Types of Fiber Bragg Grating Sensors

FBG sensors are classified based on fabrication methods, fiber types, and functional characteristics, enabling tailored applications in strain, temperature, and multi-parameter sensing.

Classification Based on Fabrication Methods

FBG sensors can be categorized according to the technique used to inscribe the grating on the optical fiber:

• UV-written FBGs using phase masks: The most common method, where ultraviolet light passes through a phase mask to create periodic refractive index variations in the fiber core .
• Direct-written FBGs during fiber drawing: Gratings are inscribed while the fiber is being drawn from preforms, allowing integration into specialty fibers .
• Femtosecond laser-written FBGs: Includes both phase mask and point-by-point inscription methods, suitable for high-precision or photosensitive fibers .

Classification Based on Fiber Type

FBG sensors are also classified according to the type of optical fiber used:

• Standard silica fibers: Commonly used for general strain and temperature sensing .
• Polyimide-coated fibers: Provide enhanced thermal and chemical resistance for harsh environments .
• Polarization-maintaining fibers: Maintain polarization state, useful in interferometric or polarization-sensitive applications .
• Multi-core fibers: Enable simultaneous multi-point or multi-parameter sensing along a single fiber .

Classification Based on Functional Characteristics

FBG sensors can be further distinguished by their sensing capabilities:

• Strain sensors: Measure mechanical deformation by detecting shifts in the Bragg wavelength .
• Temperature sensors: Detect thermal variations through wavelength shifts caused by thermal expansion and refractive index changes .
• Multi-parameter sensors: Combine strain and temperature measurements or integrate additional sensing modalities for complex monitoring applications .

Summary

FBG sensors are versatile optical devices whose classification depends on fabrication technique, fiber type, and sensing function. This classification allows engineers to select appropriate FBG sensors for applications ranging from structural health monitoring and aerospace to biochemical and environmental sensing, leveraging their high sensitivity, immunity to electromagnetic interference, and multiplexing capabilities .