Chip-sized Lasers May Replace Fiber Lasers?

Recently, researchers from the École Polytechnique Fédérale de Lausanne (EPFL) developed a chip-integrated erbium-doped waveguide laser, a new type of laser whose performance is close to that of fiber lasers, combining tunability and the practicality of chip-scale photonic integration.
It is well known that fiber lasers use optical fibers doped with rare earth elements as the gain medium. Therefore, compared with gas lasers such as carbon dioxide, they have the advantages of high beam quality, high power, high efficiency, small size, and seamless integration of fiber output and flexible processing platforms.
And to meet the demand for chip-scale fiber lasers, researchers turned to erbium as the gain medium. Erbium-based fiber lasers are particularly promising because they meet the requirements of maintaining high coherence and stability. However, miniaturization of erbium-based fiber lasers has long been difficult to achieve due to the difficulty of maintaining their unique high performance.
To this end, the researchers first constructed a meter-long on-chip optical cavity based on an ultra-low-loss silicon nitride photonic integrated circuit. According to Yang Liu, a researcher at the Laboratory of Photonics and Quantum Measurements at the École Polytechnique Fédérale de Lausanne: Despite the compact chip size, we were able to design the laser cavity to a meter-long length thanks to the integration of these micro-ring resonators, which efficiently extend the optical path without the need for physical amplifier devices.
Major breakthrough! Chip-sized lasers may replace fiber lasers?
The team then implanted a high concentration of erbium ions in the circuit to selectively generate the active gain medium required for lasing. Finally, they integrated the circuits with III-V semiconductor pump lasers to excite the erbium ions so that they could emit light and produce a laser beam.
To improve the laser's performance and enable precise wavelength control, the researchers devised an innovative intracavity design featuring a micro-ring-based vernier filter, a filter that selects light at a specific frequency to improve the laser's performance and enable precise wavelength control.
The filter allows dynamic tuning of the 40 nm laser wavelength in both the C- and L-bands, which exceeds conventional fiber lasers in both tuning and low spectral spurious metrics, while maintaining compatibility with current semiconductor manufacturing processes. The design supports stable single-mode lasing with an intrinsic linewidth of 50 Hz.
With an output power in excess of 10 mW and a side-mode rejection ratio greater than 70 dB, the chip-scale erbium-based fiber laser outperforms many conventional lasers. Their narrow linewidth allows them to emit pure and stable light, making them ideal for coherent applications such as sensing, gyroscopes, LIDAR, and optical frequency metrology.
Downsizing and integrating erbium fiber lasers into chip-scale devices can make them more affordable, opening up new applications for highly integrated mobile systems in consumer electronics, medical diagnostics and telecommunications. It could also shrink optical technologies in several other applications, including LIDAR, microwave photonics, optical frequency synthesis and free-space communications.