Researchers at Technion: Israel Institute of Technology have developed a method to fabricate freeform optical components by shaping a volume of curable liquid polymer. The work may enable faster prototyping of customized optical components for a variety of applications, including corrective lenses, augmented and virtual reality, autonomous vehicles, medical imaging, and astronomy. The current process for creating freeform optics is difficult and expensive due to the amount of specialized equipment required to mechanically process and polish their surfaces. Technion researchers used a newly developed method to make optical components with various geometries — including toroid and trefoil shapes — and sizes up to 200 mm as well as freeform surfaces. The lenses exhibited surface qualities similar to the best polishing technologies available while being orders of magnitude quicker and simpler to make. Courtesy of Technion: Israel Institute of Technology. According to Technion research team leader Moran Bercovici, the team’s approach achieves extremely smooth surfaces and can be implemented using basic equipment. “This makes the technology very accessible, even in low resource settings,” he said. Using the method, Bercovici and colleagues made freeform components with subnanometer surface roughness in a matter of minutes. Unlike other prototyping methods such as 3D printing, the fabrication time remained short — even if the volume of the manufactured component increased. “Currently, optical engineers pay tens of thousands of dollars for specially designed freeform components and wait months for them to arrive,” said Omer Luria, a contributor to the the research paper. “Our technology is poised to radically decrease both the waiting time and the cost of complex optical prototypes, which could greatly speed up the development of new optical designs.” The team said it began work on the research with the goal to develop a method to create lenses for corrective eyewear. “We set out to find a simple method for fabricating high-quality optical components that does not rely on mechanical processing or complex and expensive infrastructure,” said Valeri Frumkin, who first developed the method in Bercovici’s lab. “We then discovered that we could expand our method to produce much more complex and interesting optical topographies.” Among the primary challenges in making optics by curing a liquid polymer is that for optics larger than ~2 mm, gravity supersedes surface forces. This causes the liquid to flatten into a puddle. To overcome this, the researchers developed a way to fabricate lenses using liquid polymer that is submerged in another liquid. The buoyancy counteracts gravity, allowing surface tension to dominate and the researchers to fabricate smooth optical surfaces by controlling the surface topography of the lens liquid as a result. This entailed injecting the lens liquid into a supportive frame so that the lens liquid wets the inside of the frame and relaxes into a stable configuration. Once the required topography is achieved, the lens liquid can be solidified by UV exposure or other methods to complete the fabrication process. After using the liquid fabrication method to make simple spherical lenses, the researchers expanded to optical components with various geometries — including toroid and trefoil shapes — and sizes up to 200 mm. The resulting lenses exhibited surface qualities similar to the best polishing technologies available while being orders of magnitude quicker and simpler to make. They further expanded the method to create freeform surfaces by modifying the shape of the supportive frame. “We identified an infinite range of possible optical topographies that can be fabricated using our approach,” said Mor Elgarisi, lead author of the paper. “The method can be used to make components of any size, and because liquid surfaces are naturally smooth, now polishing is required. The approach is also compatible with any liquid that can be solidified and has the advantage of not producing any waste.” The researchers are automating the fabrication process so that various optical topographies can be made in a precise and repeatable manner. They are also evaluating various optical polymers to determine which produce the best optical components. The research was published in Optica (www.doi.org/10.1364/optica.438763).