A Sensing Interrogation System for Sagnac Interferometer With Polarization Maintaining Fiber Utilizing Microwave Photonic Filtering Technique

Abstract

In this paper, a sensing interrogation scheme for Sagnac interferometer (SI) with polarization maintaining fiber (PMF) by using microwave photonic filtering technique has been theoretically analyzed and experimentally demonstrated. In our experiment, the SI acts as the sensing element as well as a spectrum slicer in the single-passband microwave photonic filter (MPF). The central frequency of the MPF’s passband moves to lower frequency when the temperature is increased. Hence, the measurands can be demodulated by monitoring the central frequency of the MPF’s passband in Radio Frequency (RF) domain. Comparing with the interrogation by tracking dip wavelength of the interference patterns in the optical domain and using the product of birefringence and the length of PMF in the SI structure for interrogation, the proposed interrogation system converts the wavelength variations of the interferometer patterns in optical domain to the frequency changes in electronic domain directly by utilizing opto-electronic devices, and thus has an unlimited measurement range, less limitations by resolution limitation of measuring instruments and less cross-sensitivity problems.