Fig. 1. Schematic diagram of the main composition of the MWI based on heterodyne and superheterodyne absolute distance measurement method with a He–Ne laser. HWP, half-wave plate; PBS, polarizing beam splitter; M, mirror; AOFS, acousto-optical frequency shifter; QWP, quarter-wave plate; NPBS, nonpolarizing beam splitter; RR, retroreflector; P, polarizer; PD, photodetector.

Fig. 2. Generation principle of multiwavelengths.

Fig. 3. Schematic setup for the synchronous detection and demodulation. A, amplifier; LPF, low-pass filter.

Fig. 4. Phase measurement data when the phase difference was set to (a) 90° and (b) 180°.

Fig. 5. (a) Experimental setup for absolute distance measurement based on heterodyne and superheterodyne combined absolute distance interferometry. (b) Experimental results of distance measurement at 2 m.