6 research outputs found
Dynamically tunable asymmetric transmission in PT-symmetric metasurfaces
The concept of parity-time (PT) symmetry has recently expanded the toolbox to achieve active tunability in metasurfaces by modulating the imaginary part of the refractive index. In this work, we propose a hybridized static-active platform to dynamically tune the intensity and angular response of light by varying the non- Hermiticity factor in an all-dielectric metasurface. We numerically demonstrate tunable asymmetric transmission with respect to gain or loss side incidence in a vertically stacked Mie-resonant GaInP phased-array metasurface. It should be noted that the proposed system is reciprocal despite asymmetric transmission as the materials considered are in a linear regime. The primary building block consists of four PT-symmetric nanopillars of varying radii to achieve sufficient phase sampling. The overall design parameters are optimized for operation at a wavelength of 655 \textitnm (typical PL emission peak of GaInP). For loss side normal incidence, the transmission is predominantly in the 0\textrmth diffraction order (\textitη\textrml\textrm0~ 0:80, \textitη\textrml\textrm1~ 0:18), while for gain side normal incidence, an amplified transmission is in the 1\textrmst order (\textitη\textrmg \textrm0~ 0:02, \textitη\textrmg \textrm1~0:78). The observed asymmetric transmission is due to the near-field coupling between different Mie multipoles, broken in-plane mirror symmetry (meta-atoms with increasing radii along the x-axis), and the broken PT-phase along the propagation direction. An asymmetry factor, ~0:9, is observed at λ = 655 \textitnm. The symmetry in transmission can be restored by reducing the gain-loss contrast. We believe an optimal arrangement of gain-loss resonators combined with tunable pumping (either optically or electrically) could pave the way towards practical reconfigurable metasurfaces
Graphene Nanoribbons based mid-infrared photodetectors
We demonstrate tunable graphene nanoribbon-based photodetector for the wavelength range 5-12 µm. We leverage the width dependence of bandgap in nanoribbons, and their tunable plasmonic properties to demonstrate photodetection at room temperature. © Optica Publishing Group 2021, © 2021 The Author (s