Observation of temperature dependence of the IR hydroxyl absorption bands in silica optical fiber

• We measured OH absorption in silica optical fiber from 20 °C to 800 °C in-situ.
• We observed decreasing intensity in the 2200 nm band at elevated temperatures.
• We observed peak wavelength shift in the 1390 nm band when temperature was increased.
• The temperature dependence in both bands is reversible.
• The phenomenon is related to the conversion of the OH spectral components and structural relaxation.

This study reports on the temperature dependent behavior of silica based optical fibers upon exposure to high temperatures in hydrogen and ambient air. The hydroxyl absorption bands in the wavelength range of 1000–2500 nm of commercially available multimode fibers with pure silica and germanium doped cores were examined in the temperature range of 20–800 °C. Two hydroxyl-related infrared absorption bands were observed: ∼2200 nm assigned to the combination of the vibration mode of Si-OH bending and the fundamental hydroxyl stretching mode, and ∼1390 nm assigned to the first overtone of the hydroxyl stretching. The absorption in the 2200 nm band decreased in intensity, while the 1390 nm absorption band shifted to longer wavelengths with an increase in temperature. The observed phenomena were reversible with temperature and suspected to be due, in part, to the conversion of the OH spectral components into each other and structural relaxation.