Kyocera Corporation and the Research Institute of Electrical Communication (RIEC) at Tohoku University have developed a new technology that integrates optical isolators directly onto silicon photonics chips using laser annealing, a method that applies localized heat treatment using a laser.
As generative AI and other data-intensive technologies continue to expand, data centers need to process more information while using less energy. Silicon photonics can help by using light to transmit data efficiently. Silicon photonics is also important for Co-Packaged Optics (CPO), which combine optical and electronic circuits in the same semiconductor package to shorten signal paths, reduce signal loss, and lower power consumption.
However, in optical circuits, some light can be reflected back toward the laser source, reducing performance. Optical isolators help prevent this by allowing light to travel in only one direction. As optical circuits become smaller and more integrated, there is growing demand for optical isolators that can be fabricated directly onto silicon photonics chips. These isolators typically use a crystalline material called magneto-optical garnet, which must be heated to 600°C or higher to work properly. Heating the entire chip to such a high temperature, however, can damage electrodes, wiring, and other components. The challenge is therefore to heat only the magneto-optical garnet without overheating the rest of the chip.
To address this challenge, Kyocera and Tohoku University developed a monolithic integration technology that allows optical isolators to be fabricated directly onto silicon photonics chips using laser annealing. In this method, a laser is used to heat only the areas of the chip that require treatment.
A paper describing these results was published on Sep. 2, 2026, in IEEE Access, an academic journal issued by the Institute of Electrical and Electronics Engineers (IEEE).
A near-infrared laser beam is applied only to the optical isolator circuit region, which measures about 700 × 700 μm and contains a magneto-optical garnet film. The localized heating causes the garnet to crystallize, giving it the properties needed to suppress reflected light. Unlike conventional methods that heat the entire chip in a furnace, this method limits the heat exposure of surrounding optical circuits and electrodes.
Using this technology, the research team fabricated a device that uses light interference and experimentally demonstrated its operation as an optical isolator. The team compared the optical output of forward-propagating signal light with that of backward-propagating reflected light. The results confirmed an isolation ratio of 13.6 dB in the optical communication wavelength range, corresponding to an approximately 95% reduction in back-reflected light. Electron microscopy also confirmed that the magneto-optical garnet in the laser-irradiated area had successfully crystallized on the silicon waveguide.
Kyocera and Tohoku University have previously worked together to develop related optical isolator technologies that can be integrated onto optical circuits. To move them toward commercialization, the two organizations aim to achieve lower optical loss, higher efficiency, and improved productivity for mass production. They will continue their collaboration and help create a more efficient and sustainable information society.
- Publication Details:
Title: Monolithic Magneto-Optical Mach-Zehnder Isolator Using Laser-Annealed Iron Garnet on a Silicon Waveguide
Authors: Tomoya Sugita, Reona Motoji, Yuki Yoshihara, Dan Maeda, Hiroki Yamamoto, Hibiki Miyashita, Kazushi Ishiyama, Taichi Goto
Journal: IEEE Access
