Laser measurement of high-speed displacement using intensity correlation between probe and phase-modulated reference signals

In this study, the potential for displacement measurement of a high-speed moving object is experimentally investigated in a laser displacement measurement system that is based on the intensity correlation between probe and phase-modulated reference signals. Being different from typical systems that measure the intensity correlation with an electrical multiplier that multiplies the O/E converted signals of the probe and the reference, the proposed system modulates the reference light by driving a modulator with the O/E converted signal of the probe light that has been reflected from the moving object. Because high-speed electrical circuits for the correlation measurement are greatly reduced, the system configuration is simplified. In the proposed method, the reference point of distance measurement depends on the initial phase difference between the probe and the reference signals, whereas this phase difference is simply controlled by the electrical signal generator. Therefore, high-speed sweeping of the initial phase of the modulation signal is equivalent to high-speed displacement. The proof-of-concept experiment using this virtual displacement confirmed that the proposed displacement system has the potential to measure the displacement of an object moving at a high speed of 1 m/s over 160 mm with an error of less than0.8 mm.