Mid-infrared chiral planar metasurface thermal emitters based on quasiguided modes

The design of infrared circularly polarized emission sources has garnered significant interest in fields such as vibrational circular dichroism (CD) spectroscopy. This study proposes a planar chiral all-dielectric metasurface based on quasiguided modes to achieve narrowband, high CD chiral thermal emission sources in the mid-infrared (MIR) region. To address the fabrication challenges associated with traditional three-dimensional chiral structures, this design introduces in-plane displacement perturbations, achieving chiral thermal emission through Brillouin zone folding and the breaking of mirror symmetries. Theoretical analysis, combined with temporal coupled-mode theory, derives the necessary conditions for perfect chiral thermal emission and quantitatively describes the reflection characteristics of circularly polarized light using the Jones matrix. Multipole expansion analysis reveals that magnetic dipole and electric quadrupole resonances dominate the selective emission of right-handed circularly polarized light, while left-handed circularly polarized light exhibits almost no response, achieving a CD value close to ±1. Numerical simulations further validate the robustness of the structure to variations in both structural parameters and incident angles. This study provides new insights for the MIR chiral sensing and efficient thermal emission sources, offering advantages such as high Q factors, narrow bandwidths, and compatibility with planar fabrication processes, thus demonstrating significant application potential.