Liquid Silica Resin Optimizes 3D Printing for Complex Micro-Optics

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A liquid silica resin (LSR) developed by researchers at the University of Arizona has proven successful as a 3D-printing medium for complex micro-optics. The organic-inorganic hybrid material has shown high curing speeds, better mechanical properties, lower thermal treatment temperatures, and reduced shrinkage. Inorganic silica glass can be achieved by thermally treating the printed sample at 600 °C in air.

For the 3D-printing of optics and micro-optics, the silica resin is an alternative to organic polymers. Despite their lightweight and low-cost qualities, organic polymer-based optics do not offer the same level of thermal stability, chemical resistance, and imaging performance in the UV and IR bands as that which can be delivered by optics based on inorganic glass.
SEM image of a printed glass Alvarez lens, the right element can be moved to change the power of the Alvarez lens. Courtesy of Hong et al.
Researchers at the University of Arizona have used an LSR as a 3D-printing medium for complex micro-optics. This SEM image, of a printed glass Alvarez lens, shows an optic with an element (on the right) that can be moved to change the power of the lens. Courtesy of Hong et al.
Traditional grinding and polishing methods used in optical fabrication are far from the most effective when it comes to micro-optics and are not an option for freeform micro-optics. Precision glass molding has been the method of choice, though it's not without limitations. Multielement components and freeform optics with microstructures pose a barrier.

Additive manufacturing has made progress in that respect, though the resulting optics often suffer from lower resolution and require further refinement in post-processing. Two-photon polymerization (TPP) methods have shown particular promise, as the resolution obtained has been much better. Previous work from the Arizona researchers on TPP-based additive manufacturing with LSR has demonstrated success, but certain problems remain.

In the current work, the team refined its existing LSR formula used in 3D-printing applications, after noticing a tendency for it develop deformations in specific applications. This deformation occurred most often during the printing and thermal treatment processes when creating a structure with high aspect ratio, mainly due to the relatively low number of crosslinked points in the printed structure.

When printing a lens objective with a 50-μm diameter and a height of 100 μm, the supporting structure lacked the strength to support the whole objective once the printing process was completed.

To remedy this, the team focused on creating a series of LSRs with increased crosslinkable points, by adjusting the ratio of methacryloxymethyltrimethoxsilane (MMTS) during synthesis. The team varied the concentration of MMTS between 6.5 and 20 mol%. The researchers found that increasing the concentration of MMTS also increased shrinkage during thermal treatment.

To achieve the high quality needed for optics manufacturing, the shrinkage must be low to better control the shape and surface quality. The researchers therefore needed to find a balance between an increased level of MMTS for better crosslinking and the resulting increase in shrinkage. While the sample with 20 mol% of MMTS had better mechanical properties, the team ultimately chose the sample with 15 mol% as it had less shrinkage.

The printing method developed alongside the material is capable of printing almost all types of optical surfaces, the researchers said, including flat, spherical, aspherical, freeform, and discontinuous surfaces, with accurate surface shape and high surface quality for imaging applications.

The researchers demonstrated this by printing a number of structures that would not have been possible with their previous formula for LSR. This included lenses with Fresnel structures, a micro-objective with three elements, an Alvarez lens, and other elements. Lenses created with this method were able to clearly resolve images, including a focused image of a housefly’s wing.

Based on the measured surface quality and shape deviation of the optics the team created, as well as the image quality they obtained, the researchers believe that 3D printing of glass imaging optics will play a significant role in precision optical imaging. Potential applications span the ability to fabricate optics with greater flexibility for endoscopes and microspectrometers, as well as the development of freeform micro-optics, complex multielement alignment-free optical systems, and optical systems with moving elements.

The research was published in Advanced Science (

Published: June 2022
Micro-optics refers to the design, fabrication, and application of optical components and systems at a microscale level. These components are miniaturized optical elements that manipulate light at a microscopic level, providing functionalities such as focusing, collimating, splitting, and shaping light beams. Micro-optics play a crucial role in various fields, including telecommunications, imaging systems, medical devices, sensors, and consumer electronics. Key points about micro-optics: ...
A noncrystalline, inorganic mixture of various metallic oxides fused by heating with glassifiers such as silica, or boric or phosphoric oxides. Common window or bottle glass is a mixture of soda, lime and sand, melted and cast, rolled or blown to shape. Most glasses are transparent in the visible spectrum and up to about 2.5 µm in the infrared, but some are opaque such as natural obsidian; these are, nevertheless, useful as mirror blanks. Traces of some elements such as cobalt, copper and...
3d printing
3D printing, also known as additive manufacturing (AM), is a manufacturing process that builds three-dimensional objects layer by layer from a digital model. This technology allows the creation of complex and customized structures that would be challenging or impossible with traditional manufacturing methods. The process typically involves the following key steps: Digital design: A three-dimensional digital model of the object is created using computer-aided design (CAD) software. This...
Photoresist is a light-sensitive material used in photolithography processes, particularly in the fabrication of semiconductor devices, integrated circuits, and microelectromechanical systems (MEMS). It is a crucial component in the patterning of semiconductor wafers during the manufacturing process. The primary function of photoresist is to undergo a chemical or physical change when exposed to light, making it selectively soluble or insoluble in a subsequent development step. The general...
The term photochemical pertains to chemical processes or reactions that are initiated or influenced by the absorption of light. Photochemical reactions involve the interaction of light, often in the form of ultraviolet or visible radiation, with molecules, leading to changes in their chemical structure or properties. These reactions are distinct from thermal or non-light-induced chemical reactions. Key characteristics of photochemical reactions include: Light absorption: Photochemical...
Opticsmicro-opticsMaterialsResearch & TechnologyeducationUniversity of Arizonaoptical manufacturingglass3d printingliquid silica resinresin compositesresinphotoresistphotochemicalsurfacesspectroscopyoptical devicesoptical systemsTechnology News

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