Reflectometric fiber optic frequency-modulated continuous-wave interferometric displacement sensor

A practical reflectometric fiber optic displacement sensor is reported. The sensor is based on the principle of optical frequency-modulated continuous-wave (FMCW) interference and primarily consists of a single-mode laser diode, a Y-type fiber optic directional coupler, and a quarter-pitch gradient-index lens. The displacement of the target is determined by measuring the phase shift of the beat signal with a special signal-processing method. An accuracy of 0.02 µm in a measurement range of 1000 µm has been achieved.