Abstract
A Fiber Bragg grating of 369 nm pitch was inscribed in a germanium-free double-clad ytterbium doped silica fiber using a femto-second pulse train at 400 nm wavelength and a phase mask. The photo-induced refractive index modulation of higher than 4 x 10(-3) was obtained and the accompanying photo-induced losses were subsequently removed by thermal annealing, resulting in a low loss (<0.1 dB), stable and high reflectivity (>40 dB) FBG. Based on this FBG, a monolithic Ytterbium fiber laser operating at 1073 nm with slope efficiency of 71% and output power of 13 W was demonstrated.
Highlights
The refractive index change resulting from the nonlinear interaction of focused femtosecond pulses with glasses turned out to be a very promising alternative to the defect-resonant UV-induced physical process, which is commonly used for writing fiber Bragg gratings (FBGs) in silica fibers [1,2]
A Fiber Bragg grating of 369 nm pitch was inscribed in a germanium-free double-clad ytterbium doped silica fiber using a femtosecond pulse train at 400 nm wavelength and a phase mask
The photoinduced refractive index modulation of higher than 4x10−3 was obtained and the accompanying photo-induced losses were subsequently removed by thermal annealing, resulting in a low loss (40dB) FBG
Summary
The refractive index change resulting from the nonlinear interaction of focused femtosecond pulses (fs) with glasses turned out to be a very promising alternative to the defect-resonant UV-induced physical process, which is commonly used for writing fiber Bragg gratings (FBGs) in silica fibers [1,2]. It employs on a tightly focused spot of the fs pulses at 800 nm and a high precision positioning stage [7] Using this technique, a third order FBG with a peak reflectivity estimated to be 90% was inscribed directly in a ytterbium doped double-clad fiber and the laser operation of 5W at 1080 nm with a slope efficiency of 46% was first reported [8] before the power was eventually scaled up to 100W with a slope efficiency of 64% [9]. We report what we believe is the first demonstration of a fundamental order Bragg grating written directly in a non-photosensitive double-clad ytterbium doped silica fiber It is accomplished with 400 nm fs pulses and a phase-mask. Based on this FBG we demonstrate a fiber laser with a slope efficiency of 71% and a maximum output power of 13W, which was only limited by the pump power
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