The team of Liang Wei of Suzhou Nano Institute has made progress in the field of extra-cavity ultra-narrow linewidth semiconductor laser

High-performance, low-cost and miniaturized narrow-width lasers are urgently needed for many high-tech applications and major scientific research projects in the future. These applications include frequency modulation continuous wave lidar, which is likely to be used in the future autonomous driving, coherent laser communication for low-orbit satellite networks, upcoming space gravity exploration, and quantum information. In the past 10 years, the mature solid-state and fiber lasers with narrow linewidth have remained at the order of kHz in linewidth, and their large volume and high cost cannot meet the higher requirements of laser performance, cost and volume put forward by the above economic development and scientific research projects.

Using high quality optical cavity to narrow the semiconductor laser linewidth through optical feedback self-injection frequency locking is a new technology developed in recent years, which can surpass the traditional solid and fiber narrow linewidth laser in performance, volume, size and power consumption. In recent years, the sound wall and microring cavity on film are the focus of academic research. The performance of the laser with narrow line width of outer cavity has also made great progress. However, due to the limitation of material absorption and nonlinear effect, it is difficult to improve the noise and power of the laser outside the solid microcavity. The hollow FP optical cavity has very low thermal effect and nonlinear effect, so it is an ideal choice for making narrow line width laser. Traditional ultra-stable FP cavity size is too large, requires a complex system to maintain high stability, can only be used in the laboratory.

A team led by Liang Wei from Suzhou Institute of Nano Engineering, Chinese Academy of Sciences has developed FP optical cavity with mm level cavity length and > 108 high quality factor. Using self-injection locking technology, we have developed a small volume and low-cost ultra-narrow linewidth semiconductor laser with Lorentz linewidth lower than Hz and integral linewidth lower than 100Hz. The performance is better than the reported on-chip microring hybrid integrated narrow linewidth laser. The results can greatly accelerate the application of narrow-width laser technology based on FP high Q microcavity. The results were published in Optics Letters under the title Compact sub-hertz linewidth laser enabled by self-injection lock to a sub-milliliter FP cavity. The first author and corresponding author of the paper is Liang Wei.

in addition, Prof. Liang Wei co-authored a review entitled Recent advances in laser self-injection locking to high-Q microresonators with scholars from Shenzhen Quantum Academy and the United Arab Emirates and Russia. Advances in laser self-injection locking techniques are presented. Published in Frontiers of physics. The lead author of the paper is Nikita M. from the Institute of Technology Innovation in ABU Dhabi, UAE. Kondratiev, corresponding author: Nikita M. Kondratiev and Junqiu Liu, Professor of Southern University of Science and Technology.

These two projects were supported by the National Natural Science Foundation of China, the Basic Research Team Program of the Chinese Academy of Sciences, and the Foreign Experts Program of Jiangsu Province and Suzhou City.