An international team of scientists from Seoul National University and the University of Seoul has presented a revolutionary programmable photonic chip capable of slowing down light on demand. The development paves the way for a paradigm shift in optical computing: instead of traditional electrical signals, light waves can be used, which are much faster and require only slightly more energy.
The research was led by Professors Namkyoo Park and Sungkyu Yu from Seoul National University (Department of Electrical and Computer Engineering) in collaboration with Professor Xianzhi Piao from the University of Seoul. Two young scientists played an important role in the development: Dr. Seungyoun Park (Seoul National University and PICORE Innovation Center at KAIST) and graduate student Bomjun Chae (Seoul National University), who developed the theoretical basis for the research. Their work is published in the journal Advanced Science under the title “Fully Programmable Slow Light Based on Spinorial Representation of Generalized Coupled-Resonator Induced Transparency”.
The problem with optical systems has long been known: light, by definition, moves too fast and is not easily controlled. Synchronizing signals, buffering data, and creating memory in optical computing systems require controllable time delays. Traditional devices based on the coupled-resonator induced transparency (CRIT) effect had their characteristics fixed during manufacturing – they could not be reconfigured later.
The scientists proposed a fundamentally new approach. Instead of a static design, they combined two optical states – bright and dark resonator modes – into a single degree of freedom and added controllable loop coupling elements. The main innovation: the use of spinorial representation (a mathematical description from quantum mechanics) allowed for a complete set of degrees of freedom for tuning. The result: the chip can be dynamically reconfigured, even after manufacturing and during operation.
The programmable chip controls not only the speed of light propagation but also the bandwidth, optical signal shape, transmission efficiency, and frequency characteristics. Numerical simulations on a silicon nitride platform (a standard material in silicon photonics) showed the device's high resilience to real-world interference: optical losses, technological parameter variations, and thermal effects.
If the technology is commercialized, a single such microchip could perform multiple functions simultaneously – from adjusting signal delays to frequency conversion, acting as a programmable optical system. This could drastically reduce the energy consumption of data centers and artificial intelligence servers, which already require colossal power, and make optical equipment more compact and cheaper.
Professor Namkyoo Park emphasized that the new design principle using spinorial representation significantly enhances the flexibility of photonic integrated circuits and allows for the reconfiguration of light flow as needed. The authors plan to develop the technology towards large-scale systems based on silicon photonics and its hybrids with photonic artificial intelligence technologies – an area that is just beginning to reveal its potential.
Co-authors of the study, Dr. Seungyoun Park and graduate student Bomjun Chae, added that rethinking the physics of optical resonators from a new perspective opens the door to functionalities that were previously unimagined. The work received support from the Ministry of Science and ICT of South Korea through innovation research center programs, basic research laboratories, and the young researcher program.
