World-first laser method cuts back-reflected light 95% on silicon photonics chips

A new optical chip technology from Kyocera and Tohoku University could help solve a growing problem in high-speed data centers by cutting back-reflected light by about 95 percent. The technology integrates an optical isolator directly onto a silicon photonics chip using laser annealing, a process that heats only a targeted area instead of exposing the entire chip to high temperatures. That matters because optical isolators prevent light from traveling back toward the laser source. Reflected light can interfere with the laser and degrade the performance of optical communication systems. As AI workloads push data centers to move increasing amounts of information, silicon photonics is being developed to provide faster and more energy-efficient connections. The technology uses light rather than electrical signals to transmit and process data. Laser heating solves integration Optical isolators commonly rely on magneto-optical garnet, a crystalline material that needs to be heated to around 600 degrees Celsius or higher to develop the properties needed to suppress reflected light. Heating an entire silicon photonics chip to that temperature, however, can damage its electrodes, wiring, and other components. Kyocera and Tohoku University addressed the problem by directing a near-infrared laser only at the section where the isolator is being formed. The laser was focused on an area measuring roughly 700 by 700 micrometers. This localized heating crystallized the magneto-optical garnet without exposing the surrounding silicon photonics circuitry to the same thermal load. The approach could make it easier to integrate optical isolators with compact optical circuits and Co-Packaged Optics, or CPO. CPO places optical and electronic components within the same semiconductor package, reducing signal paths and potentially lowering signal losses and power consumption. For optical links, keeping light moving in the intended direction becomes increasingly important as systems become smaller and more tightly integrated. A directly fabricated isolator could therefore remove a key integration hurdle for compact photonic circuits used in future high-speed networks. Chip blocks optical interference The researchers fabricated an optical isolator on a silicon waveguide and tested how well it could distinguish between light traveling forward and light reflected backward. The device achieved an isolation ratio of 13.6 decibels in the optical communication wavelength range. According to the researchers, this corresponded to an approximately 95% reduction in back-reflected light. Electron microscopy also showed that the laser-treated magneto-optical garnet had crystallized properly over the silicon waveguide, supporting the operation demonstrated in the experiment. The result builds on earlier work by Kyocera and Tohoku University to develop optical isolators that can be integrated directly onto optical circuits. The companies now aim to improve the technology by reducing optical losses, increasing efficiency, and making the process more suitable for mass production. If those improvements are achieved, directly integrated optical isolators could become useful in future high-density optical systems, particularly as data centers adopt more silicon photonics and CPO to handle growing AI-related workloads. The research was published in IEEE Access. Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.