The switching function of traditional waveplates necessitates mechanical replacement or the superimposition of multiple waveplates, which gives rise to a complex system and a large volume. We have devised a multifunctional micro-waveplate based on the COMSOL simulation platform (v5.6), which concurrently integrates the compact nature of metasurfaces and the dynamic regulatory features of phase-change materials. When the phase-change material is in the crystalline phase, the metasurface possesses the functionality of a half-waveplate (HWP) and is capable of performing chirality inversion of circularly polarized light within the wavelength range of 1.45 μm to 1.52 μm and 1.56 μm to 1.61 μm. When the phase-change material is in the amorphous phase, the metasurface serves as a quarter-waveplate (QWP) and can achieve the conversion between linear and circular polarization through a 90° phase delay. The phase-change metasurface breaks through the constraint of fixed functions of traditional optical waveplates, facilitating the development of optical systems towards miniaturization, intelligence, and low power consumption and providing a crucial technical route for the next generation of photonic integration and dynamic optical applications.

Compared with conventional detectors, a circularly polarized detector operating at 4.26 μm effectively suppresses background noise (e.g., solar scattering and atmospheric interference), enabling high-precision CO₂ monitoring across ecosystems like farmland, forests, and wetlands. This capability allows the precise quantification of carbon sink potential and ecosystem health. Our design employs a mid-wave HgCdTe detector—a well-established platform—combined with a CMOS-compatible Si/SiO₂ metasurface. Geometric displacements were applied to break C₂ symmetry, achieving a chiral design. Through multiparameter optimization, we realized a circularly polarized photodetector (CPPD) with a CPER of 18 dB, expected to demonstrate superior CO₂ monitoring performance. These advances may offer researchers and practitioners a robust tool for both fundamental studies and field deployments.

Quantum well infrared photodetectors (QWIPs) are popular due to their following advantages: low cost, maturity of manufacturing, high uniformity, ease of wavelength adjustment, resistance to heat, and resistance to ionizing radiation. However, their low absorption efficiency due to their unique anisotropic absorption properties and ohmic loss of the metal grating severely limit their further adoption. We cleverly used cascaded dielectric metasurfaces to replace the traditional single-layer metal grating, which increased the absorption efficiency to near the upper limit of 100%. By analyzing the near-field profile of the electric field of the miniaturized device, we found that the upper grating, QWIP, and lower grating formed a high-efficiency FP cavity with a strong photon localization capability, allowing the microdevice to effectively achieve 99.3% absorption. In addition, QWIPs with cascade gratings can be incorporated into a polarimeter, allowing for the comprehensive detection of linear polarization information at a wavelength of 14 $\mathsf{\mu }\mathrm{m}$ through rational rotations. Our proposed double-layer grating coupling method can be considered a technology that can effectively address the low-absorption problem associated with QWIPs.