An optical system incorporating gradient-index lens for confocal inspection

A differential confocal measurement system features high lateral resolution and depth-discriminated sections. In comparison with conventional lens, gradient-index lens is lighter in weight, smaller in volume and easy to couple. In order to facilitate the measurement of a small irregular surface in a limited space, a small optical inspection system is presented, which combines the high axial resolution and absolute position tracking capability of a differential confocal microscopy and the compact design of gradient-index lens, and uses gradient-index lens to obtain a small detector of 1 mm in diameter. The operating principle and construction of the measurement system are detailed. The differential design of the two detectors eliminates both the fluctuation of light source and the electronic noise from probes, and increases the axial resolution as well.