Sensors and Actuators A 135 (2007) 465–471 A novel method for fabrication of self-aligned double microlens arrays Jeng-Rong Ho a,∗ , Teng-Kai Shih b , J.-W. John Cheng a , Cheng-Kuo Sung c , Chia-Fu Chen b a Graduate Institute of Opto-mechatronic Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan, ROC b Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, ROC c Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, ROC Received 19 October 2005; received in revised form 4 August 2006; accepted 7 September 2006 Available online 20 November 2006 Abstract Based on the excimer laser microdrilling and the spin coating scheme, a new fabrication method of polymeric, double microlens arrays on a thin plastic pedestal sheet is proposed in this study. On each through hole on the pedestal sheet, a double microlens pair, consisting of two microlenses with different parabolic surfaces, is sited. The two microlenses of each pair are located respectively on both ends of the through hole and arranged surface to surface and automatically share a common lens principal axis. The fabricated microlens arrays are made of PMMA that are formed on a PMMA pedestal sheet with thickness of 100 m. The diameter and height for the microlens on one layer are of 150 m and 28 m, respectively, and they are correspondingly of 130 m and 24 m on the other layer. Experimental results demonstrate that the double microlens arrays have a better focusing property than the single-layer mircolens array. Simulation results indicate that, simply by changing the thickness of the pedestal sheet, the present fabricated double microlens arrays can serve the purposes for light collimating and diffusing. Due to its inherent simplicity in fabrication, the present method has high flexibility for making double microlens arrays with different lens configurations and various lens refractive indices. The facts that precise alignment and all processing steps are performed in ambient and at low temperature render the proposed approach a potential low-cost method for fabrication of double microlens arrays. © 2006 Elsevier B.V. All rights reserved. Keywords: Microlens array; Double microlens arrays; Excimer laser microdrilling; Lens pedestal; Microdoublet lens; Beam profiler analyzer 1. Introduction Refractive microlenses with lens diameters of a few to several hundred micrometers are very important components in today’s high performance, compact optical systems including, for exam- ples, optical communication, optical storage, video camera, opti- cal scanner, high-definition projection display and optical and biomedical inspection instruments [1,2]. The use of refractive microlenses can be an effective solution in increasing optical coupling efficiency and tolerance. Thus, a need for custom- designed, low-cost, compact and lightweight microlenses is increasing. Since the 1990s, many researchers have been explor- ing various ways to fabricate refractive microlens arrays based on different lens materials [3–16]. Among these studies, several are concentrated on the glass-based lenses, which have been studied for a relatively long time. However, more are focused on ∗ Corresponding author. Tel.: +886 5 2720411x33316; fax: +886 5 2724036. E-mail address: imejrho@ccu.edu.tw (J.-R. Ho). the polymer-based materials. The microjet technique [3], pho- toresist reflow method [4], ultraviolet curing of polymer [6], hydrophobic effect method [7], LIGA method [10] and soft replica molding method [15] are all newly developed meth- ods for the polymeric lenses. With continuous improvement in material properties and advance in processabilities, a constant increase in the usage of polymeric microlenses is highly pro- jected. For applications in systems of scanning, optical coupling and interconnection, beam homogenizing, microlens projec- tion lithography and the miniaturized imaging, microlens arrays are usually arranged based on spatial superposition to achieve particular purposes of light collimating, focusing, diffusing or imaging. However, packaging and alignment of stacks of minia- turized lens systems is a rather difficult task. The classical mounting techniques are not practical and expensive. Currently, the preferred method is manufacturing on the basis of a wafer- level packaging on which the stack of planar wafers containing microoptics and electronic devices are bonded on a mask aligner and then separated into individual systems or modules by the 0924-4247/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2006.09.007