Jaeyoun Kim

10 Gb/s multiple wavelength, coherent short pulse source based on spectral carving of supercontinuum generated in fibers

We demonstrate a high-power, multi-wavelength, short pulse source at 10 Gb/s based on spectral slicing of supercontinuum (SC) generated in short fibers. We show that short fiber SC can be used for dense wavelength division multiplexing applications because of its >7.9 dBm/nm power spectral density, 140 nm spectral bandwidth, and /spl plusmn/0.5 dB spectral uniformity over 40 mn. Pulse carving up to 60 nm away from the pump wavelength and CW generation by longitudinal mode carving indicates that the coherence of the SC is maintained. By using high nonlinearity fibers, the spectral bandwidth is increased to 250 nm, which can accommodate >600 wavelength channels with 50 GHz channel spacing and >6 Tb/s aggregate data rate. We also calculate the coherence degradation due to amplification of incoherent energy during the SC generation. Theoretical results show that the SC generation in short fibers has 13 dB higher signal-to-noise ratio (SNR) compared to the SC generated in long fiber.

Gain enhancement in cascaded fiber parametric amplifier with quasi-phase matching: theory and experiment

We report a novel gain enhancement scheme for fiber-optic parametric amplifiers utilizing cascaded amplification and quasi-phase matching (QPM). The theory and method of QPM for four-wave mixing (FWM) are developed for the first time to our knowledge. In experimental implementations of the theory, we achieve >12 dB gain improvement in a three-stage dispersion-shifted (DS) fiber parametric amplifier. A 16-dB overall gain is obtained with 11 nm separation between zero-dispersion wavelength and pump wavelength. The experimental results show good agreement with theory and simulations. The influence of QPM on spectral characteristics of parametric gain is investigated with numerical simulations.

Multi-peak electromagnetically induced transparency (EIT)-like transmission from bull’s-eye-shaped metamaterial

We investigate the electromagnetic response of the concentric multi-ring, or the bulls eye, structure as an extension of the dual-ring metamaterial which exhibits electromagnetically-induced transparency (EIT)-like transmission characteristics. Our results show that adding inner rings produces additional EIT-like peaks, and widens the metamaterials spectral range of operation. Analyses of the dispersion characteristics and induced current distribution further confirmed the peaks EIT-like nature. Impacts of structural and dielectric parameters are also investigated.

Characteristics of plasmonic Bragg reflectors with insulator width modulated in sawtooth profiles.

We present a new metal-insulator-metal (MIM)-based plasmonic Bragg reflector (PBR) design that solves the technical problems of conventional step profile MIM PBRs through the use of sawtooth profiles. Our numerical study revealed that the sawtooth PBRs exhibit lower insertion loss, narrower bandgap, and reduced rippling in the transmission spectrum when compared with the step PBRs. The defect mode of the sawtooth PBR also exhibits a higher transmission, narrower linewidth, and higher Q-factor.

Microrobotic tentacles with spiral bending capability based on shape-engineered elastomeric microtubes

Microscale soft-robots hold great promise as safe handlers of delicate micro-objects but their wider adoption requires micro-actuators with greater efficiency and ease-of-fabrication. Here we present an elastomeric microtube-based pneumatic actuator that can be extended into a microrobotic tentacle. We establish a new, direct peeling-based technique for building long and thin, highly deformable microtubes and a semi-analytical model for their shape-engineering. Using them in combination, we amplify the microtube’s pneumatically-driven bending into multi-turn inward spiraling. The resulting micro-tentacle exhibit spiraling with the final radius as small as ~185 μm and grabbing force of ~0.78 mN, rendering itself ideal for non-damaging manipulation of soft, fragile micro-objects. This spiraling tentacle-based grabbing modality, the direct peeling-enabled elastomeric microtube fabrication technique, and the concept of microtube shape-engineering are all unprecedented and will enrich the field of soft-robotics.

Microsphere-assisted fabrication of high aspect-ratio elastomeric micropillars and waveguides

High aspect-ratio micropillars are in strong demand for microtechnology, but their realization remains a difficult challenge, especially when attempted with soft materials. Here we present a direct drawing-based technique for fabricating micropillars with poly(dimethylsiloxane). Despite the materials extreme softness, our technique enables routine realization of micropillars exceeding 2,000 μm in height and 100 in aspect-ratio. It also supports in situ integration of microspheres at the tips of the micropillars. As a validation of the new structures utility, we configure it into airflow sensors, in which the micropillars and microspheres function as flexible upright waveguides and self-aligned reflectors, respectively. High-level bending of the micropillar under an airflow and its optical read-out enables mm s(-1) scale-sensing resolution. This new scheme, which uniquely integrates high aspect-ratio elastomeric micropillars and microspheres self-aligned to them, could widen the scope of soft material-based microdevice technology.

Intra-particle plasmonic coupling of tip and cavity resonance modes in metallic apertured nanocavities

Based on numerical studies of apertured metallic nanocavity structures, we describe a new intra-particle plasmonic interaction pathway that couples the plasmon resonance modes of the aperture edge and the cavity. In contrast to the inter-particle coupling schemes that require precisely arrayed nanoparticles, this intra-particle coupling scheme achieves the tunability in plasmonic resonance wavelength using a single standalone nanostructure. In addition, when the aperture edge is made sharp, it functions dually as a tip that amplifies its near-field producing the local filed enhancement effect. We investigate the details of the coupling mechanism and identify the dominant role of the tip mode in determining the coupling efficiency numerically. The numerical model results in good agreement with recent experimental results. This intra-particle coupling mechanism will help the monolithic integration of plasmonic functionalities and its application for the nanoscale spectroscopy of biological structures in vivo.

Fluorescence enhancement of quantum dots enclosed in Au nanopockets with subwavelength aperture

The authors observed strong fluorescence (FL) enhancement from CdSe quantum dots (QDs) partially encapsulated in a smooth Au film with subwavelength apertures. So far, the fluorescence of QDs placed on smooth metallic surfaces has been mostly quenched unless the surface was roughened in nanoscale. The pocketed QD FL emitted through the nanoaperture exhibited up to fivefold enhancement when compared with those from QDs on plain Au or glass surfaces. The enhancement depends strongly on the film thickness and becomes maximized at 50nm. This study shows that the dependence may be closely related to the surface plasmon-polariton characteristics of the Au layer.

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 4 SLM. The experimental results agreed well with predictions based on the fluid dynamic/optical model.

PLK1 regulation of PCNT cleavage ensures fidelity of centriole separation during mitotic exit.

Centrioles are duplicated and segregated in close link to the cell cycle. During mitosis, daughter centrioles are disengaged and eventually separated from mother centrioles. New daughter centrioles may be generated only after centriole separation. Therefore, centriole separation is considered a licensing step for centriole duplication. It was previously known that separase specifically cleaves pericentrin (PCNT) during mitotic exit. Here we report that PCNT has to be phosphorylated by PLK1 to be a suitable substrate of separase. Phospho-resistant mutants of PCNT are not cleaved by separase and eventually inhibit centriole separation. Furthermore, phospho-mimetic PCNT mutants rescue centriole separation even in the presence of a PLK1 inhibitor. On the basis on these results, we propose that PLK1 phosphorylation is a priming step for separase-mediated cleavage of PCNT and eventually for centriole separation. PLK1 phosphorylation of PCNT provides an additional layer of regulatory mechanism to ensure the fidelity of centriole separation during mitotic exit.