Glass Microlens Research Articles

MICRO FORMING OF GLASS MICROLENS ARRAY USING AN IMPRINTED AND SINTERED TUNGSTEN CARBIDE MICRO MOLD

Glass microlens array with lens diameter under 100 µm was replicated by micro thermal forming process using a tungsten carbide micro mold which was imprinted and sintered from an original master. The original master was fabricated by photolithography and thermal reflow process. The effects of forming process conditions on the form accuracy and the surface roughness of the micro formed glass microlens array were examined and analyzed. Finally, to verify the effectiveness of the proposed process, glass microlens array for the purpose of laser beam focusing was designed and fabricated, and a focused laser beam profile using the fabricated microlens array was measured and analyzed.

A reflow process for glass microlens array fabrication by use of precision compression molding

A novel low-cost, high-volume fabrication method for glass microlens arrays was developed by combining compression molding and thermal reflow processes. This fabrication process includes three major steps—i.e., fabrication of glassy carbon molds with arrays of micro size holes, glass compression molding to create micro cylinders on a glass substrate, and reheating to form microlens arrays. As compared to traditional polymer microlens arrays, glass microlens arrays are more reliable and therefore may be used in more critical applications. In this research, microlens arrays with different surface geometries were successfully fabricated on a P-SK57 (Tg = 493 °C) glass substrate using a combination of the compression molding and thermal reflow processes. The major parameters that influence the final lens shape, including reheating temperature and holding time, were studied to establish a suitable fabrication process. A numerical simulation method was developed to evaluate the fabrication process. Finally, both surface geometry and optical performance of the fabricated glass microlens arrays were analyzed.

A glass reflowed microlens array on a Si substrate with rectangular through-holes

A thermally reflowed glass microlens array was fabricated on a Si substrate. Glass lenses are more durable and scratch-resistant than plastic lenses made by the same, simple thermal reflow process. The microlens was designed using the ray tracing technique and optimized by controlling the nominal diameter and height of glass cylinders. The glass cylinders were formed by wet etching a glass plate in a HF (49%) solution and reflowed to form a semi-spherical lens shape at 850 °C (glass transition temperature Tg = 820 °C) for 20 min in a furnace. Then, the Si substrate was etched in a TMAH (5%) solution to make rectangular through-holes underneath the microlens array for high optical transmission. The profile of the fabricated microlens was measured with a confocal microscope, and its optical characteristics (lens size, beam radius and focal length) were evaluated with a 633 nm laser diode beam. The experimental beam waist (minimum beam radius) at the focal point of 1000 µm was 8 µm, which was in good agreement with a calculated value. The results show that the microlens array can be used in a broad wavelength range from UV to the IR region.

Fabrication and Characterization of Three-Dimensional Microlens Arrays in Sol-Gel Glass

We propose a new replication process for the realization of thick microlenses in SiO2 glass with low organic content. We start by replicating an array of cylindrical micropillars made in SU-8 negative photoresist (Microchem) into poly-dimethylsiloxane (PDMS). The PDMS replica is filled with a photoresist (Clariant AZ 9260), applied to a glass substrate and soft-baked. After demoulding, we obtain cylindrical pillars that are given a dome-like shape by a thermal softening. This structure is used as a master in a second PDMS replication step. An in-house developed sol-gel glass material with low organic content is then poured in the second PDMS replica and subsequently thermally treated to obtain an array of thick, dense and crack-free microlenses. We characterize the shrinkage and the surface roughness of the microlenses. Using imaging of millimeter-size objects in an optical microscope setup, we characterize basic optical properties of the lenses, like focal length, magnification, and distribution of the light intensity around the focal plane

Research on micro-optical lenses fabrication technology

We present a detail investigation on the development of a series of gradient index (GRIN) optical glass microlens and polymer microlens and microlens arrays in our laboratory in recent years. The special glass material GRIN lenses have been fabricated mainly by using ion-exchange technology, which are applied to construct micro-optic devices and other applications. On one hand, we demonstrated the light propagation and imaging properties of GRIN lenses and the results analyzed. On the other hand, we have explored a drop-on-demand ink-jet printing method to produce microlens array using nano-scale polymer droplets involved with a uniform ultraviolet light and heat solidifying process. The experimental setup for manufacturing polymer microlens array and the performance of refractive microlens elements are also given in this paper.

Precision compression molding of glass microlenses and microlens arrays—an experimental study

An innovative manufacturing process utilizing high-temperature compression molding to fabricate aspherical microlenses by using optical glasses, such as BK7, K-PG325, and soda-lime glass, is investigated. In a departure from conventional approaches, a unique hollow contactless mold design is adopted. Polished glass substrates and the mold assembly are heated above the glass transition temperature first, followed by initial forming, then annealing. The forming rate is controlled in real time to ensure mold position accuracy. Mold materials used include tungsten carbides, 316 stainless steel, 715 copper nickel, and aluminum alloys. The geometric control of the microlenses or microlens arrays can be precisely controlled by the forming temperature, forming speed, mold design, and annealing time.

Rod and spherical silica microlenses fabricated by CO_2 laser melting

The fabrication and testing of glass microlenses with rod and spherical shapes are described. The sizes of the lenses range from tens of micrometers to several millimeters. The surfaces of the lenses were fabricated by the melting method. These surfaces have been studied by several methods. The theoretical behavior of the lenses was investigated by ray tracing. Some applications of the lenses are presented.

Soft-lithography-enabled fabrication of large numerical aperture refractive microlens array in hybrid SiO2–TiO2 sol-gel glass

This paper describes a low-cost soft-lithography method for building large-numerical-aperture microlenses in hybrid sol-gel glass. The fabrication processes comprise three steps, namely fabrication of large numerical aperture microlens array in photoresist as a master, replication of the master in poly-dimethylsiloxane (PDMS) as elastomeric molds and reproduction of the PDMS replica onto the hybrid sol-gel glass as an end structure. Comparing with the direct UV fabrication in the photosensitive sol-gel glass, the proposed method provides a unique advantage in terms of fabrication freedom in shape and thickness of micro-optical elements in the sol-gel glass. This eliminates the difficulties in direct photolithography in sol-gel glass for arbitrary shapes and great thickness due to ever increasing demands.

Single step fabrication of microlens arrays with hybrid HfO2-SiO2 sol-gel glass on conventional lens surface

We demonstrate a novel method for fabricating glass microlens (arrays) with single step on conventional lens surface. In this method, the glass microlens can be achieved by only one step with sol gel glass material. The microlens aperture and focus length can be controlled easily and uniformly. The fabricated sample shows good focusing property. This work will be useful to improve the performance of compound eyes optical system such as camera, telescope, 3D integral imaging and so on.

Bach Fabrication of Microlens at the end of Optical Fiber using Self-photolithgraphy and Etching Techniques

This paper describes a simple batch process for fabrication of microlens and microlens array at the end of an optical fiber or an optical fiber bundle using self-photolithography and etching techniques. A photoresist micro-cylinder was exactly formed at the core of the fiber end by exposing an UV light from the other end of the fiber and conventional development, rinse processes. A photoresist microlens was formed by thermal reflowing of the fiber at 170°C for 1 h. A measurement of transmissivity showed that the fabricated photoresist microlens is applicable for a wavelength that is longer than 450 nm. Alternatively, a glass microlens was fabricated at the core of the fiber by dry etching with an SF6 gas using the photoresist microlens as a mask. The focusing of the lensed fiber was confirmed and simulation work showed that the lensed fiber could focus the light with a beam spot of 2 μm, numerical aperture (NA) of 0.285 and a depth of focus of 16 μm.

Micro-lensed gigabit-per-second high-efficiencyquantum-well light-emitting diodes

The authors present highly efficient low-power surface-textured light-emitting diodes (LEDs) designed for optical communication at bit rates up to 1.3 Gbit/s. LEDs with an external quantum efficiency > 30% are demonstrated to perform at bit rates of 1 Gbit/s. The application of spherical glass micro-lenses improves the angular light output for enhanced coupling into optical fibres.

Theory of 2-D ion exchange in glass: optimization of microlens arrays

The equations of two-component electric field assisted ionic diffusion and exchange are formulated analyticallyand solved numerically for the problem of 2-D (cylindrical) microlenses in glass, both for individual, isolated microlenses and arrays of microlenses. The theoretical formulation represents a proposed extension of the 1-D (planar) formulation of Abou el leil and Cooper. Ray tracing through computed index of refraction distributions is used to estimate optical performance. The inclusion of interactions of neighboring microlenses is shown to be important for optimizing optical performance of a high fill factor array.

Fresnel and wide-angle equation analyses of microlenses

The applicability of the Fresnel and wide-angle formalisms to glass microlenses is analyzed. For a representative, small, one-dimensional microlens formed from a single-mode slab waveguide, paraxial and wide-angle techniques are in relatively good agreement despite the large refractive index differences at the glass-air interface. Furthermore, in a test case, a single value of n/sub 0/ could be used in the Fresnel equation for electric field propagation through the microlens, while n/sub 0/=1 should be used outside the lens, greatly simplifying the programming and calculational effort. While this conclusion is not expected to be universally valid, it should apply to many standard components in integrated optics. The accuracy of the wide-angle technique relative to other often-cited procedures is established. >

Processing of glass micro-lens by a laser ion-exchange method.

Processing of glass micro-lens by a laser ion-exchange method.

Fabrication of glass microlenses by ion diffusion under an electric field

A method was proposed to fabricate glass microlenses with a parabolic index profile by ion exchange under an electric field. The fabrication process involved two steps: the first step was migration of Ag + ions into a planar soda-lime-silica glass to give a hemispherical concentration distribution of the ion. The second step was the formation of a parabolic concentration profile of Ag + ions. On the basis of theoretical calculations, the experimental conditions were fixed as follows: First step; diffusion time = 83 min, current density = 1.8 A/m 2, and temperature = 583 K. Second step: 120 min, different current densities and 613 K. Applying 2 A/m 2 in the second step, the concentration profile of Ag + ions appeared to be parabolic. The parabolic profile of the ions was deformed toward the glass surface under a current smaller than 2 A/m 2 in the second step. The profile was also deformed toward the inside of the glass under an excess current larger than 2 A/m 2. The present theoretical model for the fabrication process provided a good representation of all the experimental concentration profiles of Ag + ions.

Some recent advances in glasses and glass-ceramics

Glass is a very old material with many uses, although it's commonly prized for what it may contain, or what may be seen through it. With the establishment within the last century of laboratories concerned with glass research and development, many new kinds of glass, with new uses, or new methods for production of glass articles, have appeared. Nine which are familiar to many people are listed in this survey. Three of these relate to inventions of new compositions, and six to new processes for forming glass into a usable product. This article discusses some newer developments in glasses, as an indication of directions of some current or recent research. They include durable low temperature glasses, durable far infra-red transmitting glasses, full-colour photosensitive glasses, glass microlens arrays, precision direct molding, specialized glass-ceramics for dental restorations, for film or paper, or for tough materials. Finally, I make some brave predictions about future directions of research and development in that fascinating materials, glass.

Photolytic technique for producing microlenses in photosensitive glass

A process is described whereby 2-D arrays of small diameter spherical lenses are produced in a homogeneous photosensitive glass by a photothermal technique. The mechanism of the lens formation is explained on the basis of the density change of the photonucleated microcrystalline phase developed relative to the unexposed glass. The lens formation is related to such variables as optical exposure, thermal schedule, glass thickness, and lens diameter. Optical characterization of the lenses produced by this technique was carried out by interferometric and MTF measurements. One-to-one conjugate erect imaging lens arrays were fabricated and tested.