The future of digital computing and communications will undoubtedly involve both electronics and photonics to move data traffic around the globe with greater energy efficiency. Against this backdrop, researchers from MIT’s FUTUR-IC research team have developed a way to co-package photonic chips with their electronic counterparts — a development that the scientists said solves several problems associated with the current co-packaging process. One advantage of the method, they said, is that the newly developed co-packaged device can be manufactured using existing equipment in traditional electronics foundries with a less-expensive passive alignment process. Currently, it is difficult and expensive to connect electronic chips with their photonic counterparts within a single package. The optical fiber, which has a core diameter of 10 μm, and the photonic chip, which has cross-sectional dimensions of only two tenths-by-five tenths of 1 μm, must be aligned almost perfectly or the light will disperse. As a result, today each connection must be actively tested with a laser to ensure that the light will come through. A newly developed device (silver, top left) could be key to faster, more energy-efficient data communication. It solves a major problem associated with packaging an electrical chip (black, center) with photonic chips (surrounding squares). This image also shows an automated tool (orange glow) placing the final photonic chip into position. Courtesy of MIT/Drew Weninger. “And the number of fibers that we will need for greater data communication is increasing exponentially, so this active alignment process won’t cut it for scaling forward,” said Drew Weninger, lead author of the study and a graduate student at MIT. The patented device, called an evanescent coupler, gives much more wiggle room for connecting the fibers within the electronic-photonic package. “Conventional couplers have a single coupling point, making alignment tolerances very tight. But our new coupler has a much larger interaction length increasing the alignment tolerance,” said Anu Agarwal, head of FUTUR-IC and a principal research scientist at MIT’s Materials Research Laboratory. As a result, robots could passively assemble the resulting integrated circuits allowing more light to pass through without being lost, remove the need for active laser alignment. Another key innovation is that the coupler allows for the vertical transmission of light between the multiple layers of chips that comprise the whole, graduate student Luigi Ranno said. That in itself is an important feat because it is difficult to direct light out of a horizontal plane. “In electronics it is very simple. Electrons can easily flow out of plane,” Weninger said. In contrast, light never wants to take right angles, he said. The newly developed coupler enables light to make the jump between stacked chips. “We have developed a packaging design [for integrating photonics with electronics] that is reliable, has a larger alignment tolerance, doesn’t lose much light, and doesn’t waste too much space. Basically, it has all the features you want for an efficient and functional interconnect,” Ranno said. The research was published in Advanced Engineering Materials (www.doi.org/10.1002/adem.202402095).