Wide Dynamic Range Optical Power Control Based on Cascaded Fused Tapered Couplers for High-Power Yb-Doped Fiber Lasers

Wide dynamic-range optical power control was achieved in a novel all-fiber device for a high-power Yb-doped fiber laser input using a serially cascaded fused tapered coupler pair. Torsional stress was independently applied over the coupling zones, which resulted in phase changes by photoelastic effects and subsequent linear shifts in transmission spectra. Dynamic range of 46 dB and low insertion loss below 1 dB were achieved for 1060-nm fiber laser with the incident fiber coupled power of 3.4 W. The detailed fabrication process of the device, characterization, and theoretical background are discussed.