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

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.

Tunable and reconfigurable metasurfaces and metadevices

“…The large optical/electronic contrast between the two states is attributed to atom re-arrangement. The thin GST layer was introduced into the metal-dielectric-metal configuration for realization of a tunable plasmonic resonance [168][169][170] , absorber 98,[171][172][173] , reflector 174 , circular dichroism 175,176 , chirality 177,178 and negative index metamaterials 179 . A non-volatile all-optical modulation of resonance in infrared is reported as a broadband switch through the combination of chalcogenide glass phase change medium with nanostructured plasmonic metamaterials 180 .…”

Hybrid metamaterial switching for manipulating chirality based on VO2 phase transition

“…The THz chiral metamaterials integrated with photoactive inclusions can accomplish tunable optical activity 35 36 , chirality switching 37 and tunable linear polarization conversion 38 , which are controlled by external light illumination. At present, thermal-controlled chirality has been seldom reported 32 41 . The mid-infrared chiral metamaterials have been demonstrated to show the reversal of the circular dichroism sign and ultrafast tuning of pronounced circular conversion dichroism, respectively, enabled by temperature-controlled phase change materials Ge 3 Sb 2 Te 6 32 and Ge 2 Sb 2 Te 5 41 .…”

“…At present, thermal-controlled chirality has been seldom reported 32 41 . The mid-infrared chiral metamaterials have been demonstrated to show the reversal of the circular dichroism sign and ultrafast tuning of pronounced circular conversion dichroism, respectively, enabled by temperature-controlled phase change materials Ge 3 Sb 2 Te 6 32 and Ge 2 Sb 2 Te 5 41 . As one of the most important phase change materials, VO 2 can exhibit an insulator-to-metal phase transition that can be electrically 27 , thermally 28 29 30 31 42 43 44 45 , or optically 46 tuned.…”

Dual-polarity metamaterial circular polarizer based on giant extrinsic chirality

“…Initially, optical activity and asymmetric transmission were regarded as inherent characteristics of intrinsically two- and three-dimensional (3D) chiral metamolecules, respectively. The recent endeavors have verified that the aforementioned chiral effects can also be observed in intrinsically non-chiral metamaterials 15 32 33 34 35 36 37 , provided that the whole arrangement formed by such metamaterials together with the wave vector of light cannot be superposed upon its mirror image. This phenomenon was termed as extrinsic chirality, where two requirements are necessary, i.e., metamolecules without 2-fold rotational symmetry and the oblique incidence 15 .…”