”

Active Tuning from Narrowband to Broadband Absorbers Using a Sub-wavelength VO2 Embedded Layer

“…However, the resonant properties of MPAs are almost fixed, which greatly reduce their practical applications. Therefore, to fully exploit the optical properties and to extend the functionality of MPAs, dynamically tunable control over resonances such as electrical [26], optical [27], and thermal [28] tuning have been studied to realize actively tunable metamaterials. Recently, the thermal tunable narrowband MPAs are emerging with possible applications such as optical modulator [29], optical switches [30], and infrared (IR) camouflage [31].…”

Detailed Experiment-Theory Comparison of Mid-Infrared Metasurface Perfect Absorbers

“…An analytical expression of the relectance coefficient was derived and showed that minimisation of reflectance is achieved by control of the intrinsic and radiative losses [8]. The ratio of the quality factors of absorption Q a and radiation Q r losses define the minimum of the achievable reflectivity r = (Q a /Q r − 1)/(Q a /Q r + 1), hence the maximum absorbance achievable by MIM structures at Q a /Q r → 1 [9]. With a MIM reflector placed on a nano-thin and flexible Si 3 N 4 -membrane with an electrically biased graphene layer, spectral tunability of the resonance wavelength of the perfect absorber at mid-IR wavelengths was recently demonstrated [9].…”

“…The ratio of the quality factors of absorption Q a and radiation Q r losses define the minimum of the achievable reflectivity r = (Q a /Q r − 1)/(Q a /Q r + 1), hence the maximum absorbance achievable by MIM structures at Q a /Q r → 1 [9]. With a MIM reflector placed on a nano-thin and flexible Si 3 N 4 -membrane with an electrically biased graphene layer, spectral tunability of the resonance wavelength of the perfect absorber at mid-IR wavelengths was recently demonstrated [9]. Simple nano-disk MIM surfaces ( Figure 1) showed a near perfect absprbance A = 99% at 1.6 µm wavelengths with high refractive index sensitivity close to the resonance [10].…”