High absorption and low splice loss properties of hexagonal double-clad fiber

An accurate experimental comparison of the pump absorption and the lasing features between Nd³⁺ -doped fiber lasers using hexagonal-shaped and D-shaped fiber is reported. The measured slope efficiencies with respect to the absorbed pump power of 805 nm are nearly identical at ∼65.3% for both fibers. Taking advantage of the near symmetrical shape of the hexagonal fiber, the lowest reported splice loss of 0.05 dB is achieved between the double-clad fiber and standard 125-μm fiber with the use of the fiber etching techniques. The pump absorption can be improved by bending the hexagonal fibers into a kidney shape.