由M－Z干涉仪组成自准直干涉装置是一种抗干扰很强的干涉法测光纤非线性科尔系数γ的装置。由于测试脉冲强度受光纤的衰减和耦合器的分流，输入段和输出段脉冲强度不一样，势必要引入系统相移扰动，造成测试相移并非完全是测试光纤SPM效应引入的相移，对准确测量光纤非线性科尔系数γ值形成误差。理论分析了这种扰动的形成机理，引入扰动相移误差量。模拟分析了影响相移误差量的参数，优化这些参数，并且找到最优参数值，使相移误差量最小，且不受输入脉冲强度变化的影响。大大地改善了该系统的性能。最后试验测试了SMF光纤，和已有测试方法比较，波动范围明显减小。

The setup based on self-aligned interferometer which consists of Mach-Zehnder (M-Z) interferometers can be used to measure optical fibers Kerr coefficient and presents the advantage of insensitive to environmental perturbations. However,there are some key issue in the setup. The phase shift is not completely induced by self-phase modulation (SPM) of tested fibers. There are some other phase shift created by the fibers of the system,due to the pulses intensity is different between a forward pass and a return pass,because the excessive phase shift,it is impossible to measure the optical fibers Kerr coefficient accurately. The forming principle of the excessive phase shifts in theory and define a new parameter △ which expresses the error of nonlinear phase shift were studied. The system parameter was analyzed and optimized to obtain the minimum △. The optimal △was a constant when the pulse intensity increases. In this way,the function of the system was improved. The result of measurement of SMF fiber is compared with the values found by the other laboratories. The deviation is smaller.