本論文為研究側面泵浦耦合器使用漸變折射系數多模光纖取代一般多模光纖作為幫浦光纖，對耦合效率和有效折射系數的影響。實驗使用Beam propagation method (BPM, Rsoft BeamPROP軟體) 進行模擬研究。在考慮幫浦光纖拉椎的長度(Length of tapering, Ltp)，末端最細直徑(Diameter of tapered fiber end, Dend)，與雙披覆層光纖互相接觸時該拉椎光纖的直徑 (Diameter of contact, Dct)以及幫浦光纖末端進入雙披覆層光纖的融合深度(Depth of fusion, Df)等因素後，在不同模態時，漸變折射系數多模光纖和一般多模光纖的差異。在耦合效率都99%的情況下，低階模態較低NA值的漸變折射系數多模光纖有較高的有效折射系數。高階模態因會受到LP模態中n值影響，纖核較大的漸變折射系數多模光纖有較高的有效折射系數。在未來實作上使用2種條件都具備的光纖，將會有更好的結果。

This thesis is to study the influence of using grade-index (GRIN) fiber instead of multi-mode fiber as the pump fiber for side pump combiners on the coupling efficiency and effective refractive index. Beam Propagation Method (Rsoft BeamPROP software) is employed for research simulation. The parameters of the length of fiber tapering (Ltp), the diameter of tapered fiber where the two fibers start to contact with each other (Dct), the diameter of the tapered fiber end (Dend) and the fusion depth of the tapered fiber into the double-cladding fiber (Df) which affect the coupling efficiency and effective refractive index of GRIN fiber and multi-mode fiber. For 99% of coupling efficiency, the effective refractive index of GRIN fiber with a low value of NA is higher than multi-mode fiber in the low mode. Affected by the value of n in the LP mode, the effective refractive index of GRIN fiber with a bigger radius of core is higher than multi-mode fiber in the high mode.
The value of NA and the radius of core are important factors of GRIN fiber on side pump combiner. We can get better results if we use the fiber which includes these conditions in the future.

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