Bidirectional Mid-Infrared Metamaterial with Ultrabroadband Polarization-Selective Absorption and Transmission

Optical metamaterials provide a versatile platform for manipulating the amplitude, phase, and polarization of light at subwavelength scales and are therefore attractive for compact polarization-control devices. However, simultaneously realizing broadband polarization-selective absorption and transmission with bidirectional operation remains challenging. Here, we propose a bidirectional mid-infrared polarization-selective metamaterial comprising multilayer strip resonators integrated with a composite Au grating. For x-polarized incidence, the final bidirectional structure maintains an absorptance above 80% from 3.95 to 12.15 μm, with an average absorptance of 90.4%. For the orthogonal y-polarized incidence, the average transmittance reaches approximately 94% over the same spectral range. The device exhibits broadband polarization selectivity, with average absorption and transmission extinction ratios of 16.5 dB and 42.6 dB, respectively. Electromagnetic-field and structural analyses indicate that the broadband x-polarized absorption is associated with multiple localized resonances together with lattice- and Fabry–Pérot-cavity-related contributions, whereas the high y-polarized transmission is primarily enabled by the polarization-selective response of the Au grating. The symmetric configuration preserves these complementary polarization responses for illumination from either side, providing a route toward broadband multifunctional polarization control in the mid-infrared.