Research On Refractive Index Sensing Technology Based On High-resolution Spectral Measurement

Refractive index is an important physical property.The content of various components contained in a gas or liquid can be analyzed by measuring the refractive index.Today,refractive index measurement has a wide range of applications in chemical processes,environmental monitoring,food production,and biomedicine.Optical fiber-based refractive index sensors have the advantages of small structure,high sensitivity,and the ability to achieve remote real-time measurement.These properties determine the great potential and value of optical fiber refractive index sensors in practical applications.Fast,high-precision refractive index sensing systems play an increasingly important role in gas and liquid composition detection and industrial production applications.Based on the tilted fiber grating,this topic explores its structure,basic theory,and refractive index sensing principle,and designs two different spectral measurement systems for different application scenarios,corresponding to two sets of fast and high-precision refractive index sensor system,and built two experimental systems to verify and analyze their measurement performance.The first system is a refractive index change sensing system based on high-linearity frequency sweeping.Firstly,the method of obtaining highlinearity scanning frequency light source was explored,and the external modulation technology and injection locking technology used in it were introduced.Subsequently,an experimental system was constructed to analyze the linearity of the swept frequency light source,and combined with the tilted fiber grating sensor to achieve a high-linearity swept frequency index-change sensing system,and further analyzed the sensor's refractive index sensitivity and the measurement of the system precision.The second system is a refractive index change sensing system based on a dual electro-optic comb.The function and generation method of the optical frequency comb and the electro-optic frequency comb are first introduced.The principle of the optical demodulation system based on the optical frequency comb,together with the principle of the dual-comb spectrometer and the principle of the dense and sparse dual-comb are introduced.A refractive index change sensing system based on a dual-comb is described,and the measurement accuracy of the system is calibrated.Then,based on the injection locking technology,a method for expanding the refractive index measurement range of the system was proposed.Experimental results show that both systems have high measurement speed and accuracy.The refractive index measurement system based on high-linearity sweep frequency has a relatively high measurement accuracy and a fixed measurement speed.The refractive index measurement system has a faster measurement speed and a higher measurement accuracy,and can choose different measurement speeds and measurement accuracy according to the actual application scenario.