Research On The Gas-liquid Sensing Method Based On Near Infrared Spectroscopy

Near-infrared spectroscopy is an important research direction in fiber sensing technology.Based on the analysis of near-infrared spectroscopy,the gas and liquid sensing was studied.Common fiber sensors can only be used for gas or liquid sensing.For gas/liquid two-phase sensing,two separate systems are required,which greatly increases the cost and operation complexity.To solve this problem,the tilted fiber Bragg grating(TFBG)is introduced into the fiber ring cavity laser system to achieve simultaneous gas and liquid sensing with a single system.In addition,an expansion module based on wavelength modulated gas sensing technology is constructed to increase the types of gases that can be detected.The major work of this paper is as follows:1.A gas and liquid sensing system based on fiber ring cavity laser technology is proposed.The tilted fiber Bragg grating(TFBG)is introduced to the fiber ring cavity laser system to measure the refractive index of the liquid.Compared to conventional intra-cavity methods and TFBG methods,the system can simultaneously detect gases and liquids.The gas and liquid sensing functions are automatically switched by program-controlled optical switches.The gas and liquid sensing experiments were carried out using this system.Taking acetylene gas as an example,in the range of 0.1%to 0.5%,the absolute error of the measurement is less than 46 ppm.And a set of glycerol-water solutions with refractive indices from 1.3959 to 1.4430 have been measured using the proposed scheme with a sensitivity of 528.2 nm/RIU.2.A fiber surface plasmon resonance sensor was fabricated by magnetron sputtering with a tilted fiber Bragg grating.The TFBG is plated with a gold film.The sensor was used for liquid refractive index measurement.Glycerol-water solutions with refractive index from 1.3330 to 1.3941 is measured and the refractive index sensitivity is 546.4 nm/RIU.3.An expansion module was designed based on the theory of wavelength modulation technique.A series of gas cells and corresponding protection devices were designed so that the module can be used for measurement in mines.Taking methane gas as an example,in the range of 100～600 ppm,the absolute error of the measurement is less than 4.2 ppm.