Fig. 2: Metasurface design with high-dimensional identification capability.
From: Deep learning-enabled ultra-broadband terahertz high-dimensional photodetector
a Schematic of the metasurface-mediated interferometric photodetector. b Theoretical results of generated OAM topological charges under LCP and RCP incidences at different frequencies, with both lines having slopes of -m/f0. c Simulated plasmonic field distributions (real part of Ez component) and d corresponding mode purities under different illuminations when structural parameters m = 1 and f0 = 0.3 THz. The OAM mode purity exhibits high purity (≈1.0). e The normalized amplitude of two generated OAM beams |Ml-1|, |Ml+1| and their phase difference angle (Ml-1–Ml+1) versus different QWP (quarter-waveplate) angle at three different frequencies, where l-1th and l+1th order vortices theoretically are the two predominant modes in OAM spectrum. Here, the QWP angle changes from −90° to 90° in increments of 22.5°, causing the polarization state to change from yLP to right-handed elliptical polarization, then back to yLP and finally transition to left-handed elliptical polarization. The OAM coefficient variation trends under diverse frequencies are basically the same.
