Phase modulation type laser feedback raster interferometer and measuring method thereof

The invention relates to a phase modulation type laser feedback raster interferometer and a measuring method thereof. The structure of the phase modulation type laser feedback raster interferometer is that: the laser emitted from a helium-neon laser enters a transmission type diffraction grating through vertical incidence; each level of diffracted lights are symmetrically arranged at two sides of a incident light path; the displacement direction of the diffraction grating is perpendicular to the output light path of the laser; an electrooptical modulator is arranged on a light path of +1 level of diffracted light for pure phase modulation; the modulated diffracted light enters into a planar mirror through vertical incidence and then returns along the original light path, and then enters into the diffraction grating again through incidence to generate secondary diffraction; a secondary +1 level of diffracted light carries the grating displacement information along the opposite direction of the emergent light of the laser and then returns to an cavity in the laser and then laser feedback interference occurs in the cavity between secondary +1 level of diffracted light and the light in the cavity; a photoelectric detector is arranged the backward output light path of the laser; the photoelectric detector is connected with an operational amplifier, a data collection card and a computer successively; and the displacement to be detected can be obtained through processing of the computer. The phase modulation type laser feedback raster interferometer has the advantages of being simple and compact in structure, being large in the measuring range, and being insensitive to the environment.