Optical image of a fully-packaged hybrid integrated erbium-laser based on silicon nitride photonic integrated circuit.
Andrea Bancora and Yang Liu (EPFL)
Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed the world’s first chip-integrated laser that matches the performance of conventional fiber-based lasers. This achievement could help develop smaller, more portable, cost-effective lasers for various fields.
Since their arrival in the 1960s, lasers have changed how our world works. From precision manufacturing to modern surgeries, telecommunications to printing, lasers have quickly become an indispensable part of the modern world.
With increasing applications, there is also a need to develop smaller lasers that are cheaper to produce and easier to operate. Researchers have been working on miniaturizing fiber-based lasers, considered the gold standard among lasers for their high-quality beams, high power output, and low noise.
Shrinking the fiber-based laser
A research team led by Tobias Kippenberg, a professor of physics at EPFL, developed an erbium-doped waveguide laser embedded on a photonic chip that delivers beam characteristics that resemble those of fiber-based lasers. Erbium is a rare-earth element that acts as the light source in a laser.
The researchers used a state-of-the-art fabrication process to achieve this and began constructing a meter-long on-chip optical cavity on a silicon nitride photonic circuit. An optical cavity is a set of mirrors that provides optical feedback.
The team then implanted erbium ions onto the circuit to create the gain needed for lasing and integrated it with a semiconductor pump to excite the erbium ions, emit light, and produce the laser beam.
Optical image of a hybrid integrated erbium-doped photonic integrated circuit-based laser, providing fiber-laser coherence and previously unachievable frequency tunability. Image credit:
How well does the laser work?
The laser beam’s narrowness allows it to produce steady light, which is necessary for applications ranging from LiDAR to sensing, making gyroscopes, and performing metrology using optical frequency.
When tested, the researchers confirmed that their laser beam generated a power output of 10 mW and had a side suppression ratio greater than 70 dB. This is far superior to conventional laser systems.
An area where the laser performed better than fiber-based lasers was wavelength tunability of over 40 nanometers in the C- and L- bands. These wavelengths are important for telecommunication applications, and the photonic chip laser could help deliver better systems.
These capabilities in the photonic-chip laser system were possible due to innovations such as intra-cavity design, where the researchers used microring-based Vernier filters.
“We were able to design the laser cavity to be meter-scale in length despite the compact chip size, thanks to the integration of these microring resonators that effectively extend the optical path without physically enlarging the device,” said Yang Liu, a doctoral researcher at EPFL who was also involved with the work.
This allowed the filter to use specific light frequencies and dynamic tuning of the laser’s wavelength over a broad range. The laser emits light at a single consistent frequency while minimizing other frequencies (side mode), which helps it deliver the superior side suppression ratio mentioned earlier.
Miniaturizing such erbium lasers into chip-scale devices is also beneficial since it reduces costs and makes them easier to integrate into applications such as telecommunications, medical diagnostics, and consumer electronics, a press release added.
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The research findings were published in the journal Nature Photonics.
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Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
