This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: EPFL researchers have developed a chip-based laser that keeps a very stable frequency across its tested operating range, without needing active electronic control. Their research is published in the journal Nature Photonics.
Lasers provide the precise light needed for atomic clocks, quantum sensors, fiber-optic monitoring, coherent communications and distance measurements. These applications depend on lasers whose optical frequency remains exceptionally stable. The most precise systems often rely on bulky laboratory lasers, which limits their use in compact and portable technologies.
Semiconductor lasers offer a practical alternative. They are small, electrically powered and suitable for large-scale manufacturing. Their frequency, though, tends to fluctuate much more than that of the fiber lasers used in precision systems.
Researchers can reduce this noise through self-injection locking. In this approach, part of the laser light enters a high-quality optical resonator and returns to the laser. This optical feedback stabilizes the laser frequency and can narrow its linewidth, a measure of frequency stability, by several orders of magnitude.
The challenge is keeping the laser stable in this state. It usually works only under very specific conditions, such as a particular electrical current and a precise phase of the returning light, determined by its path length. Small changes, like temperature shifts or tiny variations from manufacturing, can easily disturb this balance.
Because of this, most systems need extra controls and electronics to constantly adjust the laser and keep it stable. Kippenberg at EPFL has now demonstrated a photonic integrated laser that remains self-injection locked across its tested drive-current range. The researchers call the approach "endless self-injection locking." The device combines a standard semiconductor laser with a tiny optical chip that feeds some of the light back into it.
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