INSTITUTE OF APPLIED PHYSICS - Ultrashort pulse written Bragg gratings

Ultrashort pulse written Bragg gratings

Fiber Bragg grating
Fig.1: Fiber Bragg grating.

Bragg gratings are periodic modifications of the refractive index, which reflect light of a desired wavelength. These elements can be realized in various devices, most prominently in fibers [Laser Photonics Rev., Vol 6 (6) pp. 709-723 (2012)]. The applications of such Fiber Bragg gratings (FBGs) range from robust sensors to integrated cavity mirrors of fiber lasers. In contrast, Volume Bragg Gratings (VBGs) are structures generated inside bulk volume (e.g. pure fused silica) [Applied Physics A Vol. 102 (1) pp. 617-620 (2010)].

Volume Bragg grating
Fig.2: Volume Bragg grating.

They serve as important elements for frequency stabilization of lasers, free beam pulse compresssion or high power beam combining. Conventional means to fabricate Bragg gratings with long pulse UV-lasers rely on photo-sensitized glasses. This requirement limits the flexibility in terms of host material, e.g. the inscription in highly rare earth doped fiber cores or in phosphate glasses is barely possible.

If ultrashort pulse lasers are employed to inscribe Bragg gratings many of these limitations can be overcome:

Inscripion setup for FBGs
Fig.3: Inscripion setup for FBGs.

- Inscription into various non-photosensitive glasses

- Inscription into highly doped laser fibers

- Tailored multimodal response of FBG due to adjusted geometry of Bragg grating

- Resilience against bleaching and temperatures up to 1000°C.

Illuminated phase mask and fiber
Fig.4: Illuminated phase mask and fiber.