Imai M, Hara E H
Appl Opt. 1974 Aug 1;13(8):1893-9. doi: 10.1364/AO.13.001893.
The optimum condition for coupling energy into an optical fiber waveguide is theoretically computed for an incident beam with a Gaussian intensity distribution and a curved wavefront. The dependence of the modal excitation efficiencies on the tilt angle of the incident beam and on the refractive index difference of core and cladding is discussed. Numerical results show that maximum efficiency for the HE(11) mode can be achieved when the beam radius is chosen to be approximately 0.65 times the core radius. Excitation efficiencies of low-order modes, HE(1m) (m >/= 2) approach 80% at their cutoff when the beam size is suitably larger than the core diameter.
对于具有高斯强度分布和弯曲波前的入射光束，理论上计算了将能量耦合到光纤波导中的最佳条件。讨论了模式激发效率与入射光束倾斜角以及纤芯和包层折射率差的关系。数值结果表明，当光束半径选择为约为纤芯半径的0.65倍时，可实现HE(11)模式的最大效率。当光束尺寸适当地大于纤芯直径时，低阶模式HE(1m)（m≥2）在其截止时的激发效率接近80%。
