The thermal reflow process is widely used in microlens array fabrication. However, the resulting arrays are commonly criticized for their low fill factor. In this work, caulking is applied to fill the gaps between adjacent lenses. The experimental results prove that a gapless microlens array with a 100% fill factor could be successfully produced and the caulking time precisely controlled. Furthermore, an artificial neural network and genetic algorithm are used to achieve high quality using the thermal reflow and caulking. The L18 orthogonal array is used as the learning data for the artificial neural network to construct a system model that could predict the results (e.g., S/N, focal length, and roughness) for arbitrary parameter settings. The genetic algorithm is then applied to obtain the optimal parameter settings. The major objectives in using the optimal design are to reduce the variation in the focal length and the surface roughness for a microlens array. This allows improved focus and enhanced illumination brightness. The results show that microlens array quality could be significantly improved in comparison with the original design.
This paper describes a simple and inexpensive technique to design and fabricate polygon microlens array using thermal pressing technique. Polygon microlens array molds were fabricated by using lithography and electroforming process. Microlens pattern was designed on a photomask and transferred to a substrate through photoresist patterning. The electroforming technology was used to convert the photoresist microlens patterns into metallic molds. A hot pressing machine was used to replicate microlens array in PC substrate. The compression pressure, temperature, and pressing time were key parameters to design and manufacture microlens array. The optical properties of these microlenses have been characterized by measuring their focal lengths. The average cylindrical microlenses radii of curvature were 315μm~420μm and the average sag heights were 2.98μm~4.03μm.
This article describes a mass fabrication method for integrated microlens arrays mold by using UV lithography, thermal reflow, and electroforming process. The designed microlens array can be used for back light modules to enhance panel illumination. Refractive microlens with diameter 30 and 70 ?m in array are designed in certain layout. Lithographic fabrication of photoresist cylinder is applied by using the designed microlens array patterns. Thermal reflow resulted in photoresist melting and diameter shrinkage. Due to surface tension the shape of the photoresist cylinders changes to spherical shape. The sags of microlens with diameter 30 and 70 ?m are 7.5 and 25 ?m, respectively. The cross-section profile of microlens is measured by the Taylor Hobson’s profiler. It proved that thermal reflow can produce microlens array in photoresist materials. Replication process is applied by using electroforming process. Ni-Co composite electroforming can make metallic mold with hardness Hv 500 which is close to ordinary mold materials. Sputtering silver as a seed layer is applied onto microlens array in photoresist. Electroforming can start a “build-up” process to make required microlens array mold or mold insert. Refractive microlens arrays with high dense 700 lenses per mm2 were fabricated. The surface roughness of microlens arrays is less than Ra 0.02 ?m that adapt to the conventional lens surface roughness. Since the higher accuracy and lower cost of microlens fabrication methods are needed to meet the rapid growth of micro-optical devices, the contributed fabrication techniques are essential for the industry.
The design and simulation of a new optical add-drop multiplexer (OADM) made of two pairs of grating-frustrated directional couplers is presented. Design theory and simulation are introduced to support is feasibility. The directional couplers are proposed to use polymeric waveguides as the cores. The inverted-ridge waveguide fabrication is proposed using lithography and etching process. The proper dimensions and parameters of each waveguides for OADM are simulated. The designed OADM is 1550 nm wavelength with add-drip filters, bandwidth 20 nm, and 80% peak transmissions showing the application for wavelength division multiplexing (WDM).
This paper presents an innovative device for self-parking in a v-groove and a self-latching vertical mirror on the suspension diaphragm using the out of plane fiber-optical switch array technique. The self-parking offers integrating the optical fiber and mirror within the same optical switch. The self-latching vertical mirror is supported on the suspension diaphragm by four cantilever beams. The theoretical analysis includes a dynamic simulation using the ANSYS software and corner compensation using the IntelliCAD software. The fabrication process consists of wet etching mircromachining, lithography, and excimer laser ablation. This proposed process is simpler than those proposed in other works. An electrostatic driving voltage is used to operate the optical switch. The mirror is made of a photoresist coating with gold film as the switching element. The reflectivity of the gold film mirror is higher than 85% using a wavelength of 1310nm. The micro-optical switch has a maximum of displacement of 48 micrometers and the switching time is below 0.4 ms with a driving voltage of 100 VDC.
This paper presents a micromachining technique to solve the precision machining difficult for multi-fiber ferrule production. The LIGA technology is applied to make 1.2 mm thick V-groove mold inserts with dimensional tolerance 1 micrometers . It stars with x-ray mask fabrication, x-ray exposure, Ni-Co electroforming, and planarization to complete the metallic ferrule mold inserts. X-ray mask is developed here in low cost and accessible in Taiwan. The absorber thickness can be achieved to 30 micrometers in straightness. The single x- ray exposure can generate 1.2 mm thick PMMA after development process. This development proves the feasibility of many applications in x-ray micromachining. In the optical fiber passive components, connectors play a joint role int he whole system. Ferrule i the key part of a fiber connector. Since the development of the LIGA technology, high precision micro-components such the ferrule is considered to be applied. All multi-fiber ferrules require the same accuracy of pitch distance between two channels. The mold insert for ferrule fabrication becomes the most important part. Conventional precision machining has certain limitations on machining micro-components due to machining tool size and material wears. The LIGA technique can overcome these problems. It utilizes x-ray to penetrate polymer material and create molds, then applies electroforming to make metallic molds. These molds can be applied for molding process in mass production.
A successful ablation of Indium Tin Oxide (ITO) coated on PET substrate without damage the substrate is presented in this paper. ITO is a thin film coated on glass and plastic plates as used in flat panel displays (FPD). The conventional machining method is practiced by a wet chemical etching process. This process includes photoresist coating, exposure, development, wet etching, and stripping. Since the ITO coated on PET have the advantages of low cost, less weight, and ductility over than conventional ITO coated on glass. It takes more attentions on this material combination. However, direct-write laser to pattern ITO films on glass has been reported. The ablation of ITO coated on PET is unexplored so far. The experiment of this study uses the KrF ((lambda) equals 248 nm) excimer laser to selectively ablate ITO patterns coated on PET, it generates successful results. Since the excimer laser with short wavelength, high energy density, and short pulse period. It suddenly evaporates the material and minimizes the heat effect on the substrate. The micromachined profile of ITO patterns coated on PET is measured by an atomic force microscopy. The minimum line width can be down to 10 micrometers and avoid any damage to the substrate.
X-ray mask is the most important component in the x-ray micromachining. Absorber patterns have to form onto a working mask, then patterns can be transferred into the substrate. Graphite membrane has characters of low atomic number, electrical conductor, and rigid body suitable for a support diaphragm in a working mask.
Micro-electro-mechanical system technology offers a wide number of applications for the military, industrial, and consumer markets. The miniaturization of components is a common objective for all studies. Refractive microlens array with density 400 lenses per cm2 are fabricated in three minutes by using hot embossing. The higher accuracy and lower cost of microlens fabrication methods are needed to meet the rapid growth of commercial devices. Higher density of microlens is achievable by a higher density mesh mold. Microlens diameters of 250-380 micrometers are shaped with various molds. Focal lengths of 185-225 micrometers are obtained by changing compression pressure and working temperature which are discovered in this experiment. Molding temperature effects on the surface tension in lens material as explored is essential. From accuracy of microlens arrays are less than Rt 0.1 micrometers that adapt to the form accuracy of the lenses. This article describes a mass fabricating method for microlens array by using hot embossing and the experimental results show its feasibility for practice.
The fabrication of x-ray mask is an important step in the LIGA process. Thick absorber patterns for working masks to produce microstructures with high aspect ratio are desired to skip the intermediate mask fabrication. This article illustrates three x-ray mask-making methods applied for LIGA process, special for working masks. Three mask-making methods include mechanically machined mask, micro-EDM machining mask, and E- beam written mask. The mechanically machined mask method is the simplest and fastest among three methods, but it has geometry limitations and material hardness restrictions. Gold absorber and graphite membrane are composed to be a working mask, absorber patterns with dimensional bias are up to 5 micrometer in a 150 micrometer feature size. Micro-EDM machining mask method has the possibility to achieve the accuracy requirement in submicron range if its stage control is improved. The experiments showed that 2 micrometer error existed from the designed size. The E-beam written mask is the best method now available to accomplish the dimensional requirements in submicron range, its dimensional accuracy is within 0.5 micrometer after exposure. All three masks are successful to produce at least 500 micrometer thick PMMA microstructures after exposure, it also means that at least 500 micrometer thick metallic microstructures has been made by using an electroforming process.
This paper describes an application of the LIGA technology to the fabrication of optical fiber ferrule mold inserts with twelve channels. It presents the overall process from mask design, mask fabrication, deep x-ray lithography exposure, resist development, nickel electroforming, as well as surface finishing to attain the final result. Several deep x-ray mask-making methods are explored, including mechanically machined masks, micro-EDM masks, and electron beam written masks. The exposure, development and electroforming to fabricate nickel molds up to 500 micrometers thickness are reported in this study. Nickel structures for fiber ferrule mold insert with twelve channels made by electroforming are the final products. A practical method to finish the microstructure surface is presented. Channels with diameter precision -0.0/+0.5 micrometers and pitch alignment of 0.25 micrometers were accomplished to satisfy the requirements of the research sponsor for inserting and aligning 125 micrometers single-mode fibers.