A laser that stays locked without active control
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.
Researchers from EPFL have created a chip-based laser that maintains a very stable frequency throughout its operational range, without the need for any active electronic control. Laser systems are crucial for precise measurements in various technologies, including atomic clocks, quantum sensors, and fiber-optic communications, which require extremely stable optical frequencies.
Traditionally, bulky laboratory lasers have been used, but they are not suitable for compact and portable applications. Semiconductor lasers, on the other hand, are small, inexpensive, and easy to manufacture, but their frequency can fluctuate significantly.
To improve stability, researchers have employed a technique called self-injection locking. This method involves redirecting a portion of the laser light into an optical resonator, which then feeds back into the laser, stabilizing its frequency. However, maintaining this self-injection locked state can be challenging, as it often requires precise conditions, such as specific electrical currents and light phases.
The EPFL team, led by Tobias J. Kippenberg, has now developed a photonic integrated laser that remains self-injection locked across a wide range of drive currents, from 154 to 300 milliamps. They achieved this by carefully designing the optical feedback within the laser system. The researchers tested the laser under various current conditions and found that self-injection locking reduced the frequency noise by more than a factor of 5,000 compared to a free-running laser, with an intrinsic linewidth below 10 hertz.
In addition to the self-injection locking, the researchers integrated piezoelectric actuators onto the photonic chip. These actuators can adjust the resonator's properties through the stress-optic effect when voltage is applied. This feature allows the laser to maintain its stable operating state even when the drive current changes, without the need for active control of the feedback phase.
The design of this continuously self-injection locked photonic integrated laser could enable the development of compact, ultra-low-noise lasers for various applications, such as optical sensing, lidar, coherent communications, and quantum sensing. While the research demonstrates the principle in a laboratory setting, further engineering and packaging would be necessary for deployment in real-world scenarios.
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