EPFL researchers have developed a compact, high-performance erbium laser on chip that expands the possibilities of applications in technology and medicine. Since the 1960s, lasers have changed the world and become indispensable for modern applications such as advanced surgery, precision manufacturing and fiber optic data transmission.

However, as the need for laser applications increases, problems also increase. For example, there is now a growing market for fiber lasers used in industrial cutting, welding and marking.

Fiber lasers use an optical fiber doped with rare earth elements (erbium, ytterbium, neodymium, etc.) as the optical amplification source (the part that creates the laser light). They emit high-quality beams, have high output power, are efficient, require low maintenance, have a long life, and are generally smaller than gas lasers. Fiber lasers are also the “gold standard” for low phase noise, meaning their beams remain stable over time.

However, despite all this, the demand for miniaturization of fiber lasers at the microcircuit level is increasing. Erbium-based fiber lasers are of particular interest because they meet all the requirements for maintaining high coherence and laser stability. However, their miniaturization faces challenges in maintaining their performance at small scales.

Now, EPFL’s Dr. Scientists led by Yang Liu and Professor Tobias Kippenberg have created the first erbium-doped waveguide laser integrated on a chip that approaches the performance of fiber lasers by combining a wide wavelength with the tunability of chip-scale photonics. integration. . The invention was published on: Nature Photonics.

Creating a chip laser

Researchers developed erbium lasers using a state-of-the-art manufacturing process. They started by designing a meter-scale optical cavity on a crystal (an array of mirrors that provide optical feedback) based on a silicon nitride ultra-low-loss photonic integrated circuit.

“By integrating these microring cavities, which effectively expand the optical path without physically enlarging the device, we were able to design the laser cavity to be one meter long despite the compact chip size,” says Liu.

The team then introduced a circuit containing a high concentration of erbium ions to selectively create the active gain environment required for laser generation. Finally, they integrated the circuit with a III-V pump semiconductor laser to excite the erbium ions so they could emit light and create a laser beam.

To improve the laser’s performance and achieve precise wavelength control, the researchers developed an innovative in-cavity design incorporating microring-based vernier filters, a type of optical filter that can select specific frequencies of light.

Filters allow you to dynamically adjust the laser’s wavelength over a wide range, making it versatile and suitable for use in a variety of applications. This design supports stable single-mode production with an impressively narrow internal linewidth of only 50 Hz.

It also provides significant side mode suppression; the ability of a laser to emit light at a single coherent frequency while minimizing the intensity of other frequencies (“side modes”). This provides a “clean” and stable output across the light spectrum for high precision applications.

Power, precision, stability and low noise

The chip-scale erbium fiber laser has an output power of over 10 mW and a side-mode suppression ratio of over 70 dB, outperforming many conventional systems. It also has a very narrow line width; This means that the light it emits is very clean and uniform; This is important for coherent applications such as sensing, gyroscopes, LiDAR and optical frequency metrology.

A microring-based vernier filter provides a broad range of 40 nm laser wavelengths in the C and L bands (wavelength ranges used in telecommunications) and outperforms older fiber lasers in both tuning and low spectrum performance (spurs) (undesirable). frequencies) while remaining compatible with existing semiconductor manufacturing processes.

New generation lasers

Miniaturization and integration of erbium fiber lasers into chip devices could reduce their overall cost, making them cost-effective for portable and highly integrated systems in telecommunications, medical diagnostics, and consumer electronics. LiDAR can also scale down optical technologies in a variety of other applications, such as microwave photonics, optical frequency synthesis, and free space communications.

“Applications for this new class of erbium-integrated lasers are virtually unlimited,” says Liu.