Showing papers by "Chang-Ling Zou published in 2011"

Two-photon pumped lasing in single-crystal organic nanowire exciton polariton resonators.

Abstract: Single-crystal organic nanowires were fabricated with a soft-template-assisted self-assembly method in liquid phase. These nanowires with rectangular cross section can serve as resonators for exciton-photon coupling, leading to a microcavity effect and a relatively low threshold of laser actions. Two-photon-pumped blue lasing was observed in these organic waveguiding nanostructures above a threshold of 60 nJ, excited with a 750 nm near-infrared femtosecond pulse laser at 77 K.

Temperature dependent energy level shifts of nitrogen-vacancy centers in diamond

Abstract: Magnetic resonance and fluorescence spectra of nitrogen-vacancy (NV) color centers ensemble in high purity diamond sample were measured, with temperature ranging from 5.6 K to 295 K. Both microwave and optical transition energies have similar nonlinear temperature dependent changes, which might mainly originate from the local thermal expansion. As the frequency shifts will reduce the fidelity of resonant quantum control, the present results demonstrate the necessity of taking temperature fluctuation into consideration. For temperature below 100 K, the transition energies show tendencies to be constant, which indicate higher stability and performance in applications with NV centers.

Experimental observation of Fano resonance in a single whispering-gallery microresonator

Abstract: We experimentally observe Fano resonance in a single silica toroidal microresonator, in which two whispering-gallery modes (WGMs) are excited simultaneously through a fiber taper. By adjusting the fiber-cavity coupling strength and the polarization of incident light, the Fano-like resonance line shape can be engineered and further convert to the electromagnetically induced transparency (EIT) like line shape. Our theoretical analysis reveals that both the Fano and EIT resonances originate from an indirect-coupling of two originally orthogonal WGMs, which is mediated by the common fiber taper waveguide. The sharp Fano line shape holds great potential in optical switching and sensitivity-enhanced biochemical sensing.

Packaged silica microsphere-taper coupling system for robust thermal sensing application

Abstract: We propose and realize a novel packaged microsphere-taper coupling structure (PMTCS) with a high quality factor (Q) up to 5×10(6) by using the low refractive index (RI) ultraviolet (UV) glue as the coating material The optical loss of the PMTCS is analyzed experimentally and theoretically, which indicate that the Q is limited by the glue absorption and the radiation loss Moreover, to verify the practicability of the PMTCS, thermal sensing experiments are carried out, showing the excellent convenience and anti-jamming ability of the PMTCS with a high temperature resolution of 11×10(-3) ◦C The experiments also demonstrate that the PMTCS holds predominant advantages, such as the robustness, mobility, isolation, and the PMTCS can maintain the high Q for a long time The above advantages make the PMTCS strikingly attractive and potential in the fiber-integrated sensors and laser

Broadband integrated polarization beam splitter with surface plasmon

Abstract: A broadband integrated waveguide polarization beam splitter consisting of a metal nanoribbon and two dielectric waveguides is proposed and numerically investigated. This surface plasmon based device provides a unique approach for polarization sensitive manipulation of light in an integrated circuit and will be essential for future classical and quantum information processes.

Robust Spot-Packaged Microsphere-Taper Coupling Structure for In-Line Optical Sensors

Abstract: We propose and realize a spot-packaged structure for the microsphere-taper coupling system by only encapsulating and solidifying the coupling region with low refractive index polymer as the package material. After spot-package, ultrahigh quality factor ( >; 107) is obtained with the microsphere diameters around 300 μm. The robustness of the spot-packaged structure is also tested, demonstrating the remarkable anti-tensile strength ability with the bearable loaded force larger than 0.05 N for a packaged structure with the spot-package area larger than 30 μm2. In addition, the spot-packaged structure is integrated with standard fiber, promising in in-line optical practical evanescent field sensing applications, especially in harsh detecting environments demanding high overload resistance.

Quick root searching method for resonances of dielectric optical microcavities with the boundary element method

Abstract: In this paper, we developed an efficient method for searching the resonant eigenfrequency of dielectric optical microcavities by the boundary element method. By transforming the boundary integral equation to a general eigenvalue problem for arbitrary, symmetric, and multi-domain shaped optical microcavities, we analyzed the regular motion of the eigenvalues against the frequency. The new strategy can predict multiple resonances, increase the speed of convergence, and avoid non-physical spurious solutions. These advantages greatly reduce the computation time in the search process of the resonances. Moreover, this method is not only valuable for dielectric microcavities, but is also suitable for other photonic systems with dissipations, whose resonant eigenfrequencies are complex numbers.

Room-temperature steady-state optomechanical entanglement on a chip

Abstract: A potential experimental system, based on high-stress stoichiometric silicon nitride (${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$), is proposed to generate steady-state optomechanical entanglement at room temperature. In the proposed structure, a nanostring interacts dispersively and reactively with a microdisk cavity via the evanescent field. We study the role of both dispersive and reactive couplings in generating optomechanical entanglement, and show that the room-temperature entanglement can be effectively obtained through the dispersive couplings under the reasonable experimental parameters. In particular, in the limits of high temperature ($T$) and high mechanical quality factor (${Q}_{m}$), we find that the logarithmic entanglement depends only on the ratio $T/{Q}_{m}$. This indicates that improvements of the material quantity and structure design may lead to more efficient generation of stationary high-temperature entanglement.

Exciton-plasmon-photon conversion in silver nanowire: Polarization dependence

Abstract: Polarization dependence of the exciton-plasmon-photon conversion in silver nanowire-quantum dots structure was investigated using a scanning confocal microscope system. We found that the fluorescence enhancement of the CdSe nanocrystals was correlated with the angle between the excitation light polarization and the silver nanowire direction. The polarization of the emission was also related with the nanowire direction. It was in majority in the direction parallel with nanowire due to the nano-antenna effect.

Interference of surface plasmon polaritons from a "point" source

Abstract: The interference patterns of the surface plasmon polaritons (SPPs) on the metal surface from a “point” source are observed. Innovation to the previous works, a point SPPs source with diameter of 100 nm is generated at the freely chosen positions on Au/air interface using near field excitation method. Such a point source provides good enough coherence to generate obvious interference phenomenon. This point SPPs source may be useful in the investigation of plasmonics for its high coherence, deterministic position, and minimum requirement for the initial light source.

Broadband Enhancement of Light Harvesting in a Luminescent Solar Concentrator

Abstract: Luminescent solar concentrators (LSCs) are large-area devices that absorb incident sunlight and emit luminescence photons with high quantum efficiency, which will finally be collected by a small photovoltaic (PV) system. The light-harvesting area of the PV system is much smaller than that of the LSC system, potentially reducing the cost of solar cells. Here, we present a theoretical description of the luminescent process in nanoscale LSCs where the conventional ray-optics model is no longer applicable. We demonstrate that a slot waveguide consisting of a nanometer-sized low-index slot region sandwiched by two high-index regions provides a broadband enhancement of light harvesting by the luminescent centers in the slot region. This is because the slot waveguide can 1) greatly enhance the spontaneous emission due to the Purcell effect, 2) dramatically increase the effective absorption length of luminescent centers, and 3) strongly improve the fluorescence quantum yield of luminescent centers. It is found that about 80% solar photons can be re-emitted even for a low fluorescent quantum yield of 0.5, and 80% re-emitted photons can be coupled to the slot waveguide. This LSC has the potential to be constructed in to a tandem structure which can absorb nearly full-spectrum solar photons, and also may be of special interest for building integrated nano-solar-cell applications.

Negative Goos-Hänchen shift on a concave dielectric interface

Abstract: We study the Goos–Hanchen shift (GHS) on a curved surface through numerical simulation by the boundary element method. A negative GHS is first discovered on a concave dielectric interface below the critical angle, accompanied by a large positive GHS on the convexity. The simulation shows that the GHS on a planar interface is the composition of the GHS from a concave and the corresponding convex interface. This work will enrich the study of the GHS for different curved surfaces, which will have potential applications in micro-optics and near-field optics.

Mechanism of directional emission from a peanut-shaped microcavity

Abstract: Collimated directional emission is essentially required for an asymmetric resonant cavity. In this paper, we theoretically investigate a type of peanut-shaped microcavity which can support highly directional emission with a beam divergence as small as 2.5\ifmmode^\circ\else\textdegree\fi{}. The mechanism of the collimated emission of this type of peanut-shaped microcavity is explained with a short-term ray trajectory. Moreover, the explanations are also confirmed by a numerical wave simulation. This extremely narrow divergence of the emission holds great potential in highly collimated lasing from on-chip microcavities.

Movable Fiber-Integrated Hybrid Plasmonic Waveguide on Metal Film

Abstract: A waveguide structure consisting of a tapered nanofiber on a metal film is proposed and analyzed to support highly localized hybrid plasmonic modes. The hybrid plasmonic mode can be efficiently excited through the in-line tapered fiber based on adiabatic conversion and collected by the same fiber, which is very convenient in the experiment. Due to the ultrasmall mode area of plasmonic mode, the local electromagnetic field is greatly enhanced in this movable waveguide, which is potential for enhanced coherence light emitter interactions, such as waveguide quantum electrodynamics, single emitter spectrum and nonlinear optics.