Abstract
We propose a nonvolatile, reconfigurable, and narrowband mid-infrared bandpass filter based on surface lattice resonance in phase-change material GeSbTe. The proposed filter is composed of a two-dimensional gold nanorod array embedded in a thick GeSbTe film. Results show that when GeSbTe transits from the amorphous state to the crystalline state, the narrowband reflection spectrum of the proposed filter is tuned from 3.197 m to 4.795 m, covering the majority of the mid-infrared regime, the peak reflectance decreases from 72.6% to 25.8%, and the corresponding quality factor decreases from 19.6 to 10.3. We show that the spectral tuning range can be adjusted by varying the incidence angle or the lattice period. By properly designing the gold nanorod sizes, we also show that the quality factor can be greatly increased to 70 at the cost of relatively smaller peak reflection efficiencies, and that the peak reflection efficiency can be further increased to 80% at the cost of relatively smaller quality factors. We expect that this work will advance the engineering of GeSbTe-based nonvalatile tunable surface lattice resonances and will promote their applications especially in reconfigurable narrowband filters.
Highlights
Tunable narrowband mid-infrared (3 μm to 5 μm) filters are key devices in a diverse range of applications, including chemical spectroscopy, thermography, multispectral/hyperspectral imaging [1,2,3]
Results show that as the Ge2Sb2Te5 crystallization fraction m increases from 0 to 1, the reflection spectra are greatly red-shifted: the wavelength for the peak reflectance shifts from 3.197 μm to 4.795 μm. This corresponds to extremely large spectral tunability of 1.598 μm, or 2.13Λ, which is slightly larger than the RA wavelength tunability of ∼2Λ. This striking spectral tunability is larger or even much larger than most of the reported GexSbyTez-based mid-infrared filters, including those based on perfect absorbers [13,14,15,16], Fabry-Pérot cavities [18,19], extraordinary optical transmission effects [8,20], or SLRs combined with thin GexSbyTez films [26,27]
By carefully designing the gold nanorod side length, the peak reflectance can be greatly increased at the cost of the relatively smaller quality factor or the quality factor can be significantly improved at the cost of relatively smaller peak reflectance
Summary
Tunable narrowband mid-infrared (3 μm to 5 μm) filters are key devices in a diverse range of applications, including chemical spectroscopy, thermography, multispectral/hyperspectral imaging [1,2,3]. In 2013, Chen et al [26] demonstrated nonvolatile tuning of SLRs over a range of ∼500 nm in the near-infrared regime (1.89 μm to 2.27 μm) by incorporating a thin Ge2Sb2Te5 film between a gold nanodisk array and a quartz substrate. We propose a novel nonvolatile and reconfigurable mid-infrared bandpass filter based on tunable SLR supported by a two-dimensional (2D) array of gold nanorods, which are embedded in a thick Ge2Sb2Te5 film. We will show that our design has extremely large spectral tunability of 1.598 μm (from 3.197 μm to 4.795 μm), which covers the majority of the mid-infrared regime, high reflection efficiencies and relatively large quality factors (R = 72.6% and Q = 19.6 at 3.197 μm, R = 25.8% and Q = 10.6 at 4.795 μm). By investigating the effects of gold nanorod sizes, we will show that the filtering performance can be further adjusted to achieve an even larger quality factor or peak reflectance
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