Periodic Arrays Of Subwavelength Holes Research Articles

Parametric study of optical transmission through plasmonic hole arrays modulated by the phase transition of vanadium dioxide

We have performed comprehensive electromagnetic simulations and preliminary experiments to explore the effects of geometrical and material parameters on the extraordinary optical transmission (EOT) through periodic arrays of subwavelength holes in a bilayer stack consisting of a gold or silver film atop a vanadium dioxide film (Au/Ag + VO2), where the latter undergoes a semiconductor-to-metal phase transition. Using the finite-difference time-domain (FDTD) and finite-element methods (FEM), we vary iteratively the array periodicity, VO2 film thickness and hole diameters, as well as the refractive index inside the VO2-layer holes and the VO2 optical constants. For each variation, we compare the metallic-to-semiconducting ratios of the zero-order transmission (T00) peaks and find sharp maxima in these ratios within narrow parameter ranges. The maxima arise from Fabry-Perot and Fano-type resonances that minimize T00 in the semiconducting phase of the perforated bilayers. At a fixed array period, the primary factors controlling the VO2-enabled EOT modulation are the VO2 thickness, diameter of the VO2-layer holes, and absorption in the two VO2 phases. Besides uncovering the origins of the higher metallic-phase T00, this study provides a protocol for optimizing the performance of the bilayer hole arrays for potential uses as dynamically tunable nano-optical devices.

Tailoring the optical field enhancement in Si-based structures covered by nanohole arrays in gold films for near-infrared photodetection

We performed numerical simulations of plasmonic near-field enhancement in Si-based structures in near infrared region. Gold films perforated with periodic two-dimensional subwavelength hole arrays were used as the plasmonic couplers. The array periodicity was adjusted to excite the surface plasmon modes at the telecom wavelengths (between 1.3 and 1.55 μm). The field intensity enhancement factor and its spectral position, as a function of hole diameter, demonstrate the maximum at which the Bloch plasmon polariton waves propagating along the Au–Si interface change by a localized surface plasmon mode. The maximum peak wavelength and field intensity enhancement are reached at d/a = 0.5, where d is the hole diameter and a is the array periodicity. An over 14 times field intensity enhancement was obtained at λ = 1.54 μm for d = 200 nm and a = 400 nm. We found that the localized surface plasmon mode is confined mainly under the Au regions along the diagonals of the square lattice of holes. The lateral field distribution for propagating modes has either a hexagonal or square shape, reflecting in-pane symmetry of the grating. For structures with largest holes, the anticrossing of localized mode with the propagating one was observed implying coupling between the modes and formation of a mixed near-field state. The information acquired from the study is valuable for feasible device applications.

Coupling of Gain Medium and Extraordinary Optical Transmission for Effective Loss Compensation

Gain mediums attract much attention due to their excellent amplification characteristics. However, the potential applications of gain mediums are severely limited because of the requirement of a high external energy to excite the media, thereby compensating for the ohmic loss. In this paper, we developed a theoretical model by numerically solving the coupled Maxwell’s equations and semiclassical electronic rate equations using the finite-difference time-domain method. In the model, the active gain medium is represented by a four-level atomic system, and the atoms are pumped with a homogeneous pumping rate. Then, we investigated the loss compensation with the synergetic effects of gain mediums and extraordinary optical transmission (EOT) phenomena caused by the excitation of the surface plasmon polariton. With the proposal of a novel gain/metal/gain structure that is patterned to be a periodic subwavelength hole array, the self-consistent process of EOT phenomena coupled to the gain medium enables full compensation of the ohmic loss under a much lower pumping rate. This paper not only presents a novel structure but also provides deep insight into the interaction between nanostructures and gain mediums.

Plasmon polariton enhanced mid-infrared photodetectors based on Ge quantum dots in Si

Quantum dot based infrared (IR) photodetectors (QDIPs) have the potential to provide meaningful advances to the next generation of imaging systems due to their sensitivity to normal incidence radiation, large optical gain, low dark currents, and high operating temperature. SiGe-based QDIPs are of particular interest as they are compatible with silicon integration technology but suffer from the low absorption coefficient and hence small photoresponse in the mid-wavelength IR region. Here, we report on the plasmonic enhanced Ge/Si QDIPs with tailorable wavelength optical response and polarization selectivity. Ge/Si heterostructures with self-assembled Ge quantum dots are monolithically integrated with periodic two-dimensional arrays of subwavelength holes (2DHAs) perforated in gold films to convert the incident electromagnetic IR radiation into the surface plasmon polariton (SPP) waves. The resonant responsivity of the plasmonic detector at a wavelength of 5.4 μm shows an enhancement of up to thirty times over a narrow spectral bandwidth (FWHM = 0.3 μm), demonstrating the potentiality of this approach for the realization of high-performance Ge/Si QDIPs that require high spectral resolution. The possibility of the polarization-sensitive detection in Ge/Si QDIPs enhanced with a stretched-lattice 2DHA is reported. The excitation of SPP modes and the near-field components are investigated with the three-dimensional finite-element frequency-domain method. The role that plasmonic electric field plays in QDIP enhancement is discussed.

Extraordinary optical transmission of periodic array of subwavelength holes within titanium nitride thin film

We focused on the optical properties of square array of subwavelength holes created within a titanium nitride (TiN) thin film. The TiN layer was placed on top of the dielectric layer as a surface plasmonic system originated from an intermetallic–dielectric arrangement. The finite-difference time-domain method was used via an Optiwave package to simulate periodic array of square and circular holes within the TiN layer. The effect of geometrical and material parameters such as periodic constant (a), size (S), shape of the holes, and the electric permittivity of the dielectric substrate has been investigated. An extraordinary optical transmission was observed in comparison with the nonhole system. It was shown that the wavelength of plasmonic modes, as a characteristic feature of the system, was affected by changing the periodic constant and electric permittivity. Meanwhile, changing the size as well as the shape of the holes did not affect the position of the peaks. These results are in agreement with the characteristic equation for plasmonic structure, which relates the surface plasmon wavelength (λsp) to the geometrical and material parameters of the system. The intensity of excited peaks was explained by distribution of the z-component of the electric field obtained from simulation, which illustrated the role of the surface plasmon polariton, localized surface plasmon resonance, and waveguide mode in tuning the optical behavior of the system. The results showed that TiN is a promising candidate for replacing metals in a plasmonic application with particular chemical and mechanical features.

Hybrid Magnetoplasmonic Crystals Boost the Performance of Nanohole Arrays as Plasmonic Sensors

We present here a theoretical study that shows how the use of hybrid magnetoplasmonic crystals comprising both ferromagnetic and noble metals leads to a large enhancement of the performance of nanohole arrays as plasmonic sensors. In particular, we propose using Au–Co–Au films perforated with a periodic array of subwavelength holes as transducers in magneto-optical surface-plasmon-resonance sensors, where the sensing principle is based on measurements of the transverse magneto-optical Kerr effect. We demonstrate that this detection scheme may result in bulk figures of merit that are 2 orders of magnitude larger than those of any other type of plasmonic sensor. The sensing strategy put forward here can make use of the different advantages of nanohole-based plasmonic sensors such as miniaturization, multiplexing, and its combination with microfluidics.

Spoof surface plasmon polaritons in terahertz transmission through subwavelength hole arrays analyzed by coupled oscillator model.

Both the localized resonance and excitation of spoof surface plasmon polaritons are observed in the terahertz transmission spectra of periodic subwavelength hole arrays. Analyzing with the coupled oscillator model, we find that the terahertz transmission is actually facilitated by three successive processes: the incident terahertz field first initiates the localized oscillation around each hole, and then the spoof surface plasmon polaritons are excited by the localized resonance, and finally the two resonances couple and contribute to the transmission. Tailoring the localized resonance by hole size, the coupling strength between spoof surface plasmon polaritons and localized resonances is quantitatively extracted. The hole size dependent transmittance and the coupling mechanism are further confirmed by fitting the measured spectra to a modified multi-order Fano model.

Faraday effect in hybrid magneto-plasmonic photonic crystals.

We present a theoretical study of the Faraday effect in hybrid magneto-plasmonic crystals that consist of Au-Co-Au perforated membranes with a periodic array of sub-wavelength holes. We show that in these hybrid systems the interplay between the extraordinary optical transmission and the magneto-optical activity leads to a resonant enhancement of the Faraday rotation, as compared to purely ferromagnetic membranes. In particular, we determine the geometrical parameters for which this enhancement is optimized and show that the inclusion of a noble metal like Au dramatically increases the Faraday rotation over a broad bandwidth. Moreover, we show that the analysis of the Faraday rotation in these periodically perforated membranes provides a further insight into the origin of the extraordinary optical transmission.

Role of dielectric properties in terahertz field transmission

We compare the field transmission characteristics of a freestanding perforated metal film (as a conductor) and a polymethylmethacrylate–graphite composite film (as an absorber) in the terahertz frequency range. The role of dielectric properties of the materials and the contribution of surface waves toward enhanced transmission with periodic and random hole arrays are discussed. Periodic subwavelength hole arrays in metal films do support enhanced terahertz field transmission whereas random arrays do not. In contrast, neither periodic nor random arrays of subwavelength holes punctured in dielectric absorbers support such transmission. Notably, even a dielectric absorber with large holes, which is sufficiently larger than subwavelength holes, can result in features in transmission due to the shape resonance, but the effect is very small.

Broadband Extraordinary Optical Transmission Through a Multilayer Structure With a Periodic Nanoslit Array

Extraordinary optical transmission (EOT) of metallic film perforated by a periodic array of subwavelength holes is significant in photoelectric devices. In this paper, a multilayer structure with periodic nanoslit arrays is proposed to achieve broadband EOT in infrared. The optical transmission properties of such structure are simulated through the finite-element method. Greatly enhanced transmissions over a broad spectral range are observed in near-infrared wavelengths, and many enhanced electric fields occur in the narrower slit. In addition, the effects of structural parameters on transmission properties are also investigated. All these findings could guide the design of devices with broadband-enhanced transmission and high electric-field concentration.

Optical filtering properties of subwavelength Tai-chi-shaped metal hole arrays

Finite-difference time-domain (FDTD) method is employed to study the optical properties of a novel kind of periodic subwavelength hole arrays composed of Tai-chi-shaped holes in silver film, and the optical transmission properties of femtosecond optical pulse excitation is numerically calculated. We find that this Tai-chi-shaped device has better optical band-pass filtering properties, such as narrower pass band and higher transmissivity in visible wavelengths range, than other devices under consideration. Based on the generation of surface plasmons resonance mode in the dielectric–metal interface, the center wavelength of transmission can be tuned by changing the array periodicities. We observe that the tune ability mainly depends on the space period along the direction parallel to that of the incident pulse polarization. It is also found that both the strength and the wavelength of the transmission peaks of rectangularly distributed metal hole arrays are determined by the polarization of incident light. Additionally, we demonstrate the typical band-pass filtering properties of this Tai-Chi-shaped holes structure. The full-width at half-maximum (FWHM) of the narrow pass band is about 20nm in visible wavelengths range.

Enhanced transmission due to antireflection coating layer at surface plasmon resonance wavelengths.

We present experiments and analysis on enhanced transmission due to dielectric layer deposited on a metal film perforated with two-dimensional periodic array of subwavelength holes. The Si3N4 overlayer is applied on the perforated gold film (PGF) fabricated on GaAs substrate in order to boost the transmission of light at the surface plasmon polariton (SPP) resonance wavelengths in the mid- and long-wave IR regions, which is used as the antireflection (AR) coating layer between two dissimilar media (air and PGF/GaAs). It is experimentally shown that the transmission through the perforated gold film with 1.8 µm (2.0 µm) pitch at the first-order (second-order) SPP resonance wavelengths can be increased up to 83% (110%) by using a 750 nm (550 nm) thick Si3N4 layer. The SPP resonance leads to a dispersive resonant effective permeability (μeff ≠ 1) and thereby the refractive index matching condition for the conventional AR coating on the surface of a dielectric material cannot be applied to the resonant PGF structure. We develop and demonstrate the concept of AR condition based on the effective parameters of PGF. In addition, the maximum transmission (zero reflection) condition is analyzed numerically by using a three-layer model and a transfer matrix method is employed to determine the total reflection and transmission. The numerically calculated total reflection agrees very well with the reflection obtained by 3D full electromagnetic simulations of the entire structure. Destructive interference conditions for amplitude and phase to get zero reflection are well satisfied.

Highly directional spaser array for the red wavelength region

AbstractThe spaser offers an opportunity to achieve coherent optical sources at nanometer scales due to the extreme confinement of optical fields. However, achievement of spasers with directional propagation in the visible wavelength region remains a challenge thus far, owing to the unique optical feedback mechanism and large dissipative losses of the metal cavity. Here, we experimentally demonstrate for the first time a spaser showing highly directional emission in the visible by using a periodic subwavelength hole array perforated in a metal film, which function as plasmonic nanocavities, along with an organic laser dye to supply gain. The lasing occurs in the red wavelength region and shows a single mode. It is suggested that the optical feedback for spasing is provided by the SPP–Bloch wave, which is supported by the fact that no spasing was attained in aperiodic holes as well as in periodic holes that do not support the SPP–Bloch wave at the spasing wavelength.

Microscopic analysis of surface Bloch modes on periodically perforated metallic surfaces and their relation to extraordinary optical transmission

We build up a microscopic description of the surface Bloch mode (SBM) on metallic surfaces patterned with a periodic array of subwavelength holes. The SBM also is called a spoof surface plasmon when metals approach perfect electric conductors at terahertz or microwave frequencies. In the description, the SBM is found to be composed of surface waves on flat metallic surfaces, the surface plasmon polariton (SPP), and the quasicylindrical wave (QCW) launched by every individual hole in the array, which shines new light on the design of perforated metallic surfaces as plasmonic metamaterials. We also establish explicit relations between the macroscopic SBM picture and the microscopic surface-wave picture for explaining the extraordinary optical transmission (EOT) through subwavelength metallic hole arrays. Our analysis shows that the SBM is related tightly to the EOT through a complex pole of the in-plane wave vector at which the SBM and the EOT possess similar field distributions expressed as superpositions of the SPPs and QCWs.

Enhanced broadband transmission through structured plasmonic thin films for transparent electrodes

Periodic arrays of subwavelength holes in plasmonic thin films can provide for large broadband transmission in the near-infrared spectrum. The optical transmission properties of these thin films with respect to the film thickness, size, and shape of the holes and the period of the arrays was systematically investigated using finite difference time domain computations. Structured gold and silver films of 20-nm thickness can provide for up to 90% transmittance at near-infrared wavelength, thereby rendering them suitable as transparent conducting electrodes for near-infrared emitters or sensors and photovoltaic applications.

Enhanced transmission through periodic arrays of sub-wavelength holes with different media

The enhanced transmission of a metallic photonic crystal slab filled with different linear media in the hole-structure is investigated theoretically. The results show that the transmission peaks exhibit a red shift when the dielectric constants of the media are increased. By varying the thickness of the linear media, the enhanced transmission peak generated by the holes has a great shift and the one generated by the surface plasmon moves slightly. By changing the position of the linear media, these two transmission peaks have no significant shift.

Quarter-Wave Plate Based on Dielectric-Enabled Extraordinary Resonant Transmission

A compact quarter-wave plate (QWP) based on a doubly periodic subwavelength hole array lying over a dielectric slab is synthesized analytically under perfect electric conductor assumption and its validity is demonstrated numerically for real metals (aluminum and silver) at terahertz (THz) and near infrared. The form birefringence is achieved via the excitation of transverse-magnetic and transverse-electric extraordinary transmission resonances for the perpendicular and parallel polarization to the short in-plane period, respectively. To prove the generality of the approach, a prototype working at the near-infrared is designed and numerically optimized. By imposing a maximum phase deviation of ±10° from the ideal QWP response and an axial ratio smaller than 3 dB, the bandwidth of the designs are 0.6% and 0.4% for the 0.23-λ-thick THz and 0.33- λ-thick near-infrared prototype, respectively. Given the simplicity of the design, it holds promise for compact narrowband microwaves-to-visible polarizing devices.

Long vs short-range orders in random subwavelength hole arrays

We analyze the progressive introduction of disorder in periodic subwavelength hole arrays. Two models of disorder are discussed from their associated Fourier transforms and correlation functions. The optical transmission properties of the corresponding arrays are closely related with the evolutions of structure factors, as experimentally detailed. Remarkably, the optical properties of random arrays are not in general equal to those of the single hole as a result of short-range correlations corresponding to hole-to-hole interactions. These correlations are due to packing constraints that are controlled through the careful generation of random patterns. For high density pattern, short-range order can take over long-range order associated with the periodic array.

Modifying an Infrared Microscope To Characterize Propagating Surface Plasmon Polariton-Mediated Resonances

Metal films with periodic arrays of subwavelength holes (meshes) show extraordinary transmission resonances using ordinary, benchtop Fourier transform infrared (FTIR) spectrometers. However, the infrared study of single, wavelength-scale particles with an FTIR microscope typically involves an instrument with a large range of angles that will disperse surface plasmon polariton (SPP) resonances. This work shows how to add an aperture and mesh to a commercial FTIR microscope system to obtain well-defined and identifiable SPP transmission-mediated resonances using a dispersion geometry that is convenient to a microscope, that is, rotation of the mesh in the focal plane of the microscope about the microscope’s optical axis. Momentum matching equations are derived that identify the resonances and model the measured dispersion of each resonance. These equations effectively model the data and cover the parts of momentum space that fall between better-known, high symmetry geometric arrangements, which are often called ΓX and ΓM in the reciprocal space of a square lattice. Both a region of extensive overlapping of many resonances and a very narrow and isolated resonance were discovered that may be particularly useful for SPP studies.

Scattering matrix method for optical excitation of surface plasmons in metal films with periodic arrays of subwavelength holes

We present the formulation of a scattering matrix method for the study of light-scattering properties of metal films. The method is employed for the study of the optical excitation of surface plasmons in a gold film of 15-230 nm thickness, patterned periodically with subwavelength nanoholes. The gold film is placed on a thick SiO2 wafer, and the nanoholes as well as the top side of the gold film are filled with H2O. Light is incident on the gold film from either the SiO2 or the H2O side. The extinction and reflectance spectra of the system, as well as the electromagnetic field distributions at certain characteristic wavelengths, are calculated. The extinction spectra show, depending on system parameters, one or several peaks in the visible wavelength range. The extinction peaks are found to be caused by surface plasmons. A simple model based on the dispersion relation for surface plasmons in an unperforated gold film is shown to predict the peak positions of the extinction for thick perforated films very well. Even for thin films, this simple model, which includes coupling of surface plasmons on both surfaces of the film, predicts peak positions of the extinction well if the hole diameter is small enough. As the hole diameter increases, the extinction peaks of thin films show redshifts. Extinction peaks caused by surface plasmons at the SiO2/Au interface in thick films exhibit strong redshifts when the film thickness is decreased. However, the extinction peaks caused by surface plasmons at the H2O/Au interface in thick films show a completely different behavior. In this case, the extinction peaks do not move noticeably when the film thickness is decreased. Instead, they are weakened and finally disappear. It is also found that each extinction peak is accompanied by an extinction dip and that a reflectance dip is located in the wavelength between the extinction peak and the dip. This arrangement of an extinction peak, a reflectance dip, and an extinction dip is a general property of the surface-plasmon excitation. The calculated electromagnetic field distributions in both thick and thin films show clearly the signature of the excitation of surface plasmons at the extinction peaks, the extinction dips, and the reflectance dips. In thick films with small holes, the electric-field strength in the vicinity of the holes is weak at wavelengths for which surface plasmons are excited. In contrast to this, for thin films at the surface-plasmon excitations, a much stronger electric field is seen in the vicinity of the holes. (Less)