Measurement Of Feedback Strength Factor Of Optical Feedback Self-mixing Interferometry Systems

The self-mixing optical feedback interferometry (OFSMI) effect occurs when the light emitted from the laser is reflected or scattered from the external target, a portion of the laser output which contains the information of the target back into the laser cavity and mix with the original light in the laser cavity, resulting in the change of the output power. The OFSMI technique has been widely used in the measurements of semiconductor laser parameters, geometric and mechanical quantities for its significant advantages in simplicity, compactness and self-aligning.Optical feedback strength factor stands for strengths of optical feedback and it is of great importance in optical feedback self-mixing interferometry systems for its direct influences on characters of self-mixing signals. In the light of this, the measurement of optical feedback strength factor has theoretical and practical significance.The thesis mainly discusses the optical feedback strength factor measurement in the systems. Based on hysterisis phenomenon of OFSMI signals and the impacts of feedback strength factor on amplitude of OFSMI signals, the thesis proposed two methods for optical feedback strength measurement respectively. The proposed methods are tested and verified by both simulations and experiments. The main tasks are as follows:First of all, by solving the phase equation with different feedback levels described in the basic theoretical model of OFSMI effects, mode states and characters of semiconductor laser were discussed and studied in the paper.Secondly, characters of OFSMI signals with different feedback level were simulated. And a method used to measure the feedback strength factor was propose based on changes of amplitude of OFSMI signals with different feedback levels and factors that affect accuracy of the method were discussed as well.Thirdly, the hysterisis phenomenon of OFSMI signals was introduced and a formula about optical feedback strength factor was deduced by solving Lang-Kobayashi equations. Consequently, another method for measuring feedback strength factor was obtained. Then we applied two methods to the acquired experimental OFSMI signals and simulation signals, and results obtained through these two methods were contrasted. At last, conclusions are drawn from the whole paper and the further research issues are pointed out.