The Study of Refractive Index Measurement Based on the Self-Mixing Interference in Laser Diode

In this work, a refractive index measurement method based on the self-mixing interference is presented. The principles of the method used two-mirror cavity equivalent model are studied in this paper, and the mathematical model is given. Wavelength modulation of the laser beam is obtained by triangular modulating the infection current of the laser diode. Refractive index of sample is determined by Fourier analysis method. The frequency of signal from PD is linearly dependent on refractive index, but also affected by temperature and fluctuation of current source. A dual-path method, which uses the reference technique for absolute distance measurement, has been proposed. The theoretical analysis shows that the method can eliminate errors resulting from distance-independent variations in the setup. Accuracy and stability can be improved. The measuring of refractive index in the 1.33-1.45 range was simulated. Simulated results reveal the possibility to carry out low-cost refractive index measurement with a resolution of 5times10^-4.