A Phase Demodulation And Dual-Wavelength Phase Unwrapping Method Using A 3×3 Fiber Coupler

With the progress of photoelectric technology and optical communication technology,optical fiber sensoring is taken seriously due to its high detection sensitivity,large dynamic range,ultra-wide frequency band.In recent years,the interferometric optical fiber sensor has become one of the research hotspots in the field of optical fiber sensing because of its high measuring precision and easy to implement.The demodulation of phase information is the most important link in the realization of interferometric optical fiber sensing system.The method of phase demodulation with 3×3 fiber coupler is simple,easy to implement and few restrictions,which represents the direction of phase demodulation of optical fiber sensor in the future.During the demodulation of the phase,the phase is limited to the range of[-pi,+ pi]due to the characteristics of the trigonometric functions,so the phase is wrapped,i.e.phase is ambiguity.In this thesis,a variety of phase demodulation schemes are analyzed,and the phase demodulation with the 3×3 optical fiber coupler and the dual wavelength are carried out theoretical analysis and simulation by MATLAB.A phase demodulation method suitable for interferometric optical fiber sensor and wide range phase measurement is proposed.Dual light sources are introduced into the phase-demodulation system of 3 x 3 fiber coupler.Because the phase changes of different wavelengths under the same optical path are different,we can use the relationship between the phase change and phase wrapping to get a wide range,error-free phase change information.A dual-wavelength fiber Michelson interference system at 1310 nm and 1550 nm is designed and built.The large range vibration generated by the piezoelectric displacement platform is measured,and the effectiveness of the proposed scheme was verified by experiments.