Study On High-precision Absolute Distance Measurement Based On Double Polarization Modulation Method

The development of measurement techniques is the premise and foundation of all science and technology development. Length as one of seven basic physical quantities, it is an integral part of measurement. Traditional absolute distance measurement technology detects the information of the time-of-flight information or phase change, whose measurement accuracy mainly depends on the degree of precision of the test tools and instruments.To solve the problem that traditional laser range technology has a poor phase measuring accuracy and the additional phase of the system which constraint the improvement of its accuracy, we design an absolute distance measurement system and use the technology of varying frequency measurement based on double polarization modulation to improve the phase shift range finding technology. With the method of double polarization modulation, demodulation of the phase information is directly on the phase modulator which can make the system simpler. The varying frequency technology is used to replace the traditional phase measuring technology and the problem of phase measuring cannot constraint the accuracy of the system. This paper combines two theories and analyses the principles and feasibility of them deeply. In final, it presents the structure of specific experimental system.We completed the test of the stability, accuracy and range ability of measurement system based on double polarization modulation. Results show that the curve between the modulation frequency and the output light intensity is sine which is proved both on theory and experiment. The stability of frequency can be better than 10-6 and the measured accuracy approaches±10.6?m@4.5m. A 200 meters fiber is measured by the system, and the clear curve between the modulation frequency and the output of system is obtained. It shows that this system has the ability of high- accuracy absolute distance measurement.In view of its large volume, which may affect the follow-up engineering and commercializing, we improved the measurement system with embedded design. We describe the core control module in Zynq development board and the microwave source module in detail, showing their parameters and performance index. Also, we present signal processing methods with embedded system and analysis the principle and feasibility of wobber method and linear fitting algorithm. We give implementation steps based on Zynq development board and test the actual performance of this system. Compared with experiment before, the volume is much smaller than before. But the accuracy descents slightly, which is ±56?m. According to the experiment results, we analysis its reason and prepared for further work.