Apr 20, 2016 | By Tess

A team of researchers based at the University of Stuttgart in Germany have recently published a study that demonstrates their capability to 3D print micron-scale optics with more precision and reproducibility than ever before. The recent breakthrough could have a big impact on the manufacturing of micro-scale integrated optical elements, and could contribute to further miniaturizing devices necessary for sensing or telecommunication applications.

The research, which was led by Harald Giessen, the chair for ultrafast nano-optics at the University of Stuttgart, effectively shows how the team used a technique known as “femtosecond laser writing” to create optical elements as tiny as 4.4 microns, perfectly placed in the center of an optical fiber as small as 125 microns in diameter, a typically very challenging feat. According to the study, the results of the 3D printed micron-scale optics were impressively very close to those of the digital simulations.

Giessen explains, “Although femtosecond laser writing has been demonstrated in the lab, we have shown that it can be used to make high performance micro-optics in a manner that is highly repeatable and reliable. We believe our approach can be scaled up for volume manufacturing and used to directly print almost any type of optical element on a tiny scale, opening up a new era of integrated micro- and nano-optics.”

The technique used by the researchers, femtosecond laser writing, is not unlike other 3D laser writing systems, though it works on a nano-scale and is designed to be as stable and reliable as possible. Essentially, the process involves the selective hardening of a light-sensitive material by a pulsing laser, which creates a 3D structure which can be easily separated from the unhardened material surrounding it. To create the laser writing system, the team of researchers used a commercial two-photon 3D laser lithography system, made by Nanoscribe GmbH, with the capability to additively manufacture nanometer-scale structures.

Giessen explains the process saying, “We have something like a pen that we can move in 3D through a material to create structures in a manner similar to a 3D printer but at very tiny scales. If you punch a set of parameters into our system and into a system in some other place in the world, you will get the same exact result. Even months from now, it will come out the same every time.”

The innovative technology has been used by the researchers to create phase masks, which are optical elements placed onto the end of optical fibers to shape and control the light emitted from them. As a press release about the study explains, without a filter or lens, the light emitted by a fiber is Gaussian, which means that it is bright in the center and begins to dim at the sides. With the phase masks created on the end of the fiber using the femtosecond laser writing technique, the light emitted by the fiber can be focused and shaped into either a consistently bright flat-top light or a donut-shaped light.

“Because the phase masks are so small and are created directly on the end of the optical fiber, even tiny errors in the centering of the phase mask would cause the donut-shaped beam to not look nice and round,” says Giessen. “We solved one of the hardest problems: repeatedly placing a phase mask with submicron accuracy directly in the center of the single-mode fiber.”

In terms of possible applications, the phase masks created by the research team could be used to replace large, bulkier optical lenses, which could allow for the illumination of even smaller endoscopes (used in non-invasive surgeries to see what is happening inside the human body). Alternately, the donut shaped phase masks could allow for the more precise optical trapping of particles or cells when placed in a liquid.

Currently, the research team at the University of Stuttgart is using their laser writing technique to see whether they can create more types of phase masks, including one that could shape an optical fiber’s light into a twist, which could have a big impact on photon entanglement. “Now that the instrument is available, we are only limited by what we can think of to do with it,” concluded Giessen.



Posted in 3D Printing Technology



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