A scientific research team from the Joint Quantum Institute (JQI) of the University of Maryland in the United States has recently successfully developed a new chip that can stably convert and produce lasers of multiple colors without external control. This breakthrough is expected to push photonic integration technology in line with the semiconductor technology revolution, paving the way for the practical use of quantum communication networks and precision optical instruments.
For years, scientists have been working hard to miniaturize large-scale optical experimental tools such as lasers, lenses, and mirrors and integrate them onto chips the size of a fingernail. Miniaturizing these devices is key to increasing data communication speeds, creating ultra-high-precision atomic clocks, and scaling quantum computers that use light rather than electronic signals. However, how to divide a monochromatic laser into multiple components on a small chip to achieve the generation of multiple new frequencies has always been a problem that plagues this field.
A Maryland research team has now overcome this difficulty. They designed and built a chip that converts a single color of laser light into three distinct frequencies of light. More importantly, this process does not require external active input or complex fine-tuning, significantly improving the repeatability and stability of the integrated optical signal. Relevant results have been published in the magazine Science.
Unlike traditional optical devices such as prisms, which are only responsible for breaking down existing colors, this chip can "create" new light frequencies that do not originally exist. Achieving new light frequencies relies on nonlinear optical effects—only high-intensity illumination changes the optical properties of materials, which in turn affects the light itself. This type of nonlinear effect was discovered more than 60 years ago (such as "second harmonic generation" in 1961), but the effect itself is too weak and has been difficult to effectively exploit in the past.
Modern integrated photonic chips use tiny resonant cavities in which light circulates millions of times, greatly enhancing nonlinear effects. But even so, small changes in the chip's manufacturing, temperature, structure, etc. still cause the output frequency combination to be extremely unstable.
The JQI team’s new solution completely eliminates the need for repeated adjustments by designing a resonant cavity that “biases” the required nonlinear interaction. Mohammad Hafezi, project leader, JQI researcher and professor in the Department of Electrical and Computer Engineering and Physics at the University of Maryland, said that this achievement not only improves performance, but also provides replicability for mass production and actual integration. The chip can continuously output the same spectrum without the need for active control, which is expected to greatly simplify the difficulty of integrating large-scale photonic systems.
As on-chip frequency generation technology becomes reliable, it may become the core basis for photon-based quantum information transmission in the future. Each light color corresponds to a unique frequency. The atomic-level stable combination of multiple frequencies will greatly improve the accuracy of phase, distance and time-sensitive detection, benefiting cutting-edge fields such as quantum computing and portable atomic clocks.