High-power U-band femtosecond laser pulses generated by nonlinear optical gain modulation

The U-band has many applications, including atmospheric remote sensing, LiDAR, free space communication, U-band fiber optic communication, and biological tissue imaging. However, the U-band is located in the blank region of the emission spectra of erbium and thulium ions, and cannot directly generate ultrafast laser output through mode locking. Traditional nonlinear frequency transfer methods such as soliton self frequency shift, supercontinuum generation, self phase modulation, etc. produce U-band pulse conversion efficiencies below 20%, and the devices are complex and have poor coherence, making it difficult to meet the needs of U-band applications. In response to this, this work generates ultra fast pulse output in the U-band through nonlinear optical gain modulation method, with a conversion efficiency of up to 63%, which can be compressed to the near Fourier transform limit output. The structure is composed of fully polarization maintaining fiber optic devices, which are simple, efficient, stable, and easy to integrate. Simultaneously possessing high coherence inherited from single frequency lasers, with a simple spectral tuning method and a wide tuning range. It can be used as an ideal light source for U-band applications.