The invention discloses a
phase modulation direct detection
laser Doppler velometer and a velocity measuring method thereof, and relates to a direct detection
laser Doppler velometer. In order to solve the problem that a method of converting frequency change of back scattering light into the change of
transmittance by utilizing edge filters of a Fabry-Perot (F-P) interferometer in the current direct detection mode to obtain
Doppler frequency shift is low in measuring accuracy relative to a coherent detection mode, the invention provides the
phase modulation direct detection
laser Doppler velometer and the velocity measuring method thereof. According to the method, a beat frequency
signal of which the
vibration amplitude is changed with the
Doppler frequency shift of a moving target is generated by an electric-
optical phase modulator and the FP interferometer; a
vibration amplitude item is extracted by a phase shifter, a multiplying unit and a low-pass filter, and optical
wave frequency information is identified by utilizing the
vibration amplitude item; and the frequency of emitted laser and target back scattering light is measured by utilizing the turning-on state and turning-off state of a mechanical switch, and difference of two-time frequency measuring values is used as a measuring value of the
Doppler frequency shift. According to the
phase modulation direct detection laser Doppler velometer, the influence of the change of
light intensity on a measuring result is removed by the energy detection of backward
waves, so that the phase modulation direct detection laser Doppler velometer is used for measuring the movement velocity of targets in the field of
optics.