Graded‐Index Ytterbium‐Doped Optical Fiber Fabricated through Vapor Phase Chelate Delivery Technique

Herein, the fabrication of ytterbium‐doped graded refractive‐index few‐mode fiber (GRIN‐FMF) is described for the first time following a vapor phase chelate delivery technique. Investigation is carried out to find out the best possible approach to fabricate the preform. The optimization of the process steps along with composition and associated process parameters leads to a parabolic refractive‐index profile with a profile parameter of 2 in the developed fiber. A large core of 30 μm diameter and a low numerical aperture (NA) of 0.08 with graded distribution of dopant ions is achieved with a good repeatability. Amplification gain of more than 20 dB with good beam quality for pulses with kW peak power without any distortion in temporal, spectral, and spatial profile proves the potential of the fiber for many promising applications.