Meta-optics based on metasurfaces that interact strongly with light has been an active area of research in recent years. The development of meta-optics has always been driven by human’s pursuits of the ultimate miniaturization of optical elements, on-demand design and control of light beams, and processing hidden modalities of light. Underpinned by meta-optical physics, meta-optical devices have produced potentially disruptive applications in light manipulation and ultra-light optics. Among them, optical metalens are most fundamental and prominent meta-devices, owing to their powerful abilities in advanced imaging and image processing, and their novel functionalities in light manipulation. This review focuses on recent advances in the fundamentals and applications of the field defined by excavating new optical physics and breaking the limitations of light manipulation. In addition, we have deeply explored the metalenses and metalens-based devices with novel functionalities, and their applications in computational imaging and image processing. We also provide an outlook on this active field in the end.

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 mm² aperture was realized, which can generate a focused accelerating beam and a focused rotating beam at the phase transition of crystalline and amorphous Ge₂Sb₂Te₅ (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%.

Retroreflective gratings serve as fundamental optical elements in nanophotonics, with polarization-independent diffraction efficiency being one of the critical parameters for assessing their performance. In the far-infrared spectral range, traditional retroreflective gratings typically refer to metal echelette gratings, but their diffraction efficiency cannot approach 100% due to metal absorption. In the visible and near-infrared spectral ranges, metal echelette gratings have gradually been replaced by all-dielectric metasurfaces because dielectric materials exhibit negligible absorption at specific wavelengths. However, there is still a lack of relevant research in the far-infrared range, mainly due to the weak control capability of the existing devices over the polarization-independent phase. Here, we propose a kind of all-dielectric retroreflective metasurface composed of asymmetric pillars and freely tunable aperiodic multilayer films. The pillar structure can achieve polarization insensitivity, and the insufficient modulation capability of the dielectric materials can be compensated for by aperiodic Ge/ZnS films. The designed metasurface achieves the diffraction efficiency by RCWA, with the maximum larger than 99% and the overall reaching 95% (9.3–9.6 µm). We have provided detailed explanations of the design methodology and fabrication process. Our work lays the groundwork for further exploration and application of far-infrared lasers.

Chiral spectral imaging techniques, in contrast to conventional intensity imaging, can provide rich information on the multiscale chirality and spectrum of objects. However, conventional methods often require complex optical systems and multiple shots to achieve this, making the process both cumbersome and time-consuming. Here, we present an ultra-compact on-chip chiral spectral imaging (CSIM) system enabled by a dispersion-engineered chiral metalens (DECM). The meta-atoms can independently control the phase and phase dispersion of orthogonal circular polarization states through the combination of propagation and geometric phases of chiral meta-atoms. Then, the metalens generates two images on opposite sides of the image plane, corresponding to different polarization states, while images at different wavelengths are laterally separated in the focal plane. Consequently, the DECM can be integrated with a CMOS sensor, enabling the simultaneous acquisition of circular dichroism and spectral information in a single snapshot, achieving a high spectral resolution of 10 nm and an extinction ratio exceeding 6 dB. Our results represent a significant advancement toward the integration of multi-dimensional light field perception systems.

Polarization imaging has been proven as an important technique for obtaining multi-dimensional information in complex environments. As the prevalent polarizers, metal gratings are widely used especially for focal-plane detection due to their flexibility and easy integration. However, high-performance polarization gratings with high transmittance and large extinction ratios typically need a large aspect ratio in design, resulting in more difficulties in fabrication with limited practical performances. In this study, we designed and fabricated a high-performance polarizer using metallic–dielectric gratings (MDGs). Through a single CMOS-compatible procedure that included electron-beam lithography (EBL) and a collimated thermal evaporation deposition process, we achieved a high TM transmittance (~90%) and a high extinction ratio (~100:1) in the experiment. We believe that our work provides an effective approach to high-performance polarization gratings, which could contribute to the development of on-chip integrated polarization imaging.

On-chip multi-dimensional detection systems integrating pixelated polarization and spectral filter arrays are the latest trend in optical detection instruments, showing broad application potential for diagnostic medical imaging and remote sensing. However, thin-film or microstructure-based filter arrays typically have a trade-off between the detection dimension, optical efficiency, and spectral resolution. Here, we demonstrate novel on-chip integrated polarization spectral detection filter arrays consisting of metasurfaces and multilayer films. The metasurfaces with two nanopillars in one supercell are designed to modulate the Jones matrix for polarization selection. The angle of diffraction of the metasurfaces and the optical Fabry–Perot (FP) cavities determine the spectrum’s center wavelength. The polarization spectral filter arrays are placed on top of the CMOS sensor; each array corresponds to one pixel, resulting in high spectral resolution and optical efficiency in the selected polarization state. To verify the methodology, we designed nine-channel polarized spectral filter arrays in a wavelength range of 1350 nm to 1550 nm for transverse electric (TE) linear polarization. The array has a 10 nm balanced spectral resolution and average peak transmission efficiency of over 75%, which is maintained by utilizing lossless dielectric material. The proposed array can be fabricated using overlay e-beam lithography, and the process is CMOS-compatible. The proposed array enables broader applications of in situ on-chip polarization spectral detection with high efficiency and spectral resolution, as well as in vivo imaging systems.