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1Factors affecting the radiation resistance of optical fibers exposed
to ionizing radiation
LAzanova1*, Yu. Sharonova1, E. Lunegova1, D. Khisamov1
1- Open Joint-stock company "Perm Scientific-Industrial Instrument Making Company"
* azanova@pnppk.ru
Silica-based optical fibers (OF) are widely applied in various industries for telecommunication, monitoring systems and fiber-based sensors. There are severe and harsh environments, which associated with ionizing radiation. When optical fibers are under ionizing radiation it causes generation of optically active point defects - radiation color centers (RCC), which absorb light at different wavelengths. The phenomenon of the optical absorption caused by colour centers is known as radiation induced attenuation (RIA).
When using optical fibers in fiber-based systems, a certain budget for optical losses is included. This budget is determined by the optical power of the light-source and the dynamic range of the photodetector so that the total optical losses in the system do not exceed this budget over the entire operating temperature range. The loss budget includes losses at welded splices and connections, optical attenuation along the length of the optical fiber, an increase in optical attenuation caused by increased or decreased temperatures and mechanical deformations. RIA is also a part of this budget, so there is necessarily a total limit on RIA. RIA depends not only on the total ionizing dose, dose rate, type of radiation, but also on such operational factors as temperature, an operating wavelength, injected optical power level, level of stress-strain state of the optical fiber. The purpose of this work is to show the influence of operational factors on RIA levels.
Operating wavelength. The most common types of OF are germanium-doped (GeO2) or pure-silica core (PSC) (SiO2) fibers. For both types of fibers, the most disadvantageous wavelength for application in radiation environments is 850 nm, as opposed to the wavelength of 1550 nm, where RIA levels are minimal. It should be noted that the wavelength of 1550 nm has minimum losses at the hall range from 200 to 1700 nm [1,2].
Temperature and injected optical power. The RIA of optical fibers is determined by the operation temperature as well as by the injected optical power level. For same injected optical power 0.1 ^W at same operating wavelength the difference in RIA levels for temperatures +25°C and -60°C can reach more than 10 dB/km. At the same time, by increasing the optical power level to 1 -5 mW, this difference could be significantly reduced [3].
Dose rate through the example of anisotropic OF "Panda". To use OF in space it has to work at the dose rate about 10-5 Gy/s. Furthermore, to cut the time tests are usually carried at a significantly higher dose rate at about 100 Gy/s. However, for some applications there is a need to know under real irradiation conditions at average dose rates [4]. The tests results of RIA levels in the anisotropic OF "Panda" with SiO2 core have been obtained at the dose rate from 0.05 to 350 Gy/s. So, the RIA predictably increases with increasing the dose rate, but it should be noted that, starting with the dose rate of 10 rad/s, no correlation is observed.
Thus, the conscious choice of the operating wavelength, environment temperature and injected optical power allows us to reduce the RIA levels during exploitation.
[1] S. Girard, et al, Radiation effects on silica-based optical fibers: Recent advances and future challenges, IEEE Transactions on Nuclear Science, vol. 60, pp. 2015-2036, (2013).
[2] P. Kashaykin, A. Tomashuk, V. Khopin, et al, Gamma Radiation Induced Attenuation in Ge-doped Fibers in Near IR Range: Influence of Irradiation Temperature and Doping Level, GeY-center, OSA Advanced Photonics Congress, (2018).
[3] A. Paveau, G. Cros, S. Masson, R. Mangeret, S. Marioujouls, J.J. Bonnefois, Robustness of Astrix Fiber Optic Gyros in space radiative environment, CEAS Space Journal, №11, pp. 219-227. (2018).
[4] E. Friebele, M. Gingerich, D. Griscom, Survivability of optical fibers in space, Optical materials reliability and testing: Benign and adverse environments, International Society for Optics and Photonics, vol. 1791, pp. 177-189, (1993).
