With the development of high power fiber oscillators, it is urgent to fabricate fiber Bragg gratings (FBGs) on large core fibers. Here, a pair of FBGs in fibers with core diameter of 30 μm are fabricated based on femtosecond laser phase mask scanning method. The reflectivity of high-reflectivity FBG (HR-FBG) is more than 99% with the central wavelength of 1080 nm and the 3dB bandwidth of 3.6 nm. The reflectivity of output coupler FBG (OC-FBG) is about 10% with the central wavelength of 1079.8 nm and the 3dB bandwidth of 2 nm. Furthermore, an all-fiber oscillator is built based on the fs-written FBGs, and the maximum output power of 6.4 kW is realized with the optical-optical conversion efficiency of 74%. The temperatures of HR-FBG and LR-FBG are 90 and 49℃, respectively. This work demonstrates that the large core diameter FBG written by femtosecond laser has excellent performance, which is of great significance for the development of high power fiber oscillators.
We report here a monolithic all-fiber laser oscillator with femtosecond-written FBGs and side-pumping coupler. The splice-free resonant cavity is realized by directly writing a pair of fiber Bragg gratings (FGBs) into an ytterbium-doped fiber (YDF) based on the femtosecond laser phase mask scan method. Furthermore, a (2+1)×1 side-pumping coupler is fabricated in the same YDF by the taper-fused method. When pumping with two 976 nm laser diodes (LD), a maximum output power of 1218 W is realized at the 1070 nm, corresponding to the optical-optical conversion efficiency of about 71%. This work displays an extremely compact and stable fiber laser oscillator, which is of great significance to the development of high power fiber lasers.
Mid-infrared fiber lasers have shown out standing prospects in many fields, so mid-infrared fiber Bragg grating (FBG) as the most essential component in mid-infrared fiber laser oscillators has attracted much attention. Here, we fabricated mid-infrared FBGs on ZBLAN fibers operating nearby 2.8-2.9 μm by femtosecond laser direct inscription technique, and measured their transmission spectra by all-fiber measurement system, which lays the foundation of high-power all-fiber mid-infrared laser oscillators near 2.8 μm.
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