用于高功率侧向泵浦的透射光栅耦合器

Transmission grating coupler for side-pumping high-power double-clad fiber lasers

提出一种用于侧面泵浦大功率双包层光纤(DCF)激光器的双凹槽、双槽深的透射光栅耦合器,它可以被直接制作在DCF的侧面内包层上,以实现大功率的激光泵浦。利用严格的电磁场衍射理论对这种结构进行分析,并且通过结合一种梯度优化的拟牛顿算法(quasi-Newton methods)和微型遗传算法(micro-genetic algorithm)对这种结构进行优化,当侧面入射泵浦光分别为TM和TE偏振时,能实现的最大耦合效率分别为81.2%和79.7%,而且选择合适的参数可以做到偏振不敏感,对非偏振光的最大耦合效率可达72.4%,3种情况下光栅耦合器材料的折射率均大于1.8。对光栅的各个结构参数的制作容差γ、LD阵列的出射波长的漂移以及泵浦光的入射角度θ对耦合效率η的影响也进行了分析。

A dielectric binary transmission grating coupler with two grooves per period, defined by different line-widths and two depths is applied to side-pumping high-power double-dad fiber lasers. This kind of doubly grooved and doubly depths dielectric grating coupler can be fabricated directly on inner clad of double-clad fiber so that it can be used for high-power laser pumping. By combining a gradient algorithm （quasi-Newton methods） and micro-genetic algorithm,the grating is optimized and the maximum coupling efficiendes of 81.2% and 79.7% for TM and TE polarization waves respectively are demonstrated,and for an unpolarized pump light beam,72.4% efficiency can be reached. In all cases the highest achieved coupling effidendes require that the refractive index of the grating material should be greater than 1.8. Meanwhile,the fabricatin-error of the grating coupler γ and the impact on coupling effidency of the wavelength of LD-array λ and incident angle θ are also analyzed.