Abstract
We present a novel microfabrication approach for obtaining arrays of planar, polymer-based microlenses of high numerical aperture. The proposed microlenses arrays consist of deformable, elastomeric membranes that are supported by polymer-filled microchambers. Each membrane/microchamber assembly is converted into a solid microlens when the supporting UV-curable polymer is pressurized and cured. By modifying the microlens diameter (40-60 microm) and curing pressure (7.5-30 psi), we demonstrated that it is possible to fabricate microlenses with a wide range of effective focal lengths (100-400 microm) and numerical apertures (0.05-0.3). We obtained a maximum numerical aperture of 0.3 and transverse resolution of 2.8 microm for 60 microm diameter microlenses cured at 30 psi. These values were found to be in agreement with values obtained from opto-mechanical simulations. We envision the use of these high numerical microlenses arrays in optical applications where light collection efficiency is important.
Highlights
Microlenses are used in optical communication [1,2], displays [3,4], optical sensors [5,6], photolithographic systems [7,8] as well as in biomedical imaging applications [9,10,11]
We present a novel microfabrication approach for obtaining arrays of planar, polymer-based microlenses of high numerical aperture
Recent advances in micromachining technology led to the development of a variety of microlens microfabrication approaches including photoresist-reflow and transfer methods [12,13], ink jet processes of UV curable polymers [14], hot embossing techniques [15], micromolding using silicon substrates [16,17], soft lithography-based replication processes by molding various materials against rigid or elastomeric molds [18,19,20]
Summary
Microlenses are used in optical communication [1,2], displays [3,4], optical sensors [5,6], photolithographic systems [7,8] as well as in biomedical imaging applications [9,10,11]. Photoresist-reflow methods rely on the surface tension of the photoresist to form a smooth microlens surface These methods require accurate control of the microfabrication parameters (photoresist thickness, hydrophobicity) and produce microlenses with small numerical aperture (NA) due to the small aspect ratio (thickness vs diameter) of the patterned photoresist. The proposed approach has three major advantages: a) the microlens focal length can be adjusted by regulating the pressure applied to the filling polymer during curing, b) the use of PDMS as the mold material enables large membrane deflections that result in microlenses with high NA, and c) the optical properties (e.g. index of refraction) of the microlenses can be varied as there is a large collection of commercially available curable materials. We envision such microlens arrays to play a key role in various lab-on-chip detection systems for imaging micron-size objects (cells, viruses, etc.) [26,27]
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