Array Illuminator Research Articles

Super-resolution lensless on-chip microscopy based on array illumination and scattering multiplexing with polystyrene microspheres layer

The resolution of lensless on-chip microscopy is mainly limited by the pixel size of the image sensor. Many super-resolution techniques have emerged to solve the problem of insufficient imaging resolution. Most existing pixel super-resolution technologies rely on precise electric translation stage for hundreds of high-precision displacements, or on expensive tunable lasers to generate diffraction diversity. Conventional ptychography iterative engine (PIE) is considered an effective method for improving imaging resolution, but it is prone to oscillations in the early stage of iteration. In this paper, we propose a ptychography imaging technique based on scattering multiplexing, which involves coating the surface of the image sensor with a layer of polystyrene microspheres, and utilizing a 4 × 3 LED array to sequentially illuminate the sample. An innovative ptychography reconstruction algorithm based on dual amplitude gradient descent (DAGD) is designed for the reconstruction from the holograms, which effectively avoids the problems of slow convergence speed and obvious oscillation. Compared with other similar technologies, our system has no moving parts and uses inexpensive partially coherent light illumination. It only records 12 holograms and reaches the imaging resolution of 1.23 μm, which is 1.36 times pixel super-resolution compared with the pixel size of the sensor.

Sperm quality analyzer: A portable LED array microscope with dark-field imaging.

Sperm quality analysis plays an important role in diagnosing infertility, which is widely implemented by computer-assisted sperm analysis (CASA) of sperm-swimming imaging from commercial phase-contrast microscopy. A well-equipped microscope comes with a high cost, increasing the burden of assessment, and it also occupies a large volume. For point-of-care testing (POCT) of sperm quality, these factors are confronted with the challenges of low-cost and portable instruments. In this study, an encoded light-emitting diode (LED) array illumination is employed to achieve a portable microscope with multicontrast imaging for sperm quality analysis. This microscopy has dimensions of 16.5 × 14.0 × 25.0 cm, and its dark-field (DF) imaging provides high-contrast sperm image data which is suitable for CASA. According to DF imaging, we developed a software of LabCASA, which can used to assess the motility characteristics of sperm. Compared with TrackMate, the difference in motility parameters from our software was less than 10% in the coefficient of variation (CV). The sperm motility parameters vary with the chamber temperature, which further confirms the reliability of our system with DF imaging. The DF imaging provides strong robustness for tracking sperm's motion under different microscopes. For assessment of the motility parameters, our system can work at a lower cost with a plastic structure. This system with DF imaging is suitable for portable POCT of sperm quality analysis, which is highly cost-effective in resource-constrained circumstances.

A Miniaturized Large-Field Fundus Optical System Based on Aspheric Imaging and Non-Coaxial Illumination

Many diseases produce pathological changes in the fundus; analyzing the retinopathy of the fundus could help diagnose diseases in time. A fundus camera is a medical imaging device that specializes in taking fundus images to diagnose hypertension, coronary heart disease, diabetes, and others. The fundus optical imaging system is the core part of it. Nevertheless, the conventional fundus optical imaging system is large and not suitable for mobile examination and follow-up use. So, it has not been widely used in medical institutions. In this paper, a miniaturized fundus optical imaging system based on aspheric technology and non-coaxial illumination is proposed. The length of the imaging system is only 34.6 mm, the field of view is 50°, and the MTF curve is greater than 0.2 at 100 lp/mm, which can resolve the structure of 5 um. The illumination system adopts a non-coaxial annular array illumination structure to avoid occlusion of the imaging system. Our study effectively tackles the pressing predicament of fundus optical system miniaturization. This innovative paradigm harbors the potential to revolutionize fundus image data acquisition, propelling the field of fundus diagnosis forward and efficiently catering to crucial applications, improving the versatility of fundus examination, and providing technical support for the intelligent diagnosis system.

Mechanical-scan-free multicolor super-resolution imaging with diffractive spot array illumination.

Point-scanning microscopy approaches are transforming super-resolution imaging. Despite achieving parallel high-speed imaging using multifocal techniques, efficient multicolor imaging methods with high-quality illumination are currently lacking. In this paper, we present for the first time Mechanical-scan-free multiColor Super-resolution Microscopy (MCoSM) with spot array illumination, which enables mechanical-scan-free super-resolution imaging with adjustable resolution and a good effective field-of-view based on spatial light modulators. Through 100-2,500 s super-resolution spot illumination with different effective fields of view for imaging, we demonstrate the adjustable capacity of MCoSM. MCoSM extends existing spectral imaging capabilities through a time-sharing process involving different color illumination with phase-shift scanning while retaining the spatial flexibility of super-resolution imaging with diffractive spot array illumination. To demonstrate the prospects of MCoSM, we perform four-color imaging of fluorescent beads at high resolution. MCoSM provides a versatile platform for studying molecular interactions in complex samples at the nanoscale level.

Printing Completely Conformal Liquid Metal Circuits on Arbitrary Curved Surfaces via Customized Conformal Mask

Owing to the excellent mechanical adaptability to curved surfaces and high circuit flexibility, conformal electronics have been developed for extensive applications including aeronautics and wearable electronics. However, conventional methods for fabricating conformal circuits are often constrained by planar structures, limiting the design flexibility and applicability of electronic devices on more complex and varied surfaces. In this study, we propose a facial approach by combining a 3D‐printed customized conformal mask (CCM) with liquid metal inkjet printing, to establish the completely conformal liquid alloy circuits printing technique on arbitrary curved surfaces. We develop a two‐dimensional transient mathematical model to simulate the particle deposition process during inkjet printing and predict the form of the circuits on curved surfaces. Moreover, we characterize parameters such as line resistance and cross‐sectional morphology of liquid metal circuits on both deformable and non‐deformable surfaces. Various conformal liquid metal circuits, such as contour lines, expressions, text patterns, LED array illumination patterns, and multi‐channel pressure array intelligent skin on curved surfaces are demonstrated. Compared to traditional conformal electronics manufacturing methods, this new approach offers the advantages of simple processes, flexibility, low cost (within $0.01/cm2), and high efficiency (exceeding 1cm2/s), making it suitable for mass conformal electronics production.This article is protected by copyright. All rights reserved.

Commercial Soccer Ball‐Integrated Triboelectric Nanogenerator

Triboelectric nanogenerators (TENG) are representative mechanical energy harvesters that can easily generate electricity based on contact electrification and electrostatic induction. However, most TENGs have low mechanical and electrical output stabilities because of their unstable structures, in which separate TENG devices are attached to the outside surface of commercial products/items for application. Herein, a commercial soccer ball‐integrated TENG (CSB‐TENG) is proposed as a potential solution. The CSB‐TENG is designed with an electrode‐fully packaged all‐in‐one structure; thus, it can have remarkable mechanical and electrical output stability for 160 000 cycles. For one bouncing motion, the CSB‐TENG generates a maximum peak power of 480 μW. The working mechanism of the CSB‐TENG is established by considering the actual motion of a soccer ball (kicking, bouncing, and rolling). The electrical output of the CSB‐TENG is evaluated and analyzed based on various design and environmental variables (ball material, shoe material, ground material, impact force, ball drop height, and electrode size) in daily life. The CSB‐TENG demonstrates applications, including LED array illumination and capacitor charging tests.

Harnessing nonlinear frequency upconversion of Talbot effect with flexible Talbot lengths

We report on a simple experimental scheme demonstrating nonlinear frequency upconversion of the Talbot effect with controllable Talbot lengths at high conversion efficiency. Using a microlens array (MLA) as an array illuminator at 1064 nm onto a 1.2-mm-thick BiBO crystal, we have observed the second harmonic Talbot effect in green at 532 nm with a Talbot length twice that of the pump Talbot length. However, the Talbot length is constant for fixed parameters of the periodic object and the laser wavelength. With the formulation of a suitable theoretical framework, we have implemented a generic experimental scheme based on the Fourier transformation technique to independently control the Talbot lengths of the MLA in both the pump and the second harmonic, overcoming the stringent dependence of MLA parameters on the self-images. Deploying the current technique, we have been able to tune the Talbot lengths from z T = 26 cm to z T = 62.4 cm in the pump and z T = 12.4 cm to z T = 30.8 cm in the second harmonic, respectively. The single pass conversion efficiency of the Talbot images is 2.91% W−1, an enhancement of a factor of 106 as compared to the previous reports. This generic experimental scheme can be used to generate long-range self-images of periodic structures and also to program desired Talbot planes at required positions at both pump and upconverted frequency to avoid any mechanical constraints of experiments.

Super-resolution lensless on-chip microscopy based on array illumination and sub-pixel shift search.

The resolution of a lensless on-chip microscopy system is constrained by the pixel size of image sensors. This Letter introduces a super-resolution on-chip microscopy system based on a compact array light source illumination and sub-pixel shift search. The system utilizes a closely spaced array light source composed by four RGB LED modules, sequentially illuminating the sample. A sub-pixel shift search algorithm is proposed, which determines the sub-pixel shift by comparing the frequency of captured low-resolution holograms. Leveraging this sub-pixel shift, a super-resolution reconstruction algorithm is introduced, building upon a multi-wavelength phase retrieval method, enabling the rapid super-resolution reconstruction of holograms with the region-of-interest. The system and algorithms presented herein obviate the need for a displacement control platform and calibration of the illumination angles of the light source, facilitating a super-resolution phase reconstruction under partially coherent illumination.

Fluorescence-based multifunctional light sheet imaging flow cytometry for high-throughput optical interrogation of live cells

Multifunctional light sheet imaging flow cytometry of a large population of live cells at high throughput is challenging and requires new technological advancement. Existing cytometry techniques are limited due to point-based illumination that does not allow volume interrogation and biophysical parameter estimation on the go. Here, we propose a multifunctional (multichannel, multisheet and multicolor) imaging cytometry (M3IC) system that employs vertically-aligned multi-sheet array (VAMSA) illumination for interrogating cells flowing simultaneously through multiple microfluidic channels. We studied cancer cells (volume interrogation with organelle-level resolution and high signal-to-background-ratio(SBR)) at high throughput (~2500 nl/min). M3IC system demonstrates organelle-level resolution with a SBR comparable to that of confocal, especially at low flow rates. In addition, the multicolor imaging capability of the system facilitates multi-organelle investigation, determination of critical biophysical parameters, and drug (Paclitaxel) treatment studies on cancer cells. M3IC system is expected to advance the field of fluorescence microscopy, cell biophysics, disease biology and optical physics.

Design of a high-power collimating optical system based on Fresnel lenses.

In light-emitting diode (LED) illumination (e.g., LED maritime lighting for ships), creating a uniform light environment for optical systems is an important challenge. In this study, we present a high-power collimating system based on Fresnel lenses, which allows high-brightness LED illumination in the earlier-mentioned remote distance. The work presented in this article focuses on improving the power, compacting the optical structure, and promoting the brightness of the spot. To prove the claims, the system with a total power of 1 kW is designed. The system consists of a 27 W LED array, a freeform surface lens array, and a confocal Fresnel lens array. In comparison with the traditional optical system, the optical structure shortens from 390 to 120 mm, and the divergent angle decreases from 3° to 2 . Meanwhile, the illuminance of the system is obtained as high as 230 lx at the near field of 200 m and 3.0lx at the far field of 1.5 nautical miles. This new method provides a practical and effective way to solve the problem of low power, insufficient illuminance, and long optical structure for LED array illumination, which is suitable for remote illumination and guidance of ships.

Experimental demonstration of passive microwave pulse amplification via temporal Talbot effect

The temporal Talbot effect is a passive phenomenon that occurs when a periodic signal propagates through a dispersive medium with a quadratic phase response that modulates the output pulse repetition rate based on the input period. As previously proposed, this effect enables innovative applications such as passive amplification. However, its observation in the microwave regime has been impractical due to the requirement for controlled propagation through a highly dispersive waveguide. To overcome this challenge, we employed an ultra-wide band linearly chirped Bragg grating within a standard microwave X-Band waveguide. By utilizing backwards Talbot array illuminators aided by particle swarm optimization, we achieved passive amplification with a gain of 3.45 dB and 4.03 dB for gaussian and raised cosine pulses, respectively. Furthermore, we numerically verified that with higher quality substrates this gain can be theoretically increased to over 8 dB. Our work paves the way for numerous applications of the Talbot effect in the microwave regime, such as temporal cloaking, sub-noise microwave signal detection, microwave pulse shaping, and microwave noise reduction.

Hybrid full-pose parameter calibration of a freeform illuminator for Fourier ptychographic microscopy.

As a typical computational method, Fourier ptychographic microscopy (FPM) can realize high spatial resolution and quantitative phase imaging while preserving the large field of view with a low numerical aperture (NA) objective. A programmable light-emitting diode (LED) array is used as a typical illuminator in an FPM system, and the illumination parameters of each LED element are crucial to the success of the FPM reconstruction algorithm. Compared with LED arrays arranged in rectangular arrays, LED arrays with special structures such as domes or rings can effectively improve FPM imaging results and imaging efficiency. As a trade-off, their calibration difficulty is greatly increased due to the lack of geometric constraints of rectangular arrays. In this paper, we propose an effective hybrid full-pose parameter calibration method for freeform LED array illuminators, combining stereoscopic 3D imaging techniques and the geometric constraints of the microscopic platform. First, a stereovision system is used to obtain the accurate 3D position of each LED element of the freeform illuminator and to construct a rigid 3D coordinate LED array system. Then, calibration between the coordinate system of the LED array and that of the optical imaging component is realized according to the geometric features of the brightfield-to-darkfield edges. Finally, we verify the feasibility and effectiveness of the proposed method through full-pose parameter calibration of LED arrays with different arrangement rules.

An Ultra-Fast Temporal Talbot Array Illuminator

We propose an all-optical temporal Talbot array illuminator (T-TAI) enabling denoising passive amplification of broadband ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 10 GHz- bandwidth) optical signals. The key element is an ultra-fast temporal phase grating based on cross-phase modulation. Whereas previous implementations of the T-TAI suffer from the bandwidth limitations inherent to electro-optic systems, the all-optical nature of the proposed approach allows to simultaneously realize high amplification factors and sampling rates, which in turn allows for the efficient processing of broadband signals. In our experiments, we demonstrate a (signal bandwidth) × (amplification factor) product exceeding 370 GHz, more than an order of magnitude improvement as compared with previous electro-optic implementations. We show the prospects of the proposed approach through the recovery of noisy high-speed optical waveforms, namely a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 10 Gbps data signal buried in a much stronger noise background. Additionally, we experimentally demonstrate that the T-TAI samples preserve the full complex information (amplitude and phase) of the incoming signal. The proposed approach should prove useful in multiple fields requiring the detection of weak and noisy broadband signals as well as for other related applications, such as photonics-assisted analog-to-digital conversion.

Comparing x-ray phase-contrast imaging using a Talbot array illuminator to propagation-based imaging for non-homogeneous biomedical samples

Phase-contrast computed tomography can visualize soft tissue samples with high contrast. At coherent sources, propagation-based imaging (PBI) techniques are among the most common, as they are easy to implement and produce high-resolution images. Their downside is a low degree of quantitative data due to simplifying assumptions of the sample properties in the reconstruction. These assumptions can be avoided, by using quantitative phase-contrast techniques as an alternative. However, these often compromise spatial resolution and require complicated setups. In order to overcome this limitation, we designed and constructed a new imaging setup using a 2D Talbot array illuminator as a wavefront marker and speckle-based imaging phase-retrieval techniques. We developed a post-processing chain that can compensate for wavefront marker drifts and that improves the overall sensitivity. By comparing two measurements of biomedical samples, we demonstrate that the spatial resolution of our setup is comparable to the one of PBI scans while being able to successfully image a sample that breaks the typical homogeneity assumption used in PBI.

Large-Area Arrays of Polymer-Tethered Gold Nanorods with Controllable Orientation and Their Application in Nano-Floating-Gate Memory Devices.

In this work, it is reported that large-area (centimeter-scale) arrays of non-close-packed polystyrene-tethered gold nanorod (AuNR@PS) can be prepared through a liquid-liquid interfacial assembly method. Most importantly, the orientation of AuNRs in the arrays can be controlled by changing the intensity and direction of electric field applied in the solvent annealing process. The interparticle distance of AuNR can be tuned by varying the length of polymer ligands. Moreover, the AuNR@PS with short PS ligand are favorited to form orientated arrays with the assistance of electric field, while long PS ligands make the orientation of AuNRs difficult. The orientated AuNR@PS arrays are employed as the nano-floating gate of field-effect transistor memory device. Tunable charge trapping and retention characteristics in the device can be realized by electrical pulse with visible light illumination. The memory device with orientated AuNR@PS array required less illumination time (1 s) at the same onset voltage in programming operation, compared to the control device with disordered AuNR@PS array (illumination time: 3 s). Moreover, the orientated AuNR@PS array-based memory device can maintain the stored data for more than 9000 s, and exhibits stable endurance characteristic without significant degradation in 50 programming/reading/erasing/reading cycles.

Multifaceted mirror array illuminator for fluorescence excitation-scanning spectral imaging microscopy.

Hyperspectral imaging (HSI) technologies offer great potential in fluorescence microscopy for multiplexed imaging, autofluorescence removal, and analysis of autofluorescent molecules. However, there are also associated trade-offs when implementing HSI in fluorescence microscopy systems, such as decreased acquisition speed, resolution, or field-of-view due to the need to acquire spectral information in addition to spatial information. The vast majority of HSI fluorescence microscopy systems provide spectral discrimination by filtering or dispersing the fluorescence emission, which may result in loss of emitted fluorescence signal due to optical filters, dispersive optics, or supporting optics, such as slits and collimators. Technologies that scan the fluorescence excitation spectrum may offer an approach to mitigate some of these trade-offs by decreasing the complexity of the emission light path. We describe the development of an optical technique for hyperspectral imaging fluorescence excitation-scanning (HIFEX) on a microscope system. The approach is based on the design of an array of wavelength-dependent light emitting diodes (LEDs) and a unique beam combining system that uses a multifurcated mirror. The system was modeled and optimized using optical ray trace simulations, and a prototype was built and coupled to an inverted microscope platform. The prototype system was calibrated, and initial feasibility testing was performed by imaging multilabel slide preparations. We present results from optical ray trace simulations, prototyping, calibration, and feasibility testing of the system. Results indicate that the system can discriminate between at least six fluorescent labels and autofluorescence and that the approach can provide decreased wavelength switching times, in comparison with mechanically tuned filters. We anticipate that LED-based HIFEX microscopy may provide improved performance for time-dependent and photosensitive assays.

An open-source LED array illumination system for automated multiwell plate cell culture photodynamic therapy experiments

Photodynamic therapy (PDT) research would benefit from an automated, low-cost, and easy-to-use cell culture light treatment setup capable of illuminating multiple well replicates within standard multiwell plate formats. We present an LED-array suitable for performing high-throughput cell culture PDT experiments. The setup features a water-cooling loop to keep the LED-array temperature nearly constant, thus stabilizing the output power and spectrum. The setup also features two custom-made actuator arms, in combination with a pulse-width-modulation (PWM) technique, to achieve programmable and automatic light exposures for PDT. The setup operates at ~ 690 nm (676–702 nm, spectral output full-width half-maximum) and the array module can be readily adapted to other LED wavelengths. This system provides an illumination field with adjustable irradiance up to 400 mW/cm2 with relatively high spectral and power stability comparing with previously reported LED-based setups. The light doses provided by the LED array were validated with comparison to traditional laser PDT. This open-source illumination platform (including the detailed technical description, fabrication protocols, and parts list provided here) helps to make custom light sources more accessible and of practical use for photomedicine research.

Space-time analogy and its application to design schemes borrowed from Fourier optics for processing ultrafast optical signals

Square-wave pulse generation with a variable duty ratio can be realized with the help of the ideas of Talbot array illuminators formulated for binary phase gratings. A binary temporal phase modulation of continuous wave (CW) laser field propagating through a group-delay-dispersion circuit of the fractional Talbot length results in a well defined sequence of square-wave-form pulses. When P = 1 a duty ratio of the pulses D is for Q = 4 and for Q = 3 and 6. Maximum intensity of the pulses doubles and triples compared to the CW intensity for and , respectively. These pulses can be used for return-to-zero laser field modulation in optical fiber communication. For extra features between the pulses are found originating from a finite rise and drop time of phase in a binary phase modulation. A similar effect to the benefit of the time-space analogy is predicted for binary phase gratings and interpreted as gleams produced by imperfect edges of the components of the rectangular phase gratings.

Improved resolution Fourier ptychography scheme using oil‐filled dome‐shaped LED array

Utilising angular-varied illumination in Fourier Ptychography, the resolution of optical microscopes can be increased and the phase of the sample can also be recovered while maintaining a wide field-of-view. In this work, an Fourier Ptychography microscopy imaging setup is demonstrated using a 10X 0.28 NA objective lens and a dome-shaped light-emitting diode array illuminator. By increasing the refractive index of the medium between the sample and light sources using oil filled dome, a synthetic system numerical aperture of 0.68 is achieved using only 37 light-emitting diodes. The measured resolution of 345 nm at a wavelength of 530 nm closely matches the theoretical prediction. Furthermore, the results of the oil-medium illumination are compared to free-space illumination. The oil immersion on the illumination side effectively enhances the illumination numerical aperture as compared to air and reduces the need for far off-axis light-emitting diodes. The result is high-resolution Fourier Ptychography imaging with relatively fewer light-emitting diodes providing both short capture and reconstruction times.

Strain release of formamidinium-cesium perovskite with imprint-assisted organic ammonium halide compensation for efficient and stable solar cells

Residual lattice strain in halide perovskites has been recognized as a key factor that affects device efficiency and stability of perovskite solar cells (PSCs). Here, we reveal that the escape of organic ammonium halide and their inhomogeneous distribution after thermal annealing could cause severe residual strain in intrinsic thermal stable formamidinium-cesium (FACs) perovskite films. Thus, we develop an imprint-assisted organic ammonium halide compensation strategy for residual lattice strain relaxation. We demonstrate the residual lattice strain is well-released after post-treatment, along with further perovskite grain growth/coalescence, crystallinity improvement, and defect repair. As a result, the strain-free PSCs with nickel oxide based inverted architecture exhibit a power conversion efficiency as high as 21.30% and the corresponding encapsulated devices retain 98% of their initial efficiencies at 45 °C under 1-sun equivalent white-light light-emitting diode array illumination with maximum power point tracking in the ambient environment for 1000 h.