Research On Micro-nano Multi-core Fiber Seawater Salinity Measurement Technology

Seawater salinity is an indicator of the salt amount in seawater.It is a basic parameter of seawater,an important feature for studying marine dynamics,seasonal climate prediction,marine fish culture and marine resources.The fiber optic interferometer has the advantages of flexible application environment,accurate measurement results and not affected by electromagnetic interference,widely used in seawater salinity measurement field.This paper mainly studies the refractive index characteristics and temperature characteristics of micro-nano multi-core fiber sensors.First,carry out a theoretical analysis of the interference sensor.Then,perform software simulation.Finally,perform the refractive index and the temperature experiments,summarize the transmission law.The specific content and structure are as follows:Firstly,several seawater salinity measurement methods and research status of interferometric refractive index sensors are introduced.The principle of refractive index measurement of fiber-optic Michelson interferometer is analyzed.The transmission characteristics of three-core fiber are analyzed according to the theory of coupled mode,which lays a theoretical foundation for the experiment.Secondly,build the Michelson interferometric sensors.The sensing units are fabricated by the melt taper method and the long period fiber grating method.The refractive index characteristics of the two sensors are measured experimentally.The results show that the sensor with long-period grating as the sensing unit has a refractive index sensitivity of-409.91 nm/RIU in the range of 1.3324-1.3492,the linearity of the refractive index characteristics is good.Thirdly,the finite element simulation model of the three-core fiber is established,and the relationship between the refractive index sensitivity and the fiber diameter is obtained.Four kinds of micro-nano multi-core fiber Mach-Zehnder interferometers with taper lengths are fabricated.The refractive index sensitivity of four different sensors are gradually increased.The experimental results are consistent with the simulation results.The micro-nano multi-core fiber Mach-Zehnder interferometer of 16.20 mm tapered length has a refractive index sensitivity of 5815.50 nm/RIU.The temperature experiments are carried out with the sensor of 15.99 mm tapered length,the temperature sensitivity is measured to have good linearity.Finally,several seawater samples are selected as the solution to be tested,the refractive index is measured with the sensor of 16.20 mm tapered length.The experimental results show that the sensor's measurement error is less than 0.35‰,which has high practical value and research value.Finally get the conclusion that the micro-nano multi-core fiber Mach-Zehnder sensor has high sensitivity,and good linearity of refractive index characteristics.It has broad application prospects in the field of seawater salinity measurement.