Development of lens central thickness measurement system using laser differential confocal microscopy

A new non-contact lens central thickness measurement system is developed based on high precision optical confocal positioning technique. The developed system uses the high axial chromatography property of differential confocal microscopy and the absolute zero of the axial response curve to precisely identify the vertexes of the lens front and back surfaces, uses a laser interferometer instrument to record the position coordinates of the vertexes, and then uses the ray tracing algorithm to calculate the central thickness of the lens; thus the high precision and non-contact measurement of the lens central thickness is achieved. Experiment results indicate that the system has high measurement accuracy; and the standard deviation of the measurement is less than 1 μm, which meets the requirements of measurement accuracy in lens thickness measurement.