Ta Jen Yen

Asymmetric coupling between subradiant and superradiant plasmonic resonances and its enhanced sensing performance

We present symmetric and asymmetric couplings within a pair of split-ring resonators (SRRs). The former shows a single transmittance dip, following the equivalent circuit model; yet, the latter introduces an additional transmittance peak, stemming from an asymmetrically coupled resonance (ACR) between the subradiant and superradiant modes. The mechanism of such induced transparency is elucidated well by the suppression of induced currents within the SRR element with a lower quality factor. Finally, the excitation of ACR is further associated with remarkable confinement of electromagnetic field, providing a compelling sensing performance based on its excellent sensitivity and figure of merit.

Experimental verification of standing-wave plasmonic resonances in split-ring resonators

We experimentally demonstrate multiple resonances in split-ring resonators (SRRs) from direct electric excitations in midinfrared and near infrared regions. The ratio of the entire length of SRRs to the resonance modes and wavelengths presents a clear linear relationship. Such expression validates in both cases of electric and magnetic responses in SRRs excited by electric field and is further confirmed by examining the SRRs with different lengths. Therefore, our quantitative observations indicate that the multiple resonances can be interpreted by the standing-wave plasmonic resonances and further facilitate to design the desired operation frequencies and responses of SRRs for practical applications.

Inducing transparency with large magnetic response and group indices by hybrid dielectric metamaterials

We present metamaterial-induced transparency (MIT) phenomena with enhanced magnetic fields in hybrid dielectric metamaterials. Using two hybrid structures of identical-dielectric-constant resonators (IDRs) and distinct-dielectric-constant resonators (DDRs), we demonstrate a larger group index (ng~354), better bandwidth-delay product (BDP~0.9) than metallic-type metamaterials. The keys to enable these properties are to excite either the trapped mode or the suppressed mode resonances, which can be managed by controlling the contrast of dielectric constants between the dielectric resonators in the hybrid metamaterials.

Manipulation of multidimensional plasmonic spectra for information storage

We demonstrate a concept of optical data storage through plasmonic resonances of metallic nanostructures. Metallic nanostructures exhibit strong variations in their reflectance and/or transmittance spectra due to surface plasmon polariton resonances. We study the variations in spectra through 50×50 arrays of repeated unit cells covering a total area of ∼50×50u2002μm2. Each cell contains ten different nanofeatures, such as an ellipse, a ring, a circle, a triangle, a square, etc. The size of each unit-cell is 500×500u2002nm2, and the periodicity is 1.0u2002μm. The variations in spectra are obvious enough to be distinguished and then retrieved.

Vertically-Aligned of Sub-Millimeter Ultralong Si Nanowire Arrays and Its Reduced Phonon Thermal Conductivity

Well-aligned of single crystalline silicon nanowires (SiNWs) arrays are synthesized using Ag-assisted electroless etching processes. By examining a wide range of reaction periods from 1 min up to 12 h, our experimental results show that the lengths of fabricated SiNWs do not maintain the linear relationship with the reaction period but feature three evident transitions instead. We find that the diffusion of HF through Ag dendrites is the rate-limiting step for maintaining the galvanic reaction of etching processes. To overcome these limitations, we report a simple and controllable route employing HNO 3 /AgNO 3 /HF electrolyte solutions, which enables SiNW lengths ranging from several nanometers up to a few hundred micrometers to become linearly dependent on the reaction time. Transmission electron microscopy studies reveal that the SiNWs fabricated by this approach are single crystalline along [100] in axial direction with relatively rough surfaces. In addition, we further measure the thermal conductivities of SiNW arrays with various lengths at 300 K. The resulting value of thermal conductivity in SiNW arrays is only 44% in comparison with bulk Si (100) substrates; that is attributed to the effects of decreased area of phonon transport, as well as increased phonon scattering.

Electric and magnetic responses in the multiple-split ring resonators by electric excitation

We experimentally demonstrate both the electric and magnetic responses from the multiple-split-ring resonators (MSRRs) via normal reflectance measurements. All the fabricated MSRRs exhibit electric resonances under electric couplings but the magnetic resonances are only excited in MSRRs with odd numbers of splits from the asymmetrically electric couplings. Furthermore, the dependence of split numbers on the resonant positions and strengths is also investigated. In addition, the coupling mechanism of correlated resonances in the MSRRs can be well elucidated by the concept of standing-wave plasmonic resonances. Such scalable MSRRs present the tailored electromagnetic responses at desired frequencies, paving ways toward integrated nanophotonic applications.

Mid-infrared artificial magnetism directly from magnetic field coupling

Here we develop submicron L-shaped magnetic resonators with four-fold rotational symmetry to ease the burden of the orientation issue, and demonstrate a compelling artificial magnetic response up to 44.7 THz (wavelength 6.7u2009μm) along with the properties of scalability and broad bandwidth directly from magnetic field coupling. In addition, the stored electromagneticenergy is highly localized inside the resonators, resulting in a significant nonlinear enhancement to promise micro-quantitative analysis. We suggest that the artificial magnetism demonstrated at mid-infrared ranges will radically impact the field of infrared optics, biological and security imaging, and chemical sensing.

Unveiling the Electromagnetic Responses of Fourfold Symmetric Metamaterials and Their Terahertz Sensing Capability

We present the tailored terahertz responses via the hybridization of magnetic and electric resonators under normal incidence of electromagnetic wave. These cross-I sandwiched structures enable us to couple out the negative magnetic resonance followed by the effective inductance–capacitance (LC) circuit model, along with the negative electric response contributed by the excitation of diluted Drude metal resonance, thus allowing the realization of negative refraction index with a value of -2.3 at 4 THz. Furthermore, the cross-I sandwiched structures possess the compelling sensing performance based on their remarkable sensitivity and high-quality resonant behavior, holding great potential for practical applications in chemical/biological detection.

Plasmonic couplings in split-ring resonators by electric excitation

We introduce the symmetric and asymmetric coupling between two geometry-different split-ring resonators (SRRs) with dissimilar resonance frequencies and quality factors. An additional sharp transmission peak is excited as the strong coupling occurs between a narrow subradiant resonance and a broad superradiant resonance by examining the spacing of two SRR constituents. The mechanism of such induced transparency is elucidated well by the suppression of induced currents within the SRR element with a lower quality factor. Finally, the excitation of asymmetrically coupled resonance (ACR) is further associated with remarkable confinement of electromagnetic field on nanoscale, providing a dramatically sensing performance due to its pronounced sensitivity and a characteristic of sharp bandwidth.