Range-Extended Confocal Chromatic Sensor System for Double-Sided Measurement of Optical Components With High Lateral Resolution

This paper presents a strategy to break the tradeoff between the thickness measuring range of a confocal chromatic sensor (CCS) and its lateral imaging resolution. By combining the sensor with a linear stage, the thickness measuring range is no longer limited by chromatic dispersion, but by the focusing power of the sensor optics. The principle is demonstrated with a prototype setup that utilizes a CCS with a spot size of 6 μm and a spec-sheet thickness measuring range of 300 μm. By implementing the proposed mechatronic approach, a successful extension of the measuring range by a factor of 17 is achieved while preserving the lateral resolution of 2.46 μm for thickness measurements. The proposed measurement scheme is validated by measuring lateral surface features on a 1.2mm thick lenslet array from the backside.