This study investigates the problems of the complex structure, large volume, and nonlinear projection of digital light processing (DLP) projectors, which are widely used in structured light 3D imaging systems. These problems restrict the application of structured light 3D imaging technology to small detection scenes. Therefore, this study proposes a structured light projection chip integrating a metasurface array with a micro-electromechanical system (MEMS) two-dimensional scanning platform. The metasurface array realizes the structured light stripe projection including the Gray code stripe and the phase-shifted stripe, and switching of the metasurface unit is achieved using a MEMS two-dimensional scanning platform. The experimental results demonstrate that the designed structured light projection chip exhibits superior characteristics in terms of precise detection accuracy, a rapid projection rate, and compactness, thereby satisfying the stringent detection requirements for small-scale application scenarios.
The metasurface array is initially investigated based on the geometric phase principle, and an analysis is conducted on the conversion efficiency and phase modulation capability of the nanopillars in each unit toward incident light. Subsequently, the GS algorithm is employed to determine the phases of mixed-code structured light stripes. The metasurface array is designed by obtaining the sizes of the nanopillars and phase information. For the MEMS two-dimensional scanning platform, the electrostatic comb driver design is primarily investigated, and the static, modal, and transient characteristics of the two-dimensional scanning platform are analyzed using ANSYS to ensure that its performance meets design requirements. Finally, this study investigates an integrated manufacturing process for metasurface arrays and MEMS two-dimensional scanning platform, providing a comprehensive manufacturing scheme for subsequent processing.
A chip model (Fig.1) that integrates a metasurface array and an MEMS two-dimensional platform is proposed. By designing the size of the nanopillar in the metasurface unit, a high conversion efficiency of 605 nm incident light is achieved, with the highest conversion efficiency being 88.61%. Additionally, the linear phase regulation ability of the nanopillar to the incident light is verified (Fig.6). The phase information required for constructing the metasurface unit is obtained by solving the mixed-code structured light stripes using the GS algorithm. After obtaining the optimal size of the nanopillars and the phase information, we establish a metasurface element model using FDTD and conduct simulations to evaluate its optical performance. The simulation results demonstrate that the fringes generated by the metasurface unit adhere to the characteristics of both the Gray code fringe (Fig.9) and the phase-shifted method fringe (Fig.10). The generated Gray code stripe exhibits distinct step distribution characteristics in terms of light intensity while maintaining a consistent width throughout. At a projection focal length of 50 mm, the stripe width is 3 mm. The generated phase-shifting stripe exhibits obvious sine distribution characteristics in terms of light intensity, and the stripe width is uniform. At a projection focal length of 50 mm, the stripe width is 2 mm. The generated stripe satisfies the high-detection accuracy requirements of the projection chip, and the static results (Fig.12) demonstrate that the MEMS two-dimensional scanning platform exhibits a low driving voltage. Specifically, the driving voltages for achieving an 80 μm displacement in the X and Y directions are measured to be 68.1 V and 57.6 V, respectively. The modal results (Fig.13) indicate that the two-dimensional scanning platform exhibits excellent anti-vibration and anti-interference characteristics, with a first-order modal frequency of 511.91 Hz and distinct boundaries for higher-order modal frequencies. The transient analysis results (Fig.14) demonstrate that the two-dimensional scanning platform exhibits a high response rate, with a response time of 2.4 ms obtained through the full transient method. Therefore, the structured light projection chip has a high projection rate, with a projection frame rate of 333 Hz. The chip size is 3 mm×3 mm, which has the advantage of miniaturization. The integrated manufacturing process flow of the metasurface array and MEMS two-dimensional platform is ultimately designed (Figs.17,18), encompassing various manufacturing processes for MEMS devices, such as oxidation, lift-off, BOE wet etching, DRIE dry etching, and bonding.
The results demonstrate that the designed metasurface exhibits excellent modulation performance for incident light while generating a striped pattern that satisfies the detection requirements of three-dimensional imaging technology. This effectively enhances the projection linearity of conventional projectors, thereby enabling submillimeter-level detection accuracy. The designed two-dimensional scanning platform exhibits dependable performance and a high projection rate. The integrated manufacturing process of the metasurface array and the MEMS two-dimensional platform provides a theoretical model and a system solution for designing a miniaturized projection device with high detection accuracy and projection rate.
