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TECHNICAL PAPERS

# Spherical and Aspheric Microlenses Fabricated by Excimer Laser LIGA-like Process

[+] Author and Article Information
Yung-Chun Lee1

Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 701yunglee@mail.ncku.edu.tw

Chun-Ming Chen

Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 701

Chun-Ying Wu

Institute of Micro-Electro-Mechanical-System, National Cheng Kung University, Tainan, Taiwan 701

1

Corresponding author.

J. Manuf. Sci. Eng 129(1), 126-134 (Jun 26, 2006) (9 pages) doi:10.1115/1.2401622 History: Received March 02, 2006; Revised June 26, 2006

## Abstract

This paper presents an effective and low-cost method for fabricating spherical and aspheric microlenses based on excimer laser LIGA-like processes. It is based on a newly developed excimer laser micromachining technique that can accurately machine a 3D microstructure with a predetermined continuous surface profile. The method is called the planetary scanning method since it is based on a combination of sample rotation and revolution and a concept of laser machining probability. Spherical and aspheric microlenses with precise and smooth surface profiles are fabricated by direct laser machining on polymer materials. Laser-machined microlenses are replicated by electroforming to obtain inverse metal molds. Finally, plastic microlenses are replicated from these metal molds using hot embossing method. The profile accuracy and surface roughness of the produced microlenses at each stage have been measured and monitored. The average surface profile accuracy is better than $1μm$ and average surface roughness is less than $10nm$. Optical performance of the fabricated microlenses is evaluated by measuring the light intensity distribution at the focal plane and the focal length. Experimental data show that the characteristics of fabricated spherical and aspheric microlenses are well matched to the theoretical predictions, which demonstrates the controllability and accuracy of this micromachining process. Potential applications and further developments will be addressed.

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## Figures

Figure 1

Schematic diagram of the excimer laser micromachining system

Figure 2

Typical mask design for excimer laser micromachining of 3D microstructures

Figure 3

Planetary contour scanning method: (a) mask machining probability distribution, (b) sketched combined mask rotation and orbit scanning, and (c) resultant global probability distribution

Figure 4

Typical mask probability function for convex microstructures

Figure 5

Determined mask probability functions for the five microlenses

Figure 6

Comparison between calculated surface profiles based on the determined mask probability function of lens #5 to the originally designed one

Figure 7

Mask design of lens #5 based on the determined mask probability function

Figure 8

Excimer laser machining rate for polycarbonate samples

Figure 9

(a) Measured surface profile and (b) SEM micrographs of a machined microlens

Figure 10

Comparison between laser-machined surface profiles and their originally designed ones for all five microlenses

Figure 11

(a) Laser-machined microlens #5 and (b) its negative nickel replica from electro-deposition

Figure 12

Comparison between the surface profiles of laser-machined microlenses and the hot-embossed ones

Figure 13

Optical characterization system for the fabricated microlenses

Figure 14

(a) Light intensity measurements of microlenses and images taken by CCD camera at (b) the edge of lens and (c) the lens’ focal plane

Figure 15

Intensity profiles of lens #5 at focal plane for laser-machined and hot-embossed microlenses

Figure 16

Experimental measure data (in symbols) of (a) focal spot sizes and (b) focal length of laser-machined and hot-embossed microlenses along with their simulated counterparts (solid and dashed lines)

## Errata

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