Tiny Light Racetracks Built by Scientists Could Revolutionize Sensors
Scientists have built tiny “light racetracks.” These devices could supercharge the next generation of sensors.Researchers at the University of Colorado at Boulder developed these high-performance optical microresonators. A microresonator traps light in a very small space. As light circles inside, its intensity builds. This creates useful effects for sensing and other applications.”Our work is about using less optical power,” says Bright Lu, a doctoral student and lead author. “One day, these microresonators will work in many sensors. They could help with navigation or identifying chemicals.”The findings appeared February 23 in Applied Physics Letters.
Smarter Design Reduces Light Loss
The team focused on “racetrack” resonators. They have an elongated loop shape like a running track.The researchers added “Euler curves” to improve performance. These smooth curves appear in road and railway designs. Vehicles cannot handle sudden right-angle turns at high speed. Similarly, light does not travel efficiently through sharp corners.”These racetrack curves minimize bending loss,” explains Won Park, a professor and co-advisor. “Our design choice was a key innovation.”The gradual curves significantly reduce light escape. Therefore, photons circle longer and interact more strongly. If too much light leaks out, the device cannot perform well.
Special Glass Boosts Performance
The team built these devices from chalcogenide glass. This specialized semiconductor offers unique benefits.”These chalcogenides are excellent for photonics,” Park notes. “They have high transparency and nonlinearity. Our work represents one of the best-performing devices using this material.”Chalcogenides allow intense light to pass with minimal loss. However, they are challenging to process. They require careful optimization.”Chalcogenides are difficult but rewarding,” says Professor Juliet Gopinath, who collaborated on this effort for over ten years. “Minimizing bend loss enabled ultra-low loss devices.”
Built in a Precision Clean Room
The microresonators are incredibly small. Researchers built them at the COSINC clean room. They used a new electron beam lithography system.These facilities provide tightly controlled environments. Many photonic components are thinner than paper. Therefore, tiny dust particles can interfere with light movement.”Traditional lithography uses photons,” Lu explains. “It faces limits from light’s wavelength. However, electron beam lithography has no such constraint. We can achieve sub-nanometer resolution.”Lu found the fabrication process rewarding. “Clean rooms are just cool. You work with massive, precise machines. Then you see images of structures only microns wide. Turning thin glass into working optical circuits is satisfying.”James Erikson, a physics PhD student, led the testing phase. He precisely aligned lasers with microscopic waveguides. Light entered and exited the resonators while he tracked its behavior.The team searched for small “dips” in the transmitted signal. These dips reveal when photons resonate inside. Their shape indicates device quality.”We want them deep and narrow,” Erikson says. “Like a needle piercing through the signal. We chased this resonator for a long time. When we saw sharp resonances on this new device, we knew we finally cracked the code.”Understanding light absorption versus transmission is critical. As laser power increases, heating can become a concern. It may even damage the device.”Most materials interact with light based on temperature,” Erikson adds. “As a device heats up, its properties change. Therefore, it may work differently.”
Future Applications Look Bright
These microresonators could enable many new technologies. They might power compact microlasers. They could create highly sensitive chemical detectors. They may also help with biological sensors and quantum tools.”Many photonic components are being developed,” Lu says. “These include lasers, modulators, and detectors. Microresonators like ours will help tie all those pieces together.”The team envisions mass production. “Eventually, we want to build something you could hand to a manufacturer. They could create hundreds of thousands of them.”
