Laser Swept-Frequency Feedback Interferometry for Three-Dimensional Displacement Measurement

Laser feedback interference occurs when the output of a laser is reflected or scattered back to the laser cavity by a remote target, mixing with the light inside the cavity. This paper designs a laser swept-frequency feedback interferometer (LFI) for measuring three-dimensional (3D) displacement. By combining a reflective two-dimensional (2D) crossed grating with a laser feedback interferometer, the measurement system employs the grating pitch as the measurement scale rather than the wavelength, offering improved resistance to environmental disturbances. By introducing the optical frequency-modulated continuous-wave technique inspired by radar, the measurement system can perform real-time 3D displacement measurements using only a single laser source. Experimental results indicate that the relative error of 3D displacement measurement using this method is less than 0.42%, while achieving nanometer-level resolution. The proposed optical structure offers the benefits of simplicity, robustness, and cost-effectiveness.