Velocity measurement by speckle modulating an Erbium-doped fiber ring laser

In this paper, Speckle modulating an erbium-doped fiber ring (EDFR) laser is used to detect the velocity of dynamic diffused object. All-fiber structure of the speckle measurement system is set up. The autocorrelation function of speckle signal related with the velocity variable of a moving object under test is theoretically derived. By experiments, the speckle signals are acquired by a photodiode, and using the autocorrelation function, we calculated the correlation coefficient of the speckle signals. When the coefficient is equal to 1/e, the velocity of the object is determined. In order to explore the influence that the signal length affects on measurement accuracy, a group of signals with different length of time is applied to calculate the velocity, and the result indicates that when signal length is greater than the correlation length, the measurement error is very small.