Signal-processing Assisted Vernier-effect Demodulation Based On A Single Fiber Interferometer

Vernier effect can effectively magnify the sensitivity of interferometric fiber sensors and can be applied in any sensing field.The traditional Vernier effect uses two interferometers connected in series or parallel,one as a sensor interferometer and the other as a reference interferometer.To improve the magnification of sensors,it requires that the optical path difference(OPD)of the two interferometers to be very closed,which is difficult to be fabricated,the other issue is that the reference interferometer should be immune to the environmental change,which is actually difficult to be realized.This dissertation focuses on a new signalprocessing based Vernier effect demodulation via a single interferometer to overcome the difficulties mentioned above.The main research work and innovation of this paper are as follows:(1)A signal-processing-assisted Vernier effect demodulation scheme based on a single Mach-Zehnder interferometer(MZI)is proposed in this paper.Common micro-fiber is used as a MZI.MZI outputs the sensing interference spectrum,and an artificial reference spectrum(ARS)is obtained by spatial frequency down conversion of a sensing spectrum.By multiplying the measured sensing interference spectrum with the ARS,a superimposed spectrum with a Vernier effect envelope can be formed.The refractive index sensitivity is 71354.58 nm/RIU and the amplification factor is 31.01.In the proposed scheme,the ARS is not affected by the external environment change and its free spectrum range(FSR)is optional,so the amplification factor can be adjusted.(2)A Vernier effect demodulation scheme for signal processing based on single fiber Fabry-Perot interferometer(FFPI)is proposed in this paper.A core-offset fiber pair is used as an FFPI for RI sensing.And the ARS is obtained by modulating and extracting a sensing spectrum twice.The measured sensing spectrum and the ARS are added to form the superimposed spectrum with Vernier effect envelope.By optimizing the cavity length of FFPI and modulation length,the ultra-high refractive index sensitivity of 133948.33 nm/RIU was obtained with an amplification factor of 118.38.This scheme is another alternative candidate for signal-processing-assisted Vernier effect demodulation based on a single interferometer.The proposed schemes provide a general solution to improve the sensitivity for almost all interferometric sensors.