Design of multi-wavelength circularly polarized InAsSb photodetectors based on chiral silicon metasurfaces

Realizing chip-level, multi-wavelength detection of specific circularly polarized light remains a critical challenge in advanced photonics, particularly in the mid-infrared molecular fingerprint region. In this work, we report an integrated multi-wavelength circularly polarized photodetector that addresses this challenge through the monolithic integration of five wavelength-selective chiral metasurfaces with a broadband InAsSb photodetector. Each metasurface is independently optimized for a technologically important wavelength (1.55, 2.0, 2.7, 3.3, and 4.26 µm), exhibiting efficient transmission of left-handed circularly polarized (LCP) light while strongly suppressing right-handed circularly polarized (RCP) light. Consequently, pronounced circular dichroism (∼0.8) and exceptionally high circular polarization extinction ratios of up to ∼30 dB are achieved at the designed wavelengths. This multi-pixel architecture enables independent and selective acquisition of circular polarization information across five discrete spectral bands on a single chip-scale platform. Notably, the proposed device, for the first time, to our knowledge, integrates circular polarization detection in both the optical communication band (1.55 µm) and multiple characteristic vibrational absorption bands in the mid-infrared, including the O–H stretching mode at 2.7 µm and the C=O stretching mode at 4.26 µm. These results establish a compact and versatile multi-spectral polarization-resolved detection solution with strong potential for applications in high-speed optical communications, chiral molecule sensing, gas analysis, and thermal imaging.