Recent advances in high-power fiber lasers have imposed several pairs of higher requirements on fiber materials, such as larger fiber core/higher homogeneity and higher doping level/lower numerical aperture. However, these characteristics conflict with each other in silica fibers and are almost impossible to reconcile by traditional fiber preparation technologies. Here, we developed 3D nanoporous silica rods based on glass phaseseparation technology to address these conflicting requirements. Benefiting from uniformly distributed nanopores, nanoporous silica glass exhibits remarkable performance in its core diameter, doping level, refractive index controlling, and optical homogeneity. These properties make nanoporous silica glasses very suitable as a fiber core material and greatly distinguish them from other fiber materials. We have prepared a typical Yb 3+ heavily doped fiber with a core diameter of 80 μm and an ultralow numerical aperture of 0.029. The fiber exhibits an excellent laser performance with a slope efficiency of 79.5% for 600 W laser emission at 1080 nm in a 0.85 m length fiber. Our study will make 3D nanoporous silica glass emit new energy in fiber materials and boost the advancement of high-power fiber lasers.

No abstract

GHz repetition rate fundamentally mode-locked lasers have attracted great interest for a variety of scientific and practical applications. A passively mode-locked laser in all-fiber format has the advantages of high stability, maintenance-free operation, super compactness, and reliability. In this paper, we present numerical investigation on passive mode-locking of all-fiber lasers operating at repetition rates of 1-20 GHz. Our calculations show that the reflectivity of the output coupler, the small signal gain of the doped fiber, the total net cavity dispersion, and the modulation depth of the saturable absorber are the key parameters for producing stable fundamentally mode-locked pulses at GHz repetition rates in very short allfiber linear cavities. The instabilities of GHz repetition rate fundamentally mode-locked allfiber lasers with different parameters were calculated and analyzed. Compared to a regular MHz repetition rate mode-locked all-fiber laser, the pump power range for the mode-locking of a GHz repetition rate all-fiber laser is much larger due to the several orders of magnitude lower accumulated nonlinearity in the fiber cavity. The presented numerical study provides valuable guidance for the design and development of highly stable mode-locked all-fiber lasers operating at GHz repetition rates.

No abstract