Displacement Measurement And Signal Processing Based On Optical Fiber Interferometer

Fiber optic interferometer is widely used in industrial high precision measurement.It has the advantages of simple installation,compact structure,flexible light dispersing and gathering,and high precision.Using the light interference principle,solving the interference signal phase,corresponding to the optical path difference,so as to realize the measurement of optical path difference caused by change of physical quantity,is applied to the refractive index,temperature,displacement,vibration,acceleration,pressure measurement,and other fields.In order to improve the resolution,anti-noise ability and reconstruction precision of displacement measurement,the structure and method of displacement measurement by optical fiber interferometer were improved.Firstly,to solve the problem of low resolution of displacement measurement in traditional single-channel Fabry-Perot fiber interferometer,a dual-channel differential fiber interferometer structure was proposed.The structure is a displacement measurement system composed of a single-mode fiber and a coupler.The two arms of the output end of the coupler are connected with a collimating lens to form a differential structure on the positive and negative sides of the measured object.Compared with the traditional structure,the resolution of displacement measurement of this structure is doubled,reaching 1/4 wavelength of light wave,and the whole system is less affected by temperature interference,and has higher displacement reconstruction accuracy.Secondly,in order to solve the problem of poor signal quality and low precision of displacement reconstruction in high noise environment,Multiple Hilbert Transform(MHT)is used to reconstruct the displacement of FM signal based on optical fiber interferometer.In this method,the self-mixing interferometric amplitude-modulated signal is converted into high SNR frequency modulated signal by using Mach-Zehnder interferometer as edge filter,and then displacement reconstruction is carried out according to the phase information of frequency modulated signal.Compared with AM signal,FM signal has a larger signal-to-noise ratio,and for displacement measurement in large noise environment,displacement reconstruction using FM signal can obtain higher reconstruction accuracy.Finally,the simulation analysis and experimental verification of the two methods are carried out.The results show that the two methods can improve the accuracy of displacement measurement,and provide a new displacement measurement method for aerospace,automotive,chip manufacturing and building safety applications.