Jiang Shuisen, Guo Changlei, Fu Hongyan, Che Kaijun, Xu Huiying, Cai Zhiping
Opt Express. 2020 Dec 7;28(25):38304-38316. doi: 10.1364/OE.412157.
Mid-infrared (mid-IR) lasers have great applications in bio-molecular sensing due to strong vibrational fingerprints in this wavelength range. However, it is a huge challenge to realize mid-IR lasers in conventional silica materials. Here, we demonstrate the generation of mid-IR Raman lasers and Kerr-frequency combs from an all-silica microresonator/fiber laser system. A single wavelength narrow-linewidth laser at ∼2 µm is first realized by using an ultrahigh Q-factor silica whispering-gallery-mode (WGM) microresonator as mode-selection mirror, and thulium-doped silica fiber as gain medium. Due to the strong intensity enhancement in the microresonator itself, multiple third-order nonlinear optical effects are observed, which include stimulated Stokes and anti-Stokes Raman scattering, and (cascaded) four-wave-mixing (FWM). The stimulated Stokes and anti-Stokes Raman scattering shift the initial 2 µm narrow-linewidth laser to as far as ∼2.75 µm and ∼1.56 µm, respectively. While the cascaded FWM helps to form a Kerr-frequency comb with a broad bandwidth of ∼900 nm and a mode spacing of twice of the microresonator free-spectral-range. This work offers a simple and effective route to realize all-silica mid-IR lasers based on enhanced optical nonlinearity in WGM microresonators.
由于在该波长范围内存在强烈的振动指纹，中红外（mid-IR）激光器在生物分子传感方面具有巨大的应用潜力。然而，在传统的二氧化硅材料中实现中红外激光器是一项巨大的挑战。在此，我们展示了一种全二氧化硅微谐振器/光纤激光系统中红外拉曼激光器和克尔频率梳的产生。首先，通过使用超高品质因数的二氧化硅回音壁模式（WGM）微谐振器作为模式选择镜，以及掺铥二氧化硅光纤作为增益介质，实现了波长约为2 µm的单波长窄线宽激光器。由于微谐振器自身的强度显著增强，观察到了多种三阶非线性光学效应，其中包括受激斯托克斯和反斯托克斯拉曼散射，以及（级联）四波混频（FWM）。受激斯托克斯和反斯托克斯拉曼散射分别将初始的2 µm窄线宽激光波长移至约2.75 µm和约1.56 µm。而级联四波混频则有助于形成带宽约为900 nm、模式间隔为微谐振器自由光谱范围两倍的克尔频率梳。这项工作为基于WGM微谐振器中增强的光学非线性来实现全二氧化硅中红外激光器提供了一条简单有效的途径。
