Devitrification in annealed optical fiber

Abstract

Abstract-The decrease in transmittance of annealed optical fiber has been measured versus temperature and time. The annealing loss is due to the devitrification of the glass and OH absorption in the 1200 to 1500 nm wavelength region. Both loss mechanisms propagate primarily from the surface into the core. However, to increase the OH absorption significantly, annealing times greater than 10 h are required. Fibers heated from 1000 to 1300 C in an air atmosphere quickly devitrify and their transmittance approaches zero. Also, the current sensitivity of annealed fiber current sensors versus annealing time at 850 C has been measured. A decrease in the current sensitivity is attributed to devitrification in the fiber.

Test of fiber optic based current sensors on the Tore Supra tokamak

“…The reflection mode is even more attracting because the signal to noise ratio is much bigger and it allows cancelling partly the reciprocal effects such as the linear birefringence. The Verdet constant complies with the physical value given at 0.6% accuracy by [8]. Very small deviations of about 0.72% in the long term have been observed in reflection mode.…”

“…The Verdet constant of the 3 types of fiber is similar of the order of 0.7 rad/MA which is close to the expected value at = 1550 nm [8]. On the other hand, the standard deviation of the linear birefringence can vary widely underlying the influence of the external perturbation (temperature and vibration) without affecting the determination of the Verdet constant.…”

“…In addition in the case of ITER, IR wavelengths are preferable due to the low radiation-induced absorption associated to that spectral range. The Verdet constant at 1550 nm is about 0.71 rad/MA ±0.6% [8] which is sufficient to measure large plasma current.…”

“…where V is the Verdet constant (magneto-optic constant) for silica (fiber material) and depends on the light wavelength [8]; I is the current flowing through the area defined by the optical fiber; 0 is the vacuum permittivity. The circular birefringence is a nonreciprocal effect, meaning that a light beam passing a medium twice in opposite direction acquires a net rotation twice that of a single pass.…”

Effect of temperature and irradiation on fused silica optical fiber for temperature measurement

“…The spectral shape does not change though the optical intensities of the peaks become large. It is reported that the OH in optical fiber is influenced by the experimental atmosphere [7]. Thus, it is considered that the amount of OH, which is the origin of the peaks, increased during heat treatment at 1000°C in the air.…”