Researchers at Seoul National University have demonstrated a programmable system for controlling the flow of light within photonic integrated circuits, achieving fully programmable slow light based on a generalized coupled-resonator-induced transparency (CRIT) framework. The breakthrough, detailed in recent publications, utilizes a spinor representation with dual-channel gauge fields, enabling dynamic spectral engineering and addressing critical needs in optical interconnects.
The team, led by Seungkyun Park, Beomjoon Chae, and Hyungchul Park of the Department of Electrical and Computer Engineering, alongside Sunkyu Yu and colleagues, has moved beyond traditional limitations of CRIT systems by generalizing the established electromagnetically induced transparency (EIT) framework. This generalization allows for a unified description of design parameters through universal unitary operations, resulting in a programmable slow-light band within a one-dimensional lattice.
This development builds on recent advances in nanofabrication, particularly with lithium niobate-on-insulator (LNOI) platforms, which are increasingly used for monolithic integration of photon pair sources into optical circuits due to their strong second-order nonlinearity. A separate research effort, published in Nature, showcased a reconfigurable photonic integrated circuit on LNOI capable of generating entangled states with high brightness and fidelity, achieving a source brightness of 26 MHz nm-1mW-1 and a coincidence-to-accidental ratio above 100.
The ability to manipulate light propagation within photonic integrated circuits has broad implications for optical technologies, including the development of tunable delay lines, reconfigurable synchronization, and efficient linear frequency conversion. Researchers are similarly exploring the potential of photonic integrated circuits to enable programmable non-Abelian braiding for emulating anyonic systems, as demonstrated by a team that successfully implemented a programmable spinor lattice on a photonic integrated circuit. This platform allows for the realization of non-Abelian physics, where the order of operations matters.
Further advancements in the field include the demonstration of programmable Bell state generation using thin-film lithium niobate photonic circuits, achieving high-brightness generation and reconfigurable projection of path-encoded Bell states with fidelity exceeding 90%, verified through quantum state tomography. These integrated quantum photonic technologies rely on high-brightness sources of entangled quantum states, and the LNOI platform is emerging as a compelling, scalable option.
The Seoul National University team’s work on programmable slow light establishes a versatile building block for manipulating light propagation, offering a tunable slow-light band and addressing critical requirements in optical interconnects and signal processing. The research introduces a novel approach to manipulating light propagation within photonic integrated circuits, moving beyond traditional limitations of CRIT systems.
