Researchers from the University of Pennsylvania and Montana State University have now introduced a new photonic system designed to overcome that limitation. Their device combines the 2D semiconductor molybdenum diselenide (MoSe₂) with a photonic crystal nanocavity, enabling light signals to be controlled by light while consuming extremely low energy.

Photonic devices, which process information using light rather than electricity, have long been viewed as a promising path toward faster, more energy-efficient computing systems. However, one major challenge has limited their development: photons, or particles of light, do not naturally interact with one another easily.

Building a light-based computing platform

“Our primary motivation was to advance the field of all-optical computing—a long-standing dream of building systems that process information using light instead of electricity,” Li He, Assistant Professor at Montana State University and senior author of the paper, as reported by Tech Xplore.

“Because light travels faster and generates less heat than moving electrons, these systems could be significantly more powerful and energy-efficient than today’s electronic chips. However, to make this a reality, we faced a fundamental challenge: photons (i.e., light particles) typically do not interact with one another,” he continued.

To solve this issue, the researchers focused on creating stronger interactions between photons using exciton-polaritons, hybrid quasiparticles formed when photons strongly couple with excitons inside semiconductors. They used a single layer of MoSe₂ and integrated it with a silicon nitride nanobeam cavity engineered to tightly confine light.

Achieving ultralow-energy optical switching

The confined nanocavity helped amplify interactions between light and matter within the device, enabling ultrafast optical switching at very low power levels. “By forcing light to couple strongly with the matter in atom-thin MoSe₂ layers, we can effectively have photons interact and change the system’s behavior using very little optical energy,” explained He.

“We achieved this by creating a hybrid state known as an exciton-polariton. These are ‘half-light, half-matter’ quasiparticles that inherit the best properties of both: because they are part photon, they can propagate at the speed of light, and because they are part matter (excitons), they exhibit interactions via their underlying excitons.”

According to the researchers, the nanocavity acts as an ultra-precise light trap that compresses the polaritons into a tiny space, significantly strengthening particle interactions. The system achieved optical switching using roughly 4 femtojoules of energy.

Toward AI and quantum computing applications

The researchers said the platform could eventually support large-scale integrated photonic circuits and future AI or quantum computing technologies. “We demonstrated a path toward switching light at extremely low light intensities, moving toward the fundamental limits of how much energy is required for photons to interact,” said He.

“Crucially, our platform is designed for mass-producibility. By using materials and structures that can be patterned using standard manufacturing techniques, we have shown that these 2D-material devices can be integrated into large-scale integrated photonic circuits. This opens the door to chips containing thousands of interacting optical components,” he continued.

The team is now working to further optimize the nanostructures to lower the switching threshold even further and to explore ways to connect multiple nanocavities into larger optical processing circuits.

The findings were published in Physical Review Letters.

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