End-to-End Calibration and Performance Validation of a Chromatic Confocal Displacement System with a Reproducible All-Spherical Objective

Abstract

Chromatic confocal studies often report optical design and metrology performance using non-equivalent metrics, limiting reproducibility and practical comparison. We present a design-to-validation study built around a reproducible four-element, three-group all-spherical objective using CDGM catalog glasses. The objective provides an NA of 0.25, a 40 mm working distance, and a nominal 2.100 mm focal shift over 400–700 nm. The workflow separates calibration residuals, independently referenced errors, fixed-position repeatability, and paired-step response, and incorporates manufacturing-tolerance analysis. A monotonic PCHIP calibration produced a 2.31 mm empirical operating interval, while measurement and simulation agreed within 2.90% over their common 440.7–700 nm band. Positions excluded from calibration yielded an uncorrected RMSE of 1.561 µm. Under a predeclared engineering criterion, 1.0 µm centrally and 1.5 µm across the full range were the smallest tested steps that passed. Tolerance analysis identified cemented-group decenter as the dominant sensitivity with assembly refocusing. The principal contribution is a reproducible catalog-glass prescription combined with an error-separated validation protocol that establishes practical performance boundaries without conflating repeatability with absolute accuracy.