Ocean Fiber Optic Temperature And Depth Sensor And Its Dynamic Demodulation System Research

In the complex environment of the ocean,temperature and depth are the most fundamental of the many environmental parameters of the ocean,and they not only determine the distribution of marine jump layers,but also affect the propagation characteristics of underwater acoustic signals.At present,the commonly used ocean temperature and depth measurement is electrical type temperature and depth meter,which has been commonly used in the field of ocean monitoring,but there are still problems such as poor corrosion resistance,large size,electromagnetic interference,separation of measurement equipment and susceptibility to crosstalk.Fiber optic sensors have gradually become one of the research hotspots in the field of marine environmental monitoring because of their small size,low cost,resistance to electromagnetic interference,and long-distance transmission.For the current application requirements of dual-parameter sensing and high-resolution measurement of ocean temperature and depth(pressure),this paper mainly researches the multiparameter sensing technology based on Fabry-Perot(FP)interference,proposes three kinds of fiber optic FP temperature and depth sensors with high integration,small size and high resolution,and on the basis of the sensors,the algorithms of FP sensors are studied,and two demodulation algorithms with high resolution,large dynamic range and fast demodulation are proposed,and finally built a dynamic demodulation system applicable to this sensor.The specific research of this paper is as follows:1.For the demand of temperature-depth(pressure)dual parametric sensing,two technical solutions of dual parametric sensors based on silicon-based structures are designed and implemented.The design and fabrication methods of the two silicon-based structures are introduced in detail,and the preparation methods of the two sensors are elaborated,both sensors are combined with silicon-based structures and multi-core optical fibers,and parallel FP interference cavities are built on the sensing probes.The difference lies in the different shapes of silicon based structures.The two FP interference cavities of the sensor can sense temperature and pressure simultaneously,realizing the miniaturization and integration of the dual parametric sensor probes.Through experimental tests,the first sensor obtained good linear response in the range of temperature 25～55℃ and air pressure 5～40k Pa.The second sensor has good sensing capability and reversibility in the range of temperature 25～65℃ and water pressure100 k Pa～1000k Pa,and the temperature resolution reaches 0.0058℃ and the pressure(depth)resolution reaches 1.36 k Pa(0.136m).2.In order to meet the deep sea temperature and depth demand,we proposed a temperature and depth sensor technology scheme based on cascaded FP interference structure,and constructed two cascaded FP interference cavities using silicon carbide and single crystal silicon wafer on the sensing probe,and the sensing probe structure was simulated,package designed and fabricated.In order to realize the absolute measurement of FP sensor,we have studied the demodulation algorithms and proposed two kinds of demodulation algorithms with no jump,high resolution,large dynamic range and fast.After testing,both demodulation algorithms can achieve demodulation speed above 100 Hz.The first demodulation algorithm achieves 0.64 nm optical path difference resolution,and the second demodulation algorithm achieves 0.181 nm resolution,and has excellent demodulation performance in the dynamic range of 300μm～1740μm.3.In order to realize dynamic monitoring of the temperature and depth(pressure)sensor,we built a dynamic demodulation system.Based on the second demodulation algorithm proposed in this paper,we wrote the upper computer demodulation program through Labview to realize the demodulation of the sensor signal.Then we conducted experimental tests on the cascaded FP interference temperature and depth sensor proposed in this paper,and confirmed that the sensor has good linear response in the range of temperature0～45℃ and pressure(depth)0～4.8MPa(0～480m),and the temperature resolution reached 0.01℃,and the pressure(depth)resolution reached 0.6653 k Pa(0.06653m).In addition,the decoupling matrix is given in this paper to eliminate the cross-crosstalk between temperature and pressure(depth),achieving the ability to measure temperature and pressure(depth)simultaneously.Finally,we summarize the research work of this paper and prospect the next work.