The technology of 40 Gb/s has developed very slowly because of many factors, such as the nonlinear characteristic of optical fiber. All-optical regeneration is the effective way to solve this problem and the key of it is all-optical-nonlinear switch. After analyzing the transmission functions of a kind of all-optical switch (ultrafast nonlinear interferometer (UNI)), the mathematical descriptions of the UNI switch window are got. As a result, the data rate of the experiment according to UNI achieves 40 Gb/s. Combined with the experimental conditions, the influencing factors of UNI switch are analyzed. By increasing the injection current of semiconductor optical amplifier (SOA), the average power of control pulse and adjusting the power of continuous light to the optimal value, the shape and extinction ratio of UNI switch are effectively improved. Based on the experiment, this phenomenon is elementarily explained in theory. It is utilized these results to do the experiments in order to optimize the UNI system to the best conditions, which will be the theoretical and experimental foundations to all-optical regeneration and many other fields.