Distributed and side-pumped fiber laser using a laser diode bar stack

A distributed, side-pumped Yb³⁺-doped fiber laser is demonstrated using a laser diode stack as a pump source. Four subwavelength gratings fabricated on the same fused-silica substrate were aligned with four laser diode bars of the laser diode stack package for coupling pump light into double-clad fibers. Under the 975-nm pump power of 124.6 W, a 58 W Yb³⁺-doped fiber laser has been demonstrated. Due to the distributed pumping scheme, the nonuniformity of fiber heating from quantum defect is reduced as seen from the narrow linewidth of the fiber laser output across the entire pump power range. As a further step, the genetic algorithm method was used to design an aperiodic grating with a 40-nm fine structure. The adoption of the aperiodic grating, fabricated by using the E-beam lithography process, reduced the edge coupling loss effect, which allowed to reach 70% coupling efficiency. The side pumping scheme is compact and efficient, and power scaling is possible with more laser diode bars in the laser diode bar stacks. To the best of our knowledge, this is the first demonstration of a distributed pumped fiber laser using a laser diode bar stack as the pump source.