Metallo-dielectric Nanostructures Research Articles

Plasmonic Electronic Raman Scattering as Internal Standard for Spatial and Temporal Calibration in Quantitative Surface-Enhanced Raman Spectroscopy.

Ultrasensitive surface-enhanced Raman spectroscopy (SERS) still faces difficulties in quantitative analysis because of its susceptibility to local optical field variations at plasmonic hotspots in metallo-dielectric nanostructures. Current SERS calibration approaches using Raman tags have inherent limitations due to spatial occupation competition with analyte molecules, spectral interference with analyte Raman peaks, and photodegradation. Herein, we report that plasmon-enhanced electronic Raman scattering (ERS) signals from metal can serve as an internal standard for spatial and temporal calibration of molecular Raman scattering (MRS) signals from analyte molecules at the same hotspots, enabling rigorous quantitative SERS analysis. We observe a linear dependence between ERS and MRS signal intensities upon spatial and temporal variations of excitation optical fields, manifesting the |E|4 enhancements for both ERS and MRS processes at the same hotspots in agreement with our theoretical prediction. Furthermore, we find that the ERS calibration's performance limit can result from orientation variations of analyte molecules at hotspots.

Plasmonic effects in the enclosed and opened metallodielectric bowtie nanostructures

Plasmonic effects in the enclosed and opened metallodielectric nanostructures, composed of a periodically bowtie-shape metal nanoparticles (MNPs), are numerically investigated and compared. The spreading range of resonance wavelength for the opened system is larger than that of the enclosed one due to more surface plasmon resonance (SPR) and hollow plasmon resonance (HPR) effects occurred in metallodielectric bowtie nanostructures. Numerical results exhibit that the sensitivity of the opened system could reach as high as 1056.60 nm/RIU. For the thinner shell thickness, it can fully support the high-energy mode with electric field concentration extended into the more dielectric core regions in the opened system, thereby provides higher sensitivity to local refractive index (RI) varies. In addition, the open hollow is accessible to the surrounding medium, and this makes it attractive for RI sensor and filtering applications. The highly sensitive optical performances give us a qualitative idea of the optical properties of SPR and HPR modes in the opened metallodielectric bowtie nanostructure system that can be as a promising candidate for analyzing the real nanocomposites and producing the nanomaterials with novel properties.

2D-Photonic Crystal based Demultiplexer for WDM Systems – A Review

Abstract Photonic crystals (PCs) have an excellent ability to confine and control the manipulation of light. PCs are periodic or aperiodic arrangement of dielectric, metallo dielectric or super conductor micro and nanostructure materials. The periodicity of refractive index distribution in one, two and three dimensions affects the propagation of electromagnetic waves inside the PC structure. As a result of periodicity, photonic band gap (PBG) exists in a specific wavelength of PC structure and reflects the beam of light through it. This is an active part to design optical devices with a specified wavelength range. The PBG of periodic and aperiodic structures is calculated by plane wave expansion method. The wavelength division multiplexing (WDM) is an emerging technology in optical field. The multiplexer and demultiplexer are playing a prominent role for transmission and reception of light signals in WDM systems. This paper investigates and enumerates the two-dimensional (2D) PC square lattice structure-based WDM demultiplexers using quasi-square ring resonator (QSRR). The periodic array of inner rods located inside the QSRR whose shapes and refractive index justify the resonant wavelength of the channels. The channels are dropped at output ports with different resonant wavelengths by altering the size and refractive index of cavity. Typically, the resonant wavelength of the channel is shifted to higher wavelength while increasing the dielectric strength of the QSRR. The dielectric strength of the QSRR is altered by varying the inner rod radius which reflects the size of the air gap. The demultiplexer is composed of bus waveguide, scatterer rod, and reflector rod whose dimensions are also responsible to enhance or alter the performance of the systems. The finite difference time domain method is utilized to analyse the functional parameters of the structure such as the resonant wavelength, transmission efficiency, Q factor, spectral width, channel spacing and crosstalk. The impact of performance parameters is investigated through different shape of inner core and refractive index of QSRR. The observed resonant wavelength of the channels (1,525–1,610 nm) of the demultiplexers is falling under WDM systems and overall size is minimized to 434.16 μm2. The average channel spacing is about 0.75 nm, spectral width is 0.76 nm, Q factor is 2,036 and crosstalk between the channels is −30 dB. The significance of the attempt is to reduce the crosstalk which is attained by grouping odd and even numbers of channels separately. Finally, four-channel demultiplexer is designed by altering the refractive index of the inner rods (i. e. inner core) linearly and the performance parameters are investigated. Then, the point-to-point network is designed to incorporate and evaluate the performance of the demultiplexer. The observed maximum travelling distance, Bit Error Rate (BER) and receiver sensitivity of the network are 85 km, 10−9 and −16 dBm, respectively. The device could be incorporated in photonic integrated circuits for dense WDM applications.

Tape nanolithography: a rapid and simple method for fabricating flexible, wearable nanophotonic devices

This paper describes a tape nanolithography method for the rapid and economical manufacturing of flexible, wearable nanophotonic devices. This method involves the soft lithography of a donor substrate with air-void nanopatterns, subsequent deposition of materials onto the substrate surface, followed by direct taping and peeling of the deposited materials by an adhesive tape. Without using any sophisticated techniques, the nanopatterns, which are preformed on the surface of the donor substrate, automatically emerge in the deposited materials. The nanopatterns can then be transferred to the tape surface. By leveraging the works of adhesion at the interfaces of the donor substrate-deposited material-tape assembly, this method not only demonstrates sub-hundred-nanometer resolution in the transferred nanopatterns on an area of multiple square inches but also exhibits high versatility and flexibility for configuring the shapes, dimensions, and material compositions of tape-supported nanopatterns to tune their optical properties. After the tape transfer, the materials that remain at the bottom of the air-void nanopatterns on the donor substrate exhibit shapes complementary to the transferred nanopatterns on the tape surface but maintain the same composition, thus also acting as functional nanophotonic structures. Using tape nanolithography, we demonstrate several tape-supported plasmonic, dielectric, and metallo-dielectric nanostructures, as well as several devices such as refractive index sensors, conformable plasmonic surfaces, and Fabry-Perot cavity resonators. Further, we demonstrate tape nanolithography-assisted manufacturing of a standalone plasmonic nanohole film and its transfer to unconventional substrates such as a cleaved facet and the curved side of an optical fiber.

Plasmon-Enhanced Generation of Nonclassical Light

Strong light-matter interactions enabled by surface plasmons have given rise to a wide range of photonic, optoelectronic and chemical functionalities. In recent years, the interest in this research area has focused on the quantum regime, aiming to developing ultra-compact nanoscale instruments operating at the single (few) photon(s) level. In this perspective, we provide a general overview of recent experimental and theoretical advances as well as near-future challenges towards the design and implementation of plasmon-empowered quantum optical and photo-emitting devices based on the building blocks of nanophotonics technology: metallo-dielectric nanostructures and microscopic light sources.

Localized Surface Plasmon Induced Position-Sensitive Photodetection in Silicon-Nanowire-Modified Ag/Si.

Surface plasmon-based approaches are widely applied to improve the efficiency of photoelectric devices such as photosensors and photocells. In order to promote the light absorption and electron-hole pair generation in devices, metallodielectric nanostructures are used to boost the growth of surface plasmons. Here, silicon nanowires (SiNWs) are used to modify a metal-semiconductor structure; thus, Ag/SiNWs/Si is manufactured. In this system, a large increased lateral photovoltaic effect (LPE) is detected with a maximum positional sensitivity of 65.35 mV mm-1 , which is ≈53-fold and 1000-fold compared to the conventional Ag/Si (1.24 mV mm-1 ) and SiNWs/Si (0.06 mV mm-1 ), respectively. It is demonstrated that localized surface plasmons (LSPs) contribute a lot to the increment of LPE. Furthermore, through the surface-enhanced Raman scattering spectra of rhodamine-6G and finite-difference time-domain simulation, it is illustrated that silver-coated SiNWs support strong LSPs. The results propose an enhancement mechanism based on LSPs to facilitate the photoelectric conversion in LPE and offer an effective way to improve the sensitivity of photodetectors.

Chiral near-field manipulation in Au-GaAs hybrid hexagonal nanowires.

We demonstrate the control of enhanced chiral field distribution at the surface of hybrid metallo-dielectric nanostructures composed of self-assembled vertical hexagonal GaAs-based nanowires having three of the six sidewalls covered with Au. We show that weakly-guided modes of vertical GaAs nanowires can generate regions of high optical chirality that are further enhanced by the break of the symmetry introduced by the gold layer. Changing the angle of incidence of a linearly polarized plane wave it is possible to tailor and optimize the maps of the optical chirality in proximity of the gold plated walls. The low cost feasibility of the sample combined to the simple control by using linearly polarized light and the easy positioning of chiral molecules by functionalization of the gold plates make our proposed scheme very promising for enhanced enantioselective spectroscopy applications.

Lab-on-Fiber Plasmonic Probes for Ultrasound Detection: A Comparative Study

This paper deals with a numerical study on Lab-on-Fiber devices for acoustic (ultrasound) sensing applications. Specifically, four different configurations based on hybrid metallo-dielectric nanostructures—with sub-wavelength dimensions—supporting plasmonic modes are analyzed. A comparison in terms of spectral features and electric field distributions at resonant wavelengths is carried out. For each configuration, sensitivity is evaluated as the reflectivity intensity changes as function of dielectric slab thickness, in the range of a few hundreds of nanometers. We demonstrate that sensitivity can be maximized by exploiting the interplay between different plasmonic modes. The influence of the acousto-optic coefficient is also evaluated. In the plasmonic interaction regime, we find that the acousto-optic effect also contributes to improve the sensitivity performances. Overall, in comparison with Fabry–Perot cavity-based transducers made from same materials and with comparable dimensions, sensitivity enhancement factors of about 3 can be obtained.

Experimental verification of substrate-induced bianisotropy in optical metamaterials

This paper reports on substrate-induced bianisotropy in an impedance-matched near-zero-index metallodielectric fishnet nanostructure with vertical sidewalls and a supporting substrate. The effect of bianisotropy on the metamaterial optical properties is confirmed through spectral holography measurements and full-wave electromagnetic simulations, showing asymmetric reflection coefficients from opposite sides of the structure at normal incidence. The non-zero magnetoelectric coupling parameter causes a 0.03 μm shift in the near-infrared zero-index band centered at 1.5 μm and a 38% reduction in transmitted power. The substrate-induced bianisotropy is due to the excitation of an anti-symmetric plasmonic resonance mode identified by comparing simulations of the current distributions on free-standing and substrate-mounted fishnet structures. This experimental demonstration of substrate-induced bianisotropy verifies the previously proposed theory and provides valuable guidance for future plasmonic and metamaterial nanostructures that include substrates.

Broadband Light Absorption with Multiple Surface Plasmon Polariton Waves Excited at the Interface of a Metallic Grating and Photonic Crystal

Light incident upon a periodically corrugated metal/dielectric interface can generate surface plasmon polariton (SPP) waves. This effect is used in many sensing applications. Similar metallodielectric nanostructures are used for light trapping in solar cells, but the gains are modest because SPP waves can be excited only at specific angles and with one linear polarization state of incident light. Here we report the optical absorptance of a metallic grating coupled to silicon oxide/oxynitride layers with a periodically varying refractive index, i.e., a 1D photonic crystal. These structures show a dramatic enhancement relative to those employing a homogeneous dielectric material. Multiple SPP waves can be activated, and both s- and p-polarized incident light can be efficiently trapped. Many SPP modes are weakly bound and display field enhancements that extend throughout the dielectric layers. These modes have significantly longer propagation lengths than the single SPP modes excited at the interface of a metallic grating and a uniform dielectric. These results suggest that metallic gratings coupled to photonic crystals could have utility for light trapping in photovoltaics, sensing, and other applications.

Photonic Crystal Structures with Tunable Structure Color as Colorimetric Sensors

Colorimetric sensing, which transduces environmental changes into visible color changes, provides a simple yet powerful detection mechanism that is well-suited to the development of low-cost and low-power sensors. A new approach in colorimetric sensing exploits the structural color of photonic crystals (PCs) to create environmentally-influenced color-changeable materials. PCs are composed of periodic dielectrics or metallo-dielectric nanostructures that affect the propagation of electromagnetic waves (EM) by defining the allowed and forbidden photonic bands. Simultaneously, an amazing variety of naturally occurring biological systems exhibit iridescent color due to the presence of PC structures throughout multi-dimensional space. In particular, some kinds of the structural colors in living organisms can be reversibly changed in reaction to external stimuli. Based on the lessons learned from natural photonic structures, some specific examples of PCs-based colorimetric sensors are presented in detail to demonstrate their unprecedented potential in practical applications, such as the detections of temperature, pH, ionic species, solvents, vapor, humidity, pressure and biomolecules. The combination of the nanofabrication technique, useful design methodologies inspired by biological systems and colorimetric sensing will lead to substantial developments in low-cost, miniaturized and widely deployable optical sensors.

Commentary: Luster ceramics: a 9th century AD nanotechnology

Photonic crystals are composed of periodic metallo-dielectric nanostructures that affect the propagation of light. The concept was proposed by Yablonovitch 25 years ago and today is an active, ongoing field of research with high prospects for potential applications in the field of photonics. It is known that nature has provided such nanostructures in minerals and living creatures. Sparkling opals, consisting of submicron size silica spheres arranged in a face-centered cubic structure, the iridescent tail feathers of the peacock, or the Morpho butterfly's blue shining color wings consisting of regular rows of thin plates so-called scales, are examples. We can refer to the brilliancy of these colors resulting from reflection and diffraction in the nano-structured material as structural colors, in contrast to pigmentary colors that result from absorption of light by pigments. Yet, in the early Middle Ages, in the 9th century AD, Islamic potters in Iraq succeeded in decorating glazed ceramics with vivid colors showing iridescent effects, very much like structural colors. These have been revealed to be caused by metallic nanoparticles buried below the glaze surface that the ancient potters were able to diffuse through empirical, carefully controlled heat treatments.

Theoretical analysis of enhanced nonlinear conversion from metallo-dielectric nano-structures

A new configuration of sub-wavelength silver coaxial apertures filled with Lithium Niobate (LN) is proposed to enhance the Second Harmonic Generation (SHG) in transmission mode. The chosen geometrical parameters allows having both TE11 guided mode excitation for local field confinement of the fundamental signal and Fabry-Perot high transmission of the SH wave. Furthermore, an implementation of the three-dimensional Finite Difference Time Domain (3D-FDTD) method for nonlinear optical simulation is described. This method provides a direct calculation of the nonlinear polarizations before calculating the nonlinear electric and magnetic fields. FDTD studies shows that by embedding metallic nano-structures, for exciting TE11 like-mode inside a nonlinear material (LN), we achieve a SH signal 27 times higher than that generated on unpatterned LN.

Low-Loss Impedance-Matched Optical Metamaterials with Zero-Phase Delay

Metamaterials have dramatically expanded the range of available optical properties, enabling an array of new devices such as superlenses, perfect absorbers, and ultrafast switches. Most research has focused on demonstrating negative- and high-index metamaterials at terahertz and optical wavelengths. However, far less emphasis has been placed on low-loss near-zero-index metamaterials that exhibit unique properties including quasi-infinite phase velocity and infinite wavelength. Here, we experimentally demonstrate a free-standing metallodielectric fishnet nanostructure that has polarization-insensitive, zero-index properties with nearly ideal transmission at 1.55 μm. This goal was achieved by optimizing the metamaterial geometry to allow both its effective permittivity and permeability to approach zero together, which simultaneously produces a zero index and matched impedance to free space. The ability to design and fabricate low-loss, near-zero-index optical metamaterials is essential for new devices such as beam collimators, zero-phase delay lines, and transformation optics lenses.

Lab-on-Fiber Technology: Toward Multifunctional Optical Nanoprobes

We propose a reliable fabrication process enabling the integration of dielectric and metallic nanostructures on the tip of optical fibers, thus representing a further step in the "lab-on-fiber" technology roadmap. The proposed fabrication procedure involves conventional deposition and nanopatterning techniques, typically used for planar devices, but here adapted to directly operate on optical fiber tip. Following this approach, we demonstrate a first technological platform based on the integration onto the optical fiber tip of two-dimensional hybrid metallo-dielectric nanostructures supporting localized surface plasmon resonances. By means of experimental measurements and full-wave numerical simulations, we characterize these resonant phenomena and investigate the underlying physics. We show that resonances can be easily tuned by acting on the physical and geometrical parameters of the structure. Moreover, with a view toward possible applications, we present some preliminary results demonstrating how the proposed device can work effectively as an optical probe for label-free chemical and biological sensing as well as a microphone for acoustic wave detection.

Controlled detection in composite nanoresonant array for surface plasmon resonance sensing

A composite nanoresonant structure is developed for sensitivity enhancement in biorecognition reactions by coupling between the localized resonance and the propagating surface plasmon polariton waves. The resonant structure was accomplished by combining holographic lithography with an oblique metallic deposition for cost-effective, large-area, and reconfigurable fabrication. The metallodielectric nanostructure was assembled with microfluidic channels and examined for biorecognition reactions, which showed pronounced improvement in the limit of detection compared to conventional nanohole array sensing configurations. The temperature influence on the binding affinity and the effectiveness of the control channel were also investigated to demonstrate the capability of the proposed composite nanoresonant surface plasmon resonance array sensor.

Interactions between Fabry–Pérot and nanohole resonances in metallo-dielectric plasmonic nanostructures

We present results of numerical simulations for structures comprised of metallo-dielectric layers in which the metal layers are perforated with non-diffracting arrays of subwavelength holes, structures that are similar to the ‘fishnet’ structures being studied as electromagnetic metamaterials. We find for visible frequencies that such structures exhibit a stop-band in transmittance across a broad frequency range, which arises through interactions between two distinctly different types of resonant mode. Using numerical (finite element) modelling to characterise the optical response, we identify strong coupling between Fabry–Pérot resonant cavity modes within the multilayer structure and localised surface-plasmon resonances associated with the nanoholes. Our simulations show that the spectral position and width of the stop-band that occurs within the visible frequency range can be tuned by varying both the cavity spacing and the geometry of the nanohole array.

Three-dimensional composite metallodielectric nanostructure for enhanced surface plasmon resonance sensing

The authors simulated, fabricated, and characterized a mushroomlike composite metallodielectric nanostructure that shows improved characteristics for surface plasmon resonance sensing applications with an enhancement in the normal electric field compared to the conventional nanohole structure. A fabrication method is introduced to give controllable linewidth by an oblique metal deposition process. A sensor built with the composite nanostructure was then used to determine the hydrophilicity of its surface by monitoring the resonant wavelength shift and computing the corresponding adsorption thickness.

Single-layer metallodielectric nanostructures as dual-band midinfrared filters

We report a design and fabrication strategy for creating single-layer metallodielectric nanostructures with dual-band filtering properties at midinfrared wavelengths. Genetic algorithm optimization was used to determine an arrangement of nanometer-scale metal pixels within one unit cell of a two-dimensional periodic array that best satisfied the user-specified filter response and nanofabrication design rule constraints. Infrared transmission and reflection spectra measured on an optimized nanostructure array had two narrow stop bands blueshifted by 0.2μm from the designed center wavelengths of 3.3 and 4.1μm, with transmission attenuation greater than −20dB and reflection attenuation less than −1.5dB in each band. This strategy provides a practical and efficient approach to design metallodielectric nanostructures needed for photonic device applications as well as for future low-loss refractive index engineered metamaterials.

Shaping gold nanorods for plasmonic applications

Nanostructuring is a key element for the development of optics, optoelectronics, and photonics capable of operating on subwavelength scales. However, the realization of highly integrated optical devices and sensors with nanolocal electromagnetic field control requires structural elements comparable to and smaller than a wavelength of light. One widely investigated approach is to use appropriately designed metallic and metallodielectric nanostructures to manipulate light in the form of various surface plasmon excitations, such as surface plasmon polaritons and localized surface plasmons.1 These electromagnetic surface modes are associated with the coherent excitation of the free-electron density charge waves at the interface of a metal and a dielectric material. Various plasmonic circuit elements based on nanostructured metal films, such as waveguides, mirrors, lenses, resonators, and plasmonic crystals, have been designed and tested. Plasmonic nanostructures can provide both passive and active all-optical elements, the latter capable of operating at low-control light intensities due to the electromagnetic field enhancement resulting from plasmonic excitations.2 Alternative plasmonics can be developed based on discrete sets of interacting metallic particles. We have recently developed an approach to inexpensively fabricate large arrays (1cm2 with up to 1 billion nanorods) of aligned nanoscale metallic rods attached to a substrate.3 Typically, the nanorods have a diameter of some 20nm with length controllable between 50 and 450nm. These are required to tailor the linear and nonlinear behavior of plasmonic excitations. However, to develop their functionalities and integrate them in complex plasmonic circuits for sensing and telecommunication applications, the nanorod assemblies must be configured in various shapes. An attractive solution is to use femtosecond laser-based direct writing technology to restructure free-standing nanorods and Figure 1. Schematic setup for restructuring gold nanowires by femtosecond laser irradiation.