Sung-Pyo Yang

Biologically Inspired Organic Light-Emitting Diodes

Many animal species employ highly conspicuous traits as courtship signals for successful mating. Fireflies utilize their bioluminescent light as visual courtship signals. In addition to efficient bioluminescent light emission, the structural components of the firefly lantern also contribute to the enhancement of conspicuous optical signaling. Recently, these firefly lantern ultrastructures have attracted much interest and inspired highly efficient light management approaches. Here we report on the unique optical function of the hierarchical ultrastructures found in a firefly (Pyrocoelia rufa) and their biological inspiration of highly efficient organic light-emitting diode (OLED) applications. The hierarchical structures are comprised of longitudinal nanostructures and asymmetric microstructures, which were successfully replicated using geometry-guided resist reflow, replica molding, and polydimethylsiloxane (PDMS) oxidation. The external quantum efficiency (EQE) of the bioinspired OLEDs was enhanced by up to 61%. The bioinspired OLEDs clearly showed side-enhanced super-Lambertian emission with a wide-viewing angle. The highly efficient light extraction and wide-angle illumination suggest how the hierarchical structures likely improve the recognition of firefly optical courtship signals over a wide-angle range. At the same time, the biologically inspired designs provide a new paradigm for designing functional optical surfaces for lighting or display applications.

Asymmetric optical microstructures driven by geometry-guided resist reflow

We report a new method, termed geometry-guided resist reflow, for the batch fabrication of asymmetric optical microstructures. Thermoplastic microstructures reflow along the geometric boundaries of the adjacent thermoset microstructures above the glass transition temperature of thermoplastic resin. The shape profiles can be freely formed as a concave, convex, or linear shape and the slope angle can also be tuned from 7 to 68 degrees, depending on the geometric parameters. This new method provides a new route for developing functional optical elements.

Electrothermal MEMS parallel plate rotation for real time stereoscopic endoscopic imaging

This paper reports MEMS parallel plate rotation (PPR) with electrothermal actuator for real-time stereoscopic imaging. MEMS PPR allows stereoscopic imaging by generating camera shift effect with displacement in ray of the light. The device was designed opto-mechanically to operate in dynamic mode for stability, large rotation angle. The electrothermal actuation rotates over 25° in dynamic mode under low voltage, generating over 80μm baseline that indicates distance between two cameras and decides depth resolution. Finally stereoscopic images was captured by MEMS PPR and high-speed camera and reconstructed. This method can be widely used in miniaturized stereoscopic imaging system based on single camera.

Compact stereo endoscopic camera using microprism arrays

This work reports a microprism array (MPA) based compact stereo endoscopic camera with a single image sensor. The MPAs were monolithically fabricated by using two-step photolithography and geometry-guided resist reflow to form an appropriate prism angle for stereo image pair formation. The fabricated MPAs were transferred onto a glass substrate with a UV curable resin replica by using polydimethylsiloxane (PDMS) replica molding and then successfully integrated in front of a single camera module. The stereo endoscopic camera with MPA splits an image into two stereo images and successfully demonstrates the binocular disparities between the stereo image pairs for objects with different distances. This stereo endoscopic camera can serve as a compact and 3D imaging platform for medical, industrial, or military uses.

Electrothermal MEMS parallel plate rotation for single-imager stereoscopic endoscopes

This work reports electrothermal MEMS parallel plate-rotation (PPR) for a single-imager based stereoscopic endoscope. A thin optical plate was directly connected to an electrothermal MEMS microactuator with bimorph structures of thin silicon and aluminum layers. The fabricated MEMS PPR device precisely rotates an transparent optical plate up to 37° prior to an endoscopic camera and creates the binocular disparities, comparable to those from binocular cameras with a baseline distance over 100 μm. The anaglyph 3D images and disparity maps were successfully achieved by extracting the local binocular disparities from two optical images captured at the relative positions. The physical volume of MEMS PPR is well fit in 3.4 mm x 3.3 mm x 1 mm. This method provides a new direction for compact stereoscopic 3D endoscopic imaging systems.

Bioinspired hierarchical structures of firefly light organ

This work presents an engineering inspiration of hierarchical structures inspired from cuticular photonic structures of firefly light organ. Highly efficient light management of photonic structures in bioluminescent organ has been rarely reported. The efficient mechanisms can be utilized in lighting or display applications. The hierarchical structures, which have asymmetric microstructures and longitudinal nanostructures, were successfully mimicked by using geometry-guided resist reflow, replica molding, and PDMS oxidation. Transmission through the bioinspired hierarchical structures is increased up to 70%, compared with a smooth surface. This bioinspired optical device can be effectively utilized for LED and OLED based lighting or display applications.

Microprism arrays based stereoscopic endoscope

This work presents microprism arrays (MPA) based stereoscopic endoscope for 3D imaging. The MPA were monolithically fabricated using geometry-guided resist reflow method and successfully mounted in front of a single endoscopic camera module.