Ehsan Saei Ghareh Naz

Localized Surface Plasmons Selectively Coupled to Resonant Light in Tubular Microcavities.

Vertical gold nanogaps are created on microtubular cavities to explore the coupling between resonant light supported by the microcavities and surface plasmons localized at the nanogaps. Selective coupling of optical axial modes and localized surface plasmons critically depends on the exact location of the gold nanogap on the microcavities, which is conveniently achieved by rolling up specially designed thin dielectric films into three-dimensional microtube cavities. The coupling phenomenon is explained by a modified quasipotential model based on perturbation theory. Our work reveals the coupling of surface plasmon resonances localized at the nanoscale to optical resonances confined in microtubular cavities at the microscale, implying a promising strategy for the investigation of light-matter interactions.

Hybridization of photon-plasmon modes in metal-coated microtubular cavities

The coupling of resonant light and surface plasmons in metal layer coated optical microcavities results in the formation of hybrid photon-plasmon modes. Here, we comprehensively investigate the hybridization mechanism of photon-plasmon modes based on opto-plasmonic microtubular cavities. By changing the cavity structure and the metal layer thickness, weakly, moderately and strongly hybridized resonant modes are demonstrated depending on the photon-plasmon coupling strength. An effective potential approach is applied to illustrate the hybridization of photon-plasmon modes relying on the competition between light confinement by the cavity wall and the potential barrier introduced by the metal layer. Our work reveals the basic physical mechanisms for the generation of hybrid modes in metal-coated whispering-gallery-mode microcavities, and is of importance for the study of enhanced light-matter interactions and potential sensing applications.

In Situ Generation of Plasmonic Nanoparticles for Manipulating Photon–Plasmon Coupling in Microtube Cavities

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes (WGMs) is investigated by spatially resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon-plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs, selective coupling between the localized surface plasmon resonances (LSPRs) and WGMs is experimentally demonstrated. Moreover, by creating multiple plasmonic-nanoparticle spots on the microtube cavity, the field distribution of optical axial modes is freely tuned due to multicoupling between LSPRs and WGMs. The multicoupling mechanism is theoretically investigated by a modified quasipotential model based on perturbation theory. This work provides an in situ fabrication of plasmonic nanoparticles on three-dimensional microtube cavities for manipulating photon-plasmon coupling which is of interest for optical tuning abilities and enhanced light-matter interactions.

Density of optical states in rolled-up photonic crystals and quasi crystals☆

Abstract We describe the local density of optical states (LDOS) and the density of optical states (DOS) in three dimensional (3D) finite size rolled-up photonic crystals and quasi crystals calculated using optimized code based on finite difference time domain (FDTD) techniques. Because the Bloch–Floquet theorem is not used in these calculations, the code can be applied to any dielectric structures that lack discrete translational symmetry, making it ideal for experimentally fabricated structures that are finite in size and include defects. Our software can be used for either LDOS or DOS calculations, is parallelized using standard message passing interface (MPI) protocols, and is freely available at www.fpspackage.com . Program summary Program title: FPS Catalogue identifier: AFBP_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AFBP_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU GPL v3 No. of lines in distributed program, including test data, etc.: 118342 No. of bytes in distributed program, including test data, etc.: 2385803 Distribution format: tar.gz Programming language: C + + . Computer: PCs and distributed memory machines. Operating system: Linux, Unix. Has the code been vectorised or parallelized?: Parallelized using message passing interface. RAM: Depending on the problem; gigabytes. Classification: 10. External routines: Minimum: MPI; [1] fftw3; [2] optional: hdf5-tools. [3] Nature of problem: The aim of FPS is providing a fast and easy to use package for studying local density of optical states and density of optical states in arbitrary shaped finite size photonic structures. Solution method: Parallel finite difference time domain method. Restrictions: The post processing codes are not parallelized. At least two processes should be used for the calculations. Unusual features: FPS provides non-experts in computational physics an intuitive tool to obtain local density of optical states and density of optical states calculations. Inserting parameters that define the geometry and the spectrums of interest into a “txt” or “h5” file are all a user needs to do. Additional comments: The package includes a tutorial describing the package and its installation, using an example. Running time: It was found that the average time to compute a single LDOS was 21 minutes. Runtime in general depends on mesh size and the number of points that local density of optical states should be calculated. References: [1] MPICH, https://www.mpich.org . [2] FFTW3, http://www.fftw.org . [3] HDF5, https://www.hdfgroup.org/HDF5 .

Curved Nanomembrane-Based Concentric Ring Cavities for Supermode Hybridization

We report the mode interactions and resonant hybridization in nanomembrane-formed concentric dual ring cavities supporting whispering gallery mode resonances. Utilizing a rolled-up nanomembrane with subwavelength thickness as an interlayer, dual concentric microring cavities are formed by coating high-index nanomembranes on the inner and outer surfaces of the rolled-up dielectric nanomembrane. In such a hybrid cavity system, the conventional fundamental mode resonating along a single ring orbit splits into symmetric and antisymmetric modes confined by concentric dual ring orbits. Detuning of the coupled supermodes is realized by spatially resolved measurements along the cavity axial direction. A spectral anticrossing feature is observed as a clear evidence of strong coupling. Upon strong coupling, the resonant orbits of symmetric and antisymmetric modes cross over each other in the form of superwaves oscillating between the concentric rings with opposite phase. Notably, the present system provides high flexibilities in controlling the coupling strength by varying the thickness of the spacer layer and thus enables switching between strong and weak coupling regimes. Our work offers a compact and robust scheme using curved nanomembranes to realize novel cavity mode interactions for both fundamental and applied studies.