Micro ring resonators with enormous potential: hybrid devices significantly improve laser technology

The team from the Photonic Systems Laboratory at the Federal Institute of Technology in Lausanne has developed a chip level laser source that can improve the performance of semiconductor lasers while generating shorter wavelengths.

This groundbreaking work, led by Professor Camille Br è s and postdoctoral researcher Marco Clementi from the Federal Institute of Technology in Lausanne, represents significant progress in the field of photonics and is of great significance for telecommunications, metrology, and other high-precision applications.

This study, published in the journal Light: Science and Applications, reveals how PHOSL researchers collaborated with photonics and quantum measurement laboratories to successfully integrate semiconductor lasers with silicon nitride photonic circuits containing microresonators. This integration has created a hybrid device that can emit highly uniform and precise light in the near-infrared and visible light ranges, filling the technological gap that has long posed challenges to the industry.

"Semiconductor lasers are ubiquitous in modern technology, ranging from smartphones to fiber optic communication. However, their potential is limited due to a lack of coherence and the inability to effectively generate visible light," Professor Br è s explained. "Our work not only improves the coherence of these lasers, but also redirects their output to the visible spectrum, opening up new avenues for their use.".

In this case, coherence refers to the uniformity of the phase of the light waves emitted by the laser. High coherence means that light waves are synchronized, resulting in a beam of light with very precise colors or frequencies. This characteristic is crucial for applications where the accuracy and stability of laser beams are crucial, such as timing and precision sensing.

Improve accuracy and functionality
The team's approach includes coupling commercially available semiconductor lasers with silicon nitride chips. This microchip is manufactured using industry standard and cost-effective CMOS technology. Due to its excellent low loss characteristics, almost no light is absorbed or escaped.

The light from the semiconductor laser flows into a tiny cavity through a microscopic waveguide, where the beam is captured. These cavities are called micro ring resonators, carefully designed to resonate at specific frequencies, selectively amplify desired wavelengths, and attenuate other wavelengths, thereby enhancing the coherence of emitted light.

Another significant achievement is that the hybrid system can double the frequency of light from commercial semiconductor lasers, thereby achieving a transition from near-infrared spectrum to visible spectrum.

The relationship between frequency and wavelength is inversely proportional, which means that if the frequency is doubled, the wavelength will decrease by half. Although near-infrared spectroscopy is used for telecommunications, higher frequencies are crucial for building smaller and more efficient devices that require shorter wavelengths, such as atomic clocks and medical devices.

When the captured light in the cavity undergoes a process called full optical polarization, these shorter wavelengths can be achieved, which causes so-called second-order nonlinearity in silicon nitride. In this case, nonlinearity means that there is a significant change in the behavior of light, i.e. amplitude jump, which is not proportional to the frequency generated by the interaction between light and material.

Silicon nitride typically does not exhibit this specific second-order nonlinear effect, and the team has carried out an elegant engineering feat to induce it: the system utilizes the ability of light to resonate in the cavity to generate electromagnetic waves, thereby stimulating nonlinear properties in the material.

Enabling technologies for future applications
"We are not only improving existing technology, but also promoting the possibility of semiconductor lasers," said Marco Clementi, who played a key role in the project. By bridging the gap between telecommunications and visible light wavelengths, we are opening the door to new applications in fields such as biomedical imaging and precision timing.

One of the most promising applications of this technology is metrology, especially in the development of compact atomic clocks. The history of maritime progress depends on the portability of precise timepieces - from determining sea longitude in the 16th century to ensuring accurate navigation for space missions, and now achieving better geographic positioning.

"This significant progress has laid the foundation for future technologies, some of which have not yet been conceived," Clementi pointed out.

The team's profound understanding of photonics and materials science will have the potential to make equipment smaller, lighter, and reduce laser energy consumption and production costs. They are able to adopt basic scientific concepts and transform them into practical applications using industry standard manufacturing, highlighting the potential to address complex technological challenges that may lead to unforeseeable progress.

Source: Laser Net