Scientists have successfully miniaturized erbium-based erbium lasers on silicon nitride photonic chips

Scientists from the Federal Institute of Technology in Lausanne (EPFL) have successfully miniaturized a powerful erbium-based erbium laser on silicon nitride photonic chips. Due to the large volume and difficulty in shrinking of typical erbium-based fiber lasers, this breakthrough is expected to make significant progress in optical communication and sensing technology.

Since the 1960s, lasers have completely changed the world and are now indispensable in modern applications, from cutting-edge surgery and precision manufacturing to fiber optic data transmission.

It can also scale down optical technologies in various other applications, such as LiDAR, microwave photonics, optical frequency synthesis, and free space communication.

"The application fields of this new type of erbium-doped integrated laser are almost unlimited."
EDWATEC SA, a subsidiary of the laboratory, is an integrated device manufacturer that now offers devices based on rare earth ion doped photonic integrated circuits, including high-performance amplifiers and lasers.
Filters allow for dynamic tuning of laser wavelengths over a wide range, making them versatile and suitable for various applications. This design supports stable single-mode lasers, with an inherent narrow linewidth of only 50 Hz.

It also allows for significant side mode suppression - the laser can emit light at a single, consistent frequency while minimizing the intensity of other frequencies ("side modes"). This ensures a "clean" and stable output for high-precision applications throughout the entire spectrum.

Power, accuracy, stability, low noise
The output power of chip level erbium-based fiber laser exceeds 10 mW, with a side mode suppression ratio greater than 70 dB, and its performance is superior to many traditional systems.

It also has a very narrow linewidth, which means that the light it emits is very pure and stable, which is crucial for coherent applications such as sensing, gyroscopes, LiDAR, and optical frequency measurement.

The micro ring based vernier filter provides wide wavelength tunability for 40 nm lasers in the C-band and L-band (wavelength range used in telecommunications), surpassing traditional fiber lasers in tuning and low spectral stray indicators ("stray" is an unnecessary frequency) while maintaining compatibility with current semiconductor manufacturing processes.

Next generation laser
Miniaturizing and integrating erbium fiber lasers into chip level devices can reduce their overall cost, making them suitable for portable and highly integrated systems in telecommunications, medical diagnostics, and consumer electronics.

Now, scientists led by Dr. Liu Yang and Professor Tobias Kippenberg from the Federal Institute of Technology in Lausanne have established the first ever chip integrated erbium-doped waveguide laser. The performance of this laser is close to that of fiber based lasers, combining wide wavelength tunability with the practicality of chip level photon integration. This breakthrough was published in the journal Nature Photonics.

But as the demand for laser based applications continues to grow, the challenges also increase. For example, the market for fiber lasers is growing and is currently used in industrial cutting, welding, and marking applications.

Fiber lasers use fibers doped with rare earth elements (erbium, ytterbium, neodymium, etc.) as their optical gain source (the part that produces the laser). They emit high-quality beams of light, have high power output, are efficient, low maintenance, durable, and typically smaller than gas lasers. Fiber lasers are also the gold standard for low phase noise, which means their beams will remain stable over time.

However, despite this, the demand for miniaturization of chip level fiber lasers continues to grow. Erbium based fiber lasers are particularly interesting because they meet all the requirements for maintaining high coherence and stability of the laser. However, miniaturizing them poses challenges in maintaining their performance on a small scale.

Building chip level lasers
Researchers have developed their chip level erbium laser using state-of-the-art manufacturing techniques. They first built a one meter on-chip optical cavity (a set of mirrors that provide optical feedback) based on ultra-low loss silicon nitride photonic integrated circuits.

"Although the chip size is compact, we are able to design the laser cavity in meter lengths thanks to the integration of these micro ring resonators, which effectively expand the optical path without the need for physical amplification equipment," said Dr. Liu.

Then, the team implanted high concentrations of erbium ions into the circuit to selectively generate the active gain medium required for the laser. Finally, they integrated citcuit with III-V semiconductor pumped lasers to excite erbium ions, enabling them to emit light and generate laser beams.

In order to improve the performance of the laser and achieve precise wavelength control, researchers have designed an innovative cavity design with a micro ring based cursor filter, which is a filter that can select specific frequency light.

Source: Laser Net