Four-wave Coupling Micro-vibration Optical Measurements

The importance of vibration detection in industrial production and science investigation has been accepted widely, and the measurement of vibration has become the significant research problem in engineering technology. Recently, with the rapid development of micro-electro-mechanical technology and precision machining technology and many important applications, small displacement and small vibration related with objects are interested by academia and industry. Optical detection is a non-touch and scatheless measurement technology, it also has the advantage of simple structure, high accuracy and perfect stability, so it is always in the guiding position in metering. In optical detection meathods, interferometry is most used widely and the meathod using photorefractive crystal is a novel technique.In this paper, the characters of the photorefractive crystals are studied, including the principle of photorefractive effect, two-wave mixing and four-wave mixing. Photorefractive effect is the base of two-wave mixing and four-wave mixing, and in fact, four-wave mixing is expanding for two-wave mixing. The research in this chapter provides substantial theories for the next of photorefractive optical lick-in small vibration detection.Secondly, the way of optical lick-in small vibration detection based on photorefractive four-wave mixing is explored. We propose the experimental arrangement, and accomplish academic analysis and simulation calculation. The result of the simulation shows this method is capable of detecting frequency of small vibration. However, the result of the experiment shows it makes high demands on the characters of the photorefractive crystals.Further more, the method of small vibration detection by optical interferometry is investigated, and two schemes are presented to dispose the result of the detection of displacement and frequency. The second is more useful from comparing these two cases, and using the second method, the effects of small vibration detection by optical interferometry are investigated experimentally and compared to analytical results.At last, all the works above are summarized and the emphases in future investigation are also put forward.