Using ultrashort laser pulses, periodic modifications of the refractive index can be integrated into various transparent materials, e.g. pure fused silica, photosensitive glasses as well as rare earth doped glasses. With periods in the range of 1µm, these Bragg gratings reflect light of a desired wavelength and they can be written into bulk volume, as so-called volume Bragg gratings (VBGs) or into the core of fibers as fiber Bragg gratings (FBGs). Alternatively, so-called long period gratings (LPGs) 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).

Further information:
- Volume Bragg gratings (VBGs)
- Fiber Bragg gratings (FBGs)
- Long period gratings (LPGs)

1 Bragg_Overview_01_VolumeBraggGrating
Fig.1: Volume Bragg grating. (Rights: C.Voigtländer)
2 Bragg_Overview_02_FiberGrating
Fig.2: Fiber grating. (Rights: R.Krämer)