High-power tunable light sources around 1 μm wavelength region is a mature and widely used technology. Such high power, wavelength tunable Yb-doped fiber lasers (YDFLs) light sources are extensively used as excellent pump sources.  However, the stochastic self-pulse and the interactions of longitudinal modes degrade the temporal stability and performance of tunable YDFLs.  

Faced with this situation, are we really helpless? Of course not, superfluorescent fiber sources (SFSs) is the answer of the question. Unfortunately, its output power has become a stumbling block for scientists on their way forward.  

In order to overcome the problem of SFS output power, a research team led by Prof. Dr. LIU Hongjun from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) presented a high-power widely tunable all-fiber narrowband superfluorescent fiber source by employing two tunable bandpass filters and three amplifier stages. The results were published in Optics Express. 

Experimental setup of the high-power all-fiberized tunable narrowband SFS. (Image by XIOPM)

In their work, two tunable bandpass filters (TBPFs) with different bandwidths are utilized to gradually reduce the full width at half maximum (FWHM) linewidth of the tunable narrowband SFS during the power scaling process.  

Thus, a narrowband SFS with adequate power and narrower FWHM linewidth is achieved, that could surmount the low power spectral density (PSD) of broadband SFS.   

By optimizing the parameters of the broadband SFS and the amplifiers, a large tuning range of 40 nm and a power output of kilowatt (kW) level can be obtained at maximum power.  

This research result is not only the first to demonstrate tunable high-performance all-fiber narrowband SFS, but also very practical.