Researchers have developed a programmable, nonlinear photonic waveguide that allows users to implement and switch between different nonlinear optical functions on a single device. The breakthrough, reportedly the first of its kind, was made by scientists at NTT Research, Inc., a division of NTT, in collaboration with researchers at Cornell University and Stanford University. The current need to “sculpt” nonlinear optical functions into a device means the function of a device is fixed during its fabrication and cannot be changed afterwards. Consequently, one device can fulfill only one function. Also, device functionality is highly sensitive to fabrication imperfections. These drawbacks have limited the use of nonlinear optics in photonic devices. The programmable waveguide signifies a shift away from the conventional, one-device-one-function model. Just one chip with the programmable waveguide can be used to implement various functions that would otherwise require multiple devices. This capability extends nonlinear optics to scenarios that require rapid device configuration, tunable light sources, and high yields. Although the researchers used the programmable waveguide prototype to demonstrate classical nonlinear optical functions only, it could be used to increase the flexibility of both classical and quantum computations and communications. The developers of the programmable waveguide used a planar optical waveguide, whose core was made of silicon nitride (SiN), and coupled a pump light to it. They projected a structured light, which served as the programming light, onto the device. This induced optical nonlinearity inside the core with the same spatial pattern as the programming light, allowing the researchers to set and update an arbitrary distribution of nonlinearity that could be used to engineer nonlinear optical functions. Diagram of a proof-of-concept programmable, nonlinear channel waveguide fabricated by scientists at NTT Research, Cornell University, and Stanford University. Inset: Image of the device. Courtesy of NTT Research, Inc. The specific patterns of optical nonlinearity, created by the structured programming light, determine the device’s function. The projection of different light patterns enables different, reconfigurable, nonlinear optical functions on the same chip. The real-time reconfigurability of the device enables in situ inverse design and optimization of quasi-phase matching (QPM) grating structures. To showcase the diversity of their device, the researchers demonstrated spectral, spatial, and spatio-spectral engineering of second harmonic generation (SHG) with the waveguide. In addition to widely tunable SHG, they demonstrated arbitrary pulse shaping, holographic generation of spatio-spectrally structured light, and real-time inverse design of nonlinear optical functions using an approach that remained robust against fabrication errors and environmental drifts. “These results mark a departure from the conventional paradigm of nonlinear optics, where device functions are permanently fixed during fabrications,” Ryotatsu Yanagimoto, who led the research under the supervision of Cornell professor Peter McMahon, said. “This expands applications of nonlinear photonics to situations in which fast device reconfigurability and high yields are not merely convenient, but essential.” The technique to implement programmable nonlinearity could be “augmented” to various existing nanophotonic structures. As a proof of this concept, the researchers fabricated a programmable nonlinear channel waveguide where the core was a 1D ridge of SiN, enhancing the transverse confinement of light. The programmable, nonlinear photonic waveguide could lower manufacturing costs, improve production yields, and reduce the footprint and complexity of optical systems. The technology is particularly promising for quantum computing. Programmable quantum frequency converters and quantum light sources would allow more flexible computational architectures and improve quantum networking. In telecommunications, widely tunable light sources and arbitrary waveform generators could enhance 5G and 6G infrastructure and optical communication systems. Programmable, structured light sources could also enable greater precision and adaptability in advanced manufacturing and imaging. Makers of laboratory equipment and measurement devices could use the waveguide technology to reconfigure optical systems in real time. The capability to program and control nonlinearity in photonic chips will allow researchers and manufacturers to circumvent the limitations of the conventional, one-device-one-function paradigm. The programmable, nonlinear optical waveguide, and the demonstrations of reconfigurable SHG with the prototype device, could open a new frontier for nonlinear optics. “For the first time, a path forward has been created to apply nonlinear optics to large-scale optical circuits, reconfigurable quantum frequency conversion, arbitrary optical waveform synthesizers, and widely tunable classical and quantum light sources — all of which are vital to enabling advanced computing and communications infrastructure,” Yanagimoto said. The research was published in Nature (www.doi.org/10.1038/s41586-025-09620-9).
