The Study Of Polarization Controlling And Compensation Of Interferometric Arms In Fiber Optical Sensor System

In the recent years, as sensors system become more intelligent, sensitive and powerful, the fiber optical sensor system, which is a new one in sensor family, is being more popular, due to its safety, sensitivity and the ability to build the sensor network. What's more, the fiber optical sensor based on interferometer has the highest sensitivity and application. However, the fading of interferometric signal brought from the change of polarization state of input light is the key problem before the fiber optical sensor goes to the market.The main content of this paper is to design a polarization controlling system based on PC1000C, a polarization controller of Optellios. With the system, the polarization state will become more stable. First of all, the interferometric signal will be sampled. Then the data is sent to microcontroller and processed by some algorithm. Lastly, the controlling signal will be sent to PC1000C to control the polarization state of the input light. In this way, the polarization state of output light can follow the change of interferometer eigenvector dynamically in order to keep their angle at the scope of zero. The system can keep the polarization state of input signal optimum.The paper also introduces another assistant system, based on optical transceiver module RTXM191. The goal is to measure the difference of interferometric arms. The length of two interferometric arms will keep same as much as possible to avoid large coherent noise.The theory of fiber optical sensor and the feedback structure of polarization state of input light will be first discussed in this paper. Then, the detailed design of the system based on PC1000C will be introduced. The code is developed with C language in MPLAB (integration development environment) . Lastly, the detailed design of the system based on RTXM191, a light transceiver, will be introduced. The code with VHDL language is developed in Quartus-II. All the hardware design including schematic diagram and PCB(printed circuit board)are designed in EDA software.