Engineers at the University of Colorado Boulder have built microscopic light circuits that could redefine how sensors detect the world. Their optical microresonators trap light in loops so small they measure just microns across. Inside those loops, light intensifies as it circulates. Push the intensity high enough and the device unlocks optical effects powerful enough to detect chemicals, guide navigation systems or underpin quantum tools.
“Our work is about using less optical power with these resonators for future uses,” said Bright Lu, a fourth year doctoral student in electrical and computer engineering and a lead author of the study. “One day these microresonators can be adapted for a wide range of sensors from navigation to identifying chemicals.”
That ambition hinges on efficiency. Engineers know that if light leaks from a resonator too quickly, performance collapses. The Colorado team tackled that constraint head on.
Rethinking The Racetrack
They focused on “racetrack” resonators, elongated loops shaped like a running track. Traditional designs force light around tight corners, and sharp bends scatter photons. Loss increases. Performance drops.
The researchers replaced abrupt turns with “Euler curves”, smooth transitions widely used in road and railway design. Engineers deploy these curves so trains and cars can handle speed without jolts. Light behaves no differently.
“These racetrack curves minimize bending loss,” said Won Park, Sheppard Professor of Electrical Engineering and co-advisor on the study. “Our design choice was a key innovation of this project.”
By easing light through gradual bends, the team reduced escape losses and kept photons circulating longer. Longer circulation means stronger interaction. Stronger interaction means higher sensitivity.
Lu framed the trade-off clearly: if too much light leaks out, the device cannot reach the intensities required for peak performance. In business terms, it resembles capital flight. If investment drains too quickly, growth stalls before scale materialises.
Precision At The Nanoscale
The team fabricated the devices in the Colorado Shared Instrumentation in Nanofabrication and Characterization clean room using electron beam lithography. At these dimensions, dust particles rival circuit features. Control becomes non-negotiable.
“Traditional lithography uses photons and is fundamentally limited by the wavelength of light,” Lu said. “However, electron beam lithography has no such constraint. With electrons, we can realize our structures with sub-nanometer resolution, which is critical for our microresonators.”
Electron beam systems allow engineers to sculpt features smaller than the wavelength limits that constrain conventional photonics manufacturing. That precision translates directly into lower optical loss.
Lu described the appeal of the process in personal terms.
“Clean rooms are just cool. You’re working with these massive, precise machines, and then you get to see images of structures you made only microns wide. Turning a thin film of glass into a working optical circuit is really satisfying.”
Any executive overseeing advanced manufacturing will recognise the sentiment. Precision tooling demands capital and patience, yet the reward lies in products competitors struggle to replicate.
Betting On Chalcogenide Glass
Material choice shaped performance. The researchers built their resonators from chalcogenides, specialised semiconductor glasses known for transparency and optical nonlinearity.
“These chalcogenides are excellent materials for photonics because of their high transparency and nonlinearity,” Park said. “Our work represents one of the best-performing devices using chalcogenides, if not the best.”
High transparency reduces loss. Strong nonlinearity amplifies light–matter interactions. Together they create devices capable of operating at lower power while maintaining strong signals.
The trade-off sits in fabrication difficulty. Chalcogenides demand careful processing and optimisation.
“Chalcogenides are difficult, but rewarding materials to operate for photonic nonlinear devices,” said Professor Juilet Gopinath, who has collaborated with Park on this effort for more than 10 years. “Our results showed that minimizing the bend loss enables ultra-low loss devices comparable to state-of-the-art in other materials platforms.”
That statement carries strategic weight. If chalcogenides can match or exceed established material platforms, they open a pathway to compact photonic systems with enhanced capabilities. What happens if manufacturers adopt them at scale? Supply chains shift. Device architectures evolve.
Testing The Limits
Fabrication marked only the midpoint. The team then characterised the resonators using precision laser measurements. James Erikson aligned lasers with microscopic waveguides and tracked how light entered, circulated and exited.
Researchers looked for small dips in transmitted light. These dips signal resonance, the condition where photons align perfectly with the structure.
“The most obvious indicator of device quality is the shape of the resonances, and we want them to be deep and narrow, like a needle piercing through the signal background,” Erikson said. “We’ve been chasing this kind of resonator for a long time, and when we saw the sharp resonances on this new devic,e we knew right away that we’d finally cracked the code.”
Deep, narrow resonances indicate low loss and high quality. They also signal readiness for real-world integration.
Erikson emphasised thermal management as laser power increases.
“The way most materials interact with light also changes depending on the temperature of the material,” said Erikson. “So as a device heats up its properties can change and cause it to work differently.”
Heat alters material behaviour. That reality mirrors challenges in semiconductor chips and battery systems. Engineers must anticipate performance drift under load. Ignore it and reliability suffers.
From Lab Prototype To Market Scale
The implications extend beyond academic achievement. The team envisions compact microlasers, chemical and biological detectors with heightened sensitivity, and components for quantum metrology and networking.
“Many photonic components from lasers, modulators, and detectors are being developed, and microresonators like ours will help tie all of those pieces together,” Lu said. “Eventually, the goal is to build something you could hand to a manufacturer and create hundreds of thousands of them.”
That final step separates breakthrough from impact. Can these resonators transition from clean room prototypes to high-volume production? If they do, sensor systems could shrink while gaining precision. Quantum networks could gain more stable building blocks. Navigation systems could operate with lower power demands.
Every industry faces moments where incremental design changes unlock disproportionate gains. Here, smoothing a curve inside a microscopic racetrack may prove decisive. The question now shifts from whether the physics works to whether manufacturers seize the opportunity.
Author: George Nathan Dulnuan