Now showing 1 - 10 of 17
PublicationTunable Microfluidic Optical Devices with Integrated Microlens Array(2006-08-01) Hong, Kuang-Sheng; Wang, Jing; Sharonov, Alexey; Chandra, Dinesh; Aizenberg, Joanna; Yang, ShuThe interest in dynamically tuning light has attracted great attention to the fabrication of tunable microlens arrays. Here we discuss the fabrication and characterization of a simple, robust, yet tunable microfluidic optical device with integrated microlens array. The microfuidic device with desired channel structure was micromachined on a polycarbonate plate with a resolution up to 100 µm, followed by thermal bonding two plates above their glass transition temperature. The microlens arrays were replica molded on a glass slide, which was then attached to the polycarbonate plates. By simply actuating the liquids with variable refractive index into the fluidic channel to immerse the lens arrays without moving or deformation of microlenses, a large change of focal length of more than 10 times (ƒ=0.74 to 8.53) was achieved. When a dye-containing liquid was pumped into the microfluidic channel to cover the lenses, the light transmission through the lenses was reduced from about 95% to 55% when the dye concentration was increased to 10 w/v %. The knowledge we gain from these studies will provide important insights to contruct new, adaptive, micro-scale optical devices with multiple functionalities. PublicationTwo-dimensional photonic crystals with anisotropic unit cells imprinted from poly(dimethylsiloxane) membranes under elastic deformation(2008-10-24) Zhu, Xuelian; Zhang, Ying; Chandra, Dinesh; Cheng, Shih-Chieh; Kikkawa, James M; Yang, ShuWe study structural symmetries of two-dimensional (2D) photonic crystals with anisotropic unit cells, including square- and rectangular-lattices with orientationally modulated elliptic motifs, and a compound structure consisting of circles with sixfold rotational symmetry and elliptical lines with twofold symmetry, which are created through elastic deformation of a single elastomeric membrane with circular pores. We then investigate the photonic bandgap (PBG) properties of the corresponding 2D Si posts and their tolerance to the structural deviation. We find that in the compound structure the overall PBGs are dominated by the sublattice with a higher symmetry, while the total symmetry is determined by the one with a lower symmetry. PublicationPhotonic Bandgap Structures of Core-Shell Simple Cubic Crystals from Holographic Lithography(2006-03-20) Moon, Jun Hyuk; Yang, Shu; Yang, Seung-ManWe report the investigation of photonic bandgap properties of a core-shell simple cubic structure (air core with a dielectric shell) using a two-parameter level-set approach. The proposed structure can be obtained by partially backfilling high refractive index materials into a polymeric template fabricated by multi-beam interference lithography. We find that the shell formation in the inverted simple cubic structure increases the complete photonic bandgap width by 10–20% in comparison to that of a completely filled structure. The bandgap between the 5th and 6th bands begins to appear at a refractive index contrast of 2.7. This study suggests the importance to investigate the core-shell formation in three-dimensional photonic crystals through backfilling, which may offer an additional control over their photonic bandgap properties. PublicationCreating Three-Dimensional Polymeric Microstructures by Multi-Beam Interference Lithography(2005-10-01) Moon, Jun Hyuk; Yang, ShuIt is attractive to produce true three-dimensional (3D) microstructures both rapidly and economically over a large area with negligible defects for a wide range of applications. Multi-beam interference lithography is one of the promising techniques that can create periodic microstructures in polymers without extensive lithography and etching steps. This review discusses the formation of interference patterns, their dependence on beam parameters, the lithographic process, and the applications to the formation of photonic crystals. Various photoresist systems, including thick films of negative-tone and positive-tone photoresists, liquid resins, organic-inorganic hybrids, and holographic polymer-dispersed liquid crystals, are also reviewed. PublicationPorous Biomimetic Microlens Arrays as Multifunctional Optical Structures(2005-12-01) Yang, Shu; Aizenberg, JoannaMicrolenses are important optical components that image, detect and couple light. Most synthetic microlenses, however, have fixed position and shape once they are fabricated. Therefore, the attainable range of their tunability and complexity is rather limited. In comparison, biological world provides a multitude of varied, new paradigms for the development of adaptive optical networks. This review discusses a few inspirational examples of biological lenses and their synthetic analogs. We focus on the fabrication and characterization of biomimetic microlens arrays with integrated pores, whose appearance and function are similar to a highly efficient optical element formed by brittlestars. The complex microlens design can be created by three-beam interference lithography. These synthetic microlenses have strong focusing ability, and the structure can be, therefore, used as an adjustable lithographic mask, and a tunable optical device coupled with the microfluidic system. The replacement of rigid microlenses with soft hydrogels provides means for changing the lens geometry and refractive index continuously in response to external stimuli, resulting in intelligent, multifunctional, tunable optics. PublicationFabricating Three-Dimensional Polymeric Photonic Structures by Multi-Beam Interference Lithography(2006-02-17) Moon, Jun Hyuk; Ford, Jamie; Yang, ShuThe fabrication of true three-dimensional (3D) microstructures both rapidly and economically over a large area with negligible defects is attractive for a wide range of applications. In particular, multi-beam interference lithography is one of the promising techniques that can mass-produce polymeric 3D photonic crystals defect-free over a large area. This review discusses the relationship between beam geometry and the symmetry of the interference patterns, the lithographic process, and various types of photoresist systems, including thick films of negative-tone and positive-tone photoresists, organic-inorganic hybrids, hydrogels, and holographic polymer-dispersed liquid crystals. PublicationFabrication of Photonic Crystals with high refractive index(2007-03-09) Xu, Yongan; Yang, Shu; Moon, Jun Hyuk; Johnson, Alan T; Dan, Yaping; Perry, Joseph W; Adibi, Ali; Hotchkiss, Peter; Marder, Seth• Complete photonic bandgap • High contrast of refractive index (RI) • Polymer material with a low RI • Inorganic material with a higher RI, such as silicon, titania. • Fabrication of diamond-like PCs by MBIL, • Fabrication of high RI inorganic PCs via double templating, • Core-shell morphology of replica • Pinch-off problem • Development of combined level-surface to address pinch-off problem • Electrodeposition of titania 3D structure • Electrophoretic deposition of surface charged nanoparticles PublicationA Tendon-Driven Origami Hopper Triggered by Proprioceptive Contact Detection(2020-04-06) Chen, Wei-Hsi; Misra, Shivangi; Caporale, J. Diego; Yang, Shu; Sung, Cynthia R.; Koditschek, Daniel EWe report on experiments with a laptop-sized (0.23m, 2.53kg), paper origami robot that exhibits highly dynamic and stable two degree-of-freedom (circular boom) hopping at speeds in excess of 1.5 bl/s (body-lengths per second) at a specific resistance O(1) while achieving aerial phase apex states 25% above the stance height over thousands of cycles. Three conventional brushless DC motors load energy into the folded paper springs through pulley-borne cables whose sudden loss of tension upon touchdown triggers the release of spring potential that accelerates the body back through liftoff to flight with a 20W powerstroke, whereupon the toe angle is adjusted to regulate fore-aft speed. We also demonstrate in the vertical hopping mode the transparency of this actuation scheme by using proprioceptive contact detection with only motor encoder sensing. The combination of actuation and sensing shows potential to lower system complexity for tendon-driven robots. For more information: Kod*lab (link to kodlab.seas.upenn.edu) PublicationSpontaneous Formation of One-dimensions Ripples in Transit to Highly Ordered Two-dimensional Herringbone Structures Through Sequential and Unequal Biaxial Mechanical Stretching(2007-06-11) Lin, Pei-Chun; Yang, ShuThe authors report the formation of various submicron wrinkle patterns and their transition from one-dimensional (1D) ripples to two-dimensional (2D) herringbone structures on poly(dimethylsiloxane) films. Using mechanical force they can separately control the amount and timing of strain applied to the substrate on both planar directions (either simultaneously or sequentially), which appears to be critical to maneuver the pattern formation in real time. They demonstrate reversible transitions from flat to 1D ripple, to ripple with bifurcation, to ripple/herringbone mixed features, and to well-controlled formation of a highly ordered zigzag-based 2D herringbone structures. PublicationStrain responsive concave and convex microlens arrays(2007-12-20) Chandra, Dinesh; Yang, Shu; Lin, Pei-ChunWe report the fabrication of single-component, strain responsive microlens arrays with real-time tunability. The concave lens array is fabricated by patterning hard oxide layer on a bidirectionally prestretched soft elastomer, polydimethylsiloxane PDMS followed by confined buckling upon release of the prestrain. The convex microlens array is replica molded from the concave lenses in PDMS. Due to difference in lens formation mechanisms, the two types of lenses show different tunable range of focal length in response to the applied strain: large focal length change is observed from the concave microlens array, whereas that from the convex microlens array is much smaller.