Multi-head frequency-modulated continuous-wave ranging for real-time speckle suppression

Optical frequency-modulated continuous-wave (FMCW) ranging enables high-precision and high-speed distance measurements for applications requiring stable positioning and efficient inspection in factory automation. However, due to the influence of speckle, which arises while ranging a target with a rough surface, measured displacement changes more than surface roughness, leading to decreased range precision. Speckle suppression with real-time measurements is required for constructing industrial displacement sensors. Here, we demonstrate speckle suppression with multi-head interferometers based on the principle of FMCW ranging. Using a signal selection algorithm to eliminate factors that deteriorate precision due to speckle, we can experimentally reduce excess uncertainty and improve precision in real-time measurements without the need for complex techniques. This speckle-suppression strategy can be applied not only to the displacement measurements of any material but also to further extending the measuring capability of other laser-based displacement sensors.