Rearch On Thermal Damage Of Silica Optical Fiber

As one of the common fibers,silica optical fiber is widely used in optical fiber communications because of its ideal optical performance,low price,simple preparation and high stability.However,in high power laser systems,the optical fiber is prone to getting thermal damage after laser irradiation,which affects the transmission efficiency of the whole system.At present,how to improve the thermal damage resistance of quartz fiber has become one of the research hotspots.However,due to the lack of understandings on silica optical fibers’ thermal damage,various treatment methods in experiment have their limitations.In order to further improve the thermal damage resistance of optical fiber,it is necessary to explore the internal mechanism of thermal damage of optical fiber.The main contents of this paper are as follows:(1)The construction of simulated high power laser system and the calculation of laser-induced damage threshold.Through literature research,experimental devices of laser-induced thermal damage are investigated.After optimization,the model of the simulation system is constructed and the physical parameters of quartz fiber are added.With the wave functions,the effective laser-induced damage threshold of silica optical fiber is calculated by the incident and actual electric field intensity distributions.(2)The calculation of thermal effects caused by high power laser in the silica optical fiber.Based on the wave optics and geometric optics,the photothermal coupling equation is constructed.The temperature distribution of silica optical fiber is calculated under steady-state heat transfer method.The thermal coupling equation is constructed by thermal deformation theory.Then the thermal stress and axial strain of silica optical fiber are studied.With the increase of laser fluence,the tendency of the maximum temperature and thermal strain is analyzed.(3)The analysis of thermal damage types and appearance of silica optical fiber.The laser fluence is set to the value higher than the effective laser-induce damage threshold of silica optical fiber surface.Under the above laser irradiation,the temperature and thermal strain distribution of silica optical fiber are calculated.It is found that the melting damage occurs at the center of incident surface.Further research shows that the damage area of melting damage is larger than that of thermal stress damage.The study indicated that the incident surface center of silica optical fiber is the most vulnerable area to get heat damage,and the main damage type is melting damage caused by high temperature.From a macro point of view,based on the finite element method and heat transfer theory,this paper reasonably constructs the ideal silica optical fiber model and high power laser transmission system.The research can provide theoretical support for clarifying the thermal damage mechanism of silica optical fiber,improving the anti-damage ability of fibers,improving the stability of transmission system and broadening the application field of high-power laser.