Absolute distance estimation with improved genetic algorithm in laser self-mixing scheme

• Improved genetic algorithm is used in self-mixing interferometry to obtain distance.
• Exploration range shrinking technique is used to accelerate the algorithm.
• Distance resolution and stability of the proposed method are better than 20μm.
• Speckle effect has little influence in the system.
• The algorithm is even applicable to harsh SNR condition.

Absolute distance estimation by self-mixing interferometry (SMI) has superiority to other laser range finding methods due to its simplicity and compact structure, which can make it applied in narrow space and small precision parts. To ameliorate the distance resolution performance of SMI, we proposed a distance estimation method based on improved genetic algorithm, instead of traditional frequency beat detection, to process the self-mixing signal. The method establishes a cost function from the self-mixing signal and then employs the improved genetic algorithm to search for the optimum distance value by global optimization other than frequency analysis. The validity of this approach was demonstrated by experimental measurements showing resolution superior to 20μm and stability about 10μm in the range from 2.4 to 20.4 cm. The comparison with other methods and the influence of speckle and noise were discussed additionally.