Integrated optical inspection on surface geometry and refractive index distribution of a microlens array

Abstract

This paper presents an effective technique based on optical interferometry to investigate the surface geometry/profile and refractive index distribution of a planar microlens array. The experimental setup consists of a sodium light source and a He-Ne laser source, which are incorporated into a microscopy system. The two light sources with different coherence lengths are utilized alternatively for surface geometry and refractive index evaluation. The fringe patterns resulting from the sodium light and laser source illumination are analyzed by the proposed algorithms, fast Fourier transform (FFT) as well as fringe tracking. Experimental results demonstrate that surface profile and graded-index property of the micro-lenses can be readily determined in the same setup. In addition the common optical-path design enables the proposed setup to be insensitive to environment vibration. © 2003 Elsevier B.V. All rights reserved.