High-index-contrast Bragg gratings fabricated in fluoride fiber with 513-nm femtosecond laser

摘要

We report the femtosecond laser inscription of fiber Bragg gratings (FBGs) in an Er-doped fluoride glass fiber used forlasing at a mid-infrared wavelength of 2.8 μm. FBG reflectivity and laser output power are observed with varying theindex change of grating plane. We have tried to create high-index-contrast grating planes worked as Bragg reflector. Theindex change was estimated by fitting experimentally obtained reflectivity to its calculation. When using laser fluencesof 25 and 40 J/cm~2, the index change was found to be 0.7×10~（-3） and 1.1×10~（-3）, respectively. When using laser fluence of 25J/cm2, FBG reflectivity increases up to 95% at the grating length of 4.0 mm. The case of using 40 J/cm2 shows 97% atthe grating length of 2.5 mm. These results are in agreement with the reflectivity calculation. The investigation of lasingevolution will contribute to more efficient fabrications of FBG and fiber laser system.