Laser Doppler shift measuring method based on phase modulater and Fabry-Perot interferometer

A different method of laser Doppler shift measurement is proposed. By using the sinusoidal phase-modulation, the plus and minus one-order sidebands beside the original frequency component in signal light are generated. And a beat frequency signal with fixed-frequency is present when the amplitude and phase of the modulated light are turned with Fabry-Perot interferometer. The characteristic of the amplitude of this beat frequency signal changing with the frequency is used to measure the Doppler shift. By theoretically analyzing, it can be concluded that this method can possess the advantages of both the normal coherent and non-coherent methods and also has the merits of high measuring accuracy and easy fabrication. The validity and feasibility of this method are verified experimentally, and its measurement accuracy is found experimentally to be one order of magnitude higher than that of the normal non-coherent method.