Research On Absolute Distance Measurement Based On Optoelectronic Oscillators

Space coordinate measurement as well as positioning technology is one of thesupporting techniques in large mechanical manufacturing, especially in digitalmanufacturing and assembling. Length measurement is fundamental issue inlarge-scale space coordinate measurement. However, traditional large-scale distancemeasurement methods based on interference, phase, etc. are difficult to achieve highaccuracy, high efficiency and large range at the same time. Thus they are difficult tomeet a higher demand for accuracy, quality and efficiency in the developing largemanufacturing.Optoelectronic Oscillator (OEO) is a new kind of high performance oscillator incommunication with ultrahigh Oscillation frequency (as high as hundreds of GHz),ultralow phase noise (as low as-160dBm/Hz@10kHz) and ultra-long cavity length (aslong as tens of thousands of meters). The oscillation frequency of OEO depends onthe group delay. If a free optical space, containing the measured length, is introducedto the optical cavity, the measured length can be derived from the oscillationfrequency corresponding to the cavity length. By virtue of the high sensitivitybetween oscillation frequency and group delay of the loop, as well as the ultra-highdynamic range (as high as above1011) of the signal, this method promises highaccuracy absolute distance measurement at long range.In this dissertation, the principle and technology of OEO will be introduced tolarge-scale distance measurement. The absolute distance measurement method basedon OEO will analyzed in respect of theory and technology, and the experimentalverification will be carried out. The main works are as follows:1. The urgent demands for large-scale precision length measurement in modernindustrial manufacturing are summarized. The principle, method and technology oftraditional optical methods for large-scale measurement are analyzed. The source andresearch significance are explained from the aspects of research basis and applicationrequirements.2. The basic theories of OEO, including the start-oscillation condition, therelationship between OEO oscillation frequency and loop group delay, and spectralcharacteristic are discussed. Then the relationship between oscillation frequency and loop group delay is analyzed. At last, the characteristic and the principle advantage ofthis method are discussed in terms of measurement principle, measurement signal andsignal process.3. Models based on different structures of OEO are established on thefundamental of OEO theory. After evaluation and comparison among the models, theoptimal structure for distance measurement is chosen. And the static characteristic ofthis model is analyzed.4. The influence of temperature variation on distance measurement is discussed.The model of thermally-induced error is established based on the theory of opticalfiber transmission line. The influence of frequency drifting on oscillation frequencyand mode number measuring, as well as the error induced mechanism and its feature,are analyzed. Then compensation techniques for mode number error andthermally-induce error are introduced. According to the influence of fiber length onthe static characteristics of distance measurement, an optimal method of fiber length isproposed based on thermally-induced error model.5. Experimental platform is structured, and the principle and key technology areverified by experiment. The optimum length of fiber is achieved by the methodproposed above. Then, the experiment of mode number determination and errorcompensation were carried out to verify the key technology by analyzing andcomparing the experimental data.