Font Size: a A A

Study On Fiber-Optic Sensor Based On Internal-and-External-Cavity Configuration And Harmonic Vernier Effect

Posted on:2021-02-25Degree:MasterType:Thesis
Country:ChinaCandidate:C HeFull Text:PDF
GTID:2518306569497684Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Fiber-optic Fabry-Pérot interferometer(FPI)sensor translates the information that measurand acts on the FPI into spectral information with interference principle,hence the implementation of measurement.With the advantages of small size and high sensitivity,FPI refractive index(RI)sensor has important application value in biochemical test,research,food processing and other fields.As sensor technologies develop,the development direction of fiber-optic sensor is high accuracy and high sensitivity.On the one hand,temperature-induced spectral response reduces the measurement accuracy during the measurement of RI,owing to the cross sensitivity of FPI.One simple but effective method is to utilize two sets of spectral information generated by cascaded FPI to eliminate the temperature crosstalk.However,the current researches on the sensor for dual-parameter measurement are insufficient,which limits the application of cascaded FPI.In view of the shortcomings of the sensor for simultaneous measurement of two parameters,this dissertation proposes a sensor for simultaneously measuring RI and temperature based on internal-andexternal-cavity FPI(IECFPI)configuration.On the other hand,sensitivity of single FPI sensor is not high enough.Vernier effect can enhance sensitivity,but it requires critical matching between optical lengths,which leads to a difficulty in fabricating sensor.To resolve the problems of low sensitivity and difficult matching,this dissertation proposes a RI sensor based on harmonic Vernier effect.In view of the problem of temperature cross sensitivity,this dissertation proposes a sensor for simultaneous measurement of RI and tempearture based on IECFPI configuration.For the deficiency of cascaded FPI,this dissertation establishes the interference model of the IECFPI,deduces the sensitivity formular of the envelope and fine fringe,and proves the feasibility of the model to measure RI and temperature simultaneously.IECFPI sensor consists of three sections of single-mode fibers(SMFs)spliced with lateral offset,where the offset spliced SMF acts as an open cavity,and the well-cleaved SMF works as a silica cavity.The variations of RI and temperature are obtained by tracing the wavelength shifts of envelope and fine fringe,if the sensitivity-coefficient matrix is given.The crosstalks between RI and temperature are thus eliminated.Experimental results show that RI sensitivities of envelope and fine fringe are 1 010.935 nm/RIU and 124.608 nm/RIU,respectively.Temperature sensitivities of envelope and fine fringe are 3.2 pm/? and 9.5 pm/?,respectively.The result of RI measurement based on this configuration will be more accurate than that based on single FPI.In view of the problems of low sensitivity for single FPI sensor and difficult matching for traditional Vernier effect,this dissertation proposes an RI sensor based on harmonic Vernier effect.This sensor is also the type of cascaded FPI fabricated by splicing with an offset.This dissertation analyzes and numerically simulated the relationship between sensitivity and ratio of optical length of sensing FPI to that of reference FPI in harmonic Vernier effect.Theoretical analysis shows that an increase in ratio results in a larger enhancement of sensitivity.Experiment is also carried out,the result of which shows that a RI sensitivity of up to-37 905 nm/RIU is achieved.The sensitivity is magnified 33 times compared to the sensing cavity that is a single FPI.
Keywords/Search Tags:fiber-optic sensor, Fabry-Pérot interferometer, dual-parameter measurement, Vernier effect
PDF Full Text Request
Related items