Properties Of Polaritons Research Articles

Ultrafast transition between polariton doublet and alternating current Stark triplet in organic one-dimensional photonic crystal microcavity

This work investigates nonlinear transmission properties of cavity polaritons in a one-dimensional photonic crystal microcavity containing pseudoisocyanine J-aggregates. It was observed that an unexpected transmission peak appeared between the two peaks of cavity polaritons, when the incident light intensity was high. The decay time of this third peak, determined by the pump-probe transient transmission spectroscopy, was less than 1 ps. We observed ultrafast transition between the cavity polariton doublet and AC Stark triplet in an organic system.

Complete architecture of integrated photonic circuits based on and and not logic gates of exciton polaritons in semiconductor microcavities

We present a complete photonic logic gate architecture in a compact solid-state system, making use of the nonlinear and spintronic properties of exciton polaritons in semiconductor microcavities. The dynamics of the system is modeled using the spinor Gross-Pitaevskii equations, and it is shown that the proposal fulfills all the necessary criteria for fully functioning information processing devices without the use of any external electric fields.

Comparative investigations of surface plasmon polaritons on dielectric and metallic gratings

We investigate the properties of Surface Plasmon Polaritons (SPPs) on two kinds of structures: metallic and dielectric gratings loaded on a metallic layer (MM grating and DM grating). The rigorous coupled wave analysis (RCWA) is used for all the simulation in this article. The characteristics of band gap, dispersion relation, reflectivity curves and resonant electric field distributions are comparative simulated and analyzed in MM and DM gratings. Compared with the sticky short-wavelength band edge and complicated surface electric field distributions of MM grating, it is found that the band gap edges of DM grating could be controlled flexibly and the surface fields are more smoothly, which can be used to facilitate the spectral tunability and tailor the optical response of DM structure. This work would provide help for understanding the intrinsic reason of the difference of SPPs in two kinds of structures and basis for choosing suitable structure (MM or DM) of SPPs devices aiming at different functions, especially for designing the dielectric loaded surface plasmon polaritions (DLSPPs) devices.

Superfluidity and collective properties of excitonic polaritons in gapped graphene in a microcavity

We predict the formation and superfluidity of polaritons in an optical microcavity formed by excitons in gapped graphene embedded there and microcavity photons. The Rabi splitting related to the creation of an exciton in a graphene layer in the presence of the band gap is obtained. The analysis of collective excitations as well as the sound velocity is presented. We show that the superfluid density and temperature of the Kosterlitz-Thouless phase transition are decreasing functions of the energy gap.

Optimizing Substrate-Mediated Plasmon Coupling toward High-Performance Plasmonic Nanowire Waveguides

Seeking better plasmonic waveguides is of critical importance for minimizing photonic circuits into the nanometer scale. We have made a theoretical study of the properties of surface plasmon polaritons in a metallic nanowire over substrate (NWOS) configuration. The dielectric substrate breaks the symmetry of the system and mediates the coupling of different primary wire plasmons. The lowest order hybridized mode can be used for subwavelength plasmonic waveguiding for NWOS with thin wire, for a low-permittivity substrate, and in the shorter wavelength region. For NWOS with a high-permittivity substrate, leaky radiation into the substrate raises the propagation losses so that the propagation distance is shorter in the longer wavelength region. By simply adding a high-permittivity layer onto the low-permittivity substrate, we show that leaky radiation can be blocked and high-performance plasmonic waveguiding can be extended to the near-infrared region. Importantly, the NWOS configuration is compatible with current silicon technologies and can be designed into various deep subwavelength active devices such as electro-optical or all-optical modulators.

Dispersion and Field Distribution of SPP Waves at the Interface of a Metal and Nonlinear Magnetic Material

We study the properties of surface plasmon polaritons at an interface between a metal and a strongly nonlinear magnetic cladding, characterized by permeability $\mu=\mu_\textrm{l}+\mu_{\textrm{nl}} H^2$ . It is observed that the dispersion of modes has a significant dependance on the incident power. The incident power can be adjusted to control the propagation length. In addition, the structure shows strong confinement of the modes at the interface.

Bose condensation of exciton polaritons in microcavities

The current status of research on exciton polaritons in semiconductor heterostructures with microcavities and the collective properties of polaritons under the conditions of Bose condensation are discussed.

Spatial coherence properties of surface plasmon investigated by Young’s slit experiment

In this Letter, we present an original method to extract the optical properties of surface plasmon polaritons (SPPs) on silver surfaces. A two Young's slit experiment combined with a leakage radiation microscope has been built. By correlating both imagery and coherence measurements on the same area, we are able to address the evolution of the SPP spatial coherence along its propagation. The proposed method could also be useful to explore the properties of complex plasmonic systems.

Coherent control of Floquet-mode dressed plasmon polaritons

We study the coherent properties of plasmon polaritons optically excited on periodic nanostructures. The gold grains are coupled to a single mode photonic waveguide which exhibits a dramatically reduced transmission originating from the derived quantum interference. With a nonequilibrium description of Floquet-dressed polaritons we demonstrate the switching of light transmission through the waveguide due to sheer existence of intraband transitions in gold from right above the Fermi level driven by the external laser light.

Surface plasmon polariton-controlled tunable quantum-dot emission

The unique properties of surface plasmon polaritons, such as strong field confinement and local field enhancement effects, make them ideal candidates to enhance and shape the emission of luminescent nanoparticles. Of these nanoparticles, quantum dots are highly versatile, suitable for vastly different applications due to their size and material tunability. In many cases however, the emission wavelength of the quantum dots is fixed after manufacturing, allowing no control over the in situ emission properties. Here, we show fully optical, in situ tunability of the emission wavelength of quantum dots, with shifts of over 30 nm, employing surface plasmon polaritons to control the emission wavelength.

Beam focusing from double subwavelength metallic slits filled with nonlinear material surrounded by dielectric surface gratings

Based on the radiation properties of surface plasmon polaritons (SPPs) can be controlled by adjusting the refractive indexes of dielectric materials in the metallic slits, a novel plasmonic focusing structure formed by two subwavelength metal apertures filled with Kerr nonlinear material surrounded by surface dielectric gratings is proposed and demonstrated numerically. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and resonance property of each surface grating. Numerical simulations using two-dimensional (2D) Finite-Difference Time-Domain (FDTD) method verify that the deflection angle and focal length can be controlled easily by changing the intensity of incident light, dynamically tunable on-axis and off-axis focusing effects can be achieved.

Rational design of high performance surface plasmon resonance sensors based on two-dimensional metallic hole arrays

We have rationally designed two-dimensional Au and Ag hole arrays for high performing surface plasmon resonance (SPR) sensing. The figure-of-merit (FOM), which is defined as sensitivity/linewidth, is found to be highly geometry-dependent. For sensitivity, we find it is equal to the period of array when exciting low order surface plasmon modes at low incident angle. Therefore, increasing period improves sensitivity. On the other hand, narrow linewidth can be obtained from small hole size so that the radiative decay loss is minimized. By using a pair of orthogonally oriented polarizer and analyzer, the signal-to-noise ratio (SNR) can be greatly enhanced due to the elimination of the nonresonant reflection background. As a proof of our strategy, we have obtained FOM larger than 100/RIU and SNR higher than 110 from Au arrays. Our results show the importance of understanding the basic properties of surface plasmon polaritons in order to systematically optimize the performance of the plasmonic system for a given application.

Tunable surface plasmon polaritons in metal-strip waveguides with magnetized semiconductor substrates in Voigt configuration

The properties of surface plasmon polaritons (SPPs) in a magnetically tunable strip waveguide geometry comprising of a metal film of finite width deposited on a magnetized semiconductor and covered by an isotropic dielectric material were studied in Voigt configuration. The method of lines was used to compute the dispersion relation of fundamental modes, and the dependence of the propagation constant on metal film dimensions, material parameters and biasing magnetic field was considered. The bounded SPPs are nonreciprocal with respect to the direction of the biasing magnetic field, producing a nonreciprocal phase shift of the order of 2–18 rad mm−1 at a wavelength of excitation 1.55 μm. Moreover, controlled propagation of SPP modes and their effective tuning are possible in this strip geometry, which enables the design and development of tunable optoelectronic devices.

Loss mechanisms of surface plasmon polaritons propagating on a smooth polycrystalline Cu surface

We study the propagation properties of surface plasmon polaritons on a Cu surface by means of photoemission electron microscopy. Use of a CMOS process to fabricate the Cu thin film is shown to enable very high propagation distances (up to 65 μm at 750 nm wavelength), provided that the copper native oxide is removed. A critical review of the optical loss mechanisms is undertaken and shed light on the effect of single grain boundaries in increasing the propagation losses of the plasmon. A microscopic interpretation is provided, relying on groove induced electromagnetic hot spots.

Plasmonic Bloch oscillations and resonant Zener tunneling in subwavelength metal-dielectric-air waveguide superlattices

In this paper, we study the propagation properties of surface plasmon polaritons in plasmonic single-cavity superlattices and two-cavity superlattices which are composed of two kinds of alternately stacked subwavelength metal-dielectric-air waveguides with large dispersion. Theoretical predictions of plasmonic time-resolved Bloch oscillations existing in single-cavity superlattices and resonant Zener tunneling (ZT) occurring in two-cavity superlattices by the transfer matrix method (TMM) are well demonstrated by the numerical simulations on the propagation of SPPs pulse in the two kinds of superlattices by the finite-difference time-domain (FDTD) method. The two proposed superlattices can be conveniently fabricated by present nanotechnology, and the study may promote the realization of plasmonic BO and resonant ZT in nanoscale devices experimentally.

Optical Control of Plasmonic Bloch Modes on Periodic Nanostructures

We study and actively control the coherent properties of surface plasmon polaritons (SPPs) optically excited on a nanohole array. Amplitude and phase of the optical excitation are externally controlled via a digital spatial light modulator (SLM) and SPP interference fringe patterns are designed and observed with high contrast. Our interferometric observations reveal SPPs dressed with the Bloch modes of the periodic nanostructure. The momentum associated with these dressed plasmons (DP) is highly dependent on the grating period and fully matches our theoretical predictions. We show that the momentum of DP waves can, in principle, exceed the SPP momentum. Actively controlling DP waves via programmable phase patterns offers the potential for high field confinement applicable in lithography, surface enhanced Raman scattering, and plasmonic structured illumination microscopy.

Long-range surface plasmon polaritons propagating on a dielectric waveguide support

In the traditional long-range surface plasmon geometry, an ultrathin metal film is sandwiched between two layers having identical dielectric constants. Here we demonstrate the long-range surface plasmon polariton (LRSPP) properties for a new structure where a thin layer with a dielectric constant exceeding that of the surroundings is inserted within the sandwich, provided the layer thickness d satisfies the condition k(⊥)d=mπ where k(⊥) is the component of the guide wavevector perpendicular to the layer and m is an integer. The resulting plasmon modes have smaller losses and nearly the same phase velocity as the original LRSPP. This provides a strategy to support silver films having thicknesses of 10's of nanometers to create plasmonic devices for sensor applications.

Optical polariton properties in ZnSe-based planar and pillar structured microcavities

Strong coupling is demonstrated in monolithic ZnSe-based microcavities. Under nonresonant excitation the polariton dispersion has been investigated in dependence on the photon-exciton detuning for different excitation densities at low temperatures. For zero detuning indications of a polariton lasing threshold are observed like a k-space and energy dispersion narrowing of the lower polariton branch with increasing excitation density. Furthermore, it is observed that this effect is hampered for measurements at negative detunings as a result of the less effective polariton relaxation to the ground state. Latter results in the formation of a discrete polariton distribution at finite k values as known for the polariton bottleneck. In order to investigate the influence of a three-dimensional optical confinement on the polariton relaxation, pillar structured microcavities were fabricated. The formation of discrete polariton states in the k-space distribution is observed. Furthermore, indications for a softening of the k-conservation arising from the structural confinement are found leading to a more effective polariton relaxation. This process would be beneficial for the realization of efficient polariton lasing processes.

Impact of C60 Adsorption on Surface Plasmon Polaritons on Self-Assembled Ag(111) Islands on Si(111)

The influence of C60 adsorption on the properties of surface plasmon polaritons on small Ag islands is discussed. Under illumination with UV light as well as under illumination with femtosecond laser pulses, a decrease of the photoemission yield with increasing C60 coverage is observed. With angular resolved measurements, changes of the band structure during deposition are studied. Based on these experiments, an increase of the work function with increasing coverage is measured. In two photon photoemission, the surface plasmons are imaged as a periodic moire pattern, the wavelength of which changes because of a modified effective surface dielectric function. Our findings imply that the wavelength of the plasmon wave becomes shorter as a result. Finally, a decrease of the intensity of the moire pattern maxima compared with the intensity of the first maximum with increasing C60 coverage has been observed. Accordingly, the damping of the plasmon wave becomes stronger.

Zeeman splitting and diamagnetic shift of spatially confined quantum-well exciton polaritons in an external magnetic field

We report on pronounced magneto-optical effects of spatially confined polariton modes in an InGaAs quantum-well microcavity. The polaritons were trapped by a lithographically modulated cavity length. In contrast to etched structures suffering from nonradiative recombination, this approach allows for a gentle modification of the dielectric properties and results in a confinement potential of 7.5 meV. In the presence of an external magnetic field, a diamagnetic shift and Zeeman splitting of the quantized modes were observed for different trap diameters, ranging from 1 to 10 \ensuremath{\mu}m. This confirms that the polaritonic properties of the emission modes are preserved even for small traps. Moreover, a clear correlation between the magnetic response and the excitonic fraction of the polaritons was identified by magnetic field--dependent measurements.