Flat-Top Transmission Band in Periodic Plasmonic Ring Resonators

Flat-top transmission bands are found in a plasmonic structure constructed by periodic ring resonators. Fabry–Perot effects can be suppressed in a set of parameters determined by an effective medium method. Two kinds of transmission bands with flat-top profiles can emerge due to either ring resonance or Bragg scattering. These bands are both red shifted when the distance of rings increases. Both transfer matrix method and finite difference time domain method are utilized to investigate the flat-top bands. The proposed structure can be employed as a plasmonic band-pass filter and might be useful in the field of integrated optoelectronics.     

Tunable Extraordinary Optical Transmission in a Metal Film Perforated with Two-Level Subwavelength Cylindrical Holes

We propose a novel plasmonic metal structure composed of a silver film perforated with a two-dimensional square array of two-level cylindrical holes on a silica substrate. The transmission properties of this structure are theoretically calculated by the finite-difference time-domain (FDTD) method. Double-enhanced transmission peaks are achieved in the visible and infrared regions, which mainly originate from the excitation of localized surface plasmon resonances (LSPRs), the hybridization of plasmon modes, and the optical cavity mode formed in the holes. The enhanced transmission behaviors can be effectively tailored by changing the geometrical parameters and dielectric materials filled in the holes. These findings indicate that our proposed structure has potential applications in highly integrated optoelectronic devices.     

Investigation on the Optical Transition of Hexagonal Boron Nitride

Plasmonics - We study the relationship between the optical transition of hexagonal boron nitride and the direction of its optical axis. The results show that the optical transition can be tunable...     

Generation and Manipulation of Multiple Magnetic Fano Resonances in Split Ring-Perfect Ring Nanostructure

Plasmonics - The plasmon resonances and field enhancement in split ring-perfect ring (SR-PR) nanostructure are investigated numerically by using a finite element method. Multiple electric...     

Generation of Narrowband Tunable THz-Radiation via Optical Rectification in Periodically Poled Materials

The generation of tunableTHz-radiation via optical rectification offs-pulses in periodically poled nonlinearmaterials is reported and its applicationfor biomedical sensing using THz-senorsbased on planar wave guides is discussed indetail.     

Enhanced Optical Forces and Tunable LSPR of Ag Triangular Nanoplates for Plasmonic Tweezers

Plasmonics - In this work, we present a plasmonic platform capable of the enhanced electric field (E-field) intensity, tunable LSPR effect, and trapping nanoparticles in different...     

Investigation of Optical Spectrum Properties of Hexagonal Boron Nitride from Metal to Dielectric Transition

Plasmonics - Hexagonal boron nitride as a natural hyperbolic material has attracted lots of attention recently. Here, we investigate numerically the optical spectrum properties of hexagonal boron...     

Extraordinary Optical Transmission Property of X-Shaped Plasmonic Nanohole Arrays

Optical transmission properties of periodic X-shaped plasmonic nanohole arrays in a silver film are investigated by performing the finite element method. Obvious peaks appear in the transmission spectra due to surface plasmon polaritons (SPPs) on the top surface of the silver film, to the Fabry–Ferot resonance effect of SPPs in the nanohole, and to the localized surface plasmon resonance of the nanohole. Besides the topologic shape parameters of the X-shaped nanohole, transmission properties strongly depend on incident polarization. The results of this study not only present a tunable plasmonic filter, but also aid in the understanding of the mechanisms of the extraordinary optical transmission phenomenon.     

Unidirectional Optical Transmission of a Dual Metallic Grating with Grooves

In this paper, a dual grating structure for unidirectional transmission is presented. The forward and backward transmission performances have been investigated by finite element method. To enhance the forward transmission and to suppress the backward transmission simultaneously, we suggested to cut grooves on the surfaces of one of the gratings, and the effects of the grooves on the optical transmission have been studied. The numerical simulation results reveal that the transmission contrast ratio and the optical unidirectional transmission of the structure can be improved markedly by properly arranging the size and the position of the grooves. The forward transmission can be more than 90%, while the backward transmission transmittance is less than 5%.

     

Investigating the Characteristics of a Double Circular Ring Resonators Slow Light Device Based on the Plasmonics-Induced Transparency Coupled with Metal-Dielectric-Metal Waveguide System

We have numerically investigated an analog of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) waveguide bend. The geometry consists of two asymmetrical stubs extending parallel to an arm of a straight MDM waveguide bend. Finite-difference time-domain simulations show that a transparent window is located at 1550 nm, which is the phenomenon of plasmonic-induced transparency (PIT). Signal wavelength is assumed to be 820 nm. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. Multiple-peak plasmon-induced transparency can be realized by cascading multiple cavities with different lengths and suitable cavity-cavity separations. Large group index up to 73 can be obtained at the PIT window. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends. In addition, the relationship between the transmission characteristics and the geometric parameters including the radius of the nano-ring, the coupling distance, and the deviation length between the stub and the nano-ring is studied in a step further. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. For indirect coupling, formation of transparency window is determined by resonance detuning, but, evolution of transparency is mainly attributed to the change of the coupling distance. Theoretical results may provide a guideline for control of light in highly integrated optical circuits. The characteristics of our plasmonic system indicate a significant potential application in integrated optical circuits such as optical storage, ultrafast plasmonic switch, highly performance filter, and slow light devices.     

Suppressed Optical Transmission Through an Array of Ultrathin Interlayer Metal Slits

In contrast to the enhanced peak transmission in a subwavelength metal hole array structure (Ebbesen et al., Nature 391:667–669, 1998), here we theoretically investigate the spectral transmission through an array of identical metal slits with ultrathin interlayers and surprisingly find the depressed optical transmission for both infinite and finite array case. Notably, in the latter system, the narrowband dip transmission is evidently produced with the accompaniment of selective field enhancement and phase jumping across the structure. Analyses suggest that this phenomenon is intrinsically related to the penetrant coupling of intracavity surface plasmon polaritons together with the slit termination effect.     

Extraordinary Optical Transmission Performances of Nanosandwiched Grating for Wideband Multi-Function Integration

In this paper, we present a peculiar metal-dielectric-metal (MDM) nanosandwich grating structure that can achieve extraordinary optical transmission performances at normal incidence in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions. The proposed structure shows three obvious spectrum characteristics: it can obtain high transmittance up to 80 % in NUV region and efficiently blocking visible wavelengths for transverse-magnetic (TM) polarized incidence; a broadband NIR polarizer can be inspired in the wavelength range from 950 to 1400 nm; more surprisingly, these performances do not deteriorated until 30° tilting angle. Compared to other grating structures with single metal overlayer, it shows wider band-stop characteristics and higher broadband transmission transmittance and extinction ratio (ER) in the investigated wavebands. We analyze the underlying physical mechanism by using numerical simulation, which is primarily attributed to metal ultraviolet transparency, surface plasmon polariton (SPP) at metal/dielectric interface, Fabry–Perot (FP)-like cavity mode within this dielectric grating, and optical magnetic resonance especially in the dielectric interlayer of the MDM sandwiched structure. This structure is very important for developing high-performance subwavelength multifunctional integrated optical devices.     

同时应用近场光学显微镜的透射和反射模式研究单个细胞的光学性质

通常认为．在近场光学显微技术的光收集模式中,观察透光性好的样品时采用透射模式．研究不透明样品时采用反射模式。本文同时采用透射和反射两种模式观察透明性较好的PCI2细胞和淋巴细胞样品．初步研究单个细胞的反射、吸收、透射和荧光等光学性质,以促进组织光学和激光生物医学等领域的进一步发展。细胞光学的时代就要到来。     

Enhancement of Extraordinary Optical Transmission in a Double Heterostructure Plasmonic Bandgap Cavity

In this paper, a novel plasmonic bandgap cavity inducing the enhancement of extraordinary optical transmission is presented. Numerical simulations have been performed to model a free-standing structure made of a one-dimensional periodic arrangement of gold strips. Two different values of the lattice constant have been properly chosen to realize a double heterostructure-like cavity to accomplish extraordinary optical transmission assisted by the formation of a plasmonic bandgap in the adjacent regions. Numerical results prove the capability of this optical device to efficiently transmit input light beams with far-field transmission values close to 100% due to the excitation of surface plasmon polariton resonant modes.     

Interplaying Role of Particle Size and Polymer Layer Thickness on the Large Tunable Optical Response of Polymer-coated Silver Nanostructures

Plasmonics - The interplaying role of particle size and polymer layer thickness on the tunable optical response of polymer-coated Ag nanoparticles (NPs) has been studied experimentally and...     

Complex Mechanism of Enhanced Optical Transmission Through a Composite Coaxial/Circular Aperture

Making use of the FDTD simulation, we study light transmission properties of a composite coaxial/circular aperture milled in a thin metallic film. Representing the aperture as consisting of segments of coaxial and hollow waveguides, connected in series, we show that there are three characteristic frequencies (the cutoff frequencies of the coaxial and hollow waveguides and the frequency of a longitudinal standing wave in the coaxial waveguide segment) and four regimes of operation (bounded by these frequencies, as well as by low- and high-frequency limits) which determine the behavior of the transmission efficiency. For two regimes of operation (for frequencies between the cutoff frequency of the coaxial waveguide and the resonant frequency of the longitudinal standing wave), both segments can contribute to the overall transmission. For other two regimes, either no enhancement occurs or only one segment contributes to the transmission efficiency. A way is proposed to optimize the transmission through the composite aperture. In particular, as we show, the transmission efficiency of the aperture can be enhanced by decreasing the exit hole size (radius of the circular aperture). In the considered case, an increase of the transmission efficiency exceeds 50%. The effect of the enhanced transmission is shown to result from both vertical and in-plane surface plasmon resonances occurring in the aperture.     

Design of Optical Filters with Flat-on-Top Transmission Lineshapes Based on Two Side-Coupled Metallic Grooves

We investigate theoretically and numerically the resonant transmission through side-coupled metallic grooves. In the framework of coupled mode theory (CMT), a single metallic groove can be considered as a lossy optical resonator and two metallic grooves coupled via tunneling effect can be treated as a second-order cascade resonator. The relationship between the transmission lineshape of the coupled grooves and the cross-coupling between the grooves is analyzed by CMT. It is found that a flat-on-top lineshape can be obtained when the cross-coupling is equal to the total decay rate of the groove mode. Predictions based on the CMT analysis are in good agreement with the simulation results based on the finite-difference time-domain technique.     

Tunable Mid-Infrared Optical Properties of Monolayer Black Phosphorus Through Au Nanotriangle Arrays via Electric Field Reflection and Surface Plasmon Polaritons

A metamaterial system composed of monolayer black phosphorus and Au triangle arrays is designed. Absorptivity, transmittivity, and reflectivity are investigated in mid-infrared regime. A low transmissivity and high absorptivity can be obtained via surface plasmon polaritons at the black phosphorus and Au triangle array interface. By changing the geometrical parameters, such as angle magnitude and slit width of Au triangle, we can modulate the transmissivity, reflectivity and absorptivity properties. Different from other previous work, it is found the zigzag direction has a better photoresponse than that armchair by changing the slit width. The electric field of the external radiation field is reflected at the Au triangle edges. Thus, electric field component perpendicular to the polarization direction generates, which can also lead to surface plasmon polaritons and is not researched in others’ work. With increase in the angle of Au triangle, transmittivity (or absorptivity) for armchair direction has a blue shift and for zigzag direction has a red shift. The transmittivity decrease ( or absorptivity increase ) for special wavelength caused by the surface plasmon polaritons may be applied to design filter devices.

     

Quantification of a Cardiac Biomarker in Human Serum Using Extraordinary Optical Transmission (EOT)

Nanoimprinting lithography (NIL) is a manufacturing process that can produce macroscale surface areas with nanoscale features. In this paper, this technique is used to solve three fundamental issues for the application of localized surface plasmonic resonance (LSPR) in practical clinical measurements: assay sensitivity, chip-to-chip variance, and the ability to perform assays in human serum. Using NIL, arrays of 140 nm square features were fabricated on a sensing area of 1.5 mm x 1.5 mm with low cost. The high reproducibility of NIL allowed for the use of a one-chip, one-measurement approach with 12 individually manufactured surfaces with minimal chip-to-chip variations. To better approximate a real world setting, all chips were modified with a biocompatible, multi-component monolayer and inter-chip variability was assessed by measuring a bioanalyte standard (2.5−75 ng/ml) in the presence of a complex biofluid, human serum. In this setting, nanoimprinted LSPR chips were able to provide sufficient characteristics for a ‘low-tech’ approach to laboratory-based bioanalyte measurement, including: 1) sufficient size to interface with a common laboratory light source and detector without the need for a microscope, 2) high sensitivity in serum with a cardiac troponin limit of detection of 0.55 ng/ml, and 3) very low variability in chip manufacturing to produce a figure of merit (FOM) of 10.5. These findings drive LSPR closer to technical comparability with ELISA-based assays while preserving the unique particularities of a LSPR based sensor, suitability for multiplexing and miniaturization, and point-of-care detections.