Development and analysis of a fiber-optic temperature sensor based on two superposed regenerated fiber Bragg gratings

Subject of study. A fiber-optic temperature sensor based on two superposed regenerated fiber Bragg gratings is studied. Aim of study. A fiber-optic temperature sensor with a range of +25 ∘ C to +1000 ∘ C based on two superposed regenerated fiber Bragg gratings is developed, and the temperature sensitivity of the resulting sensor is determined. Method. Two superposed standard fiber Bragg gratings (length of 14 mm) with reflectivities of 90% and 70% were heated (heating rate of 500°C/h) from room temperature to the regeneration temperature of 920°C, appropriate for optical fibers meeting the G.657.A2 standard; the gratings were held at this temperature pending complete formation of the regenerated structure. Main results. The development effort and thermal studies (which were performed over a temperature range from +25 ∘ C to +1000 ∘ C with steps of 100°C) led to the development of a fiber-optic temperature sensor based on superposed regenerated fiber Bragg gratings with reflectance and temperature sensitivities of approximately 40% and 12.7 pm/°C and approximately 30% and 12.72 pm/°C, respectively. Practical significance. This paper marks the first, to our knowledge, successful superposition of two regenerated fiber Bragg gratings with reflection coefficients greater than 40% and 30%. The sensor developed based on this structure has a wider temperature measurement range with a narrow range of probe wavelengths. This paper also marks the first determination of the temperature sensitivity of a regenerated fiber Bragg grating as a function of its central reflection wavelength.