Efficient Shape Reconstruction of Microlens Using Optical Microscopy

The imaging properties of a microlens are highly related to its 3-D profile; therefore, it is of fundamental importance to measure its 3-D geometrical characteristics with high accuracy after industrial fabrication. However, common 3-D measurement tools are difficult to use for fast, noninvasive, and precise 3-D measurement of a microlens. Depth acquisition is a direct way to understand the 3-D properties of objects in computer vision, and shape from defocus (SFD) has been demonstrated to be effective for 3-D reconstruction. In this paper, a depth reconstruction method from blurring using optical microscopy and optical diffraction is proposed to reconstruct the global shape of a microlens. First, the relationship between the intensity distribution and the depth information is introduced. Second, a blurring imaging model with optical diffraction is formulated through curve fitting, accounting for relative blurring and heat diffusion, and a new SFD method with optical diffraction and defocused images is proposed. Finally, a polydimethylsiloxane (PDMS) microlens is used to validate the proposed SFD method, and the results show that its global shape can be reconstructed with high precision. The average estimation error is 77 nm, and the cost time is reduced by 92.5% compared with atomic force microscopy scanning.