Abstract
This letter reports the fabrication of fiber Bragg gratings (FBGs) within in-house fabricated fluoroaluminate (AlF<sub>3</sub>) glass fibers using femtosecond (fs) laser inscription at 800 nm. The grating strength of the FBGs was investigated for different pulse energies and different orders, and a 3rd-order FBG with Bragg wavelength at 1557 nm was found to have the highest reflectivity of 99.5%. In addition, the reflectivity of the mid-IR grating peaks for different orders was also studied, and a 2nd-order FBG with a reflectivity of 98.8% was obtained at 2864 nm. Finally, the temperature characteristics of a mid-IR FBG were studied between 30 °C and 150 °C, showing a linear wavelength dependence and an excellent stability for the refractive index modulation. Such highly reflectivity FBGs in AlF<sub>3</sub> fiber have significant potential for applications in the development of compact all-fiber mid-IR fiber lasers.
Highlights
This letter reports the fabrication of fiber Bragg gratings (FBGs) within in-house fabricated fluoroaluminate (AlF3) glass fibers using femtosecond laser inscription at 800 nm
FBGs fabricated by a direct fs laser inscription in fluoride glass fibers offers extreme flexibility in terms of structure design compared with phase mask method
This paper reports FBGs operating at λB ~1557 nm and λB ~2864 nm, which are successfully inscribed into AlF3 fibers using an fs laser and a line-by-line directwriting method
Summary
LUORIDE glass with a transmission window low phonon energy and broad ranging from Ultraviolet (UV). In 2017, Bharathan et al wrote FBGs with a reflectivity of ~50% in a Ho3+/Pr3+ co-doped double-cladding ZBLAN fiber using line-by-line direct-writing technique, and achieved a laser output efficiency of 17% at λ ~2.88 μm [10]. In 2018, Goya et al fabricated an FBG with 97% reflectivity and Δn ~1.1×10-3 in Er3+ -doped ZBLAN fiber using a planeby-plane direct-writing technique, demonstrating a laser output. AlF3 fiber has a great potential to develop a practical highpower MIR fiber laser at room temperature without the complexity of additional environmental protection, for example, Wang et al obtained a 10.4% laser output efficiency at λ ~2.9 μm by pumping a Ho3+/Pr3+ co-doped AlF3 fiber in 2019 [16]. FBGs fabricated by a direct fs laser inscription in fluoride glass fibers offers extreme flexibility in terms of structure design compared with phase mask method. A mechanical shutter was used to block the laser pulse train during the movements represented by the dashed path
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