An automatic evaluation method for the surface profile of a microlens array using an optical interferometric microscope

Abstract

In this paper, an automatic evaluation method for the surface profile of a microlens array using an optical interferometric microscope is presented. For inspecting the microlens array, an XY-table is used to position it. With a He–Ne laser beam and optical fiber as a probing light, the measured image is sent to the computer to analyze the surface profile. By binary image slicing and area recognition, this study located the center of each ring and determined the substrate of the microlens array image through the background of the entire microlens array interference image. The maximum and minimum values of every segment brightness curve were determined corresponding to the change in the segment phase angle from 0° to 180°. According to the ratio of the actual ring area and the ideal ring area, the area ratio method was adopted to find the phase-angle variation of the interference ring. Based on the ratio of actual ring brightness and the ideal ring brightness, the brightness ratio method was used to determine the phase-angle variation of the interference ring fringe. The area ratio method and brightness ratio method are interchangeable in precisely determining the phase angles of the innermost and outermost rings of the interference fringe and obtaining different microlens surface altitudes of respective pixels in the segment, to greatly increase the microlens array surface profile inspection accuracy and quality.

Automatic optical inspection system for 3D surface profile measurement of multi-microlenses using the optimal inspection path

“…According to table 1, the lens sags of microlenses with different sizes can be correctly measured by the proposed system. In comparison to the Surfcorder ET3000 and other non-contact The phase difference error in [16][17] is eliminated by the proposed method. type instruments, the proposed system is lower cost because of its simple structure, and is able to avoid scratching the lens surface and to provide the ability of rapid 3D surface profile measurement by using only a single fringe pattern.…”

“…In addition, since the phase difference in equation ( 11) is calculated through the concept of sign reversal, the possible errors in [16,17] when the inspected surface does not continuously increase or decrease are eliminated, as shown in figure 13. The microlens center positioning technique is applicable to multi-microlenses or a single microlens, and the computational process of phase retrieving is also simplified, which enhances the applicability of the proposed system.…”

“…Different from the method in [16,17], the phase difference of every neighboring pixel is calculated using equation (11) with a sign reversal. The surface height of a specific pixel on the radial line can be obtained by summing up the phase differences from the microlens edge to the target pixel, without using a phase unwrapping method: where H(i) is the surface height of the ith pixel on the radial line; λ is the wavelength of the adopted light source.…”

“…In addition, a complex experimental setup is required for introducing the special carrier, which increases the cost. In the former researches [16,17], we measured the twodimensional (2D) and three-dimensional (3D) surface profile of a single microlens by the principle of Fizeau interfrometer. The absolute value of the phase difference is directly used to calculate the lens sag, without considering the sign reversal.…”

An automatic optical inspection system for measuring a microlens array with an optical interferometric microscope and genetic algorithm

“…Then the system can obtain microlens surface altitudes of respective pixels in segment. Let the segment where center circle (x c , y c ) lies be the nth segment, then the corresponding microlens surface altitude difference dd(x) between point (x, y) and (x þ 1, y) in the ith segment can be obtained from the following equation (Lin et al, 2010b):…”