Miniaturized and high-efficiency mid-infrared lasers have been the focus of research in the mid-infrared field in recent years, which are of great significance in mid-infrared spectroscopic detection, ultrasensitive molecular remote sensing, and real-time environmental monitoring. On-chip mid-infrared lasers based on nonlinear frequency conversion are considered to be one of the most promising solutions for miniaturized mid-infrared lasers besides quantum cascade lasers due to their ability to achieve ultra-broadband spectral output and ultra-short pulse excitation. However, the current research on this type of mid-infrared lasers mainly focuses on third-order nonlinear waveguide platforms based on silicon, germanium, etc., which often require complex and fine waveguide dispersion modulation and miniature resonant cavities with high quality factors to realize high-efficiency mid-infrared laser output. Therefore, the search for simple and efficient on-chip mid-infrared laser generation based on nonlinear frequency conversion is a technical challenge that needs to be solved urgently.
Based on the above major needs and challenges, Liang Houkun's team from the School of Electronics and Information Technology of Sichuan University, together with Yang Huan's team from Shenzhen University of Technology, have successfully realized on-chip integration of birefringent crystals for the first time, based on the guiding principle that "the second-order nonlinear response of the material is much larger than the third-order nonlinear response", and combined with the existing mature technologies, such as wafer bonding, optical polishing, and laser direct writing, to develop an on-chip birefringent crystal with high efficiency. By combining the existing mature technologies such as wafer bonding, optical polishing and laser direct writing, we have successfully realized the on-chip integration of birefringent crystals for the first time, and developed a new mid-infrared waveguide platform based on nonlinear frequency conversion. Through the waveguide size design, based on birefringent phase matching, a low-threshold, high-efficiency broadband tunable long-wavelength mid-infrared laser is realized, which improves the quantum conversion efficiency by two orders of magnitude up to 74% compared to the traditional single-pass nonlinear frequency conversion light source based on a bulk crystal, and reduces the existing mid-infrared laser generation threshold by one order of magnitude. This work provides a new research direction for next-generation high-efficiency mid-infrared laser generation and a favorable guide for miniaturization of other birefringent crystals. The article is published as Highly efficient octave-spanning long-wavelength infrared generation with a 74% quantum efficiency in a χ(2) waveguide was published in Nature Communications.
Liang Houkun's team at Sichuan University has made significant progress in the study of novel on-chip mid-infrared lasers.
Waveguide fabrication flowchart
Device diagram and output laser characteristics
This work provides a new research direction for next-generation high-efficiency mid-infrared laser generation, and also provides favorable guidance for miniaturization of other birefringent crystals.
