An Efficient 4-kW Level Random Fiber Laser Based on Tandem-Pumping Scheme

In this paper, we presented a monolithic high power random fiber laser with a tandem-pumping scheme. The random fiber laser seed centered at 1064 nm was pumped by a 1018 nm fiber laser and reached an output power of 8.66 W. After the two amplifiers, the seed was amplified to 4020 W and the 3 dB width of laser spectrum was broadened from 0.78 nm to 0.99 nm. To increase the efficiency of the 4 kW laser, a specially designed high absorption coefficient (0.6 dB/m @ 1018nm) 30/250 μm Yb doped fiber and high brightness 1018 nm pump laser were adopted. The optical-to-optical efficiency could reach as high as 88.5%. No obvious mode instability was found during the experiment. Furthermore, with the same amplifier stage, we have also built another 4 kW level fiber laser seeded by an oscillator consisting of a pair of fiber Bragg gratings. The comparison of the experimental results showed that high power laser based on RFL seed would have a better control on spectral broadening.

I. Introduction

Owing to the outstanding properties [1]–[6] such as low quantum defect, cavity-free, no photo darkening effect, and compact structure, random fiber laser (RFL) based on distributed Rayleigh scattering and amplification by Raman gain has drew many attentions recently, especially in fields of speckle-free imaging[7], super continuum generation[8], sensing[9], [10] and pump source for Ho-doped fiber laser [1], et.al. In RFL, the resonant cavity is formed by utilizing distributed Rayleigh scattering along the fiber, instead of a pair of fiber Bragg gratings (FBGs). Based on whether or not a high reflection FBG (HR-FBG) is incorporated, the RFL can be divided into two types of structure, namely half open cavity and open cavity [11]. By taking the advantage of Raman gain and the choosing appropriate pump sources, the RFLs could operate at any wavelengths and have made a significant progress over the past decade.