Study On Microvibration Measurement Based On External Optical Feedback Interference

According to the fast development of the MEMS and meticulous processing technology, the study of microvibration accurate measurement has been attented increasingly. External optical feedback interference technology has the wide application foreground in the microvibration measurement. External optical feedback interference system is very simple, compact and easy alignment. It's a good solution to the problems of complexity, huge size and sensitive alignment that are typical of conventional interferometers. External optical feedback interference technology becomes research hot.The uniform external optical feedback interference mathematical theoretics model is getted from the Long-Kobayashi rate equations and three-mirror F-P cavity approach. Especialy under the condition of the external reflector producing microvibration, the mathematical theoretical model of external optical feedback interference based on the microvibration is established. And a new method of microvibration measurement based on the external optical feedback interference is proposed, which is called reconstruction measurement method. The main studies have been carried out as following:(1) The basic characteristics of external optical feedback interference have been simulated and analyzed. It includes the influence of feedback phase on the system's stability, the influence of external optical feedback intensity on inclination of the interference signal, and the specialty of the interference signal with different microvibration waveforms.(2) The nonlinear least squares method is used to estimate the external optical feedback intensity and linewidth enhancement factor, which are needed in the reconstruction measurement method.(3) The reconstruction measurement method is simulated. Two current main measurement methods which are fringe counting method and phase analysis method are also simulated. Compared with the current mian measurement methods, reconstruction measurement method has a lot of superiorities.The results indicate that: external optical feedback interference signal has the same phase sensitivity as a conventional interferometer; the interference signal is more slantwise while the external optical feedback intensity is stronger; the signal is rightward inclined when the displacement of the microvibraton is increased, vice versa. For the nonlinear least squares method can estimate the the external optical feedback intensity and linewidth enhancement factor accurately, the reconstruction measurement method can measure microvibraton of arbitrary waveforms easily. Compare with the fringe counting method, not only the accuracy has been improved but also the error declines 1~2 orders of magnitude by the reconstruction measurement method. Compare with the phase analysis method, the measurement range has been enlarged by the reconstruction measurement method. Therefore, the microvibration reconstruction measurement method is easy to implement, has larger measurement range, higher measurement accuracy and lower measurement error. It has higher practical reference value.In order to study the external optical feedback interference further, the characteristic of interference signal when multi-mode laser system used is discussed. The range of feedback intensity is calculated, when the system has three mode. The characteristic of interference signal when multiple external optical feedbacks existed is also discussed. Compare with the interference signal which only the first feedback is taken into account, we know that when the feedback intensity is strong, the high-order feedback can not be neglected.