The guided mode resonance (GMR) phenomena has been studied and exploited for applications in
sensors, polarizers, dichroic laser mirrors, and more. These micro-optical structures serve as highly
functional devices capable of narrowband spectral filtering. Their relatively simple design includes a
subwavelength periodically modulated index layer and a waveguiding layer. This configuration
yields efficient and easily tunable devices over a broad range of wavelengths. Currently GMR filters
have been fabricated exclusively on flat surfaces. In this paper, we demonstrate fabrication of GMR
filters on conformal surfaces using non-traditional techniques. Flexible molds are used as replication
templates in a micro-transfer molding process. SU-8 negative photoresist serves as the molded
polymer with good thermal characteristics compatible with subsequent deposition of dielectric
layers. Fabrication procedures for GMR filters at near-IR wavelengths on concave lens surfaces are
discussed, and initial experimental results are presented.
SU-8 is a very promising material for micro-optics. It is mechanically robust with high thermal and chemical resistance, has high transmission at visible and near-infrared wavelengths, and has relatively high refractive index after curing. While lithographic processing of SU-8 is relatively common, molding of SU-8 requires different processing parameters due to challenges with solvent removal and cross-linking. Understanding the effects of the molding process on SU-8 is necessary to optimize performance of molded micro-optical components and also to enable fabrication of more complex micro-optics through subsequent lithographic processing of molded structures. We examine properties of SU-8 as it undergoes the molding process. General characterization of SU-8 shrinkage and expansion is presented, and replication of sub-100-nm structures in SU-8 is demonstrated. Solvent content and refractive index as functions of processing parameters are also examined, along with analysis of SU-8's lithographic properties after undergoing the molding process. These characterizations further enable hybrid combinations of micromolding and lithographic processing to fabricate complex 3-D micro-optics and structures that are difficult or impossible to realize using conventional techniques.
SU-8 is a very promising material for micro-optics. It is mechanically robust with high thermal and chemical resistance,
has high transmission at visible and near-infrared wavelengths, and has relatively high refractive index after curing.
While lithographic processing of SU-8 is relatively common, molding of SU-8 requires different processing parameters
due to challenges with solvent removal and cross linking. Understanding the effects of the molding process on SU-8 is
necessary to optimize performance of molded micro-optical components, and also to enable fabrication of more complex
micro-optics through subsequent lithographic processing of molded structures. In this paper, we examine properties of
SU-8 as it undergoes the molding process. General characterization of SU-8 shrinkage/expansion is presented, and
minimum moldable feature sizes are explored. Solvent content and refractive index as functions of processing
parameters are also examined, along with analysis of the SU-8's lithographic properties after undergoing the molding
process. These characterizations further enable hybrid combinations of micro-molding and lithographic processing to
fabricate complex micro-optics that are difficult or impossible to realize using conventional techniques.
SU-8 is a very promising polymer for micro-optics. It is mechanically robust with high thermal and chemical resistance,
has high transmission at visible and near-infrared wavelengths, and has relatively high refractive index after curing.
While lithographic patterning of SU-8 is relatively common, molding of SU-8 is more difficult due to challenges with
solvent removal and cross linking. In this paper, we discuss techniques for micromolding of micro- and nano-optics in
SU-8. Elastomeric mold templates are first cast from master structures fabricated using standard techniques. The
elastomeric templates are then used in low pressure molding processes to produce high-fidelity refractive and diffractive
micro-optics in SU-8. The use of the elastomeric replica mold enables realization of a wider variety of optical surfaces
than can be achieved with conventional lithographic patterning in SU-8, and further enables conformal fabrication of
SU-8 micro-optics on non-planar surfaces. Molding processes and experimental results for both thin (diffractive) and
thick (refractive) elements are presented. Replication of SU-8 micro-optics on both planar and non-planar surfaces, and
hybrid processes combining molding and lithographic exposure are demonstrated.
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