Compact fiber optic dual-detection confocal displacement sensor.

We propose a dual-detection confocal displacement sensor (DDCDS) with a compact fiber-based optical probe. This all-fiber-optic sensor probe is simple and robust, since it only requires simple alignment of a gradient refractive index lens and a double-clad fiber (DCF). The DDCDS is composed of two point detectors, one coupled to a single mode fiber and the other coupled to a multimode fiber, which are used to measure the light intensity from a core and an inner clad of a DCF, respectively. The ratio of the axial response curves, measured by the two detectors, can be used to obtain a linear relationship between the axial position of the object plane and the ratio of the intensity signals. We demonstrate the performance of the proposed method by measuring micromovement and fast vibration.