Surface Resonance Modes Research Articles

Super-Planckian thermal radiation enabled by hyperbolic surface phonon polaritons

Excitation of surface resonance modes and presence of resonance-free hyperbolic modes are two common ways to enhance the near-field radiative energy transport, which can find wide applications in noncontact thermal management and energy harvesting. Here, we identify another way to achieve the super-Planckian thermal radiation via hyperbolic surface phonon polaritons (HSPhPs). Based on the fluctuation-dissipation theory, the near-field radiative heat flux between bulk hexagonal boron nitride (hBN) planes with the optical axis perpendicular to the radiative energy flow can be 120 times as large as the blackbody limit for a gap distance of 20 nm. When the film thickness is reduced to 10 nm, the radiative heat flux is found to increase by 26.3%. The underlying mechanism is attributed to the coupling of Type I HSPhPs inside the anisotropic hBN film, which improves the energy transmission coefficient over a broad wavevector space especially for waves with extremely high wavevectors. This work helps to deepen the understanding of near-field radiation between natural hyperbolic materials, and opens a new route to enhance the near-field thermal radiation.

Q-factor and absorption enhancement for plasmonic anisotropic nanoparticles.

We investigate the scattering and absorption properties of anisotropic metal-dielectric core-shell nanoparticles. It is revealed that the radially anisotropic dielectric layer can accelerate the evanescent decay of the localized resonant surface modes, leading to Q-factor and absorption rate enhancement. Moreover, the absorption cross section can be maximized to reach the single resonance absorption limit. We further show that such artificial anisotropic cladding materials can be realized by isotropic layered structures, which may inspire many applications based on scattering and absorption of plasmonic nanoparticles.

Optical fiber sensor based on Bloch surface wave in photonic crystals.

A new optical fiber sensor based on Bloch surface wave was theoretically proposed. An omnidirectional one-dimensional photonic crystal was designed as the multilayer coated on the outer surface of the optical fiber. Taking advantages of the omnidirectional reflection band, there is only surface mode resonance in the transmission spectrum, while guided mode resonance is avoided. The performance of the designed fiber sensor was analyzed theoretically with a ray transmission model. The presented sensor has comparable sensitivity but much higher figure of merit than other fiber sensors. The resolution can reach about 10-6 RIU or even higher.

Phase-matched third-harmonic generation via doubly resonant optical surface modes in 1D photonic crystals.

Efficient nonlinear conversion requires that interacting optical waves maintain a consistent phase relationship when traveling in a medium despite its dispersion. Birefringent phase-matching, which is often used to compensate for the dispersion, is not applicable to optically isotropic nonlinear materials. Here, we present a one-dimensional photonic crystal structure that allows the propagation of optical surface waves, both at the fundamental and third-harmonic frequencies, as an efficient medium for phase-matched third-harmonic generation. A unique advantage of this structure is that the effective refractive indices for the surface waves are similar to the refractive index of air at both frequencies. This allows phase-matching between the first and third harmonics, and a visible collinear beam of the third harmonic is produced at the prism-coupled output. Moreover, these optical surface waves propagate over long distances even if a lossy nonlinear nanofilm is deposited onto the photonic crystal surface. We provide experimental results for third-harmonic generation at a wavelength of 410 nm for a bare dielectric Ta2O5/SiO2 multilayer structure and for the same structure coated with a 15-nm GaAs film.

Polarization oscillations of near-field thermal emission

We consider the polarization of thermal emission in the near field of various materials, including dielectrics and metallic systems with resonant surface modes. We find that, at thermal equilibrium, the degree of polarization exhibits spatial oscillations with a period of approximately half the optical wavelength, independent of material composition. This result contrasts with that of Setala et al. [Phys. Rev. Lett.88, 123902 (2002)PRLTAO0031-900710.1103/PhysRevLett.88.123902], who find monotonic decay of the degree of polarization for systems in local thermal equilibrium.

Multi-kilometer Long, Longitudinally Uniform Hollow Core Photonic Bandgap Fibers for Broadband Low Latency Data Transmission

The low intrinsic nonlinearity and low signal latency characteristic of Hollow Core Photonic Bandgap Fibers (HC-PBGFs) have fueled strong interest for data transmission applications. Whereas most research to date has looked at improving the optical performance of HC-PBGFs (e.g., reducing the loss, increasing the transmission bandwidth and achieving well-tempered modal properties through the suppression of surface mode resonances). In this study, we address the challenging problem of scaling up the fabrication of these fibers to multi-kilometer lengths—an indispensable step to prove this fiber technology as viable. We report the fabrication of low loss, wide bandwidth HC-PBGFs operating both in the conventional telecoms window (1.55 μm) and in the predicted region of minimum loss (2 μm), in lengths that substantially exceed the state of the art. At 2 μm, we obtained a 3.85 km long fiber with ≈3 dB/km loss and >160 nm wide 3 dB bandwidth. Additionally, we report an HC-PBGF operating at 1.55 μm with a length of just over 11 km, transmission bandwidth in excess of 200 nm and a longitudinally uniform loss of ≈5 dB/km, measured via cutback and an integrated scattering method. We used the latter fiber to demonstrate error-free, low-latency, direct-detection 10 Gb/s transmission across the entire C-Band as well as 20 Gb/s quadrature phase shift keyed transmission. These represent the first demonstrations of data transmission over a length of HC-PBGF exceeding 10 km.

Controlling Terahertz Surface Plasmon Properties on a Periodically Structured Silicon Surface

The paper presents experimental and numerical investigations on the terahertz (THz) surface plasmon propagation in a periodically patterned doped silicon substrate. Silicon substrates are periodically patterned with 2D array of vertical structures forming a plasmonic waveguide. The waveguide configurations are found to support resonant surface modes at certain frequencies which can occur anywhere depending on the structural parameters. The 2D pattern of vertical structures is observed to affect the THz surface plasmon propagation along the waveguide configuration. The periodicities are changed in both directions to examine the change in amplitude and cut-off frequencies of the resonant surface modes. The results are confirmed independently through finite element method based numerical simulations and compared with theory. The present study should find applications in facilitating the development of futuristic ultrahigh speed networks and devices operating at the terahertz frequencies.

Role of Symmetry in Coupled Localized Surface Plasmon Resonance of a Nanosphere Pair

We investigated localized surface mode resonance of two nanospheres immersed in a continuum dielectric medium within the framework of quasistatic approximation. We solved the Laplace equation in the bispherical coordinates subjected to the boundary conditions on both spheres. By using the matrix formulation, new method for surface mode resonance calculation is derived in terms of a nonlinear eigenvalue problem. This allows us to discuss the effects of symmetry breaking due to the difference in particle materials and particle sizes. We calculated the surface plasmon resonance (LSPR) energy for pairs of Drude metallic spheres. The solutions show that the LSPR coupling in an asymmetric pair can be interpreted as the coupling between symmetric pairs of its constituent particles. we also analyzed the LSPR excitation sequence to identify the modes of peaks from optical measurement. We found that the ambiguous dipole antibonding sigma mode of the asymmetric Au-Ag pair in the experimental work (Sheikholeslami et al., Nano Lett 10(7):2655–2660, 2010) must be the quadrupole bonding sigma mode.

Spontaneous emission modulation of colloidal quantum dots via efficient coupling with hybrid plasmonic photonic crystal.

The spontaneous emission of colloidal CdSe/ZnS quantum dots (CQDs) modified by the hybrid plasmonic-photonic crystal is reported in this paper. By using a spin coater, the spatial overlap between CQDs and the surface resonance modes in this quasi-2D crystal slab is achieved. In this case, the coupling efficiency of them is enhanced greatly and most excited CQDs radiate through the surface modes. Consequently, despite the low refractive index contrast of our hybrid structure, the directionality of spontaneous emission, increased radiative probability and narrowed full width at half maximum of emission peak are all clearly observed by our home-made microscopic angle-resolved spectroscopy and time-resolved photoluminescence system. Our results manifest that the quasi-2D hybrid plasmonic-photonic crystal is an ideal candidate to tailor the radiative properties of CdSe/ZnS CQDs, which might be significant for the applications of light emitting devices.

Experimental investigation of compact metamaterial for high efficiency mid-range wireless power transfer applications

We investigate a compact metamaterial for enhanced magnetic coupling in a resonator coupled wireless power transfer system operating at around 6.5 MHz. The metamaterial is constructed by realizing an array of three-turn spiral resonators on a thin slab. Although the metamaterial has its own loss, the experimental results show that the proposed metamaterial slab enhances the power transmission capability. The number of unit cells in the array is an important parameter, because exceeding a certain number of unit cells does not enhance the efficiency due to the loss of the slab. Furthermore, strong surface mode resonance is observed when two slabs are assembled with proper gap spacing between them. By using the optimization approach, we achieve a significant efficiency improvement at a mid-range distance. The measured efficiencies are 71.1% and 54.3% at a 0.6 and 1.0 m distance, respectively. At a 1.0 m distance, this efficiency performance corresponds to a 270% improvement compared to a case with no metamaterial slab. In addition, we experimentally confirm the threshold distances above which the metamaterial shows enhanced performance.

High Q factor propagating plasmon modes based on low-cost metals

A hybrid plasmonic–photonic crystal consisting of a low-cost metal (Al or Cu) covered by self-assembly polystyrene sub-micro sphere arrays is fabricated. The angle-resolved reflection spectra show the existence of propagating optical surface modes in the structure. Especially, under normal incidence, five surface modes can be observed clearly. With the help of theoretical calculation, the origin of surface resonance modes is confirmed. From both the experiment and simulation, the surface plasmon modes supported by this structure possess high Q factors, which are comparable with those of the modes based on noble metals. Moreover, with a dielectric layer deposited on the top of the structure, its potential application for surface plasma polariton sensors is proposed.

Surface modes and acoustic scattering of microspheres and ultrasound contrast agents

Surface modes of spherical objects subject to ultrasound excitation have been recently proposed to explain experimental measurements of scattering from microspheres and ultrasound contrast agents (UCAs). In this work, the relationship between surface modes and resonance frequencies of microspheres and UCAs is investigated. A finite-element model, built upon the fundamentals of wave propagation and structural mechanics, was introduced and validated against analytical solutions (error <5%). Numerical results showed the existence of a systematic relationship between resonance frequencies and surface modes of a 30 μm microsphere driven at 1-70 MHz. On the contrary, for a 100 nm shelled, 4 μm diameter UCA, no clear relationship between the resonance frequencies and the surface modes was found in the frequency range examined. Instead, the UCA exhibited a collection of complex oscillations, which appear to be a combination of various surface modes and displacements. A study of the effects of varying the shell properties on the backscatter showed the presence of peaks in the backscatter of thick-shelled UCAs, which are not predicted by previous models. In summary, this work presents a systematic effort to examine scattering and surface modes from ultrasound contrast agents using finite-element models.

Biosensing using surface electromagnetic waves in photonic band gap multilayers

Abstract A biosensor based on the excitation of surface electromagnetic waves in photonic band gap multilayer films is demonstrated. The operating principle of this device is similar to surface plasmon biosensors with the key difference that a photonic band gap film replaces the metal film as the medium in which surface electromagnetic waves are excited. The use of photonic band gap films offers a number of advantages. First, the surface wave resonance is much sharper leading to the potential of greatly enhanced sensitivity. Second, the properties of the photonic band gap material can be engineered to make a sensor that operates at any wavelength. The experiments reported here are conducted with a surface wave resonance at 470 nm, a wavelength not generally accessible with surface plasmon sensing. Finally, the photonic band gap films are more mechanically robust than metal films and they offer new substrates for surface chemistry. The paper describes the design of the photonic band gap films, the surface chemistry and biology to create sensing chips, and the spectroscopic experimental configuration used to observe and track the surface mode resonance. Experimental results are presented on refractive index sensing, antibody–antigen reactions, and DNA binding.

Acoustic analog of electromagnetically induced transparency in periodic arrays of square rods

We theoretically demonstrate a classical analog of electromagnetically induced transparency (EIT) in an acoustic structure. Each unit in the proposed structure consists of two square polymethyl methacrylate (PMMA) rods with one rod rotating 45° relative to the other. Both square rods can support certain surface resonant modes respectively, which have almost identical resonant frequencies but highly different quality factors. Thus, the two resonant modes can act as radiative mode and dark mode in the analog, respectively, and the destructive interference of them results in EIT-like transmission effect in our structure.

Cavity resonant mode in a metal film perforated with two-dimensional triangular lattice hole arrays

The transmission property of metallic films with two-dimensional hole arrays is studied experimentally and numerically. For a triangular lattice subwavelength hole array in a 150 nm thick Ag film, both cavity resonance and planar surface modes are identified as the sources of enhanced optical transmissions. Semi-analytical models are developed for calculating the dispersion relation of the cavity resonant mode. They agree well with the experimental results and full-wave numerical calculations. Strong interaction between the cavity resonant mode and surface modes is also observed.

Coupling discrete metal nanoparticles to photonic crystal surface resonant modes and application to Raman spectroscopy

Coupling a tightly packed layer of discrete metal nanoparticles to the resonant mode of a photonic crystal surface has been demonstrated as a means for obtaining additional electromagnetic gain for surface-enhanced Raman spectroscopy (SERS), in which electric fields of the photonic crystal can couple to plasmon resonances of the metal nanoparticles. Because metal nanoparticles introduce absorption that quench the photonic crystal resonance, a balance must be achieved between locating the metal nanoparticles too close to the surface while still positioning them within the enhanced evanescent field to maximize coupling to surface plasmons. In this work, we describe a parametric study into the design of a photonic crystal-SERS substrate, comprised of a replica molded photonic crystal slab as the dielectric optical resonator, a SiO(2) "post" layer spacer, and an Ag "cap" metal nanostructure. Using the Raman signal for trans-1,2-bis(4pyridyl)ethane, the coupling efficiency was maximized for a SiO(2) "post" layer thickness of 50 nm and a Ag "cap" height of approximatey 20 nm, providing an additional enhancement factor of 21.4.

Phase effects in the enhanced transmission through compound subwavelength rectangular hole arrays

We study the enhanced transmission through compound subwavelength rectangular hole arrays in perfect electronically conductive films. It is shown that phase effects become important in the enhanced transmission when extra rectangular holes are added per period. There are two types of resonance mechanisms due to the phase effects: one is the localized waveguide mode phase resonance and the other is the surface mode phase resonance. The localized waveguide mode phase resonances, which are related to the number of holes per period and their relative positions, split the waveguide resonance peak into several peaks. The surface mode phase resonances, which appear evidently only for some special arrangements of holes in a unit cell, lead to the suppression of some surface mode resonance peaks. Our approach is advantageous to modulate the enhanced transmission in metallic hole arrays in the terahertz or microwave frequency regime.

Electromagnetic surface modes in one-dimensional photonic crystals with dispersive metamaterials

We study the electromagnetic surface modes supported by the interface between semi-infinite one-dimensional photonic crystals composed of dispersive metamaterials and a homogeneous medium in the presence of the cap layer. A new type of surface mode is found in such structure, and these surface modes can exhibit strong resonance at the first period of the photonic crystal. These resonant surface modes originate from the material dispersion. Another type of surface mode with structural resonance can appear in the thick cap layer. The influences of physical parameters of the structure on the surface modes have also been investigated.

Improved directional emission by resonant defect cavity modes in photonic crystal waveguide with corrugated surface

Directional emission of light from a photonic crystal (PC) waveguide can be observed by adding periodically corrugated surface as reported in Moreno et al. (Phys. Rev. B 69:121402, 2004). In this paper, it is being further shown by numerical simulation with finite-difference time-domain method that adding point defects to the adjacent layer of surface corrugations helps to improve directional emission. The coupling between the resonant cavity modes and surface modes is believed to account for this effect.

A W-Band Low-Loss Dual-Polarization Quasi-TEM Waveguide

As an enabling feed/interconnect element for various millimeter wave components, dual polarization quasi-transverse electromagnetic (TEM) waveguides at W-band (75-110 GHz) are investigated with two-dimensional electromagnetic crystal (EMXT) surfaces as the four boundary walls instead of the regular metallic walls. A 2.54 mm x 2.54 mm quasi-TEM square waveguide prototype with a length of 2 mm is fabricated and demonstrated. Both eigenmode and full-wave EM simulations of the prototype verify the quasi-TEM propagation at the designed frequency of 95 GHz with a bandwidth of more than 10% and the low insertion loss for the entire W-band. The prototype waveguide is measured in a WR-10 fixture and the results agree with simulations well. To better understand the loss mechanisms, various design and packaging parameters are studied. Undesirable resonant surface modes have been identified as a critical cause of loss at specific frequencies. This type of waveguides may also be useful for spatial power combining, low loss interconnects, and packaging for millimeter wave systems.