A device so tiny that it is almost invisible to the naked eye may become the key to future optical sensing chips. A research team at the University of Colorado Boulder has developed a high-performance "racetrack" optical microresonator that can significantly reduce light loss, opening the door to applications such as chemical detection, navigation equipment and even quantum measurement. The relevant paper was published in the new issue of Applied Physics Letters.
The result of this research is to create an optical waveguide microresonator on a chip. The thickness of the microresonator is only 1/10 of a human hair. The microresonator can be understood as a microdevice that "traps light." Light circulates continuously within it, gradually accumulating intensity. When the light is strong enough, scientists can use it to perform various special optical operations. Bright, the first author of the paper
According to Lu, their goal is to enable this device to operate efficiently at lower optical powers.
The team focused on "racetrack" resonators, a device named for its elongated shape that resembles a racetrack. They specifically adopted a smooth curve design called the "Eulerian curve", which is commonly seen on roads and railways, because cars cannot suddenly turn at right angles when traveling at high speeds, and the same is true for light propagation. If it bends too sharply, it will "slip".
Using such smooth bends significantly reduces optical losses, allowing photons to stay inside the resonator longer, thereby enhancing interactions. If there is too much light loss, the resonator cannot accumulate enough light and its performance will be greatly reduced.
The microresonators were fabricated using electron beam lithography in a clean room. Unlike traditional photolithography, which is limited by light wavelength, this technology can achieve sub-nanometer precision and is suitable for processing micro-scale optical structures. Due to the extremely small size of the device, even tiny dust or defects may affect the propagation of light, so a clean environment is crucial.
Material selection is equally critical. The team used a type of chalcogenide semiconductor glass material. This type of material has high transparency and strong nonlinear properties, making it very suitable for photonic devices. However, they are difficult to process, requiring a balance between performance and manufacturing difficulty. By reducing bending losses, the team successfully created ultra-low-loss devices with performance comparable to current advanced materials platforms.
The research team stated that in the future, this microresonator is expected to become a key component in photonic systems and can be used in microlasers, biochemical sensors, and quantum network devices. The ultimate goal is to develop this technology into optical chips that can be manufactured on a large scale.
