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Technion forms fluids into freeform optics

25 Nov 2021

Shaping and solidifying liquid could allow rapid prototyping of novel components.

A new route to manufacturing freeform optical components could help such items become more readily available for a range of industrial applications.

Freeform components can perform novel phase manipulations on incident light beyond those possible from traditional optical surfaces, thanks to their complex shapes and lack of conventional symmetries, opening up novel applications in eyewear and other small-scale applications.

The potential impact of freeform optics has been recognised for some years. Speaking to Optics.org in 2013, Jannick Roland of the US Center for Freeform Optics commented that freeform optics were attractive for many purposes, and that then-current advances in manufacturing techniques were outpacing the design mathematics of the items themselves.

Since then, however, manufacturing the freeform components at larger sizes using bulk production operations has remained challenging, while newer 3D printing techniques cannot as yet guarantee the surface quality required for effective freeform behavior.

A project at Haifa's Technion - Israel Institute of Technology has now developed an alternative manufacturing approach that could allow such components to be made more easily and assist their adoption in real-world uses.

Published in Optica, the breakthrough involves shaping liquid volumes into the required geometries and then solidifying the material. The approach should let researchers rapidly test freeform design concepts and allow mold-less fabrication on an industrial scale.

"Currently, optical engineers pay tens of thousands of dollars for specially designed freeform components and wait months for them to arrive," said the Technion's Omer Luria. "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."

Infinite possible topographies

The new technique builds on an approach to forming traditional optical components from liquid, recently developed by the Technion team, involving injection of a curable optical fluid into a rigid bounding frame contained within an immiscible immersion liquid environment.

Applying this principle to freeform geometries involved adjustments to the shape of the bounding frame, along with analytical models relating the shape of the frame to that of the enclosed liquid interface that would ultimately create the freeform surface.

In practice this involved injecting a lens liquid into the supportive frame so that the lens liquid wets the inside of the frame and then relaxes into a stable configuration. Once the required topography is achieved, the lens liquid can be solidified by UV exposure or other methods, according to the project's published paper.

After confirming that the technique could make simple spherical lenses, the project expanded their efforts to create freeform optical components with various geometries, including toroid and trefoil shapes, and sizes up to 200 millimeters.

"We identified an infinite range of possible optical topographies that can be fabricated using our approach," said the Technion's Mor Elgarisi. "The method can be used to make components of any size, and because liquid surfaces are naturally smooth, no polishing is required. The approach is also compatible with any liquid that can be solidified and has the advantage of not producing any waste."

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