Type I and II Bragg gratings made with infrared femtosecond radiation in high and low alumina content aluminosilicate optical fibers

Aluminosilicate fibers have very low Brillouin scattering gain coefficients, making them interesting fibers for nonlinear optical applications. We manufactured Bragg gratings in high (30 mol.%) and low (4 mol.%) alumina content optical fiber using 800 nm femtosecond pulse duration radiation and a phase mask. Grating spectral characteristics and thermal behavior are presented. Index modulations >10⁻³ were generated for fundamental pitched Bragg gratings, and >10⁻⁴ for higher-order gratings. Gratings were annealed at temperatures up to 900°C. Type II gratings written in fibers with lower alumina content showed better thermal stability than gratings written in fibers with higher alumina content. Bragg gratings in these fibers would be well suited as laser cavity mirrors in high-energy laser systems, as well as in telecommunication and sensor systems where Brillouin scattering restricts power scaling.