Distributed Fiber Diameter Measurement Based On Stimulated Forward Stimulated Brillouin Scattering

With the gradual expansion of optical fiber production and the steady development of optical communication technology,higher requirements on the accuracy and distributed capabilities of optical fiber structure measurement have been put forward.Opto-mechanical Time Domain Analysis(OM-TDA)is based on forward stimulated Brillouin scattering(FSBS).It is widely concerned because of its application to distributed liquid sensing.In addition,the characteristics of the transverse acoustic wave field involved provide it the potential for distributed measurement of fiber diameter.Therefore,this paper proposes a scheme to realize distributed high-precision fiber diameter measurement using the OM-TDA system.First,this paper studies the basic principles of FSBS.Starting from the phase matching and resonance conditions of the FSBS effect,the frequency and intensity distribution of the spectrum of the transverse acoustic waves are obtained.Then the principle of measuring the fiber diameter based on FSBS is further studied,and the changes of the resonance frequency and resonance intensity of the FSBS mediated by different acoustic wave modes with the fiber diameter are investigated.Next,we examined distributed sensing capabilities of three different distributed sensing protocols based on FSBS,and verified the merits of the OM-TDA system in terms of signal-to-noise ratio and spatial resolution.Specifically,the ability of distributed measurement of fiber diameter by OM-TDA is analyzed and simulated,which confirms the feasibility of this scheme.Next,the phase-sensitive characteristics of the coherent probing process in OM-TDA system are proposed and five-wave coupled wave equations are constructed to consider the phase influence.Combined with the phase shift between the sidebands in the FSBS,the effect of phase effects on spectral distortion is simulated.Finally,the experiment based on the OM-TDA for distributed measurement of optical fibers is carried out,during which optical fibers with different diameters of 125?m,80?m and 60?m are tested.In order to make the measurement results more visible,we selected three different locations in each fiber to be corroded to construct a more obvious diameter mutation.The OM-TDA system accurately measured the change in fiber diameter in the longitudinal direction.On this basis,we also use scanning electron microscope imaging and OM-TDA repeated measurement experiments to verify the accuracy and precision of the diameter measurement scheme.