Two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method

The invention provides a two-degree-of-freedom heterodyne grating interferometer displacement measurement system and method. The system comprises a double-frequency laser device, a grating interferometer, a measuring grating, a receiver and a signal processing unit. The grating interferometer comprises a lateral displacement light splitting prism, a polarization light splitting prism, a 1/4 wave plate, a reflecting mirror and an optical fiber coupler. The method realizes displacement measurement based on grating diffraction, the optical Doppler effect and the optical-beat frequency principle. Laser of the double-frequency laser device is incident to the interferometer and the measuring grating and then optical signals are outputted to the signal processing unit. When the interferometer and the measuring grating perform two-degree-of-freedom linear relative movement, the system can output two linear displacements; the measurement system adopts Littrow incident conditions, a measurement target has large passive movement tolerance and two linear displacements can be measured simultaneously so that precision can reach the nanoscale and higher scale; and the measurement system has advantages of short light path, small size, compact structure, low weight and low requirement for the measuring grating and is suitable for two-degree-of-freedom high-precision long-stroke displacement measurement.