熔锥型单模光纤耦合器模型的优化研究

Improved model of fused tapered single-mode-fiber coupler

在弱导和弱耦合近似条件下,对光纤耦合器的几何形状做近似处理,并采用连续函数进行描述。根据Snyderd的局部模式理论,采用三角波与高斯波的变系数叠加函数对光纤耦合器纵向各区域的光模场分布进行描述。利用局部模耦合理论和变分法计算分析光纤耦合器纵向各区域的传播常数和耦合系数,讨论耦合系数与结构参数和波长的关系。计算表明:光纤耦合器熔锥区对光纤耦合器中的光功率耦合行为的影响不可忽略,光纤纤芯半径和包层半径对耦合区和熔锥区的耦合系数的影响成相反趋势。因此,可以通过合理控制耦合器的结构参数,制作出宽带平坦光纤耦合器。

The analysis of optical mode field in the coupler was carried out, is in the condition of weakly guiding, weakly coupling, an approximate shape of fused tapered coupler and the appropriate continuous functions.description. Triangle function and Gauss function are mixed with variational coefficients to describe it. Base on local mode theory and variational technique, propagation constant and coupling coefficient are analyzed in each part of fused tapered coupler. The relations between coupling coefficient, wavelength and geometric coefficients are revealed. Numerical simulation indicates that power coupling in the taper region must be taken into account. The coupling coefficients are affected by core and cladding, besides, the effects take place in the taper region and the crossing region in the opposite way. Thereby, a wavelength-flatten symmetry fiber coupler can be obtained through controlling the shape coefficients suitably.