Classification and Characteristics of Fiber Bragg Gratings

Fiber Bragg Gratings (FBGs) are classified primarily by fabrication method, fiber type, and functional characteristics.Classification by Fabrication MethodFBGs can be categorized based on how the periodic refractive index modulation is inscribed in the fiber core :UV-written FBGs: Created using ultraviolet lasers and phase masks to induce periodic changes in the fiber core.Direct-written FBGs: Inscribed during the fiber drawing process in preforms.Femtosecond laser FBGs: Include phase mask or point-by-point inscription methods, allowing high precision and operation in harsh environments.Classification by Fiber TypeThe type of optical fiber used also defines FBG categories :Polyimide-coated FBGs: Suitable for high-temperature applications.Polarization-Maintaining FBGs: Preserve the polarization state of light, useful in interferometric sensing.Multi-Core FBGs: Inscribed in fibers with multiple cores for advanced sensing or multiplexing applications.Classification by Functional CharacteristicsFBGs can also be classified based on their optical behavior and application :Standard FBGs: Uniform periodic modulation reflecting a narrow wavelength band.Chirped FBGs: Grating period varies along the fiber length, used for dispersion compensation and pulse shaping.Apodized FBGs: Gradual variation in refractive index to suppress spectral sidelobes.Tilted FBGs: Grating planes are angled to create notch filters or couple light to cladding modes.Long-Period FBGs: Periods are much longer than standard FBGs, used for gain equalization and filtering in telecom systems.Surface-Relief FBGs: Physically etched gratings for high-temperature or harsh environment operation. These classifications help in selecting the appropriate FBG type for telecommunication filtering, fiber lasers, or sensing applications such as temperature, strain, and pressure measurements .