Research On All Fiber Velocity Measurement System

As a high time and space resolution and non-contact measurement method laser velocity measurement system is used widely in the project field of explosive detonation shockwave test, weaponry design, high velocity impact, rocket propulsion. Traditional laser velocity measurement system is difficult to progress further because of defect such as complex structure, debugging difficulty, and so on. Compared with traditional system, all fiber velocity measurement system becomes the trend owns to its advantage of compact structure, high stability, debugging difficulty. The performance of fiber source and coupler are very important to the system, also the data processing could not be neglect if want to improve the system. The content of this dissertation is as follows:Firstly, it describes the history of velocity measurement system home and abroad, the principle of system, and the difference between traditional system and all fiber system. All fiber system is detailed based on Doppler Effect and frequency mixing theory, the velocity expression is derived, and the effect of fringe number on velocity is also described.Secondly, the demand of use of fiber source in different application is analyzed based on the parameters of fiber source. The effect of parameters such as spectrum width, mean wavelength and the stability of output power of fiber source on system performance are also analyzed. The curves of output signal of the system and its fringe constant with the variation of spectrum width are given. And then the experimental testing curves are derived in different conditions.Additionally, it conducts the study of influence of coupler on velocity measurement, the mode coupling theory based on Maxwell equations is described, and the effect of coupling ratio on output interfere fringe contrast is analyzed. Coupler is affected by other external factors in the course of fabrication; it is adjusted to fabricated using fused biconical taper. The experimental testing curves of fabricated coupler are given. Finally, the correction factor of fringe constant and measurement method are conducted as to dispersion and impact characteristic of optical devices. It analyzes the phenomenon of fringe loss in detail and gives the ways to compensate it based on the characteristic of output signal of the system. The improved system is described as to the defects of single-ended detect and the corresponding data processing is given. In order to enhance the performance one method for fringe subdivision and the electrical circuit design are given.