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为了研究金属镀层对光纤宏弯损耗性能的影响,建立了带金属镀层的光纤环所受热应力及热应力引起的弹光效应的数学模型。计算了金属镀层光纤环的热应力系数和折射率热应力系数。仿真分析了光纤环向热应力系数Kθt、径向热应力系数Krt和折射率热应力系数Kn的主要影响因素。结果表明:Kθt远大于Krt,光纤主要受到环向热应力,径向热应力可忽略;热应力及其引起的折射率变化与径向位置和镀层厚度有关,与光纤环的弯曲半径基本无关;镀层厚度在0~2000μm范围内,随着厚度增加,Kθt和Kn均会先快速增大,再缓慢增大并趋于稳定;Kn为负值,随着温度增加,热应力将引起光纤折射率逐渐减小。该模型从理论上解释了金属镀层光纤环的热应力会引起光纤折射率变小,从而改变光纤的宏弯损耗。
In order to study the influence of metal coating on the performance of macro-bending loss of optical fiber, a mathematic model of thermal stress and thermal-elastic effect caused by optical fiber ring with metal coating was established. The thermal stress coefficient and refractive index thermal stress coefficient of the metal coated fiber ring were calculated. The main influential factors of the fiber hoop thermal stress coefficient Kθt, the radial thermal stress coefficient Krt and the refractive index thermal stress coefficient Kn are analyzed. The results show that Kθt is much larger than Krt. The optical fiber is mainly subjected to circumferential thermal stress and the radial thermal stress is negligible. The thermal stress and its refractive index change are related to the radial position and the thickness of the coating, The thickness of coating is in the range of 0 ~ 2000μm. With the increase of thickness, Kθt and Kn will increase rapidly first and then slowly increase and stabilize. Kn value is negative. As the temperature increases, thermal stress will cause the refractive index of fiber slowing shrieking. The model theoretically explains that the thermal stress of the metal coated optical fiber ring will cause the refractive index of the optical fiber to become smaller, thereby changing the macrobending loss of the optical fiber.