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Tunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm−1. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration. [ABSTRACT FROM AUTHOR]

Semiconductor lasers with a wavelength of 2 µm, composed of antimonide materials, find important applications in trace gas detection, laser medicine, and free-space optical communication, among others. In this paper, a more suitable microlens shape for 2 µm gallium antimonide semiconductor lasers is designed. Based on the fiber coupling efficiency model, the parameters of the designed slanting wedge-shaped microlens fiber are optimized to improve laser beam quality. The large tangent angle on both sides of the slanted, wedge-shaped microlens fiber is calculated using Snell's law, and the fiber core diameter and small wedge angle are determined through space fiber coupling experiments. After packaging the fiber coupling module with the chip, the laser output beam exhibits good overall symmetry in the spot with a uniform intensity distribution. The maximum output power is approximately 210 mW, demonstrating good power stability. [ABSTRACT FROM AUTHOR]

We present a microlens-assisted imaging approach to record the scattering light of plasmonic nanoparticles at the single particle level. The microlens can significantly enhance the backscattering of visible light from individual plasmonic nanoparticles by several dozen folds, and single gold nanoparticles with a diameter as low as 60 nm can be imaged under a conventional optical microscope. This can benefit from a significant increase in the scattering intensity afforded by the microlens, meaning that the imaging of gold nanoparticles at a high temporal resolution (up to 5000 Hz) can be achieved, which is fast enough to record single particle adhesion events on the substrate. This research presents a fast and efficient means of acquiring scattering light from plasmonic nanoparticles, which has great potential to develop plasmonic nanoparticle-based biosensors and investigate a wide range of plasmonic nanoparticle-based fast interaction processes. [ABSTRACT FROM AUTHOR]

Although monocrystalline silicon exhibits promising microstructural properties for enhancing the performance of optical systems, precise and efficient silicon fabrication is still challenging due to its brittleness. In the present work, we demonstrate the ductile machinability of copper-coated silicon by applying elliptical vibration diamond cutting. Firstly, the influence of the copper coating on the ductile machinability of silicon was experimentally investigated by applying ordinary diamond cutting, showing that the critical depth of cut (DOC) for the ductile-to-brittle transition increased from 118 to 418 nm due to the advantages of the copper coating. This provided hydrostatic pressure in the microcutting regime and the compressive force on the subsurface defects to prevent crack propagation. Subsequently, grooving tests on coated and uncoated silicon were performed by applying elliptical vibration cutting (EVC). Due to the small instantaneous uncut chip thickness in each vibration cycle, the critical DOC by EVC for uncoated silicon increased to 459 nm. Applying the favorable copper coating process, the critical DOC by EVC for coated silicon increased to about 988 nm. The ductile machinability of silicon was efficiently improved by combining EVC and the coating process. Furthermore, the influence of vibration amplitude and cutting speed on the ductile machinability of silicon was explored in detail, leading to the optimized machining conditions for the ductile machining of silicon. Finally, based on these fundamental results, ultra-precision microlenses on silicon were efficiently fabricated, which is appropriate for further industrial applications. • 1. Enhanced ductile machinability of silicon by combination of coating and elliptical vibration cutting was verified. • 2. Compared with ordinary diamond cutting of silicon, the critical depth of cut increased from about 100 nm to 1000 nm. • 3. Coating film provides hydrostatic pressure and compressive force on the subsurface defects to prevent crack propagation. [ABSTRACT FROM AUTHOR]

A newly truncated micro-cone array film as light extraction layer for organic light emitting diodes (OLEDs) has been developed, which was fabricated by process combined with photolithography, polydimethylsiloxane (PDMS) molding, self-assembled anti-adhesion, and ultraviolet (UV) forming techniques. In this study, by varying the sidewall angle and fill factor of this film, their influences on the optical properties and light extraction efficiency for OLED are fully investigated. As a result, device performance of OLED employed truncated micro-cone array film, with a high fill factor and sidewall angle of 76.49⁰, was found to be significantly enhanced up to 52% compared with the reference OLED. Notably, the proposed truncated micro-cone array film also stabilized emissive color stability while the viewing angle changes from 0° to 70°, achieving an excellent angular shift with CIE-indices of (0.0025, 0.0066). Aforementioned findings contribute to the development in advanced OLEDs for display and lighting applications.

Semiconductor lasers with a wavelength of 2 µm, composed of antimonide materials, find important applications in trace gas detection, laser medicine, and free-space optical communication, among others. In this paper, a more suitable microlens shape for 2 µm gallium antimonide semiconductor lasers is designed. Based on the fiber coupling efficiency model, the parameters of the designed slanting wedge-shaped microlens fiber are optimized to improve laser beam quality. The large tangent angle on both sides of the slanted, wedge-shaped microlens fiber is calculated using Snell’s law, and the fiber core diameter and small wedge angle are determined through space fiber coupling experiments. After packaging the fiber coupling module with the chip, the laser output beam exhibits good overall symmetry in the spot with a uniform intensity distribution. The maximum output power is approximately 210 mW, demonstrating good power stability.

Non-isothermal hot embossing has great potential in the mass production of glass micro optical components due to the relatively short heating-cooling cycle time. However, warpage was induced by the temperature gradient inside the glass replica during hot embossing, resulting in a deteriorated optical performance. Therefore, it is non-trivial to investigate the effects of process parameters on warping and filling behaviors of glass in non-isothermal hot embossing. Firstly, a high-quality microhole was fabricated on monocrystalline silicon carbide (SiC) mold by focused ion beam (FIB) lithography. By using a novel home-made gravity-assisted hot embossing machine, the geometric information (i.e., warpage and microstructures) on SiC mold was transferred into the surface of N-BK7 glass replica. The experimental results indicate that high embossing temperature enables not only the minimization of warpage but also the enhancement of microstructure replication accuracy. Furthermore, increasing embossing force enhances filling capacity but increases warpage amplitude. Interestingly, fast heating/cooling rates and short embossing time enable a small warpage as well as a high embossing efficiency. By optimizing the process parameters, especially the embossing temperature, a small warpage amplitude of 3 μm and a high transfer ratio of 99.11% were achieved, which can meet the high requirement of precision optical components. [ABSTRACT FROM AUTHOR]

Microlens arrays have been widely employed to control the reflection, refraction, and diffraction characteristics of light due to its distinctive surface properties. Precision glass molding (PGM) is the primary method for the mass production of microlens arrays, of which pressureless sintered silicon carbide (SSiC) is a typical mold material due to its excellent wear resistance, high thermal conductivity, high-temperature resistance, and low thermal expansion. However, the high hardness of SSiC makes it hard to be machined, especially for optical mold material that requires good surface quality. The lapping efficiency of SSiC molds is quite low. and the underlying mechanism remains insufficiently explored. In this study, an experimental study has been performed on SSiC. A spherical lapping tool and diamond abrasive slurry have been utilized and various parameters have been carried out to achieve fast material removal. The material removal characteristics and damage mechanism have been illustrated in detail. The findings reveal that the material removal mechanism involves a combination of ploughing, shearing, micro-cutting, and micro-fracturing, which aligns well with the results obtained from finite element method (FEM) simulations. This study serves as preliminary reference for the optimization of the precision machining of SSiC PGM molds with high efficiency and good surface quality. [ABSTRACT FROM AUTHOR]

Dip coating technique has the potential to provide a simpler and more cost-effective means of forming an optical fiber microcollimator composed of parabolic Polymethyl methacrylate microlenses for various applications. The effects of dip-coating operating parameters such as withdrawal speed on the thickness of a microlens were investigated in this work. Zemax® software was used to validate the analytical results and to assess the efficiency of the optical coupling. The obtained waist and working distance values, make possible the optimization of the optical coupling between a microcollimator and a laser beam, as well as between a microcollimator and an optical fiber. The simulation results of the coupling between the microcollimator and the laser beam show that the optical coupling efficiency η is about 99% with an optimal microlens radius R = 19.14 μm, a waist size W1 = 2.49 μm and a working distance Zw = 41.78 μm. However, the optimal microlens for the coupling between the microcollimator and the optical fiber has a minimum curvature radius about 28.78 μm. We believe that these results are of a big interest in many applications in optical experiments and laser-optical fibers applications. [ABSTRACT FROM AUTHOR]

A light-field camera is an optical system that provides multi-field-angle information in one shot. The microlens array (MLA) in a light-field camera system is the key to provide multi-field-angle information. However, its numerical aperture limits the microlens' spatial resolution and the image's quality. We proposed a new microlens array for the light-field camera in this work. This MLA consists of one larger primary microlens and 72 satellite microlenses, simultaneously providing high-resolution image information from different angles. Moreover, this MLA can be easily fabricated by nanoimprint at a low cost. The measured spatial resolution of the primary microlens is 53.74 lp/mm higher than satellite microlens when MTF = 0.3. Finally, a one-shot photograph of a light-field camera shows one high-resolution and other views from different angles of the bear doll. The high-resolution light-field camera has great potential to apply in object ranging and face recognition in the future. [ABSTRACT FROM AUTHOR]

Microneedles are highly sought after for medicinal and cosmetic applications. However, the current manufacturing process for microneedles remains complicated, hindering its applicability to a broader variety of applications. As diffraction lithography has been recently reported as a simple method for fabricating solid microneedles, this paper presents the experimental validation of the use of ultraviolet light diffraction to control the liquid-to-solid transition of photosensitive resin to define the microneedle shape. The shapes of the resultant microneedles were investigated utilizing the primary experimental parameters including the photopattern size, ultraviolet light intensity, and the exposure time. Our fabrication results indicated that the fabricated microneedles became taller and larger in general when the experimental parameters were increased. Additionally, our investigation revealed four unique crosslinked resin morphologies during the first growth of the microneedle: microlens, first harmonic, first bell-tip, and second harmonic shapes. Additionally, by tilting the light exposure direction, a novel inclined microneedle array was fabricated for the first time. The fabricated microneedles were characterized with skin insertion and force-displacement tests. This experimental study enables the shapes and mechanical properties of the microneedles to be predicted in advance for mass production and wide practical use for biomedical or cosmetic applications. [ABSTRACT FROM AUTHOR]

Microlenses have attracted increasing attention in recent years due to the emergent demand in the booming stereoscopic imaging industry and highly integrated optical systems. In this study, we propose a customized approach to design liquid crystal microlens (LCM) for subwavelength focusing, based on the vectorial Rayleigh‐Sommerfeld (VRS) method and the trust region algorithm. It is demonstrated that the computation time and computing resources can be greatly reduced by using our proposal when compared to the commercial software. Both the polarization of the incidence and diffraction field is taken into account in the design, which makes it more reliable. We fabricated the LCM by using photoalignment technology based on the digital micromirror device (DMD), and experimentally characterized the focusing performance of the sample. A Frank‐Oseen model is also established to simulate the mechanical properties of the liquid crystal (LC) layer and analyze the effect of the transition region on the LC directors. [ABSTRACT FROM AUTHOR]

We present a microlens-assisted imaging approach to record the scattering light of plasmonic nanoparticles at the single particle level. The microlens can significantly enhance the backscattering of visible light from individual plasmonic nanoparticles by several dozen folds, and single gold nanoparticles with a diameter as low as 60 nm can be imaged under a conventional optical microscope. This can benefit from a significant increase in the scattering intensity afforded by the microlens, meaning that the imaging of gold nanoparticles at a high temporal resolution (up to 5000 Hz) can be achieved, which is fast enough to record single particle adhesion events on the substrate. This research presents a fast and efficient means of acquiring scattering light from plasmonic nanoparticles, which has great potential to develop plasmonic nanoparticle-based biosensors and investigate a wide range of plasmonic nanoparticle-based fast interaction processes.

Silica microlens arrays (MLAs) with multiple numerical-apertures (NAs) have high thermal and mechanical stability, and have potential application prospects in 3D display and rapid detection. However, it is still a challenge to rapidly fabricate silica MLAs with a larger range of NAs and how to obtain multiple NAs in the same aperture diameter. Here, a wet etching assisted spatially modulated femtosecond laser pulse fabricating technology is proposed. In this technology, Gaussian laser pulse is modulated in the axial direction to create a pulse with a large aspect ratio, which is used to modify the silica to obtain a longer modification distance than traditional technology. After that, a microlens with a larger NA can be obtained by etching, and the NA variable range can be up to 0.06–0.65, and even under the same aperture, the variable NA can range up to 0.45–0.65. In addition, a single focus is radially modulated into several focus with different axial lengths to achieve a single exposure fabricating of MLA with multiple NAs. In characterization of the image under a microscope, the multi-plane imaging characteristics of the MLA are revealed. The proposed technology offers great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing.

In the present work, an induction-aided hot embossing (IHE) setup was developed in-house, to reduce the time required for embossing. Using the setup, a micro-lens array was successfully fabricated over PMMA substrate using laser engraved mold in less than half the time required compared to traditional hot embossing. The operating parameters were optimized through composite desirability (CD) method and teaching learning-based optimization (TLBO) to enhance the replication accuracy of the embossed microlens array. IHE experiments were designed as per rotatable central composite design (R-CCD). Embossing temperature (Te), embossing pressure, embossing time, de-embossing temperature were selected as control parameters, and deviation in diameter of the embossed microlens array was chosen as performance factor. A first-order linear model was employed for mathematical modeling. ANOVA result reveals that the developed model is adequate and Te has an impact of 44.63% on the replication accuracy. It was observed that the deviation in diameter decreases from 27.12 μm to 23.63 μm as Te increases from 120ᵒC to 130ᵒC. Final optimization result reveals that TLBO performs better than the CD. Deviation in diameter predicted by TLBO method at optimum condition is 15.83 μm which closely matches the experimental findings at optimum condition, that is, 16.57 μm. Abbreviations HE: Hot embossing; PMMA: Polymethyl methacrylate; ROC: Radius of curvature; RSM: Response surface methodology; TLBO: Teaching learning-based optimization; CD: Composite desirability; ANOVA: Analysis of variance; To: room temperature; Tg: Glass transition temperature; Te: Embossing temperature; Pe: embossing pressure; te: embossing time; Tde: deembossing temperature; tc: Cycle time; μ: Micro; Ffrictional: Frictional force; RIE: Reactive ion etching; EDM: Electric discharge machining; h s a g : sag height; IP: Input; OP: Output; IHE: Induction-aided hot embossing; CHE: Conventional hot embossing; WEDM: Wire electric discharge machining [ABSTRACT FROM AUTHOR]

Silicon photonics technology has attracted considerable attention these days. However, the low coupling efficiency due to the difference in spot size between silicon photonic (SiPh) chips and single-mode fibers (SMFs) remains a challenging issue. We have already proposed a unique combination of a microlens and a pillar on the facet of SMF. However, the pillar may have difficulty in keeping a single mode for a signal beam of 1. 55 μ m wavelength due to air cladding. In this study, we clarified the length of the pillar that can support the single mode through simulations and experiments. By the optimum designing, the spot size as the same level as the SiPh chip was obtained. We could show that our coupling device provides high coupling efficiency with a test sample of SiPh chip, and this device also can be applied to multi-core fibers. [ABSTRACT FROM AUTHOR]

In recent years, the demand for optical components such as microlenses has been increasing, and various methods have been developed. However, fabrication of submillimeter microlenses with tunable numerical aperture (NA) on hard and brittle materials remains a great challenge using the current methods. In this work, we fabricated a variable NA microlens array with submillimeter size on a silica substrate, using a femtosecond laser-based linear scanning-assisted wet etching method. At the same time, the influence of various processing parameters on the microlens morphology and NA was studied. The NA of the microlenses could be flexibly adjusted in the range of 0.2 to 0.45 by changing the scanning distance of the laser and assisted wet etching. In addition, the imaging and focusing performance tests demonstrated the good optical performance and controllability of the fabricated microlenses. Finally, the optical performance simulation of the prepared microlens array was carried out. The result was consistent with the actual situation, indicating the potential of the submillimeter-scale microlens array prepared by this method for applications in imaging and detection. [ABSTRACT FROM AUTHOR]

Microlens arrays have been widely employed to control the reflection, refraction, and diffraction characteristics of light due to its distinctive surface properties. Precision glass molding (PGM) is the primary method for the mass production of microlens arrays, of which pressureless sintered silicon carbide (SSiC) is a typical mold material due to its excellent wear resistance, high thermal conductivity, high-temperature resistance, and low thermal expansion. However, the high hardness of SSiC makes it hard to be machined, especially for optical mold material that requires good surface quality. The lapping efficiency of SSiC molds is quite low. and the underlying mechanism remains insufficiently explored. In this study, an experimental study has been performed on SSiC. A spherical lapping tool and diamond abrasive slurry have been utilized and various parameters have been carried out to achieve fast material removal. The material removal characteristics and damage mechanism have been illustrated in detail. The findings reveal that the material removal mechanism involves a combination of ploughing, shearing, micro-cutting, and micro-fracturing, which aligns well with the results obtained from finite element method (FEM) simulations. This study serves as preliminary reference for the optimization of the precision machining of SSiC PGM molds with high efficiency and good surface quality.

We design an optical interface system for vertical coupling between vertical-cavity surface-emitting lasers (VCSELs) and 3- $\mu \text{m}$ silicon waveguides. The system includes a photoresist lens and a total internal reflection mirror, which allows for passive alignment and flip-chip bonding (FCB) of VCSELs. The simulated coupling loss is 0.7 dB, in optimal conditions, which increases to 1 dB when 3- and 20- $\mu \text{m}$ alignment tolerances are considered in lateral and longitudinal directions, respectively. The system is built by post-processing lens and metallic wiring on the backside of a 3- $\mu \text{m}$ silicon photonic platform. After FCB and embedding of the VCSELs, the system performance is characterized, and VCSEL-to-waveguide coupling efficiency of −7.5 dB is obtained. [ABSTRACT FROM AUTHOR]

With the rapid evolution of microelectronics and nanofabrication technologies, the feature sizes of large‐scale integrated circuits continue to move toward the nanoscale. There is a strong need to improve the quality and efficiency of integrated circuit inspection, but it remains a great challenge to provide both rapid imaging and circuit node‐level high‐resolution images simultaneously using a conventional microscope. This paper proposes a nondestructive, high‐throughput, multiscale correlation imaging method that combines atomic force microscopy (AFM) with microlens‐based scanning optical microscopy. In this method, a microlens is coupled to the end of the AFM cantilever and the sample‐facing side of the microlens contains a focused ion beam deposited tip which serves as the AFM scanning probe. The introduction of a microlens improves the imaging resolution of the AFM optical system, providing a 3–4× increase in optical imaging magnification while the scanning imaging throughput is improved ≈8×. The proposed method bridges the resolution gap between traditional optical imaging and AFM, achieves cross‐scale rapid imaging with micrometer to nanometer resolution, and improves the efficiency of AFM‐based large‐scale imaging and detection. Simultaneously, nanoscale‐level correlation between the acquired optical image and structure information is enabled by the method, providing a powerful tool for semiconductor device inspection. [ABSTRACT FROM AUTHOR]

This paper aims to present a novel rapid hot embossing approach and to study filling capacity of optical glass in the hot embossing process. Firstly, a novel rapid hot embossing device is developed, which consists of a rapid heating module and a precision loading module. Particularly, the rapid heating module allows a maximum temperature of 800 °C and a heating rate of 300 °C/min, with decent temperature control accuracy and uniform temperature distribution. In hot embossing process, by incompletely filling the microhole of silicon carbide mold, a microlens would be formed on the surface of glass disc, and the filling capacity of glass is quantified by the maximum height of the microlens. The tailor-made hot embossing device was exploited to conduct a series of experiments for evaluating effects of process parameters on the filling capacity of N-BK7 glass. Experimental results indicate that the filling capacity of glass could be enhanced by increasing the embossing force, the embossing temperature, the soaking time but decreasing the annealing rate. Furthermore, compared to soaking time and annealing rate, embossing force and embossing temperature have more significant influence on the filling capacity of N-BK7 glass. Therefore, the novel rapid hot embossing is a practical and promising technology for fabricating microstructures on glass materials with high softening points. [ABSTRACT FROM AUTHOR]

Rapid manufacturing of high purity fused silica glass micro-optics using a filament-based glass 3D printer has been demonstrated. A multilayer 5 × 5 microlens array was printed and subsequently characterized, showing fully dense lenses with uniform focal lengths and good imaging performance. A surface roughness on the order of R a  = 0.12 nm was achieved. Printing time for each lens was <10 s. Creating arrays with multifocal imaging capabilities was possible by individually varying the number of printed layers and radius for each lens, effectively changing the lens height and curvature. Glass 3D printing is shown in this study to be a versatile approach for fabricating silica micro-optics suitable for rapid prototyping or manufacturing., Competing Interests: Nobula3D AB is a spin-off company from the project RMA15-0135, funded by the Swedish Foundation for Strategic Research. No competing financial interests or conflict of interests exist., (© Chunxin Liu et al. 2022; Published by Mary Ann Liebert, Inc.)

Abstract With the rapid evolution of microelectronics and nanofabrication technologies, the feature sizes of large‐scale integrated circuits continue to move toward the nanoscale. There is a strong need to improve the quality and efficiency of integrated circuit inspection, but it remains a great challenge to provide both rapid imaging and circuit node‐level high‐resolution images simultaneously using a conventional microscope. This paper proposes a nondestructive, high‐throughput, multiscale correlation imaging method that combines atomic force microscopy (AFM) with microlens‐based scanning optical microscopy. In this method, a microlens is coupled to the end of the AFM cantilever and the sample‐facing side of the microlens contains a focused ion beam deposited tip which serves as the AFM scanning probe. The introduction of a microlens improves the imaging resolution of the AFM optical system, providing a 3–4× increase in optical imaging magnification while the scanning imaging throughput is improved ≈8×. The proposed method bridges the resolution gap between traditional optical imaging and AFM, achieves cross‐scale rapid imaging with micrometer to nanometer resolution, and improves the efficiency of AFM‐based large‐scale imaging and detection. Simultaneously, nanoscale‐level correlation between the acquired optical image and structure information is enabled by the method, providing a powerful tool for semiconductor device inspection.

An ultra-sensitive microfluid device for detecting aggregation of induced emission molecules is proposed and demonstrated. The minimum detectable concentration is greatly reduced by use of a micromachined fiber tip and a liquid core waveguide. The fiber tip is a tapered-microlens structure with optimized shape parameters. The liquid waveguide is formed with low refractive index Teflon capillary. The dependence of photoluminescence intensity on the concentration change is tested with the device. The limit of detection is $0.316 \boldsymbol {\mu }\text{M}$ , the volume of the sample solution used is only $0.649 \boldsymbol {\mu }\text{L}$ and the minimum detectable concentration is down to 100 nM. It is a valuable result obtained with fiber spectrometer (a CCD-type machine), better than that obtained with traditional fluorospectro photometer (a photomultiplier tubes-type one). The reversibility and stability are also testified through experimental method. Together with the compact size, small sample volume and high sensitivity, the durable microfluidic sensing device has great potential for biosensing applications. [ABSTRACT FROM AUTHOR]

Fibre optic microlenses are small optical elements formed on the end-faces of optical fibres. Their dimensions range from a few tens to hundreds of micrometres. In the article, four optical fibre microlenses are modelled and analysed. Microlenses are used for light beam manipulation and quantitative metrics are needed to evaluate the results, for example, the size of focusing spot or intensity distribution. All four lenses tested are made of rods of the same refractive index; they were welded to a single-mode fibre. Two modelling methods were used to analyse the lenses: ray-tracing and finite-difference time-domain. The ray-tracing algorithm moves rays from one plane to another and refracts them on the surfaces. Finite-difference time-domain consists of calculating Maxwell's equations by replacing spatial and temporal derivatives by quotients of finite differences. In this paper, the results of the microlenses analyses obtained from ray-tracing and finite-difference timedomain methods were compared. Both methods of analysis showed the presence of undesirable side lobes related to lens design, namely rods too long for lens fabrication. The test results were compared with the measurements made with the knife-edge method. The use of a single tool to determine parameters of an optical fibre lens does not allow for precise determination of its properties. It is necessary to use different tools and programs. This allows a complete analysis of the beam parameters, letting us find the causes of technical issues that limit the performance of the lenses. [ABSTRACT FROM AUTHOR]

Glass microlens arrays with small unit sizes and high integration capacities are widely utilized in various optical systems, but the femtosecond laser milling produces microscale residual steps and nanoscale rough topography on microlens surface. Accordingly, an oxyhydrogen flame polishing is proposed after femtosecond laser milling, aiming to efficiently fabricate the ultrasmooth surface without damaging shape accuracy by triggering a viscoelasticity flow at nano/microscale. Through simultaneous modelling of the polishing process, a large thermal power results in a high viscoelasticity flow velocity for nanoscale topography smoothing, followed by microscale step melting. Then, a single-point polishing experiment is conducted to determine the critical transition temperatures for nanoscale smoothing and microscale melting. It is further experimentally applied to achieve an ultrasmooth surface of cylindrical microlens array with its roughness less than 0.2 nm and no hydroxyl introduction. This process also effectively repairs subsurface damage and reduces the form error to ±0.5 μm, improving the surface quality and shape accuracy. Similar results are also observed for the polishing of spherical microlenses. In conclusion, the method of combining femtosecond laser milling and oxyhydrogen flame polishing holds promise for high-efficiency and high-quality fabrication of glass components with micro features. [Display omitted] • Viscoelastic flow contributes to micro-step melting and nano-topography smoothing. • Numerical simulations confirm temperature's role in micro-to-nanoscale smoothing. • Simulations predict microlens array profile post viscoelastic flow. • Actual polishing temperature dominates micro-to-nano viscoelastic flow transition. • Control viscoelastic flow can produce a high-quality, atomically roughness surface. [ABSTRACT FROM AUTHOR]

The article is devoted to the construction of acousto-optic (AO) laser measuring systems (LMS) for measuring product displacements in three coordinates (3D): with one longitudinal Δl z and two transverse Δl x , Δl y with high resolution and an increased measurement range for the latter two. The paper discusses the circuitry of the measuring circuit based on the phase-locked loop (PLL) system, which makes it possible to achieve the maximum resolution when the AO LMS operates in the start-stop mode, i.e. starting and ending with a stationary state at v=0. The paper considers the possibilities of using a prismatic optical scheme, which makes it possible to use a one-axis (1D) AO modulator to control two-coordinate (2D) displacements Δl x , Δl y of a laser beam, a multi-aperture AO modulator, a fiber photodetector and other units.

The fabrication method of microlens arrays with diameters from 20 to 90 μm based on thermal reflow and dry etch structure transition process is demonstrated. The key process parameters of microlens design and production are obtained by theoretical calculation. And the research of photoresist (AZ4330) surface topography changes during thermal reflow process is studied in detail, which is helpful for microlens array design and process optimization. The photoresist microlens arrays are transferred into quartz by dry etching process. The measurement data indicate that the photoresist microlens arrays have good surface topography and high surface quality, and the optical property of quartz microlens is in good agreement with the theoretical design. This method can be widely used to prepare high quality microlens arrays in optical applications. [ABSTRACT FROM AUTHOR]

In order to increase the light extraction efficiency (LEE) of AlGaN deep ultraviolet light-emitting diodes (DUV LEDs), this study employed a sapphire substrate with a microlens array. Light extraction efficiency is increased by increasing transverse electric (TE) polarized light output by the use of a microlens array (MLA) created by inductively coupled plasma (ICP) etching. The construction of 2D colloidal crystals of 400 nm polystyrene (PS) particles on sapphire substrates was made possible via air-liquid interfacial colloidal assembly. The diameter, height, and spacing size of the MLA hemispheres were tailored using two separate dry colloidal etching processes. The peak EQE of DUV-LEDs with microlens arrays at depths of 205 nm and 176 nm increased by 6.6% and 7%, respectively, in comparison to DUV-LEDs without microlens arrays. The integrated microlens arrays with changing refractive index at the LED-air interface widen the light escape cone angle, enabling more light to escape the LED and reducing the amount of light trapped or absorbed within the structure. The finite difference Time domain (FDTD) modeling software was also used to simulate the microlens array light output structures. A microlens array with 400 nm spacing and 200 nm hemisphere height had the highest light extraction efficiency, which was in agreement with our experimental findings. • Improved AlGaN DUV LED light extraction efficiency by using a sapphire substrate with a microlens array. • The microlens array increases transverse electric polarized light output, increasing efficiency. • A 400 nm array with 200 nm hemisphere height with high light extraction efficiency. [ABSTRACT FROM AUTHOR]

Microneedles are highly sought after for medicinal and cosmetic applications. However, the current manufacturing process for microneedles remains complicated, hindering its applicability to a broader variety of applications. As diffraction lithography has been recently reported as a simple method for fabricating solid microneedles, this paper presents the experimental validation of the use of ultraviolet light diffraction to control the liquid-to-solid transition of photosensitive resin to define the microneedle shape. The shapes of the resultant microneedles were investigated utilizing the primary experimental parameters including the photopattern size, ultraviolet light intensity, and the exposure time. Our fabrication results indicated that the fabricated microneedles became taller and larger in general when the experimental parameters were increased. Additionally, our investigation revealed four unique crosslinked resin morphologies during the first growth of the microneedle: microlens, first harmonic, first bell-tip, and second harmonic shapes. Additionally, by tilting the light exposure direction, a novel inclined microneedle array was fabricated for the first time. The fabricated microneedles were characterized with skin insertion and force-displacement tests. This experimental study enables the shapes and mechanical properties of the microneedles to be predicted in advance for mass production and wide practical use for biomedical or cosmetic applications.

In this paper, we propose the tilted milling method for the fabrication of the precise microlens array (MLA) by eliminating the influence of tool error. In the conventional milling process, the surface morphology problem especially hump formation is often provoked by tool error on the center area of the machined surface. The hump formation initiated by tool error is very difficult to remove, unless the cutting tool is replaced by a new one. It was found that the hump formation was completely suppressed by the tilted milling method which the tool-axis angle is tilted by 35° to the on-axis of lens curvature. The form accuracy of the MLA was also drastically improved the peak-to-valley ratio from (0.991 to 0.141) µm. The tilted milling method was confirmed to be a highly robust fabrication process, because the surface morphology was rarely affected by tool error, especially the run-out deviation. [ABSTRACT FROM AUTHOR]

In recent years, the demand for optical components such as microlenses has been increasing, and various methods have been developed. However, fabrication of submillimeter microlenses with tunable numerical aperture (NA) on hard and brittle materials remains a great challenge using the current methods. In this work, we fabricated a variable NA microlens array with submillimeter size on a silica substrate, using a femtosecond laser-based linear scanning-assisted wet etching method. At the same time, the influence of various processing parameters on the microlens morphology and NA was studied. The NA of the microlenses could be flexibly adjusted in the range of 0.2 to 0.45 by changing the scanning distance of the laser and assisted wet etching. In addition, the imaging and focusing performance tests demonstrated the good optical performance and controllability of the fabricated microlenses. Finally, the optical performance simulation of the prepared microlens array was carried out. The result was consistent with the actual situation, indicating the potential of the submillimeter-scale microlens array prepared by this method for applications in imaging and detection.

The realization of high- Q single-mode lasing on the microscale is significant for the advancement of on-chip integrated light sources. It remains a challenging trade-off between Q -factor enhancement and light-field localization to raise the lasing emission rate. Here, we fabricated a zero-dimensional perovskite microcavity integrated with a nondamage pressed microlens to three-dimensionally tailor the intracavity light field and demonstrated linearly and nonlinearly (two-photon) pumped lasing by this microfocusing configuration. Notably, the microlensing microcavity experimentally achieves a high Q -factor (16700), high polarization (99.6%), and high Purcell factor (11.40) single-mode lasing under high-repetition pulse pumping. Three-dimensional light-field confinement formed by the microlens and plate microcavity simultaneously reduces the mode volume (∼3.66 μm 3 ) and suppresses diffraction and transverse walk-off loss, which induces discretization on energy-momentum dispersions and spatial electromagnetic-field distributions. The Q factor and Purcell factor of our lasing come out on top among most of the reported perovskite microcavities, paving a promising avenue toward further studying electrically driven on-chip microlasers.

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A new method for doughnut shaping based on 3D nanoprinted microlens on fiber tip is proposed. • The microlens was designed and optimized based on illumination optics, and it was fabricated by femtosecond laser induced two-photon polymerization. • Compared with diffractive optical elements, our proposed method has a larger manufacturing tolerance. • Both simulation and experiment show that the microlens can successfully transfer the Gaussian beam output into doughnut beam. Spatial beam intensity shaping is of great significance in many applications, such as laser fabrication and medical treatment. In this study we present a new method for doughnut beam shaping based on 3D nanoprinted microlens on fiber tip. The optical structure of the microlens was first designed and optimized based on illumination optics in software, and then the microlens was fabricated on a single-mode-fiber tip by femtosecond laser induced two-photon polymerization. Both simulation and experiment results have demonstrated that the Gaussian beam output from a single-mode fiber can be successfully transferred to a high-quality doughnut beam by using the fiber-tip microlens. The proposed microlens shows larger tolerance in fabrication resolution compared with optical diffraction beam shaping elements. Our research shows that the femtosecond laser induced two-photon polymerization provides a new and flexible method for the integration of micro-scaled beam shaping elements on optical fibers. [ABSTRACT FROM AUTHOR]

Light extraction efficiency (LEE) and angular-spectrum stability of organic light emitting diode (OLED) are significantly improved by using self-assembly microlens-array films (MAFs) made of a monolayer based on silica microspheres and acrylic resin as light extractor. The close-packed light MAFs with a high fill factor of 71.42% was uniformly fabricated by a facile and low-cost solution process of spin-coating. The MAFs feature highly transmissive with transmittance of 86.2–90.6% and also high haze of 78.9–82.4% in UV–Vis regime. External quantum efficiency (EQE) of OLED with MAFs was significantly improved from 3.04 to 5.04%, corresponding to an enhancement of 66% compared with reference OLED. The small angular shift of CIE-indices is in a range of (0.008, 0.004), while viewing angle changes from 0° to 60°. Besides, the origin of high LEE and angular-spectrum stability was due to high scattering effect induced by high haze, leading to a Lambertian emissive profile. Notably, the proposed fabrication for the MAFs is simple and scalable, which was believed to be a promising approach for display and lighting applications. [Display omitted] • The silica based MAFs with high fill factor, transmittance and haze of ∼71.4%, 90% and 80% in at wavelength from 380 to 780 nm. • High light extraction in EQE enhancement of 66% and angular-spectrum stability was achieved for OLED. • The proposed fabrication for MAFs is facile and scalable. • The origin of high LEE and angular-spectrum stability was deduced from high scattering effect. [ABSTRACT FROM AUTHOR]

Vein display device can significantly increase the success rate of intravenous injection. However, traditional vein display devices only contain near-infrared image information, which inevitably loses skin color information. In this article, a binocular microlens was fabricated by micro-fabrication technology. Then, a smart binocular microlens imaging system is set up. By this system, the near-infrared image with venous distribution and visible light image with actual skin color can be obtained simultaneously. In addition, an improved image fusing algorithm is proposed. The image fusing result shows that the venous details can be clearly shown and the background color of the hand also can be well preserved. Therefore, the proposed scheme can provide more real vein information. As the smart structure of the binocular microlens, the dual-bands microlens imaging system has the potential for miniaturization and could integrate with intelligent glasses for assisting intravenous injection.

This paper aims to present a novel rapid hot embossing approach and to study filling capacity of optical glass in the hot embossing process. Firstly, a novel rapid hot embossing device is developed, which consists of a rapid heating module and a precision loading module. Particularly, the rapid heating module allows a maximum temperature of 800 °C and a heating rate of 300 °C/min, with decent temperature control accuracy and uniform temperature distribution. In hot embossing process, by incompletely filling the microhole of silicon carbide mold, a microlens would be formed on the surface of glass disc, and the filling capacity of glass is quantified by the maximum height of the microlens. The tailor-made hot embossing device was exploited to conduct a series of experiments for evaluating effects of process parameters on the filling capacity of N-BK7 glass. Experimental results indicate that the filling capacity of glass could be enhanced by increasing the embossing force, the embossing temperature, the soaking time but decreasing the annealing rate. Furthermore, compared to soaking time and annealing rate, embossing force and embossing temperature have more significant influence on the filling capacity of N-BK7 glass. Therefore, the novel rapid hot embossing is a practical and promising technology for fabricating microstructures on glass materials with high softening points.

Functional micro/nano structures are promising for enhancing the performance of CaF 2 -based devices. However, it is still a challenge to precisely manufacture CaF 2 micro/nano structures due to their brittleness. In the present work, we demonstrated the machinability of ductile-mode diamond cutting of CaF 2 and the ability to sculpture sophisticated micro/nano structures on CaF 2 by applying elliptical vibration cutting. Firstly, the nanoindentation of CaF 2 reveals the crystal orientation-dependent interaction between dislocation slip and crack propagation, thus obtaining the optimal crystal orientation for plasticity. Subsequently, the grooving tests were conducted along the crystal orientation of (111) [ 1 ‾ 2 1 ‾ ]. With elliptical vibration cutting, the critical depth of cut from ductile-to-brittle transition is increased by 42 times as compared with ordinary cutting. Furthermore, considering the instantaneous uncut chip thickness in each vibration cycle, the influence of vibration amplitude on the ductile machinability of CaF 2 is discussed in detail. Finally, based on these fundamental results, ultra-precision hexagonal microlenses were successfully sculptured on CaF 2 by applying the amplitude-controlled sculpturing method in elliptical vibration cutting. • A 42 times increase in the critical depth of cut for ductile machining of CaF 2 by elliptical vibration cutting (EVC). • The dynamic motion path of cutting tool has a significant influence on ductile machining of CaF 2. • Functional textures of CaF 2 are precisely and efficiently fabricated by amplitude control sculpturing method in EVC. [ABSTRACT FROM AUTHOR]

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Photonic nanojet (PNJ) is a tightly focused diffractionless travelling beam generated by dielectric microparticles. The location of the PNJ depends on the refractive index of the material and it usually recedes to the interior of the microparticle when the refractive index is higher than 2, making high index materials unsuitable to produce useful PNJs while high index favours narrower PNJs. Here we demonstrate a design of CMOS compatible high index on-chip photonic nanojet based on silicon. The proposed design consists of a silicon hemisphere on a silicon substrate. The PNJs generated can be tuned by changing the radius and sphericity of the hemisphere. Oblate spheroids generate PNJs further away from the refracting surface and the PNJ length exceeds 17λ when the sphericity of the spheroid is 2.25 The proposed device can have potential applications in focal plane arrays, enhanced Raman spectroscopy, and optofluidic chips.

Shaped optical fiber tips have recently attracted a lot of interest for photonic jet light focusing due to their easy manipulation to scan a sample. However, lensed optical fibers are not new. This study analyzes how fiber tip parameters can be used to control focusing properties. Our study shows that the configurations to generate a photonic jet (PJ) can clearly be distinguished from more classical-lensed fibers focusing. PJ is a highly concentrated, propagative light beam, with a full width at half maximum (FWHM) that can be lower than the diffraction limit. According to the simulations, the PJs are obtained when light is coupled in the guide fundamental mode and when the base diameter of the microlens is close to the core diameter. For single mode fibers or fibers with a low number of modes, long tips with a relatively sharp shape achieve PJ with smaller widths. On the contrary, when the base diameter of the microlens is larger than the fiber core, the focus point tends to move away from the external surface of the fiber and has a larger width. In other words, the optical system (fiber/microlens) behaves in this case like a classical-lensed fiber with a larger focus spot size. The results of this study can be used as guidelines for the tailored fabrication of shaped optical fiber tips according to the targeted application.

Light field cameras have become a popular device for handheld, passive depth estimation. The geometry of the captured light rays can be equivalently described as a virtual camera array, where each view is taken from a different point on a regular grid. With this paper, we propose describing the effect of the main lens and microlens distortion on both the captured views, and on their position on this grid. It is showed that the microlens distortion affects the grid shape, implying a non-constant baseline between each view, unlike assumed in previous light field geometrical models. Moreover, we propose an end-to-end calibration method based on grid point detection. The detection is performed on raw hexagonal lattice sub-aperture images, to avoid a loss of precision in re-sampling operations. The calibration pipeline is tested on a Lytro Illum camera and is compared to the previous state of the art in this field. It is shown that the quality of the reconstructed 3D is significantly improved with our method, thanks to the fine-level description of the baseline between the virtual views. Our model is resilient to a change in the focusing distance of the main lens, making it applicable in a wide variety of scenarios. [ABSTRACT FROM AUTHOR]

Liquid crystal (LC) director and refractive index distribution in a cylindrical object (eg, micropore) with different LC boundary conditions have been simulated. Splay and bend configurations were simulated in the LC pores with Franck elastic coefficients K33/K11 ratio from 0.5 to 3. For different LC orientation configurations, parabolic profiles of radial dependence of the refractive index are obtained with focus distance up to 80 mm that makes it possible for application in different LC devices. [ABSTRACT FROM AUTHOR]