Mid-Infrared Random Fiber Laser Assisted by the Passive Feedback

Random fiber lasers (RFLs), featuring a simple open cavity but with unique lasing characteristics, have captured considerable attention in the past several decades. Particularly, RFLs assisted by the passive feedback exhibit excellent robustness and compactness owing to the combination of active amplification and passive feedback from random distributed Rayleigh scattering. However, RFLs with the aid of the passive feedback reported previously are primarily operating in the near-infrared wavelength region of 1.1 μm or 1.5 μm based on the ytterbium or erbium doped active fibers. Here, we propose and demonstrate a random fiber laser configuration combining the passive feedback from a piece of single mode fiber with the active gain based on the thulium doped fiber, and extend the operation wavelength to the critically important mid-infrared wavelength band of ~2 μm. The spectral and temporal characteristics of the lasing output are evaluated and compared with those generated in a single pass amplification structure and a conventional resonant structure. Our results show that the passive feedback assisted RFL has a stabilized lasing wavelength and notably suppressed temporal dynamics. This work not only advances the development of RFLs, but also provides a promising strategy to achieve mid-infrared laser emission with a comparatively low relative intensity noise.