Objective Polarization control in the near-infrared (NIR) regime serves as a fundamental technology for numerous advanced applications, including high-capacity optical communication, high-resolution biomedical imaging, molecular spectroscopy, and optical sensing. Traditional tools for polarization manipulation, such as wave plates, prisms, typically exhibit significant limitations in terms of size, bandwidth, functional versatility, and integration potential with modern photonic circuits. The advent of optical metasurfaces has revolutionized the mentioned limitations, enabling precise control over the amplitude, phase, and polarization of light within a ultra-thin planar film. However, a persistent challenge in this field is the realization of passive metasurfaces that can simultaneously provide multiple polarization transformation functions with high conversion efficiency and ultra-broad bandwidth. Most reported designs are restricted to a single operating mode or rely on external active tuning mechanisms, which substantially increase complexity of the system.

Methods To directly address the technological challenge, in this paper, we introduce a comprehensive design, rigorous numerical analysis, and an elucidation of the operating principle of a novel, fully passive reflective metasurface designed for ultra-broadband, high-efficiency multifunctional polarization conversion across multiple bands within NIR. The unit cell is meticulously constructed from three distinct layers: a top-layer nanostructured resonator made of silver, a middle dielectric spacer made of silica, and the bottom layer of silver film. The key innovation lies in the geometry of the top-layer resonator, which is an anisotropic notched rectangular ring — a design deliberately lacking fourfold rotational symmetry to break the symmetry for differently polarized incident light. To directly address the technological challenge, in this paper, we introduce a comprehensive design, rigorous numerical analysis, and an elucidation of the operating principle of a novel, fully passive reflective metasurface designed for ultra-broadband, high-efficiency multifunctional polarization conversion across multiple bands within NIR. The unit cell is meticulously constructed from three distinct layers: a top-layer nanostructured resonator made of silver, a middle dielectric spacer made of silica, and the bottom layer of silver film. The key innovation lies in the geometry of the top-layer resonator, which is an anisotropic notched rectangular ring — a design deliberately lacking fourfold rotational symmetry to break the symmetry for differently polarized incident light. Finite element method (FEM) is employed for all simulations. Simulation boundaries employed periodic conditions in the x-y plane and perfectly matched layers in the propagation direction. Performance evaluation is conducted under normal incidence of x polarized plane wave. A comprehensive set of metrics is calculated to quantify the performances, including co-polarized reflection coefficient, cross-polarized reflection coefficient, polarization conversion ratio, reflectance of the converted circular polarization states, as well as derived polarization rotation angle and ellipticity angle. To reveal the underly fundamental physical principles, an anisotropic decomposition method is employed to analyze the amplitude and phase responses of the electromagnetic fields along the two principal axes of the resonator. Additionally, surface current distributions and electric field distributions are examined in detail at multiple wavelengths to visualize the excitation of electric dipole moments.

Results and Discussions Simulation results validate the exceptional multifunctional polarization conversion capabilities and broadband characteristics of the proposed metasurface structure. First, it operates as a highly efficient half-wave plate within the wavelength range from 1520 nm to 1720 nm. In this range, the cross-polarized reflectance consistently exceeds 0.8, reaching a peak of 0.939 at the wavelength of 1620 nm, while the undesired co-polarized reflection is suppressed to near zero (0.0009 at the same wavelength). The corresponding polarization conversion ratio remains above 0.9 within the wavelength range of 1570−1735 nm, reaching a near-ideal maximum of 0.999 at 1650 nm, while the polarization rotation angle is maintained at approximately 90° over a broad wavelength range from 1380 nm to 1880 nm, enabling orthogonal polarization conversion. Second, the metasurface seamlessly transitions to broadband quarter-wave plate in the two adjacent wavelength bands. In the lower wavelength band from 910 nm to 1520 nm, it predominantly converts x-polarized incident light into right-handed circularly polarized light, with a reflectance rxR greater than 0.8 and a peak efficiency of 0.965 at 1350 nm. In the higher wavelength band from 1720 nm to 2500 nm, the x-polarized incident light is converted to left-handed circularly polarized light, with a reflectance rxL > 0.8 with a peak reflectance of 0.958 at 1910 nm. The ellipticity angle η quantitatively determines the degree of circular polarization, confirming the polarization conversion by remaining around −45° in the band generating right-hand circular polarization (1080−1440 nm) and around +45° in the band generating left-hand circular polarization (1800−2500 nm). The physical origin of the behavior can be traced back through anisotropic decomposition analysis, which reveals that the critical phase difference between the u and v field components is approximately −3π in the wavelength band working as half-wave plate, satisfying the condition for a 180° phase shift. In the wavelength band working as quarter-wave plate, Δφ keeps unchanged at around −3.5π and −2.5π, respectively, meeting the requirements for orthogonal polarization conversion. Surface current analysis at representative wavelengths (1130 nm, 1620 nm and 2180 nm) indicates the excitation of strongly directional electric dipoles on both the top-layer resonator and the bottom substrate. These dipoles excite electromagnetic coupling, facilitating the phase modulation required for efficient and broadband conversion.

Conclusions In conclusion, in this work, we successfully demonstrate the design and theoretical validation of a passive reflective type metasurface that integrates high-efficiency half-wave plate and quarter-wave plate functionalities within a single, ultra-thin device in the near-infrared. By exploiting the geometric anisotropy, the proposed design overcomes the traditional trade-offs between bandwidth, efficiency, and functional versatility. Through detailed numerical investigations, together with analyses of polarization ellipse parameters and current distribution, a thorough understanding of the underlying conversion mechanisms is provided. It holds immense promise for revolutionizing compact photonic systems, with potential applications including polarization-encoded optical communications, polarization-sensitive endoscopic imaging, miniaturized spectroscopic sensors, quantum optical devices, and next-generation lidar systems, offering a new design approach for multifunctional polarization control.