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.

In this study we propose an annular-beam dual-detection confocal reflectance microscopy (ADDCRM) method for high-speed three-dimensional surface measurements without longitudinal mechanical translation. ADDCRM can measure the axial position of a sample surface using the axial response curve ratio of two photodetectors, each with a different diameter pinhole. Since the height measurement range is limited by the full-width at halfmaximum of the ratio curve, an annular beam is used to extend the depth range without reducing the lateral resolution. The experimental results demonstrate that ADDCRM achieves high-speed surface profiling with a doubled-height measuring range compared to conventional Gaussian beams.

No abstract