Micro-optical Structures Research Articles

Mechanical properties investigation on recycled rubber desert sand concrete

The mechanical properties of recycled rubber desert sand concrete were studied to determine the effect of the replacement rate of recycled rubber and desert sand. The replacement rates of recycled rubber aggregates were set to 0 %, 5 %, 10 %, and 15 %, respectively, and for dessert sand aggregates were set to 0 %, 10 %, 20 %, and 30 %, respectively, during concrete preparation. The concrete's compressive, tensile, and freeze-thaw mechanical properties were tested at each replacement rate. The experimental results show that when the replacement rate of desert sand increases from 0 % to 30 %, the replacement rate of recycled rubber is 15 %, and the splitting tensile strength of concrete shows a pattern of first increasing and then decreasing. When the replacement rate for desert sand is 30 %, the replacement rate for recycled rubber rises from 0 % to 15 %, and the splitting tensile strength shows a pattern of first decreasing. With replacement rates of 10 percent for recycled rubber aggregate and 20 percent for desert sand aggregate, the damage to the concrete from external forces is relatively ideal. The compressive strength values are the highest, and the split tensile strength is the best, demonstrating good compressive and tensile strength. The results of CO2 emission analysis show that as the amount of recycled rubber increases, the CO2 emissions per unit volume of concrete also increase. The interface of the micro-optical structure in the concrete is straightforward, the pores are few, and it exhibits good mechanical properties. The concrete undergoes freeze-thaw cycles with relatively stable changes in compressive strength and split tensile strength, demonstrating a solid freeze-thaw resistive mechanical property.

Laser Direct Writing for Micromachining of Freeform Surface on n-Type GaAs via Photoelectrochemical Etching

The fabrication of microstructures featuring freeform surfaces on semiconductor substrates confronts substantial obstacles due to their inherent material difficulties, including considerable hardness and brittleness, as well as geometric complexity. In this investigation, we leverage laser direct writing (LDW) combined with photoelectrochemical etching to achieve precise material removal from semiconductor surfaces. By conducting a series of experiments on a home-made LDW apparatus under varying conditions, we established a correlation between the etching depth and both the power intensity and motion speed of the laser spot. The analysis revealed that the etching depth exhibited linearly with the power intensity of the laser spot and inversely with the motion speed. Additionally, the half widths of the grooves maintained consistently within the range of 1–2 μm. By leveraging this methodology, we successfully fabricated a freeform micro-optical structure on an n-GaAs wafer by precisely adjusting the power intensity of the laser spot during scanning, thus demonstrating the feasibility for achieving nanoscale machining precision. This research underscores the promise of this technique in significantly advancing the fabrication processes of semiconductor devices.

Highly focused beam generated with a height tuned micro-optical structure for high contrast microscopic imaging

Light sheet illumination technology improves the signal-to-noise ratio, resolution, and reduces scattered backgrounds for biological microscopic detection system. Here, we developed a novel micro-optical structure to produce a focused and uniform beam for the enhancement of imaging contrast. The beam intensity and working distance can be modified by adjusting the height and period of the structure. Our experiments successfully recorded structured light illumination, demonstrating the ability of the structure to capture high-contrast imaging data. We compared the light fields generated with and without the structure to assess the imaging quality, revealing a maximum 4.78-fold improvement in the signal-to-noise ratio. This work provides a potential method for high-resolution and high-contrast light sheet fluorescence microscopic detection.

3D Printing of Glass Micro-Optics with Subwavelength Features on Optical Fiber Tips.

Integration of functional materials and structures on the tips of optical fibers has enabled various applications in micro-optics, such as sensing, imaging, and optical trapping. Direct laser writing is a 3D printing technology that holds promise for fabricating advanced micro-optical structures on fiber tips. To date, material selection has been limited to organic polymer-based photoresists because existing methods for 3D direct laser writing of inorganic materials involve high-temperature processing that is not compatible with optical fibers. However, organic polymers do not feature stability and transparency comparable to those of inorganic glasses. Herein, we demonstrate 3D direct laser writing of inorganic glass with a subwavelength resolution on optical fiber tips. We show two distinct printing modes that enable the printing of solid silica glass structures ("Uniform Mode") and self-organized subwavelength gratings ("Nanograting Mode"), respectively. We illustrate the utility of our approach by printing two functional devices: (1) a refractive index sensor that can measure the indices of binary mixtures of acetone and methanol at near-infrared wavelengths and (2) a compact polarization beam splitter for polarization control and beam steering in an all-in-fiber system. By combining the superior material properties of glass with the plug-and-play nature of optical fibers, this approach enables promising applications in fields such as fiber sensing, optical microelectromechanical systems (MEMS), and quantum photonics.

Multiplexed Detection of Pathogens Using Solid-Phase Loop-Mediated Isothermal Amplification on a Supercritical Angle Fluorescence Array for Point-of-Care Applications.

Adaptations of new generation molecular techniques for multiplexed detection of pathogens are gaining interest in the field of point-of-care (POC) industry and onsite testing. Loop-mediated isothermal amplification (LAMP), an advanced molecular amplification technique, has proven promising due to its unique features that suits ideal for POC applications. However, application of LAMP for multiplexed detection of pathogens remains challenging because of the difficulty in the identification of specific LAMP amplicons that does not have a well-definite molecular size. In this study, we developed a solid-phase loop-mediated isothermal amplification (SP-LAMP) technique to address the challenge. Integration of LAMP with the supercritical angle fluorescence (SAF) micro-optic structures as a solid support (SS) in an array format enabled spatial separation of LAMP amplicons in a multiplexed configuration. Important parameters such as length of the SS primers, length of the primer-binding region, the effect of surface density of immobilized SS primers, and cross-reactivity among the primers of different targets were iteratively tested and optimized. With the combination of SP-LAMP and SAF techniques, it was possible to detect multiple pathogens that include Salmonella spp, Campylobater spp., Campylobacter coli, Campylobacter jejuni, avian influenza virus (AIV), and pan avian internal control (IC) under singleplex conditions. The multiplexing capacity of the SP-LAMP was demonstrated using AIV and IC with promising results. The success of SP-LAMP has opened a promising direction toward the development of a multiplex POC system for rapid detection of multiple pathogens.

Embedding Optical Microcavities in Nanoporous SiO2 Film via Infill Inkjet Printing

Embedding Optical Microcavities in Nanoporous SiO2 Film Since the transparent SiO2 nanoparticle aggregate film with a nanoporous network allows a polymer or dye solution to penetrate well, it is possible to embed a micro-optical structure such as a WGM microcavity laser inside the film by a printing method such as inkjet. In other words, it can realize an optical integrated circuit as if “drawing on paper”. More information can be found in article number 2200018 by Hiroaki Yoshioka and co-workers.

Формирование и оптические свойства нанорешеток на поверхности фторида кальция, генерируемых при фемтосекундном лазерном воздействии

Femtosecond laser structuring of dielectrics is an urgent problem for the creation of optical elements. In this work, we performed femtosecond laser nanostructuring of the calcium fluoride surface with the formation of self-organizing periodic gratings with subwavelength periods of the order of 200 and 350 nm. During the work, the dependence of the period of the structures on the wavelength of laser radiation was established, which was confirmed by the simulation results. The structures show a decrease in transmission over the entire visible range, predominantly due to diffraction and light scattering. Keywords: direct laser recording, femtosecond laser pulses, surface functional nano- and micro-optical structures, diffraction.

Highly flexible and stable perovskite/microbead hybrid photodetectors with improved interfacial light trapping

Organic-inorganic halide perovskites are considered as a core material in optoelectronics. Particularly, perovskite-based photodetectors are promising devices for sensing and imaging applications. Their two-terminal structure provides advantages in terms of fabrication, mechanical flexibility, and reproducibility. However, due to their low responsivity, they require high driving voltages (>5V). Here, we propose a simple procedure for the design of high-performance, low-power, and flexible perovskite photodetectors by employing an assembled polymeric microbead monolayer. A large-area photonic crystal comprising transfer-printed polystyrene (PS) beads on poly(methylmethacrylate) (PMMA)/perovskite layers confines the electromagnetic field in perovskite. The significant increase in the photoluminescence characteristics of perovskite improves the responsivity, detectivity, and noise equivalent power to over 8.5 times. The polarization-insensitive light absorption of perovskite by the PS bead layer promotes excellent omnidirectionality with respect to the incident light at different angles. Furthermore, the mechanical durability of the flexible devices at a submillimeter bending radius (0.2 mm) is significantly improved by employing PMMA/PS layers. The resulting device performance exhibits excellent retention of 81.5% after 20 bending cycles. The proposed approach in the design of versatile micro-optical structures on perovskite paves the way in realizing highly deformable and efficient perovskite-based optoelectronics.

Automated on-axis direct laser writing of coupling elements for photonic chips.

Direct laser writing (DLW) has recently been used to create versatile micro-optic structures that facilitate photonic-chip coupling, like free-form lenses, free-form mirrors, and photonic wirebonds. However, at the edges of photonic chips, the top-down/off-axis printing orientation typically used limits the size and complexity of structures and the range of materials compatible with the DLW process. To avoid these issues, we develop a DLW method in which the photonic chip's optical input/output (IO) ports are co-linear with the axis of the lithography beam (on-axis printing). Alignment automation and port identification are enabled by a 1-dimensional barcode-like pattern that is fabricated within the chip's device layer and surrounds the IO waveguides to increase their visibility. We demonstrate passive alignment to these markers using standard machine vision techniques, and print single-element elliptical lenses along an array of 42 ports with a 100 % fabrication yield. These lenses improve fiber-to-chip misalignment tolerance relative to other fiber-based coupling techniques. The 1 dB excess loss diameter increases from ≈ 2.3 μm when using a lensed fiber to ≈ 9.9 μm when using the DLW printed micro-optic and a cleaved fiber. The insertion loss penalty introduced by moving to this misalignment-tolerant coupling approach is limited, with an additional loss (in comparison to the lensed fiber) as small as ≈1 dB and ≈2 dB on average. Going forward, on-axis printing can accommodate a variety of multi-element free-space and guided wave coupling elements, without requiring calibration of printing dose specific to the geometry of the 3D printed structure or to the materials comprising the photonic chip. It also enables novel methods for interconnection between chips. To that end, we fabricate a proof-of-concept 3D photonic wire bond between two vertically stacked photonic chips.

Aspherical microlenses enabled by two-photon direct laser writing for fiber-optical microendoscopy

Fiber-optical microendoscopy has made significant improvements to in vivo neural imaging, minimally invasive diagnostics, and microsurgery. However, high resolution, miniaturization, and low complexity cannot be simultaneously achieved together in the lens system for fiber-optical microendoscopy because current lens systems are in shape and dimensions restricted by limitations of manufacturing. Recently, two-photon direct laser writing (DLW) has been implemented in the fabrication of low-resolution micro-optics structures. Here, we demonstrate a high-resolution miniaturized singlet aspherical microlens fabricated on the fiber facet using DLW. The microlens has a high numerical aperture (NA), of 0.9, in air with only one aspherical surface, and is 10–20 times smaller in diameter than a typical gradient refractive index (GRIN) microlens. The designs of aspherical microlenses with NAs of 0.3, 0.6, and 0.9 in air are aberration-free at three wavelengths (561, 590, and 630 nm). The full width at half maximum of the effective intensity point spread function of a 0.9 NA aspherical microlens is 0.85 μm. We demonstrate fiber-optical microendoscopy imaging with a 0.6 NA aspherical microlens. The proposed aspherical microlens can potentially be applied to the development of a high-resolution, extremely miniaturized fiber-optical microendoscope.

Micro-refractive optical elements fabricated by multi-exposure lithography for laser speckle reduction.

Laser speckle reduction with a macro refractive optical element (mROE) is restricted by the limited entrance facet size of light pipe. Here, we have fabricated a micro-ROE (μROE) that incorporates three-dimensional micro-optical structures. The μROE with 2 × 2 duplicated multi-level cells is made of SU-8 photoresist with the help of multi-exposure lithography process. When the μROE works together with the mROE, objective speckle contrast is reduced to 0.2, where the light source is a low-coherence multimode laser diode. In principle, more speckle reduction can be obtained by fabricating μROEs with more cells and larger height differences among the cells.

Photocurable Polymer Composition Based on Heat-Resistant Aromatic Polyamide for the Formation of Optical Elements by Two-Photon Polymerization

Optical properties of a polymer composition based on heat-resistant aromatic polyamide are established and an approach to the formation of three-dimensional microoptical structures by two-photon polymerization on the base of this composition is developed. Formation of prototype polymer microoptical elements is proven in several regimes involving a two-photon polymerization system with the use of a laser source with a wavelength of 525 nm. The formed structures corresponded to the initial three-dimensional model, were optically transparent in the range from 450 nm, and preserved optical transparency after several cycles of heating up to 300°C.

Фотоотверждаемая полимерная композиция на основе термостойкого ароматического полиамида для формирования оптических элементов методом двухфотонной полимеризации

The optical properties of the polymer composition based on heat-resistant aromatic polyamide were established. An approach to the formation of three-dimensional micro-optical structures by the method of two-photon polymerization based on it has been developed. The regimes of polymer microoptical elements prototyping using a two-photon polymerization system with 525 nm wavelength laser source were worked out. The formed structures corresponded to the initial three-dimensional model, were optically transparent in the range from 450 nm to 1100 nm, including maintaining optical transparency after a series of heating cycles up to 300 ° C.

Фототермическая запись микрооптических структур в модифицированном приповерхностном слое монокристаллов ниобата лития

Фототермическая запись микрооптических структур в модифицированном приповерхностном слое монокристаллов ниобата лития

Insect-Mimetic Imaging System Based on a Microlens Array Fabricated by a Patterned-Layer Integrating Soft Lithography Process.

In nature, arthropods have evolved to utilize a multiaperture vision system with a micro-optical structure which has advantages, such as compact size and wide-angle view, compared to that of a single-aperture vision system. In this paper, we present a multiaperture imaging system using a microlens array fabricated by a patterned-layer integrating soft lithography (PLISL) process which is based on a molding technique that can transfer three-dimensional structures and a gold screening layer simultaneously. The imaging system consists of a microlens array, a lens-adjusting jig, and a conventional (charge-coupled device) CCD image sensor. The microlens array has a light screening layer patterned among all the microlenses by the PLISL process to prevent light interference. The three-dimensionally printed jig adjusts the microlens array on the conventional CCD sensor for the focused image. The manufactured imaging system has a thin optic system and a large field-of-view of 100 degrees. The developed imaging system takes multiple images at once. To show its possible applications, multiple depth plane images were reconstructed based on the taken subimages with a single shot.

3D fabrication of spherical microlens arrays on concave and convex silica surfaces

Three-dimensional (3D) microlens arrays are a group of micro-optics structures on curved surfaces that offer unique optical functions such as wide field of view in a compact arrangement. This paper reports an improved rapid lapping and molding system for 3D fabrication of spherical microlens arrays on non-planar surfaces including concave and convex surfaces for optical applications. Unlike traditional approaches for 3D micro patterns on curved silicon/silica substrates, this research demonstrates a low-cost and efficient chemical mechanical polishing process by lapping precision microlenses with steel balls and diamond slurries. Different from lapping on plane surfaces, lapping parameters for each micro cavity need to be accurately calculated and controlled to obtain microlenses with same apertures. Therefore, a micro wear model for micro cavity lapping process was established to calculate cavity sag height with the knowledge of down force, relative velocity and lapping time. Several groups of microlenses lapping were then conducted under the same conditions to validate the micro wear model. Guided by the micro wear model, two groups of microlens arrays were fabricated on concave and convex surfaces respectively. The shape accuracy and surface texture of the microlens arrays were evaluated by using a white light interferometer. Afterwards, the silica molds were coated with graphene film and then utilized to copy the 3D microstructures onto polymers by rapid surface molding. The wide angle imaging characterization of the 3D polymeric microlens arrays was illustrated by a simple optical setup and the measured MTF curves using the slanted-edge method. The improved manufacturing platform demonstrates a new approach for 3D microlens arrays fabrication on hard substrates in a cost effective way.

Long-lived monolithic micro-optics for multispectral GRIN applications

The potential for realizing robust, monolithic, near-surface refractive micro-optic elements with long-lived stability is demonstrated in visible and infrared transmitting glasses capable of use in dual band applications. Employing an enhanced understanding of glass chemistry and geometric control of mobile ion migration made possible with electrode patterning, flat, permanent, thermally-poled micro-optic structures have been produced and characterized. Sub-surface (t~5–10 µm) compositional and structural modification during the poling process results in formation of spatially-varying refractive index profiles, exhibiting induced Δn changes up to 5 × 10−2 which remain stable for >15 months. The universality of this approach applied to monolithic vis-near infrared [NIR] oxide and NIR-midwave infrared [MIR] chalcogenide glass materials is demonstrated for the first time. Element size, shape and gradient profile variation possible through pattern design and fabrication is shown to enable a variety of design options not possible using other GRIN process methodologies.

Numerical optimization of the extraction efficiency of a quantum-dot based single-photon emitter into a single-mode fiber.

We present a numerical method for the accurate and efficient simulation of strongly localized light sources, such as quantum dots, embedded in dielectric micro-optical structures. We apply the method in order to optimize the photon extraction efficiency of a single-photon emitter consisting of a quantum dot embedded into a multi-layer stack with further lateral structures. Furthermore, we present methods to study the robustness of the extraction efficiency with respect to fabrication errors and defects.

Implementation of smooth nanocrystalline diamond microstructures by combining reactive ion etching and ion beam etching

Due to its extraordinary properties diamond can be used as mold in a hot embossing process which allows the replication of micro-optical structures. For this application a low surface roughness is indispensable. We investigated the ability of ion beam etching (IBE) to smooth defined rough areas after reactive ion etching (RIE). Simulations based on the influence of the angle dependence of the ion beam etch rate showed the suitability of this approach.Different surface qualities were achieved for nanocrystalline diamond films by RIE with three different oxygen-argon gas mixtures and etch depth, respectively. SEM images displayed the expected increase of surface roughness with the oxygen share of the gas mixture and the achieved etch depth.No masking layers were employed during ion beam post-processing. The comparison of different AFM images confirm that this process enlarged the etch depths corresponding to the initial surface roughness until the rough areas are smoothed completely. With increasing surface roughness the expenditure of time necessary to reach saturation rose. Etch rates measured for reactive ion etching were 5 to 6 times higher than the etch rate measured for IBE. Simply comparing the etch time the combination of RIE and IBE is up to four times faster than only employing IBE for the fabrication of structures despite using low RIE plasma powers.

Rotationally symmetric formulation of the wave propagation method-application to the straylight analysis of diffractive lenses.

We introduce a modified formulation of the wave propagation method for the efficient simulation of rotationally symmetric micro-optical components. The reformulated algorithm provides an increased computational performance of approximately two orders of magnitude and strongly reduced memory requirements, in comparison to the original formulation. This enables the efficient wave optical simulation of extended micro-optical structures beyond the common thin-element approximation. As a prototypical example, we assess the modified algorithm for the evaluation of straylight induced by diffractive lenses. We find an excellent accuracy, while comparing to rigorous simulations, which justifies the ability to overcome the limitations of the thin-element approximation.