Line-by-line type-X FBGs with high-temperature stability and low loss

We present a method for inscribing line-by-line high-temperature stable low-loss Type-X fiber Bragg gratings, producing Type-I like modification profiles with Type-II like stability, without the loss characteristics of Type-II index change. We examined the deleterious effects of overwriting the same grating plane and identified the impact of grating order on Type-X formation. A single scan for each plane, at the maximum energy before microscopic scattering damage effects are observed, at grating orders greater than m = 2 is the optimal region to inscribe low-loss high-temperature stable Type-X FBGs. Arrays of gratings are fabricated to test grating performance, and two isochronal annealing experiments confirm the high temperature stability of Type-X FBGs to >1000 °C.