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Electronics Manufacturing Extends Spectrum of Integrated Photonics | Research & Technology | Dec 2022 | Photonics.com
Electronics Manufacturing Extends Spectrum of Integrated Photonics.
SANTA BARBARA, Calif., Dec. 6, 2022 — To realize its full potential, photonics technology must become smaller, cheaper, and easier to produce. Though researchers have made progress on these fronts, challenges remain in getting circuits to work with shorter wavelengths of light. To this end, researchers from Nexus Photonics; University of California, Santa Barbara (UC Santa Barbara); and Caltech have developed a technique to enable photonic chips to operate in the visible to near-infrared spectrum. The technique relies on methods common in electronics manufacturing, making it easy to produce inexpensively at scale. “This is the kind of breakthrough that could open up possibilities no one has thought of before,” said co-lead author Ted Morin, a doctoral candidate at UC Santa Barbara. The technology supports bringing high-performance photonics into new markets and applications, such as augmented and virtual reality, health care and atomic clocks at visible and near-infrared wavelengths. In addition, large-scale production will slash the price of lasers and photonic circuits. “It will be like getting a yacht for the cost of a surfboard,” Morin said. A hurdle to photonic circuit miniaturization is connecting the laser to the photonic circuit itself? — ?plugging it into each pathway isn’t practical. “Imagine someone plugging wires in, by hand, to every few transistors on your computer processor,” Morin said. “It would completely defeat the purpose of making things more compact,” added co-lead author Minh Tran, research director at Nexus Photonics and a graduate of UC Santa Barbara. Laser light glows on the surface of a photonics chip. Courtesy of Matt Perko. The laser connection problem was solved for silicon circuitry in 2005 by researchers at UC Santa Barbara led by John Bowers. They overcame this hurdle by bonding the laser materials directly on top of the silicon and bending the light down into the waveguides. That technology and its variation have since been developed by multiple industrial and research institutes, and commercialized by Intel at multimillion dollar per annum scale. Unfortunately, these solutions only work for light with a wavelength longer than 1100 nm, deep in the infrared. Every semiconductor has a bandgap energy, and photons with a higher energy or smaller wavelength than this are absorbed by the material. Silicon’s bandgap, for example, is around 1100 nm. Ultraviolet (UV), visible light, and even some infrared is absorbed by silicon waveguides. Although silicon works well for electronics, its utility in photonics is limited. Silicon nitride’s bandgap, however, is about 250 nm, in the UV part of the spectrum. Further, because it’s a silicon compound, it easily integrates with electronic manufacturing practices. Its components, silicon and nitrogen, are also plentiful and inexpensive. “Elementally it’s sand plus air,” Morin said. With the proper material identified, the challenge of connecting lasers to waveguides emerged again as the refractive index of silicon nitride differs from that of the laser material. This makes it difficult to bend the beam of light from the laser layer into the silicon nitride waveguides below it. The team added an intermediary material with a refractive index close to that of silicon nitride on the same plane as the laser. This way, the laser light could enter the transitional waveguide head-on and then be directed down into the silicon nitride from a material with similar optical properties. And while design was a step forward, the true challenge was making the process compatible with standard electronic manufacturing processes, Tran said. The achievement marks a major breakthrough for the team. “In 2018, several of us from UC Santa Barbara founded Nexus Photonics to solve the challenge of making short-wavelength photonic integrated circuits,” said co-founder and CEO Tin Komljenovic. “Now we have finally optimized the technology to the point where it exceeds the performance of large commercial systems while being smaller than a dime.”
This fully processed, 4-in. wafer contains thousands of devices. Courtesy of Minh Tran et al.? The laser-coupling technique will make high-powered precision photonics orders of magnitude less expensive, and the applications are innumerable. The technology holds potential for biomedical sciences through applications like biosensing and DNA sequencing. It could also open avenues in atomic physics and quantum research. “The use of commercial silicon foundries is going to mean every university professor at every school in the world will be able to afford equipment and perform experiments that are now only feasible at major research institutions,” Morin said. “We’re democratizing access to quantum physics,” Tran added. According to Morin, the technology can also be used to detect where light is coming from on the same chip. “So, it is possible to shine a light somewhere and see what comes back all in one tiny package.” ? The team plans to eventually integrate photonic and electronic circuits onto the same chip, achieving even greater efficiencies in cost and capability. The research was published in Nature ( www.doi.org/10.1038/s41586-022-05119-9). .
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