Seoul Researchers Design Programmable Photonic Chip That Controls When Light Arrives

Researchers at Seoul National University and the University of Seoul have designed a programmable photonic circuit that can control how long light pulses take to travel through a chip — in effect, controlling when they arrive. Unlike today's optical hardware, whose delay is fixed at manufacture, the proposed system can be reconfigured to change an optical signal's delay, transmission bandwidth and even frequency characteristics. So far the design exists only in theory, numerical modeling and electromagnetic simulations.

Photonics — moving data as light instead of electrons — carries enormous data volumes with far less resistive heating than the metal interconnects of conventional processors. But computing also needs signals to arrive on cue. Delaying, synchronizing, buffering and filtering signals is easy in electronics and hard in photonics.

One current workaround, coupled-resonator-induced transparency (CRIT), uses optical resonators — microscopic structures in which light of particular frequencies circulates — arranged so their light waves interfere, opening a narrow window where certain frequencies pass with a substantial delay. Once built, however, a chip's behavior is fixed: a different delay or frequency response often requires a new chip altogether.

The Seoul team's architecture adds two tunable loop couplers to the resonator network, treating its strongly and weakly interacting optical states — the bright and dark modes — as one controllable system. In theoretical demonstrations, the same circuit could be retuned to adjust its transmission band's width and shape, how efficiently light passed through, and how long pulses were delayed. Numerical simulations indicated the delay could be changed dynamically while the circuit was operating, and the design could also shift the frequency of the transmitted light.

To test practicality, the team modeled the design on a silicon-nitride photonic platform in three-dimensional electromagnetic simulations that included real-world imperfections such as material losses, backscattering, phase errors and thermal crosstalk. The architecture remained functional despite these effects, suggesting it should be achievable with existing photonic fabrication technology.