Researchers have developed a technique to fold glass sheets into microscopic 3D photonic structures directly on a chip — a process they call photonic origami. The method could enable tiny, yet complex optical devices for data processing sensing and experimental physics.
“Existing 3D printers produce rough 3D structures that aren’t optically uniform and thus can’t be used for high-performance optics,” said research team leader Tal Carmon from Tel Aviv University in Israel. “Mimicking the way a pinecone’s scales bend outward to release seeds, our laser-induced technique triggers precise bending in ultra-thin glass sheets and can be used to create highly transparent, ultra-smooth 3D microphotonic devices for a variety of applications.”
In Optica, Optica Publishing Group’s journal for high-impact research, the researchers report that the new laser-induced folding method can create 3-mm-long structures that are just 0.5 microns thick — about 1/200th the width of a human hair — setting a record length-to-thickness ratio for 3D structures. They also created helix shapes as well as concave and convex mirrors with surfaces so smooth — less than a nanometer of variation — that light reflects off them without distortion.
“Similar to how large 3D printers can fabricate almost any household item, photonic origami could enable a variety of tiny optical devices,” said Carmon. “For example, it can be used to generate micro-zoom lenses that could replace the five separate cameras used in most smartphones or to fabricate microphotonic components that use light instead of electricity — helping drive the shift toward faster, more efficient alternatives to traditional electronics in our computers.”
Folded by Accident
The new photonic origami method was discovered by chance when Carmon asked graduate student Manya Malhotra to pinpoint where an invisible laser was hitting the glass by increasing the power until the spot glowed. Instead of glowing, the glass folded — revealing a simple and unexpected way to achieve glass folding. Malhotra then became the pioneering expert in photonic origami.
The glass folds because, as one side is heated with a laser, the glass liquifies and surface tension becomes stronger than gravity. As the surface tension increases, the glass is pulled into a fold precisely where the laser hits.
To apply this discovery, lab engineer Ronen Ben Daniel fabricated a thin layer of silica glass on a silicon chip and then shaped it into the required two-dimensional form. Before bending the glass, the researchers used etching to undercut the silicon beneath the glass sheet while leaving a small support region to hold it in place. Using CO2 laser pulses, they showed that thin glass sheets on a silicon chip could be folded in less than a millisecond, with a speed of 2 m/s and acceleration exceeding 2000 m/s2.
“It was exciting to see the folding silica under the microscope,” said Carmon. “The level of control we had over 3D microphotonic architecture came as a pleasant surprise — especially given that it was achieved with a simple setup involving just a single laser beam focused on the desired fold.”
Creating Microscopic Structures
Using the new photonic origami approach, the researchers were able to bend sheets of glass up to 10 microns thick into shapes ranging from a 90-degree knee to helices. They were able to do this with fine control, down to 0.1 microradians.
They also used the new approach to create an extremely lightweight and precise table structure containing a concave cavity mirror, a type of mirror that focuses light. This structure was inspired by a theoretical paper by P.K. Lam from the Australian National University that proposed exploring potential deviations from Newtonian gravity at very small scales using optically levitated cavity mirrors that might be possible to fabricate using photonic origami.
To make the tiny table light enough, the researchers began with a glass sheet just 1/20 the thickness of a human hair (5 microns). They patterned the sheet much like a child’s foldable paper table toy and used their photonic origami technique to fold it into a 3D table after fabricating a concave mirror at the base of the table.
According to the researchers, this ultra-light, compact table could, in principle, be optically levitated and used to explore possible deviations from Newtonian gravity. These types of experiments could provide insights into astronomical mysteries associated with dark matter —the only area in physics where experimental observations consistently defy current theoretical predictions.
“High-performance, 3D microphotonics had not been previously demonstrated,” said Carmon. “This new technique brings silica photonics — using glass to guide and control light — into the third dimension, opening up entirely new possibilities for high-performance, integrated optical devices.”