Angle measurement method based on speckle affected laser self-mixing interference signal

Abstract Due to the speckle effect in the laser self-mixing interference (SMI), the signal amplitude will fluctuate greatly, which will affect the measurement accuracy and range. The angle measurement method based on speckle affected SMI signal is presented. The high frequency and low frequency noises in SMI signal can be filtered out simultaneously by variable mode decomposition. The envelope of SMI signal is calculated by Hilbert transform and the envelope signal is used to normalize the speckle affected SMI signal. The angle is calculated indirectly according to displacement measurement results obtained by fringe counting method. The experimental results show that the relative error of angle is ± 2% with the angle measurement range of 1°.