In both classical and quantum communication, it is crucial to keep the stability and contrast of interference. The stability of interferometer could influence the proportion of feedback time and the running time of the system. Besides, the contrast affacts the error rates of the system. Serious deterioration of contrast even stops the communication. So, it is necessary to stablize the contrast of interferometer dynamically in real time. In addition, high request on the stability and contrast is present in various coherent solutions among quantum cryptography processing.

The QFPS fiber phase shifter is a key device in an interferometer. The phase shifter achieves fine adjustment by adopting piezoelectric (PZT) ceramics to draw the optical fiber. Located in anspecific feedback system, the phase shifter can compensate in real time the phase drifts and contrast degradation due to environment temperature changing and mechanical vibration. Take advantage of the compact structure and special process management, QFPS series features miniaturized size and high stability.