Updating an old technology for the quantum age
The device known as the Fabry-Perot resonator is indispensable for optical clocks, quantum technologies, and other applications. It’s a structure made of two mirrors that reflect light back and forth. Its stability, which makes it such a crucial component, comes from operating in a vacuum. Optimizing their use on certain microchips, though, has proved tricky. Recently a team of researchers in the lab of Peter Rakich, the Dubinsky Professor of Applied Physics, developed an ingenious solution. The results are published in Nature Photonics.
The problem:
Ushering in the next-generation of quantum communications, computation, and timekeeping technologies will require researchers to find a way to incorporate these resonators into photonic integrated circuits. These are microchips that use light, or photons, to provide significant advantages over conventional electronics in terms of efficiency, speed and allowing for smaller devices. One challenge, though, is that the strong mirror-like reflections of Fabry-Perot resonators can destabilize or even damage an on-chip laser.
The solution:
In the lab of Peter Rakich, a team of researchers introduced “reflection transformation circuits” that essentially transform the light produced by a tiny, millimeter-scale Fabry-Perot resonator and tune it to the frequency of the on-chip laser. As a result, they demonstrated for the first time, an ultra-stable “self-injection” locked laser using a Fabry-Perot resonator. The study’s lead author, Haotian Cheng, formerly a grad student in Rakich’s lab and now an optics engineer at Apple, explains that “self-injection” means that a laser can effectively synchronize the laser oscillator with the resonance of this Fabry-Perot cavity, inheriting the remarkable low-noise properties of the cavity.
The result of their innovation is a device that produces an unprecedented suppression of fluctuations - or “noise” - in the laser’s frequencies.
Why this matters:
In general, a laser with lower noise “gives us the ability to detect smaller signals or to sense motion, vibrations, etc. with much more precision,” Rakich says. These features are crucial in that they have potential benefits for communications, sensing, laser radar, and imaging technologies. Such low-noise laser oscillators could also help improve the stability of quantum communications networks.
Going forward:
The researchers say they plan to use their current ultra-stable laser system as a building block for fiber-optic sensing applications. With a low-noise laser, such a system can sense any vibration in the fiber and detect earthquakes, submarines and other things. They also plan to put the system to use in making a low-noise microwave oscillator, which could enable next-generation radar, navigation, and communications systems.
Bonus fact: The Fabry-Perot resonator was invented in 1899 by the French physicists Charles Fabry and Alfred Perot. Fourteen years later, Fabry also co-discovered the ozone layer.
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Published Date
Jun 6, 2025
