Scientists Built a Programmable Chip That Can Slow Light on Command

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Technology<br>Scientists Built a Programmable Chip That Can Slow Light on Command<br>By Seoul National University July 25, 2026No Comments7 Mins Read

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Conceptual diagram of the programmable CRIT photonic integrated circuit: illustrates how optical pulses experience changes in temporal delay and frequency characteristics as they propagate through the circuit. Credit: Seoul National University College of EngineeringNew technology enables light to be stored, delayed, and controlled within a single photonic chip, with potential applications in low-power optical computing for AI servers and next-generation optical communication systems.<br>Light moves quickly enough to transmit enormous amounts of information, but that speed creates a problem when a computer needs to hold, delay, or synchronize an optical signal. Researchers from Seoul National University and the University of Seoul have now designed a programmable photonic integrated circuit that can slow light whenever needed.<br>The project was led by Professors Namkyoo Park and Sunkyu Yu of the Department of Electrical and Computer Engineering at Seoul National University, working with Professor Xianji Piao of the School of Electrical and Computer Engineering at the University of Seoul.<br>The rapid growth of generative AI and large-scale artificial intelligence models has sharply increased computing demands. Conventional electronic semiconductors face persistent constraints, including heavy power use and limited data transfer speeds, driving interest in optical computing systems that process information rapidly with less energy. Yet because light naturally travels at a fixed speed, creating the buffers and memory functions needed for optical computing has remained difficult.<br>Structure of the programmable CRIT photonic integrated circuit: shows how the flow of light can be freely controlled by adjusting coupling between optical resonators. Credit: Advanced Science, originally published in Advanced ScienceThe researchers addressed this limitation with a programmable photonic circuit that controls both the speed and shape of optical signals. Their approach provided greater control over &ldquo;slow light&rdquo; than previously proposed methods.<br>The findings were published in Advanced Science.<br>Fixed optical delays limit computing<br>Photonic integrated circuits process information with light and are being developed for faster, more efficient computing. Data centers, optical communication networks, and computing systems need more than rapid transmission. They must also coordinate when signals arrive and hold them briefly when necessary.<br>Researchers have explored structures based on coupled-resonator-induced transparency (CRIT), which use interference among several optical resonators to perform these functions. CRIT selectively allows light within a particular frequency range to pass while reducing the speed at which the optical signal travels.<br>Coupled-resonator-induced transparency (CRIT): An optical phenomenon that selectively transmits and delays light within a specific frequency range through interference among multiple resonators.<br>Optical resonator: A photonic device that confines or circulates light of a specific frequency for a certain period; used in signal delay, filtering, and modulation.<br>The problem is that conventional CRIT devices are generally locked into their operating characteristics after fabrication. Changing the frequency range or producing a longer delay often requires an entirely new device.<br>(From left) Sunkyu Yu (co-corresponding author), Department of Electrical and Computer Engineering, Seoul National University; Namkyoo Park (co-corresponding author), Department of Electrical and Computer Engineering, Seoul National University; Xianji Piao (co-corresponding author), School of Electrical and Computer Engineering, University of Seoul; Seungkyun Park (co-first author); Beomjoon Chae (co-first author); Hyungchul Park (co-author). Credit: Seoul National University College of EngineeringThat inflexibility makes optical communication hardware and data center systems more complex, while increasing the expense and development time required to add new capabilities. For AI servers and next-generation data centers processing vast quantities of information in real time, fixed optical hardware has become a significant barrier.<br>Two couplers make light programmable<br>The researchers approached the problem by treating two optical states in CRIT systems, the bright mode and dark mode, as one unified degree of freedom. They then added two adjustable loop couplers, producing a design in which resonator structures can be reconfigured after fabrication rather than remaining permanently...