Metalens Array Research Articles

Metalens array for quantum random number

Quantum random number generation (QRNG) leveraging intrinsic quantum uncertainty has attracted significant interest in the field of integrated photonic architecture, with applications in quantum cryptography, tests of quantum nonlocality, and beyond. The demand for compact, low-energy consumption, robust, fast, and cost-effective QRNGs integrated into photonic chips is highlighted, whereas most previous works focused on bulk optics. Here, based on the metalens array entangled source, we experimentally realized a miniaturized, high-dimensional quantum random number generator via a meta-device without post-randomness extraction. Specifically, the device has a high-density output with 100 channels per square millimeter. This chip-scale quantum randomness source can obtain random number arrays without post-randomness extraction and enable compact integration for quantum applications needing secure keys or randomness. Our approach demonstrates potential in secure key generation and randomness for quantum applications.

Photodetector with a metalens packaging module for visible light communication based on RGBY illumination LED light source

A novel, to the best of our knowledge, photodetector with a metalens packaging module used as the visible light communication (VLC) receiver is proposed and designed. An LED consisting of red, green, blue, and yellow chips (RGBY-LED) is adopted as the transmitter for intensity modulation direct detection VLC systems. A metalens array with a numerical aperture (NA) of 0.707 used as a polarization-insensitive planar lens of the VLC system receiver is designed at wavelengths of 457, 523, 592, and 623 nm corresponding to blue, green, yellow, and red for high efficiency. Compared with a traditional Fresnel lens positive-intrinsic-negative (PIN) photodetector module as the VLC receiver, the introduction of a metalens module can decrease the form factor of the VLC receiver module and, in particular, it is much thinner. The combination of the multi-color LED transmitter and photodetector metalens packaging module receiver can increase the modulation bandwidth due to four different wavelengths used for the VLC system. Finite-difference time domain (FDTD) simulations are performed to validate the performance of the photodetector with a metalens module. It is revealed that the corresponding efficiencies of 57.5%, 55.4%, 57%, and 56.3% were achieved at wavelengths of 623, 592, 523, and 457 nm, respectively, based on a metalens array with a 0.707 NA and 2.5 µm radius of the active area of the photodetector. It is a promising technology for indoor VLC systems such as those for smart phones and other Internet of Things devices due to the need for compact packaging for the receiver.

Wide-angle metalens array with quadratic phase for terahertz polarization detection

Abstract With the advances of micro/nano fabrication technology, metasurface has become an alternative to design functional devices for manipulating electromagnetic wave. Metalens is one of the basic electromagnetic functional devices that can be applied in various fields. Currently, polarization measurement based on metalens arrays has been widely investigated, but most of them can only work for normal incident wave due to the limited field-of-view of metalens. Herein, a dielectric wide-angle metalens array (WMA) for the terahertz polarization detection is presented. The WMA is composed of three wide-angle metalenses, each wide-angle metalens is constructed by utilizing quadratic phase profile. The angle tolerance of meta-atoms which constitute the wide-angle metalens is elucidated in detail. The WMA can decompose incident terahertz wave into four channels, and the full Stokes parameters of incident wave is determined by intensities in these four channels. Simulated results show that the WMA proposed here has excellent performance for the polarization detection within incident angle of ±40°. In addition, this WMA can also be used to detect the phase gradient of incident terahertz wave, the detection error is less than 1.1%. This WMA is promising in the fields of terahertz polarization generation, detection and imaging.

A wide-field-of-view metalens array for CMOS image sensors’ conical light focusing

Microlens array combined with CMOS sensors have recently been the subject of intensive research due to their ability to significantly enhance imaging sensitivity. However, existing microlens arrays suffer from a limited field-of-view, necessitating complex lens assemblies that increase system cost, size and weight. In this study, we present a novel approach utilizing a single layer metalens array composed of low loss and high-index α-Si materials. The metalens array was designed using a phase compensation method to efficiently focus conical light with arbitrary cone angles onto the center pixels of the CMOS sensor. Theoretical analysis demonstrates that the metalens is capable of focusing ± 20° conical light with an impressive efficiency of 83.6 %, which can be extended to arbitrary cone angles. Experimental results reveal a measured focusing efficiency of 73 % under an incidence angle of ± 8.3° for conical light, representing an improvement of 8 % compared to parallel light incidence. This research presents a promising solution for wide-field-of-view metalens arrays in integrated CMOS imaging systems.

Pitch‐Switchable Metalens Array for Wavefront Profiling at Multiwavelength

AbstractThe wavefront sensor is a crucial component in the adaptive optics system (AOS), responsible for detecting aberrated wavefronts. However, The Shack–Hartmann wavefront sensor with single‐pitch microlens array is limited in its adaptability to different observing conditions, affecting wavefront reconstruction accuracy. And conventional microlens arrays are wavelength‐specific. Here, a polarization‐dependent pitch‐switchable metalens array based on non‐interleaved silicon metasurfaces is proposed, capable of working at multiple wavelengths. By controlling the incident and outgoing light polarization, three metalens arrays with customized pitches can be switched at will. Furthermore, achromatic performance is achieved in the 950 nm and 1030 nm wavelengths through structural dispersion engineering. Finally, wavefront detection experiments are finally conducted to demonstrate the phase reconstruction with variable spatial resolution. The metalens array with high flexibility in wavefront sensor can further enhance the adaptability of AOS and has great potential for applications in light‐field imaging, and machine vision, etc.

Metasurface for programmable quantum algorithms with classical and quantum light

Abstract Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. Here, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical and quantum light with single photons. Our approach encodes multiple programmable quantum algorithms and operations, such as Grover’s search algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the interference patterns captured by a single-photon camera are used to extract information about the output state at the selected output directions. Our programmable quantum metasurface approach holds promising potential as a cost-effective means of miniaturizing components for quantum computing and information processing.

Integral imaging near-eye 3D display using a nanoimprint metalens array

Integral imaging (II) display, one of the most critical true-3D display technologies, has received increasing research recently. Significantly, an achromatic metalens array has realized a broadband metalens-array-based II (meta-II). However, the past micro-scale metalens arrays were incompatible with commercial micro-displays; furthermore, the elemental image array (EIA) rendering is always slow. The two hinders in device and algorithm prevent meta-II from being used for practical video-rate near-eye displays (NEDs). This research demonstrates a meta-II NED combining a commercial micro-display and a metalens array. The large-area nanoimprint technology fabricates the metalens array, and a novel real-time rendering algorithm is proposed to generate the EIA. The hardware and software efforts solve the bottlenecks of video-rate meta-II displays. We also build a see-through prototype based on our meta-II NED, demonstrating the feasibility of augmented reality. Our work explores the potential of video-rate meta-II displays, which we expect can be valuable for future virtual and augmented reality.

High performance DFB laser array combiner enabled by all-dielectric metalens array

Metalens have the advantages of ultra-thin, low loss, easy integration and flexible phase control mechanism, which have attracted intensive attention in the field of on-chip photonic chips. By designing Si nanocylinder meta-atom on SiO2 substrate, the structure size is optimized to achieve the optimal light transmittance and phase change covers the range of 2π. In order to achieve the effect of coupling Distributed Feedback Laser (DFB) array into a fiber, it is necessary to accurately arrange the above optimized Si nanocylinder according to a certain phase profile to achieve the effect of off-axis focusing. Here, we designed an off-axis focusing metalens array to efficiently couple the parallel 4-channel DFB laser array into the few-mode fiber (FMF), and the total coupling efficiency reaches 56.48 %. This result provides a new idea for compact, low loss on-chip light sources.

Multifocal meta-fiber based on the fractional Talbot effect.

Multi-focusing of light is a crucial capability for photonic devices that can be effectively achieved by precisely modulating the phase delay on the incident wavefront. However, integrating functional structures into optical fibers for remote light focusing remains challenging due to the complex device design and limited fabrication approaches. Here, we present the design and fabrication of metalens array on the end-face of a tailored single-mode step-index fiber for focusing light field into closely packed focal spot array. The metalenses are configured based on the fractional Talbot effect and benefit a modular design capability. Light passing through the optical fiber can be focused into different focal planes. With a synergistic 3D laser nanoprinting technique based on two-photon polymerization, high-quality meta-fibers are demonstrated for focusing light parallelly with a uniform numerical aperture (NA) as high as approximately 0.77. This may facilitate various applications such as optical trapping, generation of sophisticated beam profiles, and boosting light coupling efficiencies.

Metalens array miniaturized microscope for large-field-of-view imaging

Miniaturized microscopes with large field-of-view (FOV) have wide applications in biomedical imaging and automated machine vision. Conventional microscopes with a single objective lens have tradeoffs among FOV, resolution and device thickness. Thanks to the high compactness and design flexibility, metalens has a great potential for building the next generation compact imagers. However, there have been various challenges and performance tradeoffs in the design, fabrication and implementation of metalens that could support a large FOV. Here, we present a metalens array based miniaturized microscope that provides extremely high compactness and large FOV. Each metalens unit can image the object tile immediately below it. By tiling such metalens units, we can scale up the FOV while keeping the same device thickness and imaging quality as the microscope with a single metalens unit. Our metalens array enables a compact microscope that can perform large FOV imaging through arbitrary polarized light. We experimentally demonstrated the miniaturized metalens array microscope in 1310 nm wavelength, which has an FOV of 3 × 4 mm2 and can resolve 6.9 μm lines, with 4 mm distance between the sample surface to the camera sensor. Although this is a proof-of-concept demonstration, our metalens array microscope provides a promising solution for portable and implantable camera for large-FOV high-resolution imaging.

High-efficiency broadband achromatic metalenses for visible full-stokes polarization imaging.

Polarization-imaging technology has important applications in target detection, communication, biomedicine, and other fields. A polarization imaging system based on metalenses, which provides new possibilities for the realization of highly integrated full-Stokes polarization imaging systems, can solve the problems of traditional polarization imaging systems, such as complex structures, large volumes, and the inability to simultaneously obtain linear and circular polarization states. However, currently designed metalens arrays that can achieve real-time full-Stokes polarization imaging can generally only be used for monochromatic detection, which significantly limits the amount of measured information of the object. Broad-spectrum polarization color imaging allows more image degrees of freedom, enabling more accurate characterization of polarization for multi-target object scenes in complex environments. To achieve broad-spectrum polarization imaging, we propose and design a metalens array that can achieve full-Stokes polarization imaging in the broadband visible range, in which the design process of metalenses for splitting and focusing broadband orthogonal circularly polarized light is emphasized. To design metalenses that can achieve polarization splitting and efficient focusing, we simulate and optimize the height and period of the nano-units and show that smaller periods and larger heights do not always result in higher-performance devices when designing multifunctional metalenses. The designed metalens array can split and diffraction-limited focus the orthogonal polarized incident light to the designated position with average focusing efficiencies of 59.2% under 460-680 nm TM linearly polarized light, 53.1% under TE linearly polarized light, 58.8% under left-handed circularly polarized light, and 52.7% under right-handed circularly polarized light. The designed metalenses can be applied to imaging systems, such as polarization imaging and polarization light-field imaging systems.

44‐3: Invited Paper: Metalens Array for Integral‐Imaging‐Based Near‐Eye Display

We propose a novel integral‐imaging (II) based near‐eye display (NED) combined with high‐pixel‐density display screen, voxel‐based rendering method and nano‐imprint metalens array. The effect of depth of field in AR and VR of such II‐based NED is shown, and the 3D parallax effect on the real mode is demonstrated. We successfully miniaturize the II‐based NED which shows a great potential using in AR and VR.

Cryogenic etching and characterization of nano-sized silicon metadevice

The dielectric materials were usually deposited as hard masks for etching in the fabrication of dielectric metasurfaces, which increased fabrication steps and the distortion of the devices. We present a simplified process for preparing nano-sized silicon structure. The samples after photolithography were cooled and directly etched without deposited the hard mask. The cryogenic etching process reduce the fabrication steps and distortion caused by the transfer of photolithographic patterns. Here, a transmission middle-wavelength infrared (MWIR) metalens array was designed and fabricated as a demonstration. The optimal temperature for cryogenic etching was proved and found at 163 K by comparing the etching effects at different temperatures. The side walls of metalens prepared by the proposed process are steep, and the depth-width ratio meets the requirements. The metalens with operating at λ=4μm, can focus the light to a spot with a full-width at half-maximum (FWHM) of 20.308μm at the focal plane. The converging efficiency of the metalens reaches 95%, and the focal length is 385μm. Considering the increasingly complex and finer size of metasurface, this process may have great potentials in the preparation of nanostructures.

An Autofocus Method Based on Improved Differential Confocal Microscopy in Two-Photon Lithography

Two-photon lithography (TPL) plays a vital role in microstructure fabrication due to its high processing accuracy and maskless characteristics. To optimize the manufacturing quality deteriorated by the defocus of the substrate, an autofocus approach based on improved differential confocal microscopy (IDCM) is proposed in this paper. Through analyzing the intensity response signals from two detectors with symmetrical axial offset, the defocus amount is measured and compensated for with high precision and noise immunity to stabilize the substrate. The verification experiments on the coverslip reported a detection sensitivity of 5 nm, a repetitive measurement accuracy of less than 15 nm, and a focusing accuracy reaching around 5 nm. The consistency between simulation and characterization demonstrated the effectiveness and superior performance of the autofocus system for the high production quality of the metalens array. The proposed autofocus method shows promise for further application to the fabrication of complex structures on various substrates.

Wide field of view and full Stokes polarization imaging using metasurfaces inspired by the stomatopod eye

Abstract Wide field of view and polarization imaging capabilities are crucial for implementation of advanced imaging devices. However, there are still great challenges in the integration of such optical systems. Here, we report a bionic compound eye metasurface that can realize full Stokes polarization imaging in a wide field of view. The bionic compound eye metasurface consists of a bifocal metalens array in which every three bifocal metalenses form a subeye. The phase of the bifocal metalens is composed of gradient phase and hyperbolic phase. Numerical simulations show that the bifocal metalens can not only improve the focusing efficiency in the oblique light but also correct the aberration caused by the oblique incident light. And the field of view of the bionic compound eye metasurface can reach 120° × 120°. We fabricated a bionic compound eye metasurface which consists of three subeyes. Experiments show that the bionic compound eye metasurface can perform near diffraction-limited polarization focusing and imaging in a large field of view. The design method is generic and can be used to design metasurfaces with different materials and wavelengths. It has great potential in the field of robot polarization vision and polarization detection.

Highly angle-sensitive and efficient optical metasurfaces with broken mirror symmetry

Abstract Optical metasurfaces have great potential to overcome the functional limitations of conventional optical devices. In addition to polarization- or wavelength-multiplexed metasurfaces, angle-multiplexed metasurfaces can provide new degrees of freedom, enabling previously unrealized complex functionality in diverse applications such as LiDAR, augmented reality glasses, and imaging. However, there have been fundamental trade-offs in transmission efficiency and angular sensitivity for practically important paraxial rays. In this paper, we overcome this limitation by breaking mirror symmetries of single-layer metasurface structures. Based on an effective medium theory, we intuitively explain which material parameters affect the sensitivity and efficiency and prove that high sensitivity and high efficiency can be achieved simultaneously by breaking the mirror symmetry. Based on this, we propose optimized metasurfaces for two applications: an angle-multiplexed beam-steering device with up to 93% relative efficiency and an angle-multiplexed metalens array that can break the fundamental resolution–density trade-off of microlens arrays with high efficiency. The proposed angle-selective designs could pave the way for the development of new classes of compact optical devices with novel functions.

Ultracompact Multimode Meta-Microscope Based on Both Spatial and Guided-Wave Illumination

Microscopic imaging technology is an indispensable foundation in the biomedical field, which enables powerful capability in bio-investigations. Aiming for more convenience and adaptability, a multifunctional microscope with a miniaturized scheme is a new requirement, but remains a challenge. Here, we propose an ultracompact microscope based on both spatial and guided-wave illumination that can work in bright-field, dark-field, and fluorescence imaging modes separately and simultaneously by conveniently switching the light source. The proposed guided-wave illumination not only provides a noise-free imaging mode, but also further reduces the system size. Moreover, a metalens array is specifically designed by a hexagonal arrangement to enable multi-field imaging and enlarge the field of view. The experiment results demonstrate that the half-pitch resolution is about 714 nm with an imaging magnification of 3.5×, with a field of view of 0.543 mm 2 and a space-bandwidth product of 4.26 megapixels. As examples, the multimode microscope is applied to image different cells and flowing microspheres in microtubules, showing comparable image quality with the images taken through the traditional microscope under guided-wave illumination. This demonstrates the possibility of the meta-microscope to be combined with microfluidic technology and further realize miniaturized microfluidic imaging systems. Our ultracompact multimode microscope has shown powerful capabilities for a new scheme of bio-observation and investigations.

A Single-Celled Metasurface for Multipolarization Generation and Wavefront Manipulation.

Due to their unprecedented ability to flexibly manipulate the parameters of light, metasurfaces offer a new approach to integrating multiple functions in a single optical element. In this paper, based on a single-celled metasurface composed of chiral umbrella-shaped metal-insulator-metal (MIM) unit cells, a strategy for simultaneous multiple polarization generation and wavefront shaping is proposed. The unit cells can function as broadband and high-performance polarization-preserving mirrors. In addition, by introducing a chiral-assisted Aharonov-Anandan (AA) geometric phase, the phase profile and phase retardation of two spin-flipped orthogonal circular polarized components can be realized simultaneously and independently with a single-celled metasurface via two irrelevant parameters. Benefiting from this flexible phase manipulation ability, a vectorial hologram generator and metalens array with spatially varying polarizations were demonstrated. This work provides an effective approach to avoid the pixel and efficiency losses caused by the intrinsic symmetry of the PB geometric phase, and it may play an important role in the miniaturization and integration of multipolarization-involved displays, real-time imaging, and spectroscopy systems.

Ultraviolet metalens and metalens array of focused vortex beams

The solar-blind ultraviolet (UV) wavelength is particularly interesting within the range of 200 nm–300 nm. Here, we propose a focusing metalens, focusing vortex beam (VB) metalens and metalens array that specifically work in the UV band to focus a beam or VB. Firstly, a high numerical aperture (NA) focusing metalens working at a wavelength of 214.2 nm was designed, and the NA reached 0.83. The corresponding conversion efficiency of the unit structure reached as high as 94%, and the full width at half maximum was only 117.2 nm. Metalenses with large NA can act as optical tweezers and can be applied to trap ultracold atoms and molecules. Secondly, a focused VB metalens in the wavelength range of 200 nm–300 nm was also designed, which can convert polarized light into a VB and focus the VB simultaneously. Finally, a metalens array was developed to focus VBs with different topological charges on the same focal plane. This series of UV metalenses could be widely used in UV microscopy, photolithography, photonics communication, etc.

A Meta-Device for Intelligent Depth Perception.

The optical illusion affects depth-sensing due to the limited and specific light-field information acquired by single-lens imaging. The incomplete depth information or visual deception would cause cognitive errors. To resolve this problem, an intelligent and compact depth-sensing meta-device that is miniaturized, integrated, and applicable for diverse scenes in all light levels is demonstrated. The compact and multifunction stereo vision system adopts an array with 3600 achromatic meta-lenses and a size of 1.2 × 1.2 mm2 to measure the depth over a 30cm range with deep-learning support. The meta-lens array can act as multiple imaging lenses to collect light field information. It can also work with a light source as an active optical device to project a structured light. The meta-lens array can serve as the core functional component of a light-field imaging system under bright conditions or a structured-light projection system in the dark. The depth information in both ways can be analyzed and extracted by the convolutional neural network. This work provides a new avenue for the applications such as autonomous driving, machine vision, human-computer interaction, augmented reality, biometric identification, etc.