Metrological Characterization of a High-Temperature Hybrid Sensor Using Thermal Radiation and Calibrated Sapphire Fiber Bragg Grating for Process Monitoring in Harsh Environments.

Fiber Bragg gratings inscribed in single crystalline multimode sapphire fibers (S-FBG) are suitable for monitoring applications in harsh environments up to 1900 °C. Despite many approaches to optimize the S-FBG sensor, a metrological investigation of the achievable temperature uncertainties is still missing. In this paper, we developed a hybrid optical temperature sensor using S-FBG and thermal radiation signals.

High temperature sensing with fiber Bragg gratings in sapphire-derived all-glass optical fibers.

A structured sapphire-derived all-glass optical fiber with an aluminum content in the core of up to 50 mol% was used for fiber Bragg grating inscription. The fiber provided a parabolic refractive index profile. Fiber Bragg gratings were inscribed by means of femtosecond-laser pulses with a wavelength of 400 nm in combination with a two-beam phase mask interferometer.

Inscription of first-order sapphire Bragg gratings using 400 nm femtosecond laser radiation.

The paper describes the implementation of fiber Bragg gratings inscribed by femtosecond laser pulses with a wavelength of 400 nm. The use of a Talbot interferometer for the inscription process makes multiplexing practicable. We demonstrate the functionality of a three-grating multiplexing sensor and the temperature stability up to 1200 °C for a single first-order Bragg grating.