Researchers at the University of Colorado at Boulder have created highly efficient optical microresonators that significantly improve the ability to trap and manipulate light. This breakthrough could pave the way for innovative sensor technologies across various applications, from navigation systems to chemical detection.
The study, published in Applied Physics Letters on February 23, 2026, highlights the team’s focus on “racetrack” resonators, named for their elongated design resembling a running track. These microresonators utilize “Euler curves,” a smooth curve design that minimizes abrupt bends, crucial for maintaining light intensity. As Bright Lu, a fourth-year doctoral student in electrical and computer engineering and lead author of the study, explained, “Our work is about using less optical power with these resonators for future uses.”
Innovative Design Cuts Light Loss
The researchers found that by guiding light through these smoothly curved pathways, they could dramatically reduce light loss. Won Park, Sheppard Professor of Electrical Engineering and co-advisor on the study, noted, “Our design choice was a key innovation of this project.” This advancement enables photons to circulate longer within the device, enhancing their interactions and leading to higher performance.
These microresonators are incredibly small, fabricated in a clean room using advanced electron beam lithography. This method ensures precision at the microscopic scale, allowing for the construction of devices smaller than the width of a piece of paper. “Traditional lithography uses photons and is fundamentally limited by the wavelength of light,” Lu stated. “However, electron beam lithography has no such constraint, enabling us to achieve sub-nanometer resolution.”
The fabrication process was particularly satisfying for Lu, who described the experience as rewarding. “Turning a thin film of glass into a working optical circuit is really satisfying,” he said.
Material Selection and Performance Testing
A significant aspect of this research was the use of chalcogenides, specialized semiconductor glasses known for their high transparency and nonlinearity. Juliet Gopinath, a professor involved in the project, explained the challenges and benefits of these materials: “Chalcogenides are difficult but rewarding materials to operate for photonic nonlinear devices.” The study indicates that these resonators represent one of the best-performing devices using chalcogenides.
After fabrication, the microresonators underwent rigorous testing led by James Erikson, a physics Ph.D. student specializing in laser-based measurements. He aligned lasers with microscopic waveguides, monitoring how light behaved within the device. The team analyzed data for “dips” in transmitted light, which signify resonance as photons become trapped.
“The most obvious indicator of device quality is the shape of the resonances,” Erikson said. They aimed for these resonances to be deep and narrow, which would indicate high performance. The success of this project could lead to the development of compact microlasers and advanced sensors for chemical and biological applications.
Lu concluded that the ultimate goal is to create a product that can be easily manufactured on a large scale. “Many photonic components from lasers, modulators, and detectors are being developed, and microresonators like ours will help tie all of those pieces together.” As the researchers look to the future, their work marks a significant step towards integrating advanced optical technologies into various fields.
