Ultrashort Pulse Written Volume & Fiber Gratings
Using ultrashort laser pulses, periodic modifications of the refractive index can be integrated into various transparent materials, e.g. pure fused silica, photosensitive glasses and rare earth doped glasses. With periods in the range of 1 µm, these Bragg gratings reflect light of a desired wavelength. The reflected spectrum can be highly tailored to individual needs by adapting the grating properties. Two approaches for the inscription are used: flexible direct inscription via point-by-point or line-by-line, and highly reproducibly and stable phase mask inscription technique.
Written into bulk volume, these so-called volume Bragg gratings (VBG) can be utilized for a broad range of applications such as beam frequency filters, combiners as well as spectral stabilizers of laser diodes and diode bars. Inscribed directly into fused silica, they show excellent thermal stability under high power conditions.
Written into the core of fibers, these so-called fiber Bragg gratings (FBG) offer vast application possibilities ranging from robust sensors, dispersive elements, integrated cavity mirrors for (high) power fiber lasers to compact tailored wavelength filters. Alternatively, so-called long period fiber gratings (LPFG) have periods in the range of 100µm to 1000µm, acting as transmission gratings, where modal content of specific modes at desired wavelengths can be transferred into other modes (e.g. cladding modes).