Jiwon Lee

Elastomeric microwire-based optical gas flowmeter with stretching-enabled tunability in measurement range

We report the utilization of transparent poly(dimethylsiloxane) (PDMS) microwires as the transducer for optical gas flowmetry. The elasticity of the PDMS microwire was exploited not only to miniaturize and simplify the flowmeter but also to widen and tune the measurement range through mechanical stretching. Using a 9 mm long microwire, we achieved 2.8~9.8 dB/SLM sensitivity. A 500 μm stretching of the microwire also shifted the measurement range from 1 to 4u2009SLM. The experimental results agreed well with predictions based on the fluid dynamic/optical model.

Fabrication of strongly anchored, high aspect ratio elastomeric microwires for mechanical and optical applications

We present a new technique for fabricating microwires with high elasticity and aspect ratio. Thanks to the adoption of lost-wax casting in the fabrication, the microwires can be directly grown from their supporting structure in the out-of-plane, surface-normal direction, automatically accomplishing strong, monolithic anchoring. The microwires can also be anchored at both ends in an arrayed format, making themselves more useful for mechanical and optical applications. Using the new technique, we fabricated arrays of poly(dimethylsiloxane) (PDMS) microwires 150–250 µm thick and 2–20 mm long. The microwires can withstand >400% elongations and >70 mN of pulling force with little degradation in their surface smoothness. Optical characterizations revealed that the PDMS microwires can function as flexible lightpipes connecting two points in miniaturized systems.

Bio-inspired thin and flat solar concentrator for efficient, wide acceptance angle light collection.

We present a novel thin and flat solar concentrator design, inspired by the structure and optical functionality of the ommatidium in the compound eye of insects. By combining a microlens with a curved light guide, rather than the conventionally employed dielectric or metallic reflectors, we could simultaneously achieve low-loss light redirection and wide acceptance angle without compromising the overall thinness or flatness of the concentrator. Through design optimizations, we could achieve optical concentration factors up to 39 and acceptance angle up to ±15° while maintaining the thickness of the concentrator under 1.1 cm for a length of 20 cm. We also showed that the optical concentration factor can be further increased to 81 through tapering of the geometry.

Growing a patterned array of double-anchored elastomeric microwires using lost-wax casting

We propose and demonstrate a new, lost-wax casting-based technique for fabricating elastomeric microwires that are anchored to external supporting structures at both ends monolithically. The technique will grow the microwires, allowing them aligned in the out-of-plane, surface-normal direction and facilitating the formation of patterned arrays. With the new technique, we fabricated PDMS microwires with diameter ranging 150∼250 µm which withstood >400% elongations and >70 mN of pulling force with little degradation in surface smoothness. Optical characterization also revealed that the PDMS microwires can function as elastic lightpipes optically connecting two points in miniaturized systems.

Numerical investigation of quasi-coplanar plasmonic waveguide-based photonic components

Using 3-dimensional numerical simulations, we investigated the characteristics and performance of essential photonic components based on the recently proposed quasi-coplanar waveguide (QCPW) including bends, couplers, and splitters. The results confirmed the QCPWs potential in high density photonic integration. We also explored the application of various RF-originated concepts and techniques to QCPW-based photonic components to enhance and enrich their functionalities.

Separatrix modes in weakly deformed microdisk cavities

Optical modes in deformed dielectric microdisk cavities often show an unexpected localization along unstable periodic ray orbits. We reveal a new mechanism for this kind of localization in weakly deformed cavities. In such systems the ray dynamics is nearly integrable and its phase space contains small island chains. When increasing the deformation the enlarging islands incorporate more and more modes. Each time a mode comes close to the border of an island chain (separatrix) the mode exhibits a strong localization near the corresponding unstable periodic orbit. Using an EBK quantization scheme taking into account the Fresnel coefficients we derive a frequency condition for the localization. Observing far field intensity patterns and tunneling distances, reveals small differences in the emission properties.

Two-dimensional optofluidic liquid-core waveguiding based on optimized integration of single- and multiple-layer antiresonance reflection optical waveguides

We present a novel two-dimensional (2D) liquid-core waveguiding scheme that combines two different types of antiresonance reflection optical waveguides (ARROWs) to achieve ease of fabrication and richer optofluidic functionalities. We established the conditions for the optimal integration of the two ARROW schemes theoretically and validated them with 2D numerical mode analysis. The proposed scheme also provides a convenient means to install supporting solid-core waveguides without additional burden in fabrication.

Quasi-coplanar plasmonic waveguide for ultracompact photonic integrated circuits

We demonstrate a novel metal-dielectric structure called quasi-coplanar waveguide for subwavelength scale confinement and guiding of surface plasmon-polaritons. 2D/3D simulations show that various nanoscale photonic integrated circuit elements can be implemented with the structure.