Teams at MIT and the University of Texas at Austin (UT Austin) have fabricated a proof-of-concept chip-based 3D printer. The device, which is small enough to fit on a U.S. quarter, consists of a single millimeter-scale photonic chip that emits reconfigurable beams of light into a well of resin that cures into a solid shape when light strikes it. The prototype eschews moving parts in favor of an array of tiny optical antennas to steer a beam of light into the rapid-cure resin, combining silicon photonics with photochemistry to print arbitrary 2D patterns. MIT’s Notaros group, led by professor Jelena Notaros, had previously developed integrated optical-phased-array systems that steer beams of light using a series of microscale antennas fabricated on a chip using semiconductor manufacturing processes. By speeding up or delaying the optical signal on either side of the antenna array, the beam of emitted light can be moved in a certain direction. When further developed, the chip-based 3D printer could be used to quickly create small, customized objects on the go. Courtesy of Sampson Wilcox/MIT Research Laboratory of Electronics. The group teamed up with UT Austin’s Page Group, led by assistant professor Zak Page, who had demonstrated specialized resins that can be rapidly cured using wavelengths of visible light. “With photocurable resins, it is very hard to get them to cure all the way up at infrared wavelengths, which is where integrated optical-phased-array systems were operating in the past for lidar,” said lead author Sabrina Corsetti. Their prototype consists of a single photonic chip containing an array of 160 nm-thick optical antennas. When powered by an off-chip laser, the antennas emit a steerable beam of visible light into the well of photocurable resin. The chip sits below a clear slide, like those used in microscopes, which contains a shallow indentation that holds the resin. The researchers use electrical signals to nonmechanically steer the light beam, causing the resin to solidify wherever the beam strikes it. Instead of heating the chip to modulate the visible wavelength light, the researchers used liquid crystal to fashion compact modulators they integrated onto the chip. The material’s unique optical properties enabled the modulators to be extremely efficient and only about 20 microns in length. A single waveguide on the chip holds the light from the off-chip laser. Running along the waveguide are tiny taps which allow a little bit of light to each of the antennas. The researchers actively tune the modulators using an electric field, which reorients the liquid crystal molecules in a certain direction. In this way, they can precisely control the amplitude and phase of light being routed to the antennas. The groups worked closely to carefully adjust the chemical combinations and concentrations of the resin to hone a formula that provided a long shelf-life and rapid curing. In practice, the prototype was able to print shapes in a matter of seconds. In the long run, the researchers envision a system in which a photonic chip sits at the bottom of a well of resin and emits a 3D hologram of visible light, rapidly curing an entire object in a single step. According to Notaros, this would require an entirely new chip design, which is partially laid out in the paper, she said. The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-024-01478-2).