Ma Zhiyuan, Dong Siyu, Dun Xiong, Wei Zeyong, Wang Zhanshan, Cheng Xinbin
MOE Key Laboratory of Advanced Micro-Structured Materials, Shanghai 200092, China.
Institute of Precision Optical Engineering, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China.
Micromachines (Basel). 2022 Apr 13;13(4):607. doi: 10.3390/mi13040607.
Depth imaging is very important for many emerging technologies, such as artificial intelligence, driverless vehicles and facial recognition. However, all these applications demand compact and low-power systems that are beyond the capabilities of most state-of-art depth cameras. Recently, metasurface-based depth imaging that exploits point spread function (PSF) engineering has been demonstrated to be miniaturized and single shot without requiring active illumination or multiple viewpoint exposures. A pair of spatially adjacent metalenses with an extended depth-of-field (EDOF) PSF and a depth-sensitive double-helix PSF (DH-PSF) were used, using the former metalens to reconstruct clear images of each depth and the latter to accurately estimate depth. However, due to these two metalenses being non-coaxial, parallax in capturing scenes is inevitable, which would limit the depth precision and field of view. In this work, a bifunctional reconfigurable metalens for 3D depth imaging was proposed by dynamically switching between EDOF-PSF and DH-PSF. Specifically, a polarization-independent metalens working at 1550 nm with a compact 1 mm aperture was realized, which can generate a focused accelerating beam and a focused rotating beam at the phase transition of crystalline and amorphous GeSbTe (GST), respectively. Combined with the deconvolution algorithm, we demonstrated the good capabilities of scene reconstruction and depth imaging using a theoretical simulation and achieved a depth measurement error of only 3.42%.
深度成像对于许多新兴技术非常重要，例如人工智能、无人驾驶车辆和面部识别。然而，所有这些应用都需要紧凑且低功耗的系统，而这超出了大多数最先进深度相机的能力范围。最近，基于超表面的深度成像利用点扩散函数（PSF）工程已被证明可以小型化且单次成像，无需主动照明或多视角曝光。使用了一对具有扩展景深（EDOF）PSF和深度敏感双螺旋PSF（DH-PSF）的空间相邻的金属透镜，利用前者金属透镜重建每个深度的清晰图像，利用后者精确估计深度。然而，由于这两个金属透镜是非同轴的，在捕捉场景时视差是不可避免的，这会限制深度精度和视野。在这项工作中，通过在EDOF-PSF和DH-PSF之间动态切换，提出了一种用于3D深度成像的双功能可重构金属透镜。具体而言，实现了一种在1550 nm工作的具有紧凑1 mm孔径的偏振无关金属透镜，它可以在结晶和非晶态锗锑碲（GST）的相变时分别产生聚焦加速光束和聚焦旋转光束。结合去卷积算法，我们通过理论模拟展示了场景重建和深度成像的良好能力，并且实现了仅3.42%的深度测量误差。
