Research On The Path Imbalance Measurement Of Fiber Optic Interferometer Based On Frequency Scanning Interferometry

Because MI or MZI based FOISs are found to give the combination of high sensitivity and sufficient multiplexing ability,they have been widely used to monitor physical,chemical and biological parameters.The path imbalance(PI)of the two-arm FOIS is an essential parameter for many applications.Not only it directly affects the performance of the interferometric sensors,but also it affects the consistence of the array.Besides,some multiplexing topologies is based on precisely measuring and setting the PI of each pair of both sensor and receiver interferometer pairs.With the development of optical fiber sensing technology,how to design a large measurement range,high accuracy,simple and robustness instrument for path imbalalnce measurement is important.Based on the principles of frequency scanning interferometry,we developed and investigated an easy implemented path imbalance measurement system with wide measurement range and high measurement accuracy,which can be used to measure path imbalance undamaged.The major contents of this paper are as follows.Firstly,based on the principle of frequency scanning interferometry,the paper analyzes the limitations of different measurement methods.And the basic theory of frequency scanning interferometry is developed for the purpose of providing the basis of the subsequent works.Secondly,the optical path and the mechanical structure are designed.And the path imbalance measurement system is built by selecting the key devices.The programes of controlling the scanning stage and finishing the synchronization of the laser and acquisition card are developed.Thirdly,we programmed the initial signal processing procedure.The methods of accurately extracted the fringes and the methods of precisely measure the changeable value of reference interferometry were investigated.In order to improve the measurement accuracy of the path imbalance measurement system.Eventually,different optical fiber interferometer with different path imbalances wered measured by frequency scanning interferometry and our method.And the validity of the method investigated in this paper was verified.The uncertainty of the measurement results is calculated and the uncertainty contributor in the system were analyzed to provide the guidance for subsequent works.Above all,the results have shown that the measurement uncertainty and the path imbalance are linearly dependent and the combined relative uncertainty of 4.9×10-6(1σ)in path imbalance measurement over a range of 50 m is achieved without applying bulky setups and complicated data processing algorithms.