Laser Stays Locked Without Control

EPFL researchers have made a breakthrough in laser technology, developing a chip-based laser that remains stable without active electronic control. The laser, which uses a technique called 'endless self-injection locking', was able to maintain a stable frequency across its tested operating range.

The research, published in the journal Nature Photonics, demonstrates the laser's ability to stay locked even when its drive current is varied from 154 to an unspecified upper limit. This is achieved through a carefully designed optical feedback system, which combines a standard semiconductor laser with a tiny optical chip that feeds some of the light back into it.

The 'endless self-injection locking' technique allows the laser to smoothly move between stable states without losing its lock as the drive current changes. This is made possible by the overlapping of the stable operating regions of the laser, ensuring that it remains stable even as conditions change.

The device was developed by a team led by Tobias J. Kippenberg, who ensured the laser's stability by carefully designing the optical feedback. The result is a laser that is suitable for applications such as atomic clocks, quantum sensors, fiber-optic monitoring, coherent communications, and distance measurements.

## Why it matters The development of this laser is significant because it provides a compact and portable alternative to bulky laboratory lasers. Lasers are essential for precise applications, but their frequency stability is often limited by their size and complexity. The EPFL researchers' breakthrough could enable the use of lasers in a wider range of applications, from atomic clocks to coherent communications.

The stability of the laser is crucial for these applications, as it allows for precise measurements and communications. The 'endless self-injection locking' technique used in this device could pave the way for the development of more compact and portable lasers, enabling their use in a wider range of fields.