CHIRPED FIBER BRAGG GRATINGS
Due to a variation of the refractive index modulation within the FBG along the fiber, an optical chirp of the wavelength is generated. This FBGs have a broad bandwidth of several nm and a flat top profile instead of the typical Gaussian shape. Typical applications are WDM 1300/1550nm band rejection filter, ASE filtering, noise suppression or in-fiber mirrors.
LASER DIODE STABILIZERS (LDS)
A very common application of FBGs is the stabilization of DFB laser modules. They are applicable to pump lasers for EDFAs 980/1480nm as well as for WDM modules for the 1300/1550nm band. Typical applications include also in-fiber resonators for RAMAN fiber lasers or tunable laser modules.
WAVELENGTH SELECTIVE FILTERS FOR TELECOMMUNICATIONS
FBGs are widely used in optical communications as in-fiber narrow band filters, e.g. for DWDM technology for 2.5 Gbps and 10 Gbps systems, ASE filtering or Add/Dropmultiplexers for 100GHz and 50GHz channel spacing.
The fiber Fabry-Perot Interferometer is a pair of matching FBGs. In this case an extremely small phase shift can be detected; for sensing purposes and to evaluate small vibrations or acoustic signals. By coating the fiber between the gratings with an electric, magnetic or acoustic enhancing coating small changes can be measured.
Special fibers show advantages for certain applications. Sapphire fibers for example have extreme temperature stability and therefore expand the sensing range above 1,000°C. Radiation hard fibers withstand high radiation and can be used in nuclear environments.