The study of error about the measurement of the nonlinear Kerr coefficient using a self-aligned interferometer

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 A which expresses the error of nonlinear phase shift were studied. The system parameter was analyzed and optimized to obtain the minimum A. The optimal A 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.