REAL-TIME DISPLACEMENT MEASUREMENT USING SYNCHRONOUS DETECTION IN A SINUSOIDAL PHASE MODULATING INTERFEROMETER

A real-time displacement measurement system using a sinusoidal phase modulating interferometer is proposed and demonstrated. The system utilizes the frequency components of the interference signal to detect the desired phase or the displacement in real time. The real-time phase detector is constructed with simple electronic circuits. The system also has a feedback loop to eliminate external disturbance. It is easy to measure the relatively large displacement that exceeds a half wavelength of the light because the compensation circuit is incorporated into the system to obtain continuous phase outside the region from 0 to 2pi.