Joo Yeon Kim

Hybrid polymer microlens arrays with high numerical apertures fabricated using simple ink-jet printing technique

Microlens arrays fabricated by a direct ink-jet printing of UV-curable hybrid polymer are reported. A periodic pattern of polymer drops was ink-jet printed on the surface-treated glass substrate and cured in the UV-light. Using this simple technique, we demonstrated periodic arrays of almost semi-spherical microlenses of 50 µm diameter size and a focal distance of 48µm. The optical characteristics of solitary µ-lenses and arrays comprising up to 64x64 microlenses are measured both in the near- and far-field zones. Large numerical aperture and short focal distance make the ink-jet printing of microlenses very attractive for applications in optical interconnects, large 2D VCSEL arrays and pixelated imagine sensors utilizing CCD or SPAD arrays, offering thus an efficient, simple and a cheap alternative to the conventionally used photolithography technique.

Directly fabricated multi-scale microlens arrays on a hydrophobic flat surface by a simple ink-jet printing technique

A shape-tunable approach is demonstrated for the fabrication of multi-scale polymer microlenses (μ-lenses) and microlens arrays (MLAs) using an ink-jet printing (IJP) technique. Also, the influence of the surface wetting conditions on the geometrical and optical characteristics of the printed μ-lenses is investigated. A photo-curable organic–inorganic hybrid polymeric resist (H-resist) is used; it is printed on a hydrophobic-treated glass substrate with different number of drops per μ-lens and cured using an ultraviolet lamp (UV lamp). High quality μ-lenses and MLAs with good uniformity and reproducibility were fabricated. The lens diameters and heights were controllable by changing the number of H-resist drops together with tuning the surface wetting conditions; these shape changes affect the optical properties of the μ-lenses and MLAs such as the numerical aperture (NA) and focal distance (f), as well as the f-number (f#), which indicates the light-gathering power. The optical properties of the tunable μ-lenses and MLAs are very attractive for application in optical systems such as interconnects and pixelated imagine sensors that use CCD or SPAD arrays, offering an efficient, simple and cheap alternative to the conventionally used photolithography technique.

Inkjet‐Printed Multicolor Arrays of Highly Luminescent Nanocrystal‐Based Nanocomposites

Inkjet technology is a compelling method for the flexible and cost-effective printing of functional inks. We show that nanocomposite solutions based on polystyrene and differently sized core/shell-type nanocrystals (NCs) formed by a CdSe core coated with a shell of ZnS (CdSe@ZnS) in a single solvent, chloroform, can be reliably dispensed into luminescent, multicolor pixel arrays. This study demonstrates the relevance of parameters like polymer concentration and nozzle diameter, highlighting how the optimal conditions to print NCs embedded in 5 wt% polystyrene nanocomposite are given by a 70-microm-diameter nozzle. The obtained structures show that the bright size-dependent emission of the NCs in the nanocomposite is retained in the printed pixels.

Inkjet printing of SU-8 for polymer-based MEMS a case study for microlenses

This paper describes a novel method to fabricate polymer MEMS based on the inkjet printing of SU-8, with a special emphasis on integrated micro-optical lens arrays. Inkjet control parameters are optimized in order to enable a stable and reproducible ejection of SU-8 drops in both continuous and drop-on-demand (DOD) modes. Arbitrary patterns of single and multiple polymer drops and arrays of convex microlenses are printed on different substrates. The influence of surface wetting properties on the size and the shape of the printed patterns is investigated. The optical properties of the microlenses are investigated in details. A model for inkjet printing of high-viscous functional materials for polymer MEMS has been used.

Simple and easily controllable parabolic-shaped microlenses printed on polymeric mesas

A simple and easy shape-controllable approach is demonstrated for the fabrication of parabolic-shaped polymer microlenses (μ-lenses), which are widely used in bio-imaging systems such as microfluidic and lab-on-a-chip systems for improving the image quality due to their ability to efficiently focus light into the devices. The μ-lenses were printed directly on micro-structured polymeric SU-8 mesas and they were formed on these mesas using a photo-curable organic–inorganic hybrid material (H-resist) using a drop-on-demand (DOD) ink-jet printing technique. The parabolic-shape μ-lenses with a fixed diameter resulting from the micro-structured SU-8 mesas are controlled by surface wetting conditions (i.e., the comparison between hydrophobic and hydrophilic) that efficiently improve the boundary confinement effect, and by printing different numbers of drops per μ-lens. The influence of the geometrical changes on the optical properties is also investigated. The high numerical aperture (NA) parabolic-shaped μ-lenses controlled by the hydrophobic surface-treated micro-structured polymeric SU-8 mesas, which are able to confine the drops at the edge, can be integrated on a microfluidic system and they allow high resolution image quality.