Research On Optical Fiber Sensor Based On Bowknot-type Taper

Fiber optic sensors have been widely studied and applied in various sensing fields for their advantages of compact,lightweight,and immune to electromagnetic interference.The main contents are shown as follows:There are many types of optical fiber sensors,such as intensity modulation,phase modulation,wavelength modulation and polarization modulation.The phase modulated optical fiber sensors were researched in this paper.The main research contents are as follows:1.Some typical optical fiber sensing structures and their sensing principles were introduced.In addition,a novel optical fiber sensing structure?BTT:Bowknot Type Taper?was briefly introduced.2.A simple liquid flow rate sensor cascaded Bowknot Type Taper structure based Mach-Zehnder Interferometer?MZI?is proposed.When the BTT was immersed in water,the refractive index of the external medium of the fiber has changed?from air n=1 to water n=1.33?,which eventually caused the spectrum changed.By observing the time when the spectrum changed on the spectrometer?T?,the flow rate of the liquid can be obtained by the length of the interferometer divided by the T.This method can detect flow rates range from 0.66 mm/s to 10.6 mm/s.The relative error between the measured value and the actual value is about 8%.In order to improving the sensitivity of the sensor,the original flow rate sensor has been improved.The relative error of the new sensor is 3%less than the original sensor.3.A water droplet weight sensor based Maher-Zehnder interferometer?MZI?cascaded Bowknot Type Taper?BTT?was proposed.In this paper,we record the time?t₁?when the fluid pumped with a peristaltic pump flows through two BTTs,and then drops a droplet into the liquid tube with a needle tubing meanwhile recording the time?t₂?of the fluid flowing through the two BTTs.By measuring the time change of droplet with different weight,this method can be used to determine the droplet weight in the range of 0²00mg.4.A high sensitivity liquid surface deformation sensor based Mach-Zehnder interferometer?MZI?cascaded with Bowknot Type Taper?BTT?was demonstrated.As the liquid surface changes from a position higher than the optical fiber to a position lower than the optical fiber,the medium outside the optical fiber gradually changes from the liquid to air,which will result in a change of the interference of the MZI.By measuring the intensity changes of the dip-max resonant wavelength,the liquid surface deformation in the range from 0 to 5.22 mm can be determined with a high sensitivity of 0.99 dB/mm.