Research On All-fiber-optic Polarization Pressure Sensor

In recent years, with the development of the optical fiber communication, computer technique, fiber technique and semi-conductor photoelectric compounds technique, optical fiber sensing technology becomes more and more important and develops rapidly during the past 30 years in the international fiber field because they have more advantages, such as wide application extent, high sensitivity, insensitivity to influence of electromagnetic field, good solution, small volume, low price, etc.The purposes of this thesis are to study the all-fiber-optic polarization pressure sensor by utilizing modulated polarization, and simplify and improve the structure of the fiber-optic polarization pressure sensor used in the past. And it is achieved not by taking photoelastic materials as sensitive elements, but by directly using ordinary single mode optical fiber which can not only sense but also transmit the pressure information. It has some unique qualities, for example, its structure is simple, easy to maintain and with fewer gears; the number of optical couplings is reduced as well as the degree of difficulty of producing a sensor; it cuts the cost of polarization-maintaining fiber; the parted structures can be applied to realize the long-distance information transmission; a laser with multiple detectors can be used as light source to lower the energy lost and costs. In a word, it has a great future from the point of view of practical utility.The content of thesis includes:1. The basic principles, categories and the development in and out of China of the fiber-optic sensor, especially the principles, advantages and disadvantages of different types of optical fiber sensor modulation are well studied and described at the beginning of the thesis.2. The details of the structure and principles of all-fiber-optic pressure sensor are designed and introduced in the second part. The double-beam structure is used to compensate the fluctuation of the source's intensity. Only ordinary single mode optical fibers are used because polarization is insensitive in transmittable section of the optical fiber. The theoretical mathematical model as well as the small angle defection error is constructed by using the Mueller Matrix; the confirmation of the theoretical model, the analysis of internal birefringence in general situation as well as internal residual birefringence in three types of different situations is displayed by Jones'Matrix in the same part.3. The experimental data which verifies theoretical structure is well analyzed, and the index of the sensor is also figured out at the same time. With the help of MATLAB, the experimental data is perfectly fitted to theoretical result by using the Method of Lowest Two Multiplication.4. The research on how to apply the all-fiber-optic pressure sensor to the liquid-level detection for oil tanks is introduced in the end by analyzing several schemes of measuring the liquid-level, comparing them with their advantages and disadvantages. The relative principles, structures, and packaging are designed, too.