Design And Simulation Of Micro-Displacement Measurement Based On Self-Mixing Interference With Laser Diode

Self-mixing Interference (SMI) technology arose some years ago. The system based on SMI has high sensitivity and precisionf. Moreover, the structure of the self-mixing interferomiter with the laster-diode is simpler, cheaper and smaller than traditional interference technology. So it must has well prospect.The ascendancy of SMI technology just consists in the measurement of geometric sense. The resulting instrument offers sub-μm resolution in the measurement of displacement up to 1m of total shift. We use the technology to detect micro-displacement. The developments of Self-mixing Interference technology an ites application have been elaborated. By using the rate equations first derived by Lang and Kobayashi and the model of a three-mirror cavity, the mechanics of theself-mixing interference effect can be analyzed. The main emphasis of research is the method based on fringe count and peripheral circuits are designed in detail.Both the hardware design and software design are elaborated. In order to get more accurate result and faster processing speed, we use FPGA instead of other MCU as the CPU of the system. The operating frequency of FPGA is high and it has poweful and flexible function especially to the high frequency digital.The Speckle Tracking system is disigned inorder to improve the precision of self-mixing Interference signal processing. We can use the servo loop to keep the photodetected signal amplitude at a maximum, and this means that we lock the optical system to a bright speckle. FPGA is also used as CPU of the PID control system. The processing speed and accuracy of the PID controller based on FPGA are much higher than classical PID controller. The resource of FPGA are fully utilize, so the size of digital circuit is decrease which is beneficial to the development and design of embedded system.VB is used to develop system interface, which can shorten development sycle of the software construction. Meanwhile it can implement fully user-defined fuction and generate friendly user interface. RS-232 is used to communicate with PC and FPGA, which make the real-time monitoring result possible.Using computer and EDA software, SMI theoretical model and upper and lower computer systems are simulated. The results of simulation indicate that it is accord with actual requirements and the feasibility of this system is demonstrated.