Research On Vernier Effect Of Fiber Sensor Cascaded By Mach-zehnder Interferometers

Recent years,in-fiber Mach–Zehnder interferometer(MZI)sensors have been extensively investigated,owing to their ability of compact size,high sensitivity,immunity to electromagnetism and easy fabrication.They have wide application prospect in many fields.As a means to improve the sensitivity,the Vernier effect has been employed in optical sensor.However,the vernier-effect of fiber sensor cascaded by Mach-zehnder interferometers is relatively unexplored.The purpose of this paper is to study the sensing mechanism of research on Vernier-effect of fiber sensor cascaded by Mach-zehnder interferometers.Several Mach-zehnder interferometers are manufactured to utilize Vernier-effect,and they are also applied to the sensing of external physical quantities.The details are arranged as following: 1.By consulting and investigating domestic and foreign literatures,the formation mode,common structure and amplification mechanism of the optical fiber sensor which can improve the sensitivity are deeply studied.Several representative optical fiber sensor structures with amplification sensitivity are systematically introduced.2.The single Mach-Zehnder interferometer and its interferometric principle are introduced.On this basis,the principle of Vernier-effect of fiber sensor cascaded by Mach-zehnder interferometers is proposed.Unlike other Vernier-effect based on non-Mach-Zehnder interferometers,a new envelope extraction method based on band-pass filter is proposed for the first time.3.A novel system consisting of two fiber sensor based on double spherical-shape structures is proposed.Spectral frequency analysis is carried out to determine the band-pass filtering range.Then,sensor 1 and sensor 2 are used as sensors respectively to measure curvature and strain.The magnifications which are in accordance with the theory and the high sensitivity are obtained.4.We also proposed double bi-taper structures taking the place of double spherical-shape structures to study Vernier-effect.Spectral frequency analysis is carried out to determine the band-pass filtering range.Then,sensor 1 and sensor 2 are used as sensors respectively to measure curvature and strain.It is found that Vernier-effect of sensor 1 has a higher magnification and sensitivity in accordance with the theory.The Vernier-effect of sensor 2 is weak because of the opposite drift direction of the two valleys.