中文说明：
修正BBO晶体折射率色散公式中错误的系数 ，完成βBBO晶体Ⅱ类匹配的SPDC（共线情况）并计算相位匹配角。此时的相位匹配角为能 产生纠缠光子对的最小切割角。另附一份参考文献，详细的说明此类实验的步骤与细节。
English Description：
Correct the wrong coefficient in the refractive index dispersion formula of BBO crystal, complete the SPDC (collinear case) of type II matching of β BBO crystal, and calculate the phase matching angle. At this time, the phase matching angle is the minimum cutting angle that can produce entangled photon pairs. In addition, a reference is attached to explain the steps and details of this kind of experiment in detail.