Fiber Bragg Grating High Temperature Sensor

High temperature resistant Fiber Bragg Grating (FBG) sensors are specialized optical sensors capable of operating reliably at temperatures exceeding 600°C, with some designs tolerating up to 1000°C or more.

Overview

High temperature FBG sensors are optical devices inscribed in fibers that reflect specific wavelengths of light, which shift in response to temperature or strain changes. Unlike conventional FBGs, these sensors are engineered to withstand extreme thermal, mechanical, and chemical conditions, making them suitable for applications in turbines, aerospace, oil and gas exploration, power plants, and nuclear reactors ( ). Types of High Temperature FBGsType I and Type 1n FBGs: Stabilized gratings suitable for moderate high temperatures, typically up to 400–500°C.

They are created by UV inscription and subsequent thermal annealing to improve stability ( ).

Regenerated FB

Gs (R-FBGs): These are designed to survive temperatures above 600°C. The original grating is thermally erased and a new, thermally stable grating is regenerated, often using hydrogen-free silicate fibers and prolonged UV or continuous-wave irradiation ( ).

Femtosecond Laser-

Written FB

Gs (IR-fs-FBGs): Inscribed point-by-point using femtosecond infrared lasers, these gratings can operate in extreme environments, including temperatures beyond 800°C, and are resistant to thermal erasure and radiation, making them suitable for nuclear reactor monitoring ( ).

Sapphire Fiber FB

Gs: Made from single-crystal sapphire fibers, these gratings can withstand ultrahigh temperatures exceeding 1000°C and are ideal for harsh industrial or aerospace applications ( ).

Coatings and Packaging

To enhance durability, high-temperature FBGs often use metallic coatings such as gold, copper, aluminum, or steel. These coatings provide mechanical protection, hermetic sealing, corrosion resistance, and improved sensitivity. Polyimide coatings are also used for high-temperature applications up to 400–500°C ( ).

Applications

Industrial Monitoring: Temperature profiling in furnaces, turbines, and combustion engines ( ). Energy Sector: Monitoring diesel engines, geothermal wells, and oil drilling operations at depths with temperatures exceeding 500°C ( ). Nuclear Reactors: On-line monitoring of liquid sodium-cooled fast reactors, where sensors must withstand high temperatures, radiation, and strain ( ).

Aerospace: Turbine and engine monitoring under extreme thermal and mechanical stress ( ).

Advantages

High sensitivity and precision in temperature and strain measurement. Immunity to electromagnetic interference. Capability for multiplexing multiple sensors on a single fiber.

Long-term stability in harsh environments when properly regenerated or coated ( ). High temperature FBG sensors represent a critical technology for real-time monitoring in extreme environments, combining optical precision with thermal and mechanical resilience.