Master of Engineering by Research
School of Electrical, Computer and Telecommunications Engineering
Fan, Yuanlong, Improvement of measurement performance for self-mixing interferometry based displacement sensing system, Master of Engineering by Research thesis, School of Electrical, Computer and Telecommunications Engineering, University of Wollongong, 2011. http://ro.uow.edu.au/theses/3213
The core components of a Self-Mixing Interferometry (SMI) based displacement sensing system, consists of a Laser Diode (LD), a micro-lens and a moving target which forms an external cavity of the LD. Displacement information of the moving target is carried in the laser power emitted by the LD. The laser power is called a Self-Mixing Signal (SMS). The existing methods for extracting displacement from a SMS are not perfect, e.g. (or assuming a SMI with a constant optical feedback level, or not fully considering all SMS waveforms). By studying the features of SMSs at different cases, the thesis proposes an improved algorithm used for displacement reconstruction using a SMI sensing system. The algorithm can theoretically achieve an unbiased displacement measurement for all feedback cases. Meanwhile, considering the time-slow changing optical feedback level factor (denoted by ), the thesis presents a simple and fast estimation method of the value. Real-time updating for further improves the measurement performance for a SMI based displacement sensing system.
A SMI based experimental system is built to verify the proposed algorithm. Signal pre-processing methods for experimental SMSs in terms of filtering and normalization are also presented in this thesis. A commercial sensor is used for confirming the results from our experimental set-up. The comparison between the commercial sensor and our SMI system shows that the proposed algorithm in the thesis can achieve accurate displacement reconstruction.
The studies in this thesis on SMSs build a solid foundation for developing a SMI based displacement sensor.