VezelBragggratings

VezelBragggratings, more commonly known in English as fiber Bragg gratings, are periodic variations in the refractive index of an optical fiber core that reflect specific wavelengths of light while transmitting others. They are typically inscribed within the core of standard optical fibers and can be designed as narrowband reflectors or broader filters.

The reflected wavelength, called the Bragg wavelength, is approximately lambda_B = 2 n_eff Lambda, where n_eff is the effective refractive index of the core mode and Lambda is the grating period. Small changes in temperature or axial strain alter either n_eff or Lambda, causing a shift in lambda_B. This sensitivity enables precise wavelength-based sensing and tuning.

Manufacture of fiber Bragg gratings commonly uses ultraviolet light to induce index modulations in photosensitive, often germanium-doped, silica fibers. A phase mask or interferometric setup defines the grating pattern. Variants include chirped gratings (varying Lambda for broader reflection), apodized gratings (reduced sidelobes), and tilted gratings (coupling to cladding modes). Femtosecond-laser inscription is another method, enabling gratings in photosensitive and non-photosensitive fibers.

Applications span telecommunications and sensing. In communications, FBGs act as wavelength-selective mirrors in fiber lasers and as narrowband filters or dispersion controls. In sensing, they monitor temperature, strain, or pressure, enabling structural health monitoring and distributed sensing when used in arrays. Their all-fiber form offers compactness and immunity to electrical interference but requires careful temperature and strain compensation and a suitable interrogation system.