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Erbium laser miniaturized on chip scale | Research & Technology | June 2024

LAUSANNE, Switzerland, June 11, 2024 – At the intersection of growing demand for fiber lasers and chip-scale lasers, researchers at the École Polytechnique Fédérale de Lausanne (EPFL) have developed a chip-integrated erbium-doped waveguide laser that improves the performance of fiber-based lasers. It combines broad wavelength tuning with the utility of chip-scale photonic integration.

Fiber lasers use an optical fiber doped with rare earth metals as optical amplification. These lasers are preferred for their stable, high-quality beams, their high output power, but also for their efficiency, low maintenance requirements, durability and their smaller size compared to gas lasers.

In response to the demand for chip-scale fiber lasers, the researchers turned to erbium as an amplification source. Erbium-based fiber lasers meet the requirements for maintaining high coherence and stability. However, miniaturization is difficult to achieve due to the challenges in maintaining their characteristic high performance.

The researchers started by constructing a meter-long optical cavity on the chip, based on an ultra-low loss silicon nitride photonic integrated circuit.

“We managed to design the laser cavity so that it has a length of one meter despite the compact chip size, thanks to the integration of these micro-ring resonators that effectively extend the optical path without physically enlarging the device,” said Yang Liu, a researcher at EPFL’s Laboratory for Photonics and Quantum Measurements.

Researchers at EPFL developed a hybrid integrated circuit-based erbium-doped photonic laser (pictured), overcoming frequency tuning challenges to meet the growing demand for chip-scale fiber lasers.  Thanks to Yang Liu/EPFL.


Researchers at EPFL developed a hybrid integrated circuit-based erbium-doped photonic laser (pictured), overcoming frequency tuning challenges to meet the growing demand for chip-scale fiber lasers. Thanks to Yang Liu/EPFL.


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The team then implanted the circuit with high-concentration erbium ions to selectively create the active gain medium needed for lasing. Finally, they integrated the circuit with a III-V semiconductor pump laser to excite the erbium ions so they could emit light and produce the laser beam.

To fine-tune the laser’s performance and achieve precise wavelength control, the researchers developed an innovative intracavity design using microring-based Vernier filters, a type of optical filter that can select specific light frequencies.

The filter enables dynamic tuning of the laser’s wavelength over 40 nm within the C and L bands, outperforming older fiber lasers in both tuning and low spectral traces (unwanted frequencies), while remaining compatible with today’s semiconductor manufacturing processes. The design supports stable, single-mode laser operation with a narrow intrinsic linewidth of 50 Hz.

It also enables significant side mode suppression: the laser’s ability to emit light at a single, consistent frequency while minimizing the intensity of other frequencies (“side modes”). In practice, this ensures a “clean” and stable output across the entire light spectrum for highly precise applications.

The chip-scale erbium-based fiber laser has an output power of more than 10 mW and a side mode rejection ratio of more than 70 dB, outperforming many conventional systems. Its narrow linewidth allows it to emit pure and stable light desirable for coherent applications such as sensing, gyroscopes, lidar and optical frequency metrology.

The ability to produce chip-scale erbium fiber lasers could reduce overall costs and increase accessibility for portable integrated systems in telecommunications, medical diagnostics and consumer electronics. Moreover, it could scale back optical technologies in applications such as lidar, microwave photonics, optical frequency synthesis and free-space communications.

The research was published in Nature Photonics (www.doi.org/10.1038/s41566-024-01454-7).