It may seem counterintuitive, but chaos can be a good thing in science and engineering. Xu Yi, assistant professor of electrical and computer engineering at the University of Virginia, in collaboration with Yun-Feng Xiao’s group from Peking University and researchers at Caltech, turned to chaos theory to improve devices that create and manipulate light.
Yi and the team applied chaos theory to a specific type of photonic device called a microresonator-based frequency comb, or microcomb. The microcomb efficiently converts photons from single to multiple wavelengths. “It’s like turning a monochrome magic lantern into a technicolor film projector,” Yi said. The researchers demonstrated the broadest (i.e., most colorful) microcomb spectral span ever recorded.
The broad spectrum of light generated from the photons increases its usefulness in spectroscopy, optical clocks and astronomy calibration to search for exoplanets. Their innovation provides an additional degree of freedom in the design of photonic devices, which, in turn, may accelerate optics and photonics research in quantum computing and other applications that are vital to future economic growth and sustainability.
The microcomb works by connecting two interdependent elements: a microresonator, which is a ring-shaped micrometer-scale structure that envelopes the photons and generates the frequency comb, and an output bus-waveguide. The waveguide regulates the light emission: only matched speed light can exit from the resonator to the waveguide. As Xiao explained, “it’s similar to finding an exit ramp from a highway; no matter how fast you drive, the exit always has a speed limit.”
The research team figured out a smart way to help more photons catch their exit. Their solution is to deform the microresonator in a way that creates chaotic light motion inside the ring. “This chaotic motion scrambles the speed of light at all available wavelengths,” said co-author and Peking University research team member Hao-Jing Chen. When the speed in the resonator matches that of the output bus-waveguide at a specific moment, the light will exit the resonator and flow through the waveguide.
As photons accumulate and their motion intensifies, the frequency comb generates light in the ultraviolet to infrared spectrum. This research builds on the department’s solid foundation in semiconductor materials and device physics that extends to advanced optoelectronic devices. Yi’s microphotonics lab conducts research on high-quality integrated photonic resonators, with a dual focus on microresonator-based optical frequency combs and continuous-variable-based photonic quantum computing.
Chen et al. (2020). Chaos-assisted two-octave-spanning microcombs. Nature Communications. DOI: https://doi.org/10.1038/s41467-020-15914-5
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