Yb³⁺-Doped Double-Clad Fiber Laser Pumped by Rectangular Inner Cladding

A novel Yb³⁺-doped double-clad silica fiber with rectangular inner cladding was designed and developed by using the modified chemical vapour deposition process, solution-doping and optical machining altogether. The dimension of inner cladding is 100 x 70μm, and Yb³⁺-doped concentration in the core is about 0.24wt.%. The operation of the fiber laser pumped by inner cladding is reported. The threshold of the laser is 34mW. When the pump power launched is 141mW, the laser output is 84mW at the wavelength 1075.6nm, and the slope efficiency is 77%.