用波动理论分析双包层光纤的吸收效率

Analysis of Absorption Efficiency of Double-Clad Fiber Using Wave Theory

基于波动理论,运用WKB方法,根据双包层光纤中单模掺杂纤芯的半径和偏心距离,计算光纤中的模式在从能被纤芯吸收到不被吸收这一临界条件下对应的周向模数、传播常数和焦散面半径值.然后判断光纤中有多少模式的焦散面半径值大于上述在临界条件下算得的焦散面半径值(即有多少模式的传播路径不经过纤芯),用数学公式推导出不能被掺杂纤芯吸收的模数,将之与总传播模数作一比较,得出此双包层光纤的吸收效率.用波动理论得出的计算结果与用射线法算得的结果完全一致.

According to the radius and offset distance of the RE-doped core in double-clad fiber （DCF）, the wave theory and WKB method are used to calculate circumferential mode number, propagating constant and the value of caustic radius, which are in a critical condition of the modes in fiber from absorbable to nonabsorbable by the core. The mode is not absorbable by the RE-coped core if the value of caustic radius of the mode is greater than the critical value calculated above, namely the ray trajectory of the mode that does not contain the RE-doped core. Then the absorption efficiency of DCF is obtained by comparing the non-absorbable modes with the overall propagation modes in DCF. The wave theory result is in good agreement with the result obtained by ray method.