Distance measurement for curved surface based on confocal technique

A new method based on confocal microscopy is presented to measure the distance between the focus of an objective lens and the curved surface. The focus error signal based on this method is constructed. And this signal features not only the possession of the linear relationship to the defocus, that is the distance between the focus of the objective lens and the curved surface, and direction information of defocus and a wide measuring range, but also the independence of the tilt angle of curved surface, the power fluctuation and the like.