The CU Boulder team has forged a new path in photonics by creating high-performance optical microresonators that trap and amplify light with far less input power.
By pairing elongated racetrack geometries with smooth Euler curves, they minimize bending losses that previously limited performance. This lets photons circulate longer and interact more strongly.
They fabricated these devices in the COSINC clean room using electron beam lithography. The process achieves sub-nanometer patterning and relies on chalcogenide glasses for high nonlinearity and broad transparency.
The result? It’s among the best demonstrated performance for chalcogenide-based microresonators. That has clear implications for scalable manufacturing and integration with other photonic components.
Geometric and material innovations enable low-power nonlinear photonics
The researchers took a fresh look at both geometry and materials to push nonlinear photonics into compact, low-power regimes. Using an elongated racetrack design with carefully tuned curves, they managed to reduce scattering and radiation losses at bends—a stubborn bottleneck in chip-scale resonators.
This geometry supports longer photon lifetimes and stronger light–matter interactions without needing more input power. They also picked high-nonlinearity, broadband transparent chalcogenide glasses, giving the resonators robust nonlinearity and keeping optical losses in check.
The design philosophy focused on bend-loss control from the beginning, which is pretty crucial when working with tough-to-process materials. The result is ultra-low overall loss that stands up to leading platforms and paves the way for scalable integration.
Racetrack geometry and Euler curves to minimize bending loss
The big advance here is an elongated racetrack resonator with bends shaped by smooth Euler curves—an idea borrowed from road and rail engineering. This approach cuts down on abrupt directional changes that usually mess with light propagation and sharply reduces bending loss.
With less loss, photons can make more revolutions inside the device. That boosts the effective interaction length and enables nonlinear operations like optical switching or frequency conversion at practical power levels.
Fabrication choices, materials, and testing methods
They built everything in the COSINC clean room using electron beam lithography. This gives sub-nanometer patterning fidelity, which goes way beyond what conventional lithography can do and nails the precise geometry needed for ultra-low bend loss.
The team picked chalcogenide semiconductor glasses for their standout optical nonlinearity and wide transparency. They had to balance performance with the realities of processing these tricky materials in a cleanroom setting.
Since chalcogenides can be tough to handle, the layout was designed to suppress bend-induced losses. That step is key to getting ultra-low total loss—comparable to the best platforms out there.
They ran laser-based tests to see how light couples into microscopic waveguides and how the devices behave under high-intensity illumination.
Testing and characterization: absorption, transmission, and thermal management
During testing, they coupled light into microscopic waveguides and scanned across sharp resonance dips to measure absorption and thermal behavior. By analyzing these resonance features, they could separate absorption from transmission and see how heating shifts resonance positions and affects quality factors.
Managing heat and avoiding damage is essential for stable operation at higher laser powers. That’s a must for reliable nonlinear photonic functionality.
Applications, impact, and outlook
The CU Boulder team sees a wide range of on-chip uses. We’re talking about everything from compact microlasers to chemical and biological sensors that are way more sensitive than before.
They also imagine these resonators working right alongside modulators and detectors on a single photonic chip. That could mean more powerful, compact photonic systems—and, honestly, a big leap for scalable manufacturing.
- Compact microlasers for integrated photonics
- Advanced chemical and biological sensors with enhanced sensitivity
- Quantum metrology components enabling precise time and frequency measurements
- Networking hardware with improved stability and low power
- Scalable, wafer-scale photonics compatible with existing semiconductor fabs
Racetrack-based optical microresonators with Euler-curved bends are edging closer to real commercial use. The mix of clever geometry, advanced lithography, and carefully picked chalcogenide materials could soon make photonic chips—small, efficient, and low-power—the backbone of sensors, communications, and precision measurement in all sorts of industries.
Here is the source article for this story: Researchers build ultra-efficient optical sensors shrinking light to a chip