Chromatic aberration is a major challenge faced by metalenses. Current methods to achieve broadband achromatic operation in metalenses usually suffer from limited size, numerical aperture, and working bandwidth due to the finite group delay of meta-atoms, thus restricting the range of practical applications. Multiwavelength achromatic metalenses can overcome those limitations, making it possible to realize larger numerical aperture (NA) and sizes simultaneously. However, they usually require three layers, which increases their fabrication complexity, and have only been demonstrated in small sizes, with low numerical aperture and modest efficiencies. Here, we demonstrate a 1 mm diameter red−green−blue achromatic metalens doublet with a designed NA of 0.8 and successfully apply the metalens in a digital imaging system. This work shows the potential of the doublet metasurfaces, extending their applications to digital imaging systems such as digital projectors, virtual reality glasses, high resolution microscopies, etc.

Dielectric metasurfaces have significant potential for delivering miniaturized optical systems with versatile functionalities, leading to applications in various fields such as orbital angular momentum generation, imaging, and holography. Among the different materials, crystalline silicon has the advantage of technological maturity and high refractive index, which increases design flexibility and processing latitude. The second, and often overlooked, advantage of silicon is that it affords embedding the metasurface in a protective material such as silica, which is essential for practical applications. The trade‐off against this high refractive index is silicon's absorption at visible wavelength, which requires new design strategies. Here, such a strategy based on metasurfaces supporting air modes is identified that can lead to a transmission efficiency as high as 87% at a wavelength of 532 nm. This exceptional efficiency is obtained by using the high index to confine the electric field in the periphery of the meta‐atoms, thereby reducing absorption losses. As an example, the design of a fully embedded metasurface is described that can generate vortex beams with various orders of orbital angular momentum. It is envisioned that the proposed strategy paves the way for practical applications of high‐efficiency metasurfaces based on crystalline silicon.

Stereoscopic microscopy is a promising technology to obtain three-dimensional microscopic images. Such microscopes are based on the parallax effect, and as such require two lenses to focus at two different points. Geometrical constraints, however, restrict their numerical apertures to about 0.2, thus limiting the system’s resolution. Higher numerical apertures ( ∼ 0.35 ) can be achieved with designs using only one bulk lens, but such systems are ∼ 10 times more costly than the conventional ones. Thus, there is a pressing need for alternative solutions to improve the resolution of stereoscopic systems. Here, we show that high-resolution and low-cost stereoscopic systems can be obtained using birefringent single-layer metalenses. We design and fabricate a birefringent metalens operating at 532 nm with a numerical aperture as high as 0.4. The metalens is then used to demonstrate high-resolution stereoscopic imaging of biological samples. The microscopic images are further displayed and perceived vividly in an autostereoscopic display. Our demonstration paves the way to a new strategy to achieve high-resolution and low-cost stereoscopic microscopes.

Due to the total internal reflection caused by the mismatch of the refractive indices between organic layers and oxide layers within an organic light‐emitting diode (OLED), most of the light energy is trapped inside the device; if the size of an OLED is further limited to a few micrometers, most of the light will be lost on the side wall, which will further reduce the light outcoupling efficiency. Herein, the mechanism of the light extraction efficiency of micro‐OLEDs with metalens is studied. The results show that the metalens has a better optical extraction efficiency for single‐reflection light rather than requiring light to be multireflected by the conventional photonic structures. As a result, it effectively improves the light‐emitting coupling efficiency and even the OLED size shrinks to 1 μm. This technique is expected to boost the efficiency in ultrahigh‐pixel‐density microdisplays required in emerging augmented reality (AR)/virtual reality (VR) and is extrapolated to other light‐emitting devices such as quantum‐dot light‐emitting diodes (QLEDs), micro‐light‐emitting diodes (μLEDs), and perovskite light‐emitting diodes (PeLEDs).

Beam combiners are widely used in various optical applications including optical communication and smart detection, which spatially overlap multiple input beams and integrate a output beam with higher intensity, multiple wavelengths, coherent phase, etc. Since conventional beam combiners consist of various optical components with different working principles depending on the properties of incident light, they are usually bulky and have certain restrictions on the incident light. In recent years, metasurfaces have received much attention and become a rapidly developing research field. Their novel mechanisms and flexible structural design provide a promising way to realize miniaturized and integrated components in optical systems. In this paper, we start from studying the ability of metasurfaces to manipulate the incident wavefront, and then propose a metasurface beam combiner in theory that generates an extraordinary refracted beam based on the principle of phase gradient metasurface. This metasurface combines two monochromatic light incidents at different angles with identical polarization but arbitrary amplitudes and initial phases. The combining efficiency, which is defined as the ratio of the power in the combining direction to the total incident power, is 42.4% at the working wavelength of 980 nm. The simulated results indicate that this proposed method is able to simplify the design of optical combiners, making them miniaturized and integrated for smart optical systems.