“In the recent decade, tremendous efforts have been spent towards the generation of ultra-broadband mid-infrared (MIR, 3–20 μm) laser sources for various applications including frequency metrology and trace-gas sensing.Among various approaches, quantum cascaded lasers show good promise in device compactness. However, quantum cascaded lasers still face limitations in producing ultra-broadband emissions and ultrashort pulses, particularly in the femtosecond time scale. Up to now, nonlinear frequency conversions have become the main route for generating coherent ultra-broadband MIR radiations, which however generally consist of large and complicated laser apparatuses and exhibit relatively low conversion efficiency.” (Introduction)

In light of the significant needs and challenges mentioned above, the team of Houkun Liang cooperated with the team of Huan Yang from Shenzhen Technology University and successfully integrated birefringent crystals and developed a waveguide platform foron-chip MIR nonlinear photonics and practical applications of MIR spectroscopy and metrology.“---Here, we propose and demonstrate for the first time aχ⁽²⁾micrometer waveguide platform based on birefringence phase matching for long-wavelength infrared (LWIR) laser generation with a high quantum efficiency. In a ZnGeP₂-based waveguide platform, an octave-spanning spectrum covering 5–11 μm is generated through optical parametric generation (OPG). A quantum conversion efficiency of 74% as a new record in LWIR single-pass parametric processes is achieved. The threshold energy is measured as ~616 pJ, reduced by more than 1-order of magnitude as compared to those of MIR OPGs in bulk media. Our prototype micro-waveguide platform could be extended to otherχ⁽²⁾birefringence crystals and trigger new frontiers of MIR integrated nonlinear photonics.” (Abstract) The research progress was published in Nature Communications under the title of “Highly Efficient Octave-Spanning Long-Wavelength Infrared Generation with a 74% Quantum Efficiency in a χ(2) Waveguide”.(Abstract）

Bo Hu, a Class 2021 doctoral student, and Xuemei Yang, a Class 2023 doctoral student of the School of Electronics and Information Engineering, are the co first authors (3 in total), Sichuan University is the first work unit of the paper, and Prof. Houkun Liang and Associate Researcher Han Wu are the co corresponding authors (3 in total).

This is the latest achievement that Houkun Liang’s team has made in the research on mid-infrared lasers. Being dedicated to solving problems in the generation and application of ultrafast MIR lasers, the team has worked out high-quality light sources, including high-efficiency on-chip MIR lasers (Nat. Commun. 2023), solid-state high order harmonics driven by MIR ultrafast lasers (Nature Commun.Phys.2023,6:228), and fiber laser pumped high-freedom lasers (Photon. Res. 2023, 11:808). In terms of MIR applications, the team explored the application scenarios of MIR ultrafast lasers in biomedical fields (Laser Photonics Rev. 2023, 2300421) and took the lead in proposing a new blueprint for the application of MIR lasers in high-precision surgical procedures, helping human life and health to reach new heights.

Fig. 1. Fabricationsteps of theχ⁽²⁾waveguide with birefringence PM based on a ZGP crystal.

Fig. 2.Experimental setup and characterizations of the spectra, output power, pump threshold and parametric gain of theχ⁽²⁾micro-waveguide with birefringence PM based on a ZGP crystal.

Source： https://www.nature.com/articles/s41467-023-42912-0