Variable ultrafast fiber Bragg grating inscription with a phase mask and a deformed wave front

Femtosecond inscribed fiber Bragg gratings (FBGs) have become more and more an integral part for monolithic fiber lasers in high power systems. These gratings overcome the requirements for photosensitive fibers in conventional UV-fabricated FBGs. Thus, the FBGs can be written directly into the active rare-earth doped fiber avoiding additional losses due to splices. One well established approach to inscribe gratings in fibers is the phase mask scanning technique. However, this method is limited in the flexibility due to the fixed period of the phase mask.