A new fabrication method for enhancing the yield of linear micromirror arrays assisted by temporary anchors.

As one of the most common spatial light modulators, linear micromirror arrays (MMAs) based on microelectromechanical system (MEMS) processes are currently utilized in many fields. However, two crucial challenges exist in the fabrication of such devices: the adhesion of silicon microstructures caused by anodic bonding and the destruction of the suspended silicon film due to residual stress. To solve these issues, an innovative processing method assisted by temporary anchors is presented. This approach effectively reduces the span of silicon microstructures and improves the Euler buckling limit of the silicon film. Importantly, these temporary anchors are strategically placed within the primary etching areas, enabling easy removal without additional processing steps. As a result, we successfully achieved wafer-level, high-yield manufacturing of linear MMAs with a filling factor as high as 95.1%. Demonstrating superior capabilities to those of original MMAs, our enhanced version boasts a total of 60 linear micromirror elements, each featuring a length-to-width ratio of 52.6, and the entire optical aperture measures 5 mm × 6 mm. The linear MMA exhibits an optical deflection angle of 20.4° at 110 Vdc while maintaining exceptional deflection flatness and uniformity. This study offers a viable approach for the design and fabrication of thin-film MEMS devices with high yields, and the proposed MMA is promising as a replacement for digital micromirror devices (DMDs, by TI Corp.) in fields such as spectral imaging and optical communication.

Monitoring SF6 Gas Leakage Based on a Customized Binocular System.

Sulfur hexafluoride (SF6) gas is extensively utilized as an insulating and arc-quenching medium in the circuit breakers and isolating switches of electrical equipment. It effectively isolates the circuits from the atmosphere and promptly extinguishes arcs. Therefore, the issue of SF6 gas leakage poses a significant threat to the related application fields, and the detection of SF6 gas leakage becomes extremely important. Infrared imaging detection offers advantages including non-contact, high precision, and visualization. However, most existing infrared detection systems are equipped with only one filter to detect SF6 gas. The images captured contain background noise and system noise, making these systems vulnerable to interference from such noises. To address these issues, we propose a method for monitoring SF6 gas leakage based on a customized binocular imaging (CBI) system. The CBI system has two filters, greatly reducing the interference of system noise and background noise. The first filter features the absorption resonant peak of SF6 gas. The second filter is used to record background noise and system noise. One aspect to note is that, in order to avoid the interference of other gases, the central wavelength of this second filter should keep away from the absorption resonant peaks of those gases. Accordingly, the central wavelengths of our customized filters were determined as 10,630 nm and 8370 nm, respectively. Then, two cameras of the same type were separately assembled with a customized filter, and the CBI prototype was accomplished. Finally, we utilized the difference method using two infrared images captured by the CBI system, to monitor the SF6 gas leakage. The results demonstrate that our developed system achieves a high accuracy of over 99.8% in detecting SF6 gas. Furthermore, the CBI system supports a plug-and-play customization to detect various gases for different scenarios.

Large-aperture electromagnetically actuated MEMS Fabry-Perot filtering chips for visible spectral imaging.

Benefitting from the inherent merits of tiny volume, customizable performance, good system compatibility and high-yield production, micro-electro-mechanical-system-based Fabry-Perot filtering chip (MEMS-FPFC) with a large aperture size gives a feasible way for the realization of miniaturized spectral imagers which can serve in many civilian and military scenarios. Although the aperture size of MEMS-FPFCs in mid-wave and long-wave infrared has reached to the centimeter scale, that of visible wavelength (VIS) MEMS-FPFC is always unsatisfied which is mainly limited by micromachining stress, especially in the thin films. In this work, we propose a large-aperture electromagnetically actuated MEMS-FPFC based on Si3N4 supporting membrane for VIS spectral imaging, which is designed with the assistance of multi-field coupling simulation model. A low-stress wafer-scale bulk micromachining process is developed to guarantee the high-quality and high-yield production for the aimed VIS MEMS-FPFCs. Finally, by the strictly controlling and rationally allocating the film stress of multi-layer film stack, VIS MEMS-FPFCs with 6 mm aperture size are thus developed, which can be tuned bidirectionally and continuously in 612-678 nm waveband with a good linear response of better than 95%. The achieved VIS MEMS-FPFCs can be utilized to construct miniaturized spectral imagers directly, aiming for such applications as intelligent agriculture, environmental protection and industrial inspection.

Column coded scanning aperture hyperspectral imaging system.

The line scanning hyperspectral imaging system (LS-HIS), which relies on a mechanical slit or spatial light modulation device for single channel spatial scanning, is widely used in various fields such as biomedical imaging and remote sensing. However, in scenes that require low light illumination, a decrease in luminous flux will increase exposure time, leading to a significant decrease in scanning efficiency and signal-to-noise ratio (SNR). To address this issue, we present a flexible column coded scanning aperture hyperspectral imaging system (CCSA-HIS) using a spatial light modulator digital micromirror device (DMD). By introducing the concept of multiplex and constructing a multiplexing encoding matrix, we form a one-dimensional multi-column coded scanning aperture, which greatly improves scanning efficiency. Experimental comparisons demonstrate that this approach achieves higher SNR and equivalent spatial and spectral resolution in significantly less sampling time compared to LS-HIS. In short, our scheme provides a new imaging technology for the field of hyperspectral imaging with good theoretical value and engineering significance.

Super-resolution multicolor fluorescence microscopy enabled by an apochromatic super-oscillatory lens with extended depth-of-focus.

Planar super-oscillatory lens (SOL), a far-field subwavelength-focusing diffractive device, holds great potential for achieving sub-diffraction-limit imaging at multiple wavelengths. However, conventional SOL devices suffer from a numerical-aperture-related intrinsic tradeoff among the depth of focus (DoF), chromatic dispersion and focusing spot size. Here, we apply a multi-objective genetic algorithm (GA) optimization approach to design an apochromatic binary-phase SOL having a prolonged DoF, customized working distance (WD), minimized main-lobe size, and suppressed side-lobe intensity. Experimental implementation demonstrates simultaneous focusing of blue, green and red light beams into an optical needle of ~0.5λ in diameter and DOF > 10λ at WD = 428 µm. By integrating this SOL device with a commercial fluorescence microscope, we perform, for the first time, three-dimensional super-resolution multicolor fluorescence imaging of the "unseen" fine structures of neurons. The present study provides not only a practical route to far-field multicolor super-resolution imaging but also a viable approach for constructing imaging systems avoiding complex sample positioning and unfavorable photobleaching.

Sidelobe-suppressed sub-diffraction-limit quasi-non-diffracting light sheets achieved by super-oscillatory lenses.

Sub-diffraction-limit quasi-non-diffracting light sheets (SQLSs) are crucial for a resolution-enhanced and field of view (FOV)-enlarged light sheet microscope. However, it has aways been plagued by sidelobes inducing severe background noise. Here, a self-trade-off optimized method is proposed to generate sidelobe-suppressed SQLSs based on super-oscillatory lenses (SOLs). An SQLS thus obtained shows sidelobes of only 15.4%, first realizing the sub-diffraction-limit thickness, quasi-non-diffracting characteristic, and suppressed sidelobes simultaneously for static light sheets. Moreover, a window-like energy allocation is realized by the self-trade-off optimized method, successfully further suppressing the sidelobes. In particular, an SQLS with theoretical sidelobes of 7.6% is achieved within the window, which provides a new strategy to deal with sidelobes for light sheets and shows great potential in high signal-to-noise ratio light sheet microscopy (LSM).

Modular snapshot multispectral-panchromatic imager (MSPI) with customized filter arrays.

As one of the simplest methods to construct snapshot spectral imagers, multispectral filter array (MSFA) has been applied to commercial miniatured spectral imagers. While most of them have fixed configurations of spectral channels, lacking flexibility and replaceability. Moreover, conventional MSFA only comprises filtering channels but lacks the panchromatic channel which is essential in detecting dim and indistinct objects. Here, we propose a modular assembly method for snapshot imager which can simultaneously acquire the object's multispectral and panchromatic information based on a customized filter array. The multispectral-panchromatic filter array is batch fabricated and integrated with the imaging senor through a modular mode. Five-band spectral images and a broadband intensity image can be efficiently acquired in a single snapshot photographing. The efficacy and accuracy of the imager are experimentally verified in imaging and spectral measurements. Owing to the modular architecture, our proposed assembly method owns the advantages of compactness, simple assembling, rapid replacement, and customized designing, which overcomes the expensiveness and complexity of scientific-level snapshot spectral imaging systems.

Dual Structural Design of Platinum-Nickel Hydrogels for Wearable Glucose Biosensing with Ultrahigh Stability.

Wearable glucose sensors are of great significance and highly required in mobile health monitoring and management but suffering from limited long-term stability and wearable adaptability. Here a simultaneous component and structure engineering strategy is presented, which involves Pt with abundant Ni to achieve three-dimensional, dual-structural Pt-Ni hydrogels with interconnected networks of PtNi nanowires and Ni(OH)2 nanosheets, showing prominent electrocatalytic activity and stability in glucose oxidation under neutral condition. Specifically, the PtNi(1:3) dual hydrogels shows 2.0 and 270.6 times' activity in the glucose electro-oxidation as much as the pure Pt and Ni hydrogels. Thanks to the high activity, structural stability, good flexibility, and self-healing property, the PtNi(1:3) dual gel-based non-enzymatic glucose sensing chip is endowed with high performance. It features a high sensitivity, an excellent selectivity and flexibility, and particularly an outstanding long-term stability over 2 months. Together with a pH sensor and a wireless circuit, an accurate, real-time, and remote monitoring of sweat glucose is achieved. This facile design of novel dual-structural metallic hydrogels sheds light to rationally develop new functional materials for high-performance wearable biosensors.

Large-aperture, widely and linearly tunable, electromagnetically actuated MEMS Fabry-Perot filtering chips for longwave infrared spectral imaging.

Longwave infrared spectral imaging (LWIR-SI) has potential in many important civilian and military fields. However, conventional LWIR-SI systems based on traditional dispersion elements always suffer the problems of high cost, large volume and complicated system structure. Micro-electro-mechanical systems Fabry-Perot filtering chips (MEMS-FPFC) give a feasible way for realizing miniaturized, low cost and customizable LWIR-SI systems. The LWIR MEMS-FPFC ever reported can't meet the demands of the next-generation LWIR-SI systems, due to the limitation of small aperture size and nonlinear actuation. In this work, we propose a large-aperture, widely and linearly tunable electromagnetically actuated MEMS-FPFC for LWIR-SI. A multi-field coupling simulation model is built and the wafer-scale bulk-micromachining process is applied to realize the design and fabrication of the proposed MEMS-FPFC. Finally, with the rational structural design and fabrication process, the filtering chip after packaging has an aperture size of 10 mm, which is the largest aperture size of LWIR MEMS-FPFC ever reported. The fabricated electromagnetically actuated MEMS-FPFC can be tuned continuously across the entire LWIR range of 8.39-12.95 µm under ±100 mA driving current with a pretty good linear response of better than 98%. The developed electromagnetically actuated MEMS-FPFC can be directly used for constructing miniaturized LWIR-SI systems, aiming for such applications as military surveillance, gas sensing, and industry monitoring.

Non-paraxial diffraction analysis for developing DMD-based optical systems.

We propose a non-paraxial diffraction model of the digital micromirror device (DMD) by combining the conventional Fraunhofer diffraction and a simple method of coordinative mapping. It is equivalent to adding aberrations of diffracted wave fields to the aberration-free Fraunhofer diffraction instead of complex integral calculations, allowing the simulated diffraction patterns to be consistent with the actual experimental counterparts. Moreover, it is verified by the experiments and literature that the diffraction angles, orders, and efficiency can all be well predicted for arbitrary incident angles and wavelengths. Especially for diffracted zenith angles within 50°, the predicted values reveal ∼1% error, and in a broader range, the predicted errors of diffracted azimuth angles are less than 4%. To the best of our knowledge, it is the first model capable of describing the non-paraxial diffraction behavior of the DMD. The proposed model with universality and effectiveness will help users to optimally construct DMD-based optical systems by guiding optical layouts, selection of light sources, and utilization and suppression of diffraction effects.

Sub-diffraction-limit light sheet enabled by a super-oscillatory lens with an enlarged field of view and depth of focus.

Static light sheets are widely used in various super-resolution three-dimensional (3D) imaging applications. Here, a multifocal diffraction-free optimized design method is proposed for super-oscillatory lenses (SOLs) owning an enlarged field of view (FOV) to generate sub-diffraction-limit light sheets with reduced divergence. Various propagation lengths of sub-diffraction-limit thickness for light sheets can be obtained by adopting corresponding numbers of discrete foci and spacing between them. In particular, the propagation lengths of 150.4λ and 118.9λ are obtained by SOLs with an enlarged FOV of 150λ and 820λ, respectively, which show the longest depth of focus (DOF), as far as we know, and are the first to realize the combination of enlarged DOF and FOV for SOLs. We show a way of using binary-amplitude modulation to generate static light sheets with sub-diffraction-limit thickness and reduced divergence, which is simple, easy to integrate, and sidelobe-suppressed.

MEMS-based linear micromirror array with a high filling factor for spatial light modulation.

A smart digital micromirror device (DMD) was employed to realize the on-chip scanning in versatile hyperspectral imaging (HSI) systems in our previous research. However, the rotation manner around the diagonal of the DMD makes the imaging subsystem and the spectral dispersion subsystem unable to be in the same horizontal surface. This leads to the difficulty in designing the opto-mechanical structures, system assembly and adjustment of the light path to a certain extent. On the other hand, the HSI system also needs a larger space to accommodate the two subsystems simultaneously since either of them has to incline against the horizontal surface. Moreover, there exists the interference of the reflected light between the adjacent micromirrors during the scanning process performed by the DMD, causing the loss of optical information about the object. Here, a novel linear micromirror array (MMA) based on the microelectromechanical system process that rotates around one lateral axis of the micromirror is developed, which is helpful to simplify the optical system of HSI and obtain more optical information about the detected target. The MMA has 32 independent linear micromirrors across an aperture of 5mm×6.5mm, under which there are dimple structures and a common bottom electrode. Finally, the MMA with a 98.6% filling factor is successfully fabricated by employing the bulk micromachining process. The experimental results show that the maximum rotational angle is 5.1° at a direct current driving voltage of 30 V. The proposed micromirror array is promising to replace the DMD and shows potential as a spatial light modulator in the fields of hyperspectral imaging, optical communication, and so on.

Flexible dynamic structural color based on an ultrathin asymmetric Fabry-Perot cavity with phase-change material for temperature perception.

Dynamic structural color has attracted considerable attentions due to its good tunable characteristics. Here, an ultrathin asymmetric Fabry-Perot (FP)-type structural color with phase-change material VO2 cavity is proposed. The color-switching performance can be realized by temperature regulation due to the reversible monoclinic-rutile phase transition of VO2. The various, vivid structural color can be generated by simply changing the thickness of VO2 and Ag layers. Moreover, the simple structural configuration enables a large-scale, low-cost preparation on both rigid and flexible substrates. Accordingly, a flexible dynamic structural color membrane is adhered on a cup with a curved surface to be used for temperature perception. The proposed dynamic structural color has potential applications in anti-counterfeiting, temperature perception, camouflage coatings among other flexible optoelectronic devices.

Batch fabrication and compact integration of customized multispectral filter arrays towards snapshot imaging.

Snapshot multispectral imaging (MSI) has been widely employed in the rapid visual inspection by virtues of the non-invasive detection mode and short integration time. As the critical functional elements of snapshot MSI, narrowband, customizable, and pixel-level multispectral filter arrays (MSFAs) that are compatible with imaging sensors are difficult to be efficiently manufactured. Meanwhile, monolithically integrating MSFAs into snapshot multispectral imagers still remains challenging considering the strict alignment precision. Here, we propose a cost-efficient, wafer-level, and customized approach for fabricating transmissive MSFAs based on Fabry-Perot structures, both in the pixel-level and window-tiled configuration, by utilizing the conventional lithography combined with the deposition method. The MSFA chips own a total dimension covering the area of 4.8 mm × 3.6 mm with 4 × 4 bands, possessing the capability to maintain narrow line widths (∼25 nm) across the whole visible frequencies. After the compact integration with the imaging sensor, the MSFAs are validated to be effective in filtering and target identification. Our proposed fabrication method and imaging mode show great potentials to be an alternative to MSFAs production and MSI, by reducing both complexity and cost of manufacturing, while increasing flexibility and customization of imaging system.

Integrating Highly Porous and Flexible Au Hydrogels with Soft-MEMS Technologies for High-Performance Wearable Biosensing.

Wearable biosensors for real-time and non-invasive detection of biomarkers are of importance in early diagnosis and treatment of diseases. Herein, a high-performance wearable biosensing platform was proposed by combining a three-dimensional hierarchical porous Au hydrogel-enzyme electrode with high biocompatibility, activity, and flexibility and soft-MEMS technologies with high precision and capability of mass production. Using glucose oxidase as the model enzyme, the glucose sensor exhibits a sensitivity of 10.51 µA mM-1 cm-2, a long durability over 15 days, and a good selectivity. Under the mechanical deformation (0 to 90°), it is able to maintain an almost constant performance with a low deviation of <1.84%. With the assistance of a wireless or a Bluetooth module, this wearable sensing platform achieves real-time and non-invasive glucose monitoring on human skins. Similarly, continuous lactic acid monitoring was also realized with lactate oxidase immobilized on the same sensing platform, further verifying the universality of this sensing platform. Therefore, our work holds promise to provide a universal, high-performance wearable biosensing platform for various biomarkers in sweat and reliable diagnostic information for health management.

DMD-based hyperspectral microscopy with flexible multiline parallel scanning.

As one of the most common hyperspectral microscopy (HSM) techniques, line-scanning HSM is currently utilized in many fields. However, its scanning efficiency is still considered to be inadequate since many biological and chemical processes occur too rapidly to be captured. Accordingly, in this work, a digital micromirror device (DMD) based on microelectromechanical systems (MEMS) is utilized to demonstrate a flexible multiline scanning HSM system. To the best of our knowledge, this is the first line-scanning HSM system in which the number of scanning lines N can be tuned by simply changing the DMD's parallel scanning units according to diverse applications. This brilliant strategy of effortless adjustability relies only on on-chip scanning methods and totally exploits the benefits of parallelization, aiming to achieve nearly an N-time improvement in the detection efficiency and an N-time decrease in the scanning time and data volume compared with the single-line method under the same operating conditions. To validate this, we selected a few samples of different spectral wavebands to perform reflection imaging, transmission imaging, and fluorescence imaging with varying numbers of scanning lines. The results show the great potential of our DMD-based HSM system for the rapid development of cellular biology, material analysis, and so on. In addition, its on-chip scanning process eliminates the inherent microscopic architecture, making the whole system compact, lightweight, portable, and not subject to site constraints.

Novel Bilayer Micropyramid Structure Photonic Nanojet for Enhancing a Focused Optical Field.

In this paper, synthetically using refraction, diffraction, and interference effects to achieve free manipulation of the focused optical field, we firstly present a photonic nanojet (PNJ) generated by a micropyramid, which is combined with multilayer thin films. The theory of total internal reflection (TIR) was creatively used to design the base angle of the micropyramid, and the size parameters and material properties of the microstructure were deduced via the expected optical field distribution. The as-designed bilayer micropyramid array was fabricated by using the single-point diamond turning (SPDT) technique, nanoimprint lithography (NIL), and proportional inductively coupled plasma (ICP) etching. After the investigation, the results of optical field measurement were highly consistent with those of the numerical simulation, and they were both within the theoretical calculation range. The bilayer micropyramid array PNJ enhanced the interference effect of incident and scattered fields; thus, the intensity of the focused light field reached 33.8-times that of the initial light, and the range of the focused light field was extended to 10.08λ. Moreover, the full width at half maximum (FWHM) of the focal spot achieved was 0.6λ, which was close to the diffraction limit.

Spatial and temporal super-resolution for fluorescence microscopy by a recurrent neural network.

A novel spatial and temporal super-resolution (SR) framework based on a recurrent neural network (RNN) is demonstrated. In this work, we learn the complex yet useful features from the temporal data by taking advantage of structural characteristics of RNN and a skip connection. The usage of supervision mechanism is not only making full use of the intermediate output of each recurrent layer to recover the final output, but also alleviating vanishing/exploding gradients during the back-propagation. The proposed scheme achieves excellent reconstruction results, improving both the spatial and temporal resolution of fluorescence images including the simulated and real tubulin datasets. Besides, robustness against various critical metrics, such as the full-width at half-maximum (FWHM) and molecular density, can also be incorporated. In the validation, the performance can be increased by more than 20% for intensity profile, and 8% for FWHM, and the running time can be saved at least 40% compared with the classic Deep-STORM method, a high-performance net which is popularly used for comparison.

Fiber optic Fabry-Perot sensor that can amplify ultrasonic wave for an enhanced partial discharge detection.

Ultrasonic wave is a powerful tool for many applications, such as structural health monitoring, medical diagnosis and partial discharges (PDs) detection. The fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensor has become an ideal candidate for detecting weak ultrasonic signals due to its inherent advantages, and each time with a performance enhancement, it can bring great application potential in broadened fields. Herein, an EFPI ultrasonic sensor for PDs detection is proposed. The sensing diaphragm uses a 5-µm-thickness and beam-supported structure to improve the responsive sensitivity of the sensor at the resonant frequency. Furthermore, the ability of the sensor to detect characteristic ultrasonic signal of PDs is further enhanced by assembling a Fresnel-zone-plate (FZP)-based ultrasonic lens with the sensing probe to amplify the ultrasonic wave before it excites the sensing diaphragm. The final testing results show that the originally developed sensor owns the sensitivity of - 19.8 dB re. 1 V/Pa at resonant frequency. While, when the FZP is assembled with the probe, the sensitivity reaches to - 12.4 dB re. 1 V/Pa, and leads to a narrower frequency band, which indicates that the proposed method has a great potential to enhance the detection ability of sensor to characteristic ultrasonic wave of PDs.