Numerical study of achiral phase-change metamaterials for ultrafast tuning of giant circular conversion dichroism.

Tun Cao,Chenwei Wei,Libang Mao

doi:10.1038/srep14666

Abstract

Control of the polarization of light is highly desirable for detection of material’s chirality since biomolecules have vibrational modes in the optical region. Here, we report an ultrafast tuning of pronounced circular conversion dichroism (CCD) in the mid-infrared (M-IR) region, using an achiral phase change metamaterial (PCMM). Our structure consists of an array of Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) dielectric layer, where the Au square patches occupy the sites of a rectangular lattice. The extrinsically giant 2D chirality appears provided that the rectangular array of the Au squares is illuminated at an oblique incidence, and accomplishes a wide tunable wavelength range between 2664 and 3912 nm in the M-IR regime by switching between the amorphous and crystalline states of the Ge2Sb2Te5. A photothermal model is investigated to study the temporal variation of the temperature of the Ge2Sb2Te5 layer, and shows the advantage of fast transiting the phase of Ge2Sb2Te5 of 3.2 ns under an ultralow incident light intensity of 1.9 μW/μm2. Our design is straightforward to fabricate and will be a promising candidate for controlling electromagnetic (EM) wave in the optical region.

Highlights

Photoexcitation[22,23,24,25,26]
We demonstrate that the resonant frequency of giant circular conversion dichroism (CCD) can be tuned in the M-IR regime using an achiral phase change metamaterial (PCMM)
The achiral PCMM is composed of an array of thin Au squares separated from a continuous Au film by an active dielectric interlayer of prototypical phase change material (PCM): Ge2Sb2Te5, where the Au squares occupy the sites of a rectangular lattice

Summary

Results

Tuning of chiroptical response at a large power input may sound challenging, since the high power illumination gives rise to unwanted heating to prevent polarization tuning To solve this problem, an Au-Ge2Sb2Te5-Au trilayers structure is proposed, where the Au bottom layer will interact with the upper Au patches to form electric and magnetic dipoles that efficiently couple the incident light into the dielectric interlayer of Ge2Sb2Te531. An Au-Ge2Sb2Te5-Au trilayers structure is proposed, where the Au bottom layer will interact with the upper Au patches to form electric and magnetic dipoles that efficiently couple the incident light into the dielectric interlayer of Ge2Sb2Te531 It has the advantage of transiting the phase of Ge2Sb2Te5 under RCP and LCP illumination with an ultralow light intensity of 1.9 μ W/μ m2 and may not prevent the polarization tuning. By means of the external stimulus, the phase transition of Ge2Sb2Te5 can be carried out separately not interacting with the polarization tuning

Discussion

Methods