Experimental Research On Optical Ifber Sensor Based On Multimode Interference And Fabry-perot(F-P) Interference

In the society with high capacity of information, people pay much attention to sensorswhich are used to obtain information.Optical fiber sensing technology, a new type of sensortechnology, has attracted much attention internationally from the date of birth due to theiradvantages such as good stability, immunity to electromagnetic interference, capability forremote control, etc. It has been widely used in the fields of defense and military, energy andenvironmental protection, biomedical, aeronautics and astronautics, etc.As one kinds of fiber optical sensors, fiber-optic interferometric sensor has a highresolution and sensitivity due to interferometric techniques to demodulate the phasemodulation. It has been widely used in the measurement of the various parameters and has abroad development prospect. This paper focuses on theoretical and experimental research onmultimode interference based fiber-optic sensor and F-P interferometric sensor. The maincontent is as follows:1. Generally describe the principle and classification of fiber optic sensor, discuss four typesof fiber-optic interferometric sensors in detail, summarize research status of themultimode interference based fiber-optic sensor and F-P interferometric sensor, finally,analyze the problems of fiber-optic interferometric sensor in practical applications.2. Discuss fiber-optic phase modulation mechanism in detail. Analyze the interferencepattern of single-mode--multi-mode--single-mode(SMS) based on multimodeinterference and multi-beam interference principle of fiber F-P interferometric sensor, dothe simulation by using BPM software and Matlab software which provides a theoreticalbasis for the follow-up study.3. Make a sensor with the structure of SMS and FBG cascaded by using the same lengthmultimode fibers with the core diameter of 50μm and 60μm. We etch the multimode fiberand conduct a comparative research on the temperature and refractive index sensingcharacteristics in the experiment. Experimental results show that for the same MMF, thetemperature sensitivity of the SMS structure is essentially the same, the refractive indexsensitivity is greatly increased after etch. Experimental results also show, after etch, thetemperature sensitivities of 50μm and 60μm are 0.095 nm/℃and 0.127 nm/℃,therefractive index sensitivities of 50μm and 60μm are 61.96nm/RIU and 128.11nm/RIU inSMS structure. The temperature sensitivity and refractive index sensitivity are improvedby using large core diameter multimode fiber in SMS structure after etch. In particular,the refractive index sensitivity of 50μm is two times as much as 60μm. The sensor can beused for the simultaneous measurement of temperature and refractive index.4. Make a novel fiber F-P sensor probe by using chemical etching method. Discuss theproduction process(including the etch process of the MMF end-face and the fusion splicing process of SMF and MMF-etched) in detail.We make a novel fiber F-P sensorprobe with the structure of single-mode-air cavity-multimode under the guidance of theoptimum process which is summarized by a large number of experiments, analyze itssensing principle and conduct the experimental research on its sensing characteristics.Experimental results show that the fiber F-P sensor probe is not sensitive to temperature.The strain sensitivity is about 0.0058nm/με. Therefore, the sensor can be used to measurethe strain and solve the temperature cross-sensitivity problem.