Subwavelength Cavity Research Articles

Enhancement of Electromagnetic Fields Caused by Interacting Subwavelength Cavities

This article is devoted to the asymptotic analysis of the electromagnetic elds scattered by a perfectly conducting plane containing two sub-wavelength rectangular cavities. The problem is formulated through an integral equation, and a spectral analysis of the integral operator is performed. Using the generalized Rouche theorem on operator valued functions, it is possible to localize two types of resonances, symmetric and anti-symmetric, in a neighborhood of each zero of some explicit function, associated to the limiting geometry. For the symmetric modes, the elds in the cavities interact in phase, and the system of two cavities essentially acts as a dipole. In the anti-symmetric case, the fields oscillate in anti-phase, and the system behaves like a quadripole. Asymptotic expansions of the resonances, the far-eld and the near-eld are given.

High Gain Circularly Polarized Antenna using Sub-Wavelength Resonant Cavity

A novel high gain circularly polarized antenna using sub-wavelength resonant cavity is presented. The resonant cavity consists of a single partially reflective surface (PRS) and an artificial impedance surface (AIS). By adjusting reflection phases of the PRS and AIS at the operating frequency, the cavity height that is the distance between these two reflectors can be reduced to about λ/8. The measured results show that this method is effective, and this structure can greatly increase the circular polarization gain of the antenna.

Achieving Antenna Isolation within Subwavelength Directive Cavity

Antenna arrays embedded within a compact Fabry-Perot cavity have to be optimized to limit interactions between elementary antennas. In this article, we propose to use a superstrate metamaterial to design a highly isolated antenna array. This superstrate is based on the microstrip technology. It is made of an inductive and a capacitive grid respectively etched on the top and the bottom of epoxy plate. Metallic vias are then inserted through the superstrate to connect the two etched grids. This superstrate combined with a metallic ground plane leads to the design of a subwavelength cavity. The proposed cavity allows a significant antenna profile reduction and performance enhancement. More importantly, this structure provides a high isolation for an antenna array.

Subwavelength silicon microcavities

We present a study of the first silicon microdisk resonators which are smaller than the free-space resonant wavelength in all spatial dimensions. Spectral details of whispering gallery modes with azimuthal mode number m = 4-7 are measured in microdisks with diameters between 1.35 and 1.89microm and are studied at wavelengths from 1.52 to 1.62microm. For the structures considered here, m = 5 is the highest azimuthal mode order in a subwavelength cavity and has measured Q = 1250. These results agree well with theoretical calculations using a finite difference frequency domain method and fit an exponential scaling law relating Q to disk radius via m.

Plasmonic Fabry-Pérot Nanocavity

We experimentally demonstrate a novel, all-plasmonic nanoscopic cavity exhibiting Q-factors up to 200 at visible frequencies. The Fabry-Pérot type resonator uses tall metallic fins that reflect up to 98% of incident surface plasmon to concentrate light within a subwavelength cavity mode. High aspect ratio metal fins, constructed using lithography and electroplating, reduce surface plasmon scattering out of the surface, while a short cavity length reduces the propagation loss. A simple Fabry-Pérot cavity model adapted for surface plasmon dispersion and reflection describes the underlying physics of the nanocavities and the results agree well with Johnson's and Christie's permittivity data. The occurrence of an optimum wavelength for plasmon storage in these cavities allows us to clearly visualize the fundamental trade-off between propagation loss and the spatial extent of surface plasmon polaritons. The subwavelength optical mode area within these cavities enables the enhancement of weak optical processes such as spontaneous emission and nonlinear optics at nanoscale dimensions.

Modal Decomposition of Surface−Plasmon Whispering Gallery Resonators

We resolve the resonant whispering gallery modes of plasmonic subwavelength ring cavities defined by circular grooves patterned into a gold surface. An interesting interplay is observed between subwavelength confinement and guiding along the groove. Full spatial and spectroscopic information is directly obtained using cathodoluminescence, including details of the nanoscale intensity distribution (spatial resolution 11 +/- 8 nm). Excellent agreement between measurements and rigorous electromagnetic theory is obtained, thus allowing us to assess the symmetry, ordering, degree of confinement, and near-field enhancement of the modes with unprecedented detail.

Asymptotic of the Green function for the diffraction by a perfectly conducting plane perturbed by a sub-wavelength rectangular cavity

This work is aimed at understanding the amplification and confinement of electromagnetic fields in open sub-wavelength metallic cavities. We present a theoretical study of the electromagnetic diffraction by a perfectly conducting planar interface, which contains a sub-wavelength rectangular cavity. We derive a rigorous asymptotic of the Green function associated with the Helmholtz operator when the width of the cavity shrinks to zero. We show that the limiting Green function is that of a perfectly conducting plane with a dipole in place of the cavity. We give an explicit description of the effective dipole in terms of the wavelength and of the geometry of the cavity. Copyright © 2009 John Wiley & Sons, Ltd.

Directive metamaterial-based subwavelength resonant cavity antennas – Applications for beam steering

This article presents the use of composite resonant metamaterials for the design of highly directive subwavelength cavity antennas. These metamaterials, composed of planar metallic patterns periodically organized on dielectric substrates, exhibit frequency dispersive phase characteristics. Different models of metamaterial-based surfaces (metasurfaces), introducing a zero degree reflection phase shift to incident waves, are firstly studied where the bandwidth and operation frequency are predicted. These surfaces are then applied in a resonant Fabry-Perot type cavity and a ray optics analysis is used to design different models of ultra-compact high-gain microstrip printed antennas. Another surface presenting a variable reflection phase by the use of a non-periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna application. Finally, the incorporation of active electronic components on the metasurfaces, allowing an electronic control of the phase responses, is applied to an operation frequency reconfigurable cavity and a beam steering cavity. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of lambda/60. To cite this article: A. Outir et al., C R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Subwavelength metamaterial‐based resonant cavities fed by multiple sources for high directivity

AbstractThe analysis and design of subwavelength metamaterial‐based resonant cavity antennas are presented. The antennas under investigation are formed by embedding a feeding source in a Fabry‐Perot (FP) cavity composed of a Perfect Electrical Conductor (PEC) surface and a metasurface reflector. The embedded feeding source used in this study is a 2 × 2 microstrip patch array. The influence of the interelement spacing of the patch array feed on the radiation patterns is investigated and reported. The effect of the cavity thickness is also considered. Finally, the design of highly directive subwavelength cavity antennas is presented. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1883–1888, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24485

Comment on “Stability and quality factor of a one-dimensional subwavelength cavity resonator containing a left-handed material”

Comment on stability and quality factor of a one-dimensional subwavelength cavity resonator containing a left-handed material

Reply to ‘‘Comment on ‘Stability and quality factor of a one-dimensional subwavelength cavity resonator containing a left-handed material’ ’’

Received 23 February 2009DOI:https://doi.org/10.1103/PhysRevB.79.207102©2009 American Physical Society

Enhanced modulation bandwidth of nanocavity light emitting devices

We show that the direct modulation bandwidth of nano-cavity light emitting devices (nLEDs) can greatly exceed that of any laser. By performing a detailed analysis, we show that the modulation bandwidth can be increased by the Purcell effect, but that this enhancement occurs only when the device is biased below the lasing threshold. The maximum bandwidth is shown to be inversely proportional to the square root of the modal volume, with sub-wavelength cavities necessary to exceed conventional laser speeds.

Subwavelength Surface Plasmon Optical Cavity—Scaling, Amplification, and Coherence

Scaling, coherence, and amplification of a subwavelength surface plasmon micropillar optical cavity have been studied using 3-D finite-difference time-domain calculations. Two experiments have also been conducted for the demonstration of the gain-assisted propagation of surface plasmon polaritons in a planar metal-semiconductor waveguide and the enhancement of the cavity-Q factor in a subwavelength surface plasmon micropillar cavity.

Left-Handed/Right-Handed Transmission Line Subwavelength Cavity Resonators

In this letter, a new kind of cavity resonator based on left-handed/right-handed transmission lines is presented. The left-handed transmission line (LHTL), which can realize a negative phase shift, is formed by resonant-slot coupled cavity chain unit cells, while the right-handed transmission line (RHTL), which can realize positive phase shift, is made of coaxial waveguides. Resonance condition can be satisfied by setting the total phase shift between two ends of the cavity resonators to be zero. The design approach of the subwavelength cavity resonator is presented. Simulation and experimental results prove that the lengths of these cavity resonators can be much shorter than the conventional half-wavelength while working at the same frequency.

Cavity formation in split ring resonators

We report that it is possible to obtain a cavity structure by the deformation of a unit cell of an split ring resonator (SRR) structure. We presented the Q-factor of the cavity resonance as 192 for an SRR-based single cavity. Subsequently, we brought two and three cavities together with an intercavity distance of two metamaterial unit cells and investigated the transmission spectrum of SRR-based interacting 2-cavity and 3-cavity systems. The splitting of eigenmodes due to the interaction between the localized electromagnetic cavity modes was observed. Eventually, in taking full advantage of the effective medium theory, we modeled SRR-based cavities as 1D Fabry–Perot reflectors (FPRs) with a subwavelength cavity at the center. Finally, we observed that at the cavity resonance, the effective group velocity was reduced by a factor of 67 for an SRR-based single cavity compared to the electromagnetic waves propagating in free space.

Analysis and Design of Sub-Wavelength Resonant Cavity Type 2-D Leaky-Wave Antennas

A rigorous analysis is presented together with novel designs of high-gain sub-wavelength resonant cavity antennas. The antennas under investigation are formed by partially reflective surfaces placed in close proximity over artificial periodic metamaterial ground planes with specific reflection phase responses. A full-wave periodic leaky-wave analysis is applied to this class of antennas for the first time and the results are reported and discussed. Finite-size antenna designs are studied at wireless LAN frequencies (3.7 GHz) using 3-D full-wave software and the results are compared to the predictions of the leaky-wave analysis. Furthermore, the field distribution and the effect of losses are investigated. Finally, practical designs of sub-wavelength 2-D leaky-wave antennas with high-gain performance are presented.

Light reflection from a metal surface with subwavelength cavities

The interaction of light with the localized/delocalized system, i.e., a metal surface with rectangular cavities of finite depth, has been studied. Reflection spectrum has been measured in the optical frequencies, and resonant minima have been observed. We have developed an analytical model, which agrees well with the experiment. The localized waveguide resonance and delocalized surface resonance have been identified and discussed. The results may be useful for manipulating the coupling between light and matters.

Experimental observation of cavity formation in composite metamaterials

In this paper, we investigated one of the promising applications of left-handed metamaterials: composite metamaterial based cavities. Four different cavity structures operating in the microwave regime were constructed, and we observed cavity modes on the transmission spectrum with different quality factors. The effective permittivity and permeability of the CMM structure and cavity structure were calculated by use of a retrieval procedure. Subsequently, in taking full advantage of the effective medium theory, we modeled CMM based cavities as one dimensional Fabry-Perot resonators with a subwavelength cavity at the center. We calculated the transmission from the Fabry-Perot resonator model using the one-dimensional transfer matrix method, which is in good agreement with the measured result. Finally, we investigated the Fabry-Perot resonance phase condition for a CMM based cavity, in which the condition was satisfied at the cavity frequency. Therefore, our results show that it is possible to treat metamaterial based cavities as one-dimensional Fabry-Perot resonators with a subwavelength cavity.

Spontaneous emission from within a metal-clad cavity mediated by coupled surfaceplasmon–polaritons

The emission of light from within a sub-wavelength metal-clad cavity is investigated.We find that emitters placed inside such a cavity emit into the coupled surfaceplasmon–polariton mode supported by this structure. We use grating structures to couplethe non-radiative coupled surface plasmon–polariton modes to light and present the resultsof measurements of photoluminescence from such structures in the form of dispersioncurves. We discuss our findings in the context of sub-wavelength cavities as a means tocontrol the emission of light.

Surface plasmon resonance in two-dimensional nanobottle arrays

We report our recent work on surface plasmon polaritons manipulation of two-dimensional arrays of subwavelength bottle-shaped cavities on gold surface. By tuning the geometry of such "nanobottle" it is possible to control the resonant frequencies and near field patterns of different surface plasmon resonances. The plasmonic band structures are not sensitive to the sizes and depths of the nano-bottles, but depend strongly on the polarization. In particular, by using different polarizations, it is observed that different types of plasmonic resonances, whether propagating or localized, can be excited independently. Moreover, we find that the local field and field intensity can by fine-tuned by controlling the topology of the bottleneck of the nanobottle. As a result, we believe these nanobottle arrays are useful for making plasmonic devices.