Fabrication Of Lenses Research Articles

Emerging Role of Hydrogels in Drug Delivery Systems, Tissue Engineering and Wound Management.

The popularity of hydrogels as biomaterials lies in their tunable physical properties, ability to encapsulate small molecules and macromolecular drugs, water holding capacity, flexibility, and controllable degradability. Functionalization strategies to overcome the deficiencies of conventional hydrogels and expand the role of advanced hydrogels such as DNA hydrogels are extensively discussed in this review. Different types of cross-linking techniques, materials utilized, procedures, advantages, and disadvantages covering hydrogels are tabulated. The application of hydrogels, particularly in buccal, oral, vaginal, and transdermal drug delivery systems, are described. The review also focuses on composite hydrogels with enhanced properties that are being developed to meet the diverse demand of wound dressing materials. The unique advantages of hydrogel nanoparticles in targeted and intracellular delivery of various therapeutic agents are explained. Furthermore, different types of hydrogel-based materials utilized for tissue engineering applications and fabrication of contact lens are discussed. The article also provides an overview of selected examples of commercial products launched particularly in the area of oral and ocular drug delivery systems and wound dressing materials. Hydrogels can be prepared with a wide variety of properties, achieving biostable, bioresorbable, and biodegradable polymer matrices, whose mechanical properties and degree of swelling are tailored with a specific application. These unique features give them a promising future in the fields of drug delivery systems and applied biomedicine.

Gold Nanocomposite Contact Lenses for Color Blindness Management.

Color vision deficiency (CVD) is an ocular congenital disorder that affects 8% of males and 0.5% of females. The most prevalent form of color vision deficiency (color blindness) affects protans and deutans and is more commonly known as “red–green color blindness”. Since there is no cure for this disorder, CVD patients opt for wearables that aid in enhancing their color perception. The most common wearable used by CVD patients is a form of tinted glass/lens. Those glasses filter out the problematic wavelengths (540–580 nm) for the red–green CVD patients using organic dyes. However, few studies have addressed the fabrication of contact lenses for color vision deficiency, and several problems related to their effectiveness and toxicity were reported. In this study, gold nanoparticles are integrated into contact lens material, thus forming nanocomposite contact lenses targeted for red–green CVD application. Three distinct sets of nanoparticles were characterized and incorporated with the hydrogel material of the lenses (pHEMA), and their resulting optical and material properties were assessed. The transmission spectra of the developed nanocomposite lenses were analogous to those of the commercial CVD wearables, and their water retention and wettability capabilities were superior to those in some of the commercially available contact lenses used for cosmetic/vision correction purposes. Hence, this work demonstrates the potential of gold nanocomposite lenses in CVD management and, more generally, color filtering applications.

Structurally and morphologically engineered chalcogenide materials for optical and photonic devices

We discuss several recent advances in the development of methodologies and techniques used to structurally and morphologically engineer chalcogenide (ChG) materials. We introduce two ChG patterning techniques both offering spatial resolution beyond the classical single-photon diffraction limit: multiphoton lithography and thermal scanning probe lithography (TSPL). The former was applied to produce nanoscale modifications in thermally deposited As2S3, and we realized gradient refractive index (GRIN) effective medium lens fabrication in multilayer As2S3-As2Se3 films with features as small as 120 nm using this approach. The GRIN lens was shown to be optically functional. ChG Ge-Sb-Se-Te (GSST) material was also explored for its potential as a phase-change material (PCM). We demonstrated nanoscale feature patterning using TSPL in PCMs with critical dimensions below 100 nm. In addition, new patterning methods, we also report solution processing of GSST PCMs as an alternative route for ChG film deposition. These new material processing and structuring techniques will offer new pathways for creating functional planar optical and photonic devices.

Design of a Multimodal Light Sheet Optical System for Multivariate Applications in Phytopathology

The design of optical instruments is an active subject due to improvement in lens techniques, fabrication technology, and data handling capacity. Much remains to do to expand its application to phytopathology, which would be in particular quite useful to improve crop growth monitoring in countries like Mali. An optical multimodal system for plant samples has been developed to improve the characterization of leaf disease symptoms, provide information on their effects, and avoid their spread. Potentially inexpensive components (laser, lens, turntables camera and sample, filter, lens, camera and computer) have been selected, assembled and aligned on an optical table into a multimodal system operating in transmission, reflection, diffusion and fluorescence. The illumination and observation angles can be adjusted to optimize viewing conditions in the four modes. This scientific contribution has been an initiation into the design and implementation of an optical instrument. Initial results are shown and will now be extended in cooperation with agronomic laboratories in African countries for tests on specific plant diseases in relation with prevailing climate conditions.

Integrated contact lens sensor system based on multifunctional ultrathin MoS2 transistors

Smart contact lenses attract extensive interests due to their capability of directly monitoring physiological and ambient information. However, previous demonstrations usually lacked efficient sensor modalities, facile fabrication process, mechanical stability, or biocompatibility. Here, we demonstrate a flexible approach for fabrication of multifunctional smart contact lenses with an ultrathin MoS2 transistors-based serpentine mesh sensor system. The integrated sensor systems contain a photodetector for receiving optical information, a glucose sensor for monitoring glucose level directly from tear fluid, and a temperature sensor for diagnosing potential corneal disease. Unlike traditional sensors and circuit chips sandwiched in the lens substrate, this serpentine mesh sensor system can be directly mounted onto the lenses and maintain direct contact with tears, delivering high detection sensitivity, while being mechanically robust and not interfering with either blinking or vision. Furthermore, the in vitro cytotoxicity tests reveal good biocompatibility, thus holding promise as next-generation soft electronics for healthcare and medical applications.

Thermal stress cleaving of glass-based X-ray telescope lenses by heated wire to eliminate microdefects

Abstract The satellite borne X-ray telescope (XRT) is a key technical tool for studying major astronomical problems in the universe. During the fabrication of ultra-thin glass lenses for XRTs, conventional glass cutting technologies yield micro-cracks along the cut surface or micro-damage on the surfaces of the glass normal to the cut. These micro-defects will cause the lenses to be damaged by the strong vibration and jerk of the launch process. In this paper, we seek to resolve this issue by developing a non-destructive cutting technique for glass lenses. Specifically, in this study we propose a heated wire thermal stress cleaving method. We derived the principal parameters affecting the thermal stress fracture behavior of lenses and furthermore calculated the relationship between the length of the initial crack and the minimum temperature. Experimental studies are performed to investigate the process parameters that affect the propagation of a crack in the telescope lens during the thermal stress cleaving process. In particular, we have successfully achieved thermal stress cleaving of a 0.3mm thick lenses with a surface roughness Ra of less than 0.5nm. When assessed in a satellite launch vibration test with a maximum accelerations amplitudes of 5g and 6g in the Y- and Z-directions, respectively, no crack propagation or damage was observed on the surface of the obtained telescope lenses. The study lays a foundation for the manufacture of glass-based XRT.

Design of an optical system for a laser beam shaping system based on aspheric polymer lenses

Conversion of laser beam profiles is required in a wide variety of applications, such as producing a plane-parallel beam with a uniform intensity distribution. Traditional collimator systems are not capable of modifying the laser beam profile. High-quality uniformity of light can conveniently be achieved using high-order aspheric lens surfaces, which require expensive technology and equipment when they are manufactured from optical glass. A technique for using polymer optical materials for lens fabrication enables surfaces of any complexity to be obtained. In this paper, we describe the design of an aspheric-polymer-lens laser beam shaping system using ZEMAX software. We compare the quality parameters for systems using polymer optics and glass optics and provide recommendations for prudent selection of materials.

Enhanced Responsivity of Diamond UV Detector Based on Regrown Lens Structure

In this work, the regrowth method is used on lens-structure diamond ultraviolet (UV) detector to suppress the surface defects caused by the lens fabrication process. After the regrowth of thin diamond film, the structure of the lens remains. Therefore, in the UV region, the regrown lens detector exhibits the highest responsivity compared with the original lens detector and the regrown planar detector. Moreover, the regrown lens detector two response peaks at around 240 nm and 240 nm. Under 220 nm or 240 nm illumination, the regrown lens detector display a fast response speed without obvious persistent photoconductive effect. This provides an efficient way to extend the the detection range of diamond UV detector while not sacrificing the performance of transient response.

Development of an intelligent grinding system for fabricating aspheric glass lenses

Precision optical systems, such as lithographic projection lens or cameras for satellites, typically composed of glass or ceramics optical components. In the manufacturing processes of glass and ceramics components, grinding is a key technique for curvature generation (CG) of optical surface. However, dimension errors and sub-surface damage (SSD) of components occur during the CG process. High material removal rates during the CG leads to deeper SSD on optical surface. The SSD must be removed by subsequent lapping and polishing processes to ensure high optical surface quality. However, these processes are complex, and a precise process to remove SSD from the aspheric surfaces with tens or hundreds of microns of departure from best fit sphere (BFS) is required. Thus, an efficient precision lens fabrication method can reduce the depth of SSD and help to control the dimension error during the CG process. We developed a five-axis grinding system with intelligent machining techniques to improve the quality of CG process. The intelligent grinding system based on the Tongtai five-axis machine (GT-630) was combined with two measurement modules of the Renishaw measurement probe. A customized computer-aided manufacturing software was developed and applied to this grinding system. Spherical and aspherical components with a maximum diameter of 600 mm can be fabricated using the grinding system. To improve the grinding efficiency, an ultrasonic-assisted module was combined with the BBT 40 tool arbor. The frequency range, amplitude, and power of the ultrasonic device were 15–40 kHz, 0.2–2 μm, and 1000 W, respectively. The intelligent grinding system included several vibration, temperature, and acoustic emission sensors and a microphone to monitor the dynamic status of machine during the grinding process and help to quality control. The wear of the diamond grinding wheel could be predicted immediately by analyzing the collected data in this system. A five-axis machine was applied to an intelligent grinding system for large glass lenses. The fabrication time of 200 mm diameter aspheric lenses reduced about 3 weeks by using this intelligent grinding system to integrate aspherization processes into curvature generation to become an aspheric curvature generation step.

Envelope grinding of micro-cylinder array lenses using a near arc-profile wheel without on-machine precision truing

Abstract A large demand for micro cylinder array lenses on the scale of 0.1∼10 mm exists for laser beam shaping in optical communication and measurement devices. Envelope grinding is an attractive method for the efficient fabrication of optical lenses. However, precision truing of micro-diamond grinding wheels is very arduous. In this paper, a novel method of envelope grinding using a near arc-profile wheel (EGNAW) without on-machine precision truing is proposed for micro-cylinder array lenses fabrication. The mathematical models of near arc-profile wheels and the wheel path in the workpiece profile plane are established. Comparative experiments of conventional envelope grinding and the EGNAW method are conducted on BK7 glass elliptical curved micro-cylinder array lenses. The three step strategies for the EGNAW method, that is, the iso-parametric, iso-distance and iso-residual strategies, are investigated for their effects on the grinding results. The normal error (in PV) of the micro-lens ground using the conventional envelope grinding is 33.48 μm. The normal error in the EGNAW method is minimized to 2.05 μm. For the EGNAW method, the grinding accuracy and surface roughness of a lens ground using the iso-distance or iso-residual strategy are superior to those of the iso-parametric strategy at the same efficiency. The EGNAW method can be applied to cylindrical surfaces as well as rotationally symmetric and non-rotationally symmetric freeform surfaces.

Realization of Modified Elliptical Shaped Dielectric Lens Antenna for X Band Applications with 3D Printing Technology

Placing dielectric lens structures into an antenna's aperture has proven to be one of the most reliable methods of enhancing its gain. However, the selected material and the prototyping method usually limit their fabrication process. With the advances in 3D printing technology and their applications, the microwave designs that were either impractical or impossible in the past to manufacture using traditional methods, are now feasible. Herein, a novel prototyping method by using 3D-printer technology for low-cost, broadband, and high gain dielectric lens designs has been presented. Firstly, the elliptical lens design has been modeled in the 3D EM simulation environment. Then fused deposition modeling based 3D-printing method has been used for the fabrication of the dielectric lens. The measured results of the 3D printed antenna show that the lens antenna has a realized gain of 17 to 20.5 dBi over 8-12 GHz. Moreover, the comparison of the prototyped antenna with its counterpart dielectric lens antenna in the literature has indicated that the proposed method is more efficient, more beneficial, and has a lower cost.

Engineering Aspheric Liquid Crystal Lenses by Using the Transmission Electrode Technique

The transmission electrode technique has been recently proposed as a versatile method to obtain various types of liquid-crystal (LC) lenses. In this work, an equivalent electric circuit and new analytical expressions based on this technique are developed. In addition, novel electrode shapes are proposed in order to generate different phase profiles. The analytical expressions depend on manufacturing parameters that have been optimized by using the least squares method. Thanks to the proposed design equations and the associated optimization, the feasibility of engineering any kind of aspheric LC lenses is demonstrated, which is key to obtain aberration-free lenses. The results are compared to numerical simulations validating the proposed equations. This novel technique, in combination with the proposed design equations, opens a new path for the design and fabrication of LC lenses and even other types of adaptive-focus lenses based on voltage control.

Using SiO<sub>2</sub> Hard Mask for Fabrication of Micro Fresnel Focusing Lens for Ultrasonic Ejectors

The fabrication of Fresnel focusing lenses operating at frequencies of 100 and 200 MHz was investigated in order to enhance the focusing efficiency of ultrasonic energy. The effects of process parameters on the four-level Fresnel lens profiles were discussed to find a most feasible fabrication procedure through these experiments. The quality of Fresnel lenses was improved when two-and three-mask processes using SiO2 film as the hard mask were employed. Besides, a better side-wall profile of Fresnel lens was obtained by using the three-mask process as compared to the two-mask one.

Portable deep learning singlet multi-spectral microscope

Compared with monochromatic or RGB imaging technologies, multi-spectral imaging technology is beneficial for obtaining more information details from images of different wavelengths with better contrast. A novel portable and cost-effective multispectral microscope is proposed, whose highlights are firstly imaging by a special designed singlet lens with only controlled rotational symmetric aberrations and then removing the controlled aberrations by deep learning computational imaging method to improve the resolution. Our method helps to reduce the extreme difficulties of singlet lens fabrication due to its simple surface produced by the unnecessarily supreme aberration optimization, while ensuring the resolution. In this manuscript, we introduce singlet lens design methods to connect Zernike polynomial coefficients with singlet lens parameters through wavefront aberrations. Then, the deep learning networks, parameters and working environments are provided to computationally enhance the resolution. By imaging a gold standard resolution pattern and typical bio-samples, experiment results demonstrate that our method and demo-setups achieve multi-spectral microscopy well and cost-effectively. It is believable that our portable deep learning singlet multi-spectral microscope would be an alternate to the conventional approaches and applied in biology, chemistry, environmental science, especially in resource-limited areas.

Birefringence- and Optical Distortion-Free Isotropic Polymer Lens Assisted by Photonic Microspheres.

Development of low-cost and light polymer optical devices to substitute for inorganic materials is a major trend. Traditional molten processing methods are direct and have been extensively applied in optical product manufacturing. However, the inevitable intrinsic birefringence and optical distortion due to polymer molecular chain anisotropy limit their application in high-end optical devices. Here, we report a novel thermocompression strategy for isotropic polymer lens fabrication, in which a cross-linked photonic crystal (PC) consisting of closely stacked polymer microspheres is used as a precursor and then heated and pressed under the rubbery state. A polymethyl methacrylate microsphere-based PC is used as a demonstration, and the obtained isotropic lenses exhibit superior performance compared to the traditional counterpart, which are birefringence-free (Δn < 1 × 10-5) and optical distortion-free and have excellent mechanical properties (hardness reaches 0.28 GPa), and the hidden mechanism is carefully studied. These properties enable the isotropic lens to be applied in precision optical components such as the lens of spectacles, microscope, telescope and endoscope, industrial camera, and astronaut helmet, and the proposed general method can extend to various polymers and provide new opportunities for the development of three-dimensional PCs.

Microfluidic fabrication with silver nanowires for optofluidic structures with three-dimensional operation

With the current design of modern optical lens technology, the optical parameters and field-of-view are restricted, preventing maximum functionality. Such restrictions can be mitigated with the implementation of a three-dimensional compound-eye lens, however, the fabrication of this three-dimensional compound-eye lens is associated with several challenges. Such challenges include the development of a semi-transparent and flexible electrode material and the operation and adherence of out-of-plane optofluidic lenses to oblique interfaces. This work addresses these challenges through two experimental analyses. The first experimental analysis is a study of silver nanowires with feature size of approximately 90 nm for use as a flexible and semi-transparent electrode material, and the effects of filtering and processing methods on the electrode sheet resistance. With optimal preparation of the silver nanowires, the fabricated electrode is seen to have favourable properties for this application. The second experimental analysis is a study of the optimal hydrophobic coating for minimal hysteresis and the optical operation of out-of-plane optofluidic lenses situated on oblique interfaces, as is required for peripheral out-of-plane optofluidic lenses in a three-dimensional compound-eye lens. The out-of-plane optofluidic lenses are seen to have favourable operation and voltage control with minimal hysteresis. The results show promise towards development of wide field-of-view systems with tunable optical parameters.

Ptychographic X-ray speckle tracking with multi-layer Laue lens systems.

The ever-increasing brightness of synchrotron radiation sources demands improved X-ray optics to utilize their capability for imaging and probing biological cells, nano-devices and functional matter on the nanometre scale with chemical sensitivity. Hard X-rays are ideal for high-resolution imaging and spectroscopic applications owing to their short wavelength, high penetrating power and chemical sensitivity. The penetrating power that makes X-rays useful for imaging also makes focusing them technologically challenging. Recent developments in layer deposition techniques have enabled the fabrication of a series of highly focusing X-ray lenses, known as wedged multi-layer Laue lenses. Improvements to the lens design and fabrication technique demand an accurate, robust, in situ and at-wavelength characterization method. To this end, a modified form of the speckle tracking wavefront metrology method has been developed. The ptychographic X-ray speckle tracking method is capable of operating with highly divergent wavefields. A useful by-product of this method is that it also provides high-resolution and aberration-free projection images of extended specimens. Three separate experiments using this method are reported, where the ray path angles have been resolved to within 4 nrad with an imaging resolution of 45 nm (full period). This method does not require a high degree of coherence, making it suitable for laboratory-based X-ray sources. Likewise, it is robust to errors in the registered sample positions, making it suitable for X-ray free-electron laser facilities, where beam-pointing fluctuations can be problematic for wavefront metrology.

Towards high-throughput large-area metalens fabrication using UV-nanoimprint lithography and Bosch deep reactive ion etching.

We demonstrate the fabrication of diffraction-limited dielectric metasurface lenses for NIR by the use of standard industrial high-throughput silicon processing techniques: UV nano imprint lithography (UV-NIL) combined with continuous reactive ion etching (RIE) and pulsed Bosch deep reactive ion etching (DRIE). As the research field of metasurfaces moves towards applications, these techniques are relevant as potential replacements of commonly used cost-intensive fabrication methods utilizing electron beam ithography. We show that washboard-type sidewall surface roughness arising from the Bosch DRIE process can be compensated for in the design of the metasurface, without deteriorating lens quality. Particular attention is given to fabrication challenges that must be overcome towards high-throughput production of relevance to commercial applications. Lens efficiencies are measured to be 25.5% and 29.2% at wavelengths λ = 1.55μm and λ = 1.31μm, respectively. A number of routes towards process optimization are proposed in relation to encountered challenges.

An aspherical microlens assembly for deep brain fluorescence microendoscopy

Fluorescence microendoscopy is becoming a standard technique in neuroscience for visualizing neuronal activity in the deep brain. Gradient refractive index (GRIN) lenses are increasingly used for fluorescence microendoscopy; however, they inherently suffer from strong aberrations and distortion. Aspherical lenses change their radius of curvature with distance from the optical axis and can effectively eliminate spherical aberrations. The use of these lenses has not been fully explored in deep brain fluorescence microendoscopy due to technical difficulties in manufacturing miniature aspherical lenses. In this study, we fabricated a novel microendoscope lens assembly comprised two nested pairs of aspherical microlenses made by precision glass molding. This assembly, which was 0.6 mm in diameter and 7.06 mm in length, was assembled in a stainless steel tube of 0.7 mm outer diameter. This assembly exhibited marked improvements in monochromatic and chromatic aberrations compared with a conventional GRIN lens, and is useful for deep brain fluorescence microendoscopy, as demonstrated by two-photon microendoscopic calcium imaging of R-CaMP1.07-labeled mouse hippocampal CA1 neurons. Our aspherical-lens-based approach offers a non-GRIN-lens alternative for fabrication of microendoscopic lenses.

Design of diffractive lenses operating at several wavelengths.

We propose a method for designing diffractive lenses having a fixed-position focus at several prescribed wavelengths, which we refer to as spectral diffractive lenses (SDLs). The method is based on minimizing an objective function describing the deviation of the complex transmission functions of the spectral lens at the operating wavelengths from the complex transmission functions of diffractive lenses calculated separately for each of these wavelengths. As examples, SDLs operating at three, five, and seven different wavelengths are designed. The simulation results of the calculated lenses confirm high efficiency of the proposed method. For experimental verification of the design method, we fabricate using direct laser writing and experimentally investigate an SDL operating at five wavelengths. The presented experimental results confirm the efficiency of the proposed method in practical problems of designing SDLs. The obtained results may find applications in the design and fabrication of novel flat diffractive lenses with reduced chromatic effects.