Dynamically Tunable Asymmetric Transmission in PT-Symmetric Phase Gradient Metasurface

Abstract

Active optical metasurfaces have attracted significant research attention in recent times. The conventional thermal and free-carrier induced index-tuning mechanisms have been widely explored to realize dynamic modulation of the optical properties. However, their modulation efficiency is limited by the intrinsic response of functional materials. The recent advances in the concept of PT (parity-time) symmetry and spatiotemporal modulation of permittivity have opened new avenues to realize dynamic tunability. In this work, we propose an all-dielectric PTsymmetric metasurface to tune the intensity and angular response of light through dynamic gain−loss modulation. Our approach shows tunable asymmetric transmission in a vertically stacked Ga 0.5 In 0.5 P phased-array metasurface. The overall metasurface is optimized for operation at a wavelength of 655 nm (typical PL emission peak of Ga 0.5 In 0.5 P). The transmission is predominantly in the zeroth diffraction order (η 0 ∼ 0.80, η 1 ∼ 0.18) for loss side normal incidence, and an amplified transmission is observed in the first diffraction order (η 0 ∼ 0.04, η 1 ∼ 0.79) for gain side incidence. In addition to the asymmetric transmission for normal incidence, the proposed metasurface also exhibits asymmetric amplification in transmission for oblique incidence. An optimal arrangement of gain−loss resonators combined with tunable pumping (either optical or electrical) can pave the way toward on-chip reconfigurable nanophotonic devices.

Molecular Plasmonics with Metamaterials

“…By exploiting non-Hermitian effects due to the interplay between gain and losses, it is possible to achieve very strong circular birefringence and CD . The interplay between the PT symmetry and the non-Hermitian physics can find numerous applications in, e.g., sensing, optical cloaking, lossless guiding, active components , for electromagnetic field manipulation and imaging, and nonlinear and quantum optics. , …”

Analysis of the Limits of the Optical Response of a Metallic Nanoparticle with Gain

“…More recently, metallic nanostructures with gain are being combined with conventional, i.e., passive, metallic nanostructures, to build systems with parity-time symmetry. − The balance between active and passive responses in these systems results in extraordinary properties such as anisotropic emission − and scattering. − Unfortunately, in many cases, the complexity of the problem under investigation demands the use of simplified approaches to model the gain. These approaches usually describe the effect of gain through the inclusion of a term in the dielectric function with a negative imaginary part.…”