Study On Failure Mechanism Of Optical Fiber In Near Earth Orbit Environment

The space station built in near-Earth orbit is a national advanced equipment.Its significance lies in the development of large-scale space science experiments with human participation.It is also a pioneer in exploration of the universe.Therefore,the stable operation of the space station is of great significance to all countries.Optical fiber,as an important equipment of space cable communication,has the advantages of light weight,compact size,anti-electromagnetic interference and high stability.However,the complex environment of near-Earth orbit makes the operation of optical fiber challenging.Specifically,temperature and irradiation would introduce undesired transmission loss in optical fiber.In this dissertation,silver-doped fiber is coated to the outermost layer of the optical fiber to improve the irradiation resistance.In order to improve the performance of the low and high temperature resistance of the optical fiber,silicone rubber and acrylate are introduced and coated on the optical fiber cladding.The normal optical fiber is redesigned to meet requirement of working in the near-Earth space environment.The improved optical fiber is tested by low temperature,high temperature,irradiation,fourier transform infrared spectroscopy analysis and X-ray photoelectron spectroscopy experiment.The results achieved are as follows:(1)The transmission loss of optical fiber at high temperature(150℃)is about0.2d B/km,and that the counterpart at low temperature(-150℃)is about 3.5d B/km.The transmission loss does not change significantly at low temperature,indicating that low temperature is the main temperature factor affecting the transmission loss of optical fiber,and coating material of optical fiber is sufficient to cope with low temperature environment.(2)When the irradiation dose rates are 10rad/s,20rad/s and 50rad/s,respectively,Si-F defects and C=C defects will occur in optical fiber,while Si-OH defects only exist when the irradiation dose rates are 20rad/s and 50rad/s.It shows that different irradiation dose rates release different energies,which affect the binding between different molecules and thus lead to the formation of different defects.The defects formed under both low and room temperature conditions are basically the same,indicating that temperature is not the main reason for the formation of defects in optical fiber.(3)The fitting degree of the normal optical fiber under power rate model and piecewise multi-exponential saturation model is close to 0.99.The fitting degree of the radiation-resistant optical fiber in the segmented multi-exponential saturation model is close to 0.99,while the fitting degree in the power-law model is only about 0.7.It shows that the power rate model can only be used for the normal irradiation conditions,and the piecewise multi-exponential saturation model is suitable for complex irradiation environment.At the total irradiation dose of 18 Mrad,the maximum transmission loss of the irradiated optical fiber is 1.3d B/100 m,while that of the normal optical fiber is3.5d B/100 m.The transmission loss of irradiation-resistant optical fiber grows slowly in the pre-irradiation period and increases rapidly only in the post-irradiation period.This indicates that the silver-doped fiber barrier can significantly improve the irradiation resistance of optical fiber.