Polymer Microlens Research Articles

Enhancing Light Extraction in Top‐Emitting Organic Light‐Emitting Devices Using Molded Transparent Polymer Microlens Arrays

The light extraction efficiency in organic light-emitting devices (OLEDs) is enhanced by up to 2.6 times when a close-packed, hemispherical transparent polymer microlens array (MLA) is molded on the light-emitting surface of a top-emitting device. The microlens array helps to extract the waveguided optical emission in the organic layers and the transparent top electrode, and can be manufactured in large area with low cost.

Adhesion Force Change by Electrowetting on a Polymer Microlens Array

In addition to contact angle changes, adhesion force changes by electrowetting on a polymer microlens are reported in this paper. A flexible poly(dimethylsiloxane) (PDMS) microlens array was fabricated with an embedded Cr/Au double-layered electrode and a dielectric layer of parylene and Teflon. On microlens structures with a Teflon layer, a deionized water droplet on the microlens array surface shows a high contact angle of 137° before electrowetting. The contact angle is decreased to 63° by electrowetting with an external bias of 250 V. The electrowetting process carried out on the microlens array also enhances the adhesion force between the water droplet and the microlens array. This change in the adhesion force after electrowetting is demonstrated by a water droplet that hangs upside down on the fabricated microlens array. From the computed work of adhesion, it is shown that a larger difference in the adhesion force by electrowetting can be achieved on the fabricated microlens array than on a flat Teflon surface.

Near-field optical imaging with a nanotip grown on fibered polymer microlens

Pointed carbon nanotips have been deposited on polymer microlensed optical fibers and used as highly resolving scattering nanoprobes. Optical characterizations supported by simulations demonstrate an efficient spatial filtering where the light scattered by the carbon tip is selectively coupled into the fiber core. As an application, a channel surface waveguide was characterized in collection mode. A special attention was given to the polarization response, and the s-polarized field is found to be slightly favored due to the detection direction. The proposed hybrid probe’s robustness, the symmetric detection and design flexibility it offers, makes it an attractive tool for nano-optics.

Replication of precise polymeric microlens arrays combining ultra-precision diamond ball-end milling and micro injection molding

A simple and novel combination of ultra-precision diamond ball-end milling and micro injection molding technique is described to produce precise microlens arrays out of polycarbonate (PC), polymethylmethacrylate (PMMA) as well as polystyrene (PS). The microlens arrays consist of 100 lenses in a 10 × 10 array with a lens radius of 273 μm, a lens diameter of 300 μm and a lens depth of 45 μm. Pitch between the lenses is fixed at 800 μm. The injection molding parameters were optimized to get precise microlens geometries with low surface roughness. The results show a precise diamond milled mold insert and injection molded microlens arrays with minor deviations in radius and surface roughness of the microlenses, particularly for microlens arrays out of PMMA.

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.

A universal optical approach to enhancing efficiency of organic-based photovoltaic devices

We report a new optical approach that can be used to enhance light harvesting in many different organic-based photovoltaic cells. A transparent polymer microlens array moulded on the light incident surface increases the light path in the active layer and reduces surface reflection, resulting in a 15–60% relative increase in overall cell efficiency.

Collective Micro-Optics Technologies for VCSEL Photonic Integration

We describe the main recent technological approaches that associate micro-optical elements to VCSELs in order to control their output beam and to improve their photonic integration. These approaches imply either a hybrid assembly or a direct integration technique. They are compared with regards to their tolerance to alignment errors and to their ease of implementation onto arrays of devices at a wafer level. In particular, we detail the integration techniques we have developed for self-aligned polymer microlens fabrication for beam collimation and short distance beam focusing. Finally, designs to achieve active micro-optics or to exploit novel nanophotonic effects are discussed.

All-optical controlling of the focal intensity of a liquid crystal polymer microlens array

The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an all-optically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.

Microlens Array on Flip-Chip LED Patterned With an Ultraviolet Micro-Pixelated Emitter

A direct-write lithographic technique for the fabrication of micro-lens arrays with an ultraviolet (UV) micro-light-emitting diode (LED) array serving as an exposure source is reported. Polymer microlens arrays of high optical quality have been fabricated on the sapphire side of a flip-chip truncated-conic (TC) LED. The properties of the lenses are evaluated by optical microscopy and atomic force microscopy. The determined focal length is close to the predicted value. The effects of microlens integration on the optical properties of the LED are investigated.

A hybrid polymer–glass achromatic microlens array fabricated by compressionmolding

This paper presents the feasibility of creating a hybrid polymer–glass achromatic microlensarray by compression molding. This affordable and high precision microlens array designhas potential applications in the optical industry for its capability of correcting chromaticaberration. In this research a doublet design was investigated. Specifically, polycarbonateand P-SK57 glass were selected as the equivalents of flint and crown glass for their oppositedispersion properties. Ultraprecision diamond machining was utilized to manufacture themold with an asymmetric pattern. The optical quality in the mold surface was obtainedwithout post-machining–polishing. Both the glass and polymer microlens arrays werefabricated by thermal compression molding at different forming temperatures. After theglass microlens array was molded, it was used as the top mold half for polymer compressionmolding. Two chisel-shaped cavities were fabricated simultaneously when theglass lens array mold was machined. These two cavities were used as fiducialmarks for assembling the P-SK57 glass part and the polycarbonate part duringthe second molding action. The single uninterrupted operation was developed inthis study to create both optical surfaces and the fiducial marks such that highassembly tolerance could be achieved. Furthermore, numerical simulation forcompression molding was conducted to study the geometry profile error of themicrolens. Finally, the geometry and optical measurements were performed todemonstrate the effectiveness of the hybrid polymer–glass achromatic microlens array.

Exploring the capabilities of Digital Holography as tool for testing optical microstructures

A demonstration of the capabilities of Digital Holography (DH) in microscope configuration is presented for inspecting and qualifying optical microstructures. Different structures with dimensions ranging from hundreds to few tens of microns are investigated, analyzed and characterized by DH showing that the technique is suitable either for liquid as well as polymeric microlenses. Thanks to the numerical reconstruction of the complex wavefields, we show that DH is able to retrieve not only the morphology of each single structure element but also to furnish accurate information on all the changes (spontaneous or induced) occurring during the inspection time, such as the curvature variation of liquid microlenses or the wavefront distortion.

Integration of polymer microlens array at fiber bundle extremity by photopolymerization

We present a novel route to directly integrate an array of microlenses at the extremity of an optical fiber bundle. The method is based on photopolymerization at the end of the fiber. The method is based on the control of exposure dose and volume of the deposited droplet of photopolymerizable formulation. Optical properties of the integrated microlenses are discussed on the basis of FDTD calculations.

Two-Dimensional MEMS Stage Integrated With Microlens Arrays for Laser Beam Steering

A novel microelectromechanical stage with one uniaxial set of combs capable of 2-D actuation is presented. A polymer microlens array (MLA) is mounted vertically onto the stage. Driven at resonance, the stage deflects 124 μm out of plane and 34 μm in plane. Finally, laser beam steering is demonstrated using two cascaded MLAs.

Fabrication of polydimethylsiloxane microlens arrays by surface tension induced liquid separation

This Letter presents a novel fabrication method to build polymer microlens arrays. The key mechanism of the fabrication process is surface tension, which induces liquid separation phenomenon when a post is immersed and detached from a bottom liquid mixture. The surface tension also acts on the formation of lens surface at liquid-air interface resulting in an excellent surface roughness. The surface profile of lenses is well fitted with an ideal lens profile. The other feature of the presented fabrication method is self-positioning of the lens into the post. The range of focal lengths was between 110.4 and 282.0--m, which were determined by three parameters such as a post radius, gap and bottom liquid thickness. In summary, the STILS method can be a powerful tool to create microlens arrays with a smooth surface and a high scalability for the future applications in optoelectronics or microfluidics.

自写入光波导聚合物微透镜阵列的设计与制作

自写入光波导聚合物微透镜阵列的设计与制作

Photopolymerized self-assembly microlens arrays based on phase separation

In the past decades, there has been much effort in developing and improving new techniques for the production of microlens arrays. Here a low-temperature self-assembly method using phase separation is demonstrated for the first time for the fabrication of polymer microlens arrays. In this paper, we present a simple method for producing microlens arrays based on liquid crystal/photopolymer blends via phase separation. The morphology of the microlens arrays has been measured by SEM, AFM and scanning white light interferometry. Our results show that the microlens arrays obtained from our experiments have a comparable light-gathering capability and can be applied in optical systems.

自写入光波导聚合物微透镜阵列的设计与制作

自写入光波导聚合物微透镜阵列的设计与制作

自写入光波导聚合物微透镜阵列的设计与制作

自写入光波导聚合物微透镜阵列的设计与制作

Thermally Tunable Polymer Microlenses for Biological Imaging

We present polydimethylsiloxane (PDMS) microlenses capable of thermally tuning their focal lengths via optically transparent indium tin oxide (ITO) microheaters. Microlenses with various diameters are created by molding PDMS over microstructures of reflowed photoresist. Due to a relatively large thermal expansion coefficient, these PDMS microlenses exhibit measurable thermal expansion with relatively small temperature changes. By adjusting the temperature of the microlenses using ITO microheaters, we can actively control their radii of curvature and focal lengths without requiring moving mechanical components. To demonstrate the tunability of the microlenses, we characterize temperature-dependent changes by focal length and magnification factor measurements. We also investigate the ability to use the microlenses for tunable observation of cells, demonstrating their potential application to biological imaging.

Spotted Custom Lenses to Tailor the Divergence of Vertical-Cavity Surface-Emitting Lasers

We demonstrate the output beam collimation of GaAs-based vertical-cavity surface-emitting lasers by means of self-aligned polymer microlenses deposited on SU-8 pedestals using a cantilever-based spotter. We show that this fabrication technique ensures a reproducible lens shape because the contact angle and the deposited volume are constant for a given surface. Device properties are presented and compared to optical beam propagation modeling results. We demonstrate that the final beam divergence is only controlled by pedestal design parameters and can be reduced with this method by a factor 10 (to 1.2° for single-mode devices) with no significant lasing performance modification.