A tapered fourcores phase-shift FBG probe for three-dimensional micro-scale measurement

The minimum measurable dimension and accuracy are the most considerable performances of the micro-scale dimensional measurement methods. The fourcores FBG probe has such advantages as three-dimensional tactile sense, high measurable depth, small probing system in size, and low risk of mechanical interference with the measuring components. To further extend the minimum measurable dimension at the least cost of its sensitivity and accuracy, a design of tapered and phase-shift FBG stylus is proposed. Direct analysis of the fine spectral structure of the π/2 phase-shift point is found to have significant suppression effects on spectral signal distortion induced by the tapered stylus. Experimental results indicate that the central wavelength error of signal spectrum is improved from 9 to 0.45 pm. Simultaneously, the tapered design can extend the minimum measurable dimension by twofold to 99.24 μm and has nearly no influences on its sensitivity. To the best of our knowledge, it is the first time to achieve a fourcores FBG probe with a spherical tip of less than 100μm in diameter. Moreover, its three-dimension tactile displacement resolution can reach 30 nm and the positioning repeatability of tactile points is better than 31.1 nm. It would be widely used in measuring micro-scale features for industry inspection and metrology.