Experimental Technology and Management

[Objective] This study undertakes a comprehensive investigation of the phase modulation properties of subwavelength dielectric gratings(SWDGs), emphasizing the role of key structural parameters—namely, grating period, duty cycle, substrate refractive index, and grating height—in determining the resulting phase retardation. This research aims to demonstrate that SWDGs function as highly tunable optical elements that enable precise two-dimensional light-field manipulation, thereby offering distinct advantages over conventional birefringent waveplates in terms of angular stability, broadband performance, and integration flexibility. Ultimately, this study seeks to establish theoretical and experimental frameworks to support the implementation of SWDGs in advanced photonic platforms, including metasurfaces, polarization control devices, and integrated optical systems. [Methods] A dual approach was employed, integrating numerical simulations and experimental measurements. The finite element method(FEM) was employed in COMSOL Multiphysics to develop a rigorous electromagnetic model of the SWDG, enabling the simulation of phase retardation under variable structural parameters and incident conditions. The behavior of TE-and TM-polarized waves, their transmission efficiency, and the resulting phase difference were the specific focus of the simulations. In the experimental phase, a quartz-based subwavelength grating with a period of approximately 826 nm and a height of 1 280 nm was fabricated via ultraviolet nanoimprint lithography. A bespoke optical configuration was engineered to assess the phase retardation characteristics at 1 550 nm under normal incidence. The system employed Mueller matrix polarimetry, using a laser source, linear polarizers, and a rotating analyzer, in conjunction with a power meter. The resulting intensity profiles as a function of analyzer angle were recorded and fitted using MATLAB to extract the exact phase delay and optical axis orientation. [Results] The phase retardation is principally dictated by the grating height and the substrate's refractive index. An approximate linear relationship with height is observed, with a monotonic increase at higher refractive indices. The impact of variations in grating period on phase delay was found to be minimal, whereas the duty cycle showed a nonlinear effect, with an optimal value of approximately 0.4. The experimental measurements corroborated the numerical predictions, yielding a phase retardation of 0.44 rad, which closely matched the simulated value of 0.43 rad, resulting in a minor error of only 2.3%. The optical axis orientation was approximately 1.71 rad. The minor discrepancies observed between the simulation and the experiment were attributed to three factors: fabrication imperfections, slight misalignments in the optical path, and non-ideal polarization elements. The SWDG exhibited high transmission and consistent performance across a range of incident angles, thereby underscoring its robustness and suitability for practical applications. [Conclusions] This study successfully illustrates that SWDGs can be designed and fabricated to achieve tailored phase retardation. This offers a versatile and efficient alternative to conventional waveplates. The strong correlation between simulation and experimental results validates the use of FEM-based modeling for the design and optimization of SWDGs. Notable advantages of these gratings include broad angular acceptance, wavelength flexibility, and compatibility with standard nanofabrication processes. These characteristics render them highly promising for applications in metasurfaces, adaptive optics, optical sensing, and on-chip photonic systems. Subsequent research endeavors should explore dynamic and reconfigurable grating designs, as well as their integration with other functional optical elements to further expand their utility in next-generation optical technologies.