Development of a double fiber probe with a single fiber Bragg grating for dimensional measurement of microholes with high aspect ratios.

A fiber Bragg grating (FBG)-based probe is developed by designing a novel double fiber structure to make the probe sensitive to both axial and radial contact displacements. A matched FBG pair interrogation system for the probe is modeled, and the best matched initial condition is found to make the probing system work in the linear and most sensitive mode. Actual measurements of ring gauges and fuel injection nozzles indicate that, for a microhole with an aspect ratio of greater than 14∶1, an axial resolution of 8 nm and a radial resolution of 30 nm can be achieved with the developed probe. It is therefore concluded that the double fiber probe with a single FBG developed can be used to measure high aspect ratio microholes.