Are fiber Bragg gratings heat-resistant and at what temperature

Fiber Bragg gratings can be heat-resistant, with certain types operating reliably at temperatures from 300°C up to 1,900°C depending on the material and fabrication method.Standard and High-Temperature FBGsStandard FBGs, typically written in silica fibers, are generally designed for operation up to 100–400°C, depending on the fiber coating and grating type. Polyimide-coated FBGs, for example, can withstand temperatures up to 400°C for extended periods, though their performance may degrade if exposed to higher temperatures for long durations (thermal cycling experiments have tested up to 1,000°C with partial signal recovery) . High-temperature resistant FBGs, such as regenerated FBGs (R-FBGs) or femtosecond-written FBGs (IR-fs-FBGs), are specifically engineered to survive extreme environments. These gratings can operate continuously at temperatures exceeding 600°C, with some designs functioning reliably up to 800°C and beyond 1,000°C, making them suitable for applications like nuclear reactor monitoring .Sapphire Fiber Bragg Gratings (SFBGs)For ultra-high temperature applications, sapphire fiber Bragg gratings offer exceptional thermal stability. First-order SFBGs have been tested short-term up to 1,900°C and for 28 days at 1,400°C, maintaining precise temperature sensing capabilities. These gratings are also resistant to electromagnetic interference and can operate in air or inert atmospheres, making them ideal for industrial processes involving molten metals, glass, or ceramics .Summary of Temperature RangesStandard FBGs: -40°C to ~100–400°CHigh-temperature FBGs (R-FBG, IR-fs-FBG): 300°C to >1,000°CSapphire FBGs (SFBG): up to 1,900°C short-term, 1,400°C long-term In conclusion, the heat resistance of FBGs depends on the fiber type, grating fabrication method, and protective coatings. For extreme high-temperature applications, regenerated or sapphire-based FBGs are recommended, while standard FBGs are suitable for moderate temperatures.