Far-field Emission Research Articles

Unidirectional emission and nanoparticle detection in a deformed circular square resonator.

We propose a novel deformed square resonator which has four asymmetric circular sides. Photons leak out from specific points, depending on the interplay between stable islands and unstable manifolds in phase space. By carefully breaking the mirror reflection symmetry, optical modes with strong chirality approaching 1 and unidirectional emission can be achieved simultaneously. Upon binding of a nanoparticle, the far-field emission pattern of the deformed microcavity changes drastically. Due to the EP point of the degenerate mode pairs in the deformed cavity, chirality-based far-field detection of nanoparticles with ultra-small size can be realized.

Non-Planckian infrared emission from GaAs devices with electrons and lattice out-of-thermal-equilibrium

With the downscaled device size, electrons in semiconductor electronics are often electrically driven out-of-thermal-equilibrium with hosting lattices for their functionalities. The thereby electrothermal Joule heating to the lattices can be visualized directly by the noncontact infrared radiation thermometry with the hypothetic Planck distribution at a single characteristic temperature. We report here that the infrared emission spectrum from electrically biased GaAs devices deviates obviously from Planck distribution, due to the additional contribution from non-equilibrium hot electrons whose effective temperature reaches much higher than that of the lattice (Te>Tl). The evanescent infrared emission from these hot electrons is out-coupled by a near-field metamaterial grating and is hence made significant to the total far-field emission spectrum. Resonant emission peak has also been observed when the electron hotspots are managed to overlap spatially with the optical hotspots at the grating resonance. Our work opens a new direction to study nonequilibrium dynamics with (non-Planckian) infrared emission spectroscopy and provides important implications into the microscopic energy dissipation and heat management in nanoelectronics.

Bright Telecom-Wavelength Single Photons Based on a Tapered Nanobeam.

Telecom-wavelength single photons are essential components for long-distance quantum networks. However, bright and pure single photon sources at telecom wavelengths remain challenging to achieve. Here, we demonstrate a bright telecom-wavelength single photon source based on a tapered nanobeam containing InAs/InP quantum dots. The tapered nanobeam enables directional and Gaussian-like far-field emission of the quantum dots. As a result, using above-band excitation we obtain an end-to-end brightness of 4.1 ± 0.1% and first-lens brightness of 27.0 ± 0.1% at the ∼1300 nm wavelength. Furthermore, we adopt quasi-resonant excitation to reduce both multiphoton emission and decoherence from unwanted charge carriers. As a result, we achieve a coherence time of 523 ± 16 ps and postselected Hong-Ou-Mandel visibility of 0.91 ± 0.09 along with a comparable first-lens brightness of 21.0 ± 0.1%. These results represent a major step toward a practical fiber-based single photon source at telecom wavelengths for long-distance quantum networks.

Plasmonically Enhanced Thermal Radiation by Means of Surface Phonon Polaritons

Radiative heat transfer at the nanoscale has the potential to produce thermal emission with both spectral feature and intensity different from the bulk materials. Specifically, the idea of coupling the energy states of photons and phonons using surface phonon polaritons (SPhPs) blurs the boundary between light and heat, opening a path to the manipulation of heat transfer through photonic engineering and breaking the classical limit established by Planck's law. SPhPs can generate a strong energy confinement effect near the surface; however, this effect is only valid within a narrow spectral regime, the so-called reststrahlen band. In this study, we employ a hybrid structure to broaden the effective energy regime for thermal emission by coupling SPhPs and surface plasmon polaritons (SPPs). We report remarkably enhanced thermal emission of a hybrid structure made of a ${\mathrm{Si}\mathrm{O}}_{2}$ nanoribbon decorated with Au nanoparticles by a factor of 4 over that of a bare ${\mathrm{Si}\mathrm{O}}_{2}$ nanoribbon. We introduce an experimental technique to quantify the emissivity from the complex nanostructured surface using frequency-dependent heat-transfer measurement. Not only does it enable us to detect feeble emission from a single nanoemitter, but it also differentiates two distinct heat-conducting processes of conduction and radiation, simultaneously. Our work may offer insights to engineer far-field thermal emission using hybrid structures combining the surface plasma and phonon polaritons.

Experimental investigation of the far-field emission pattern of microdisk laser modes

We studied a far-field emission pattern for microlasers with InGaAs/GaAs quantum well-dots in the active region. Angular-resolved electroluminescence spectra measurement revealed various far-field patterns depending on current and resonance mode.

Weakly deformed optical microdisks: A third-order perturbation theory for transverse-magnetic modes

In the past years weakly deformed optical microdisks have become a focus for fundamental and applied research with lots of interesting new findings. A commonly used method to study such cavities is a perturbation theory based on weak boundary deformations (Dubertrand et al 2008 Phys. Rev. A 77, 013 804). In this paper we extent the perturbation theory to the third order which allows us to improve its accuracy significantly. We discuss various example systems in regard of Q-spoiling, frequency splitting, and far-field emission pattern. The results from the perturbation theory are in a very good agreement to full numerical simulations.

Highly Focused Fluorescence Emission Generated by a Cylinder on Sharp Convex Gold Groove

To satisfy the requirement for analyzing low concentration analyst in microfluidic bio-detection, it is extremely crucial to enhance the sensitivity of fluorescence bio-sensing. The emission efficiency of fluorescent nanoparticles (FNPs) is low and the fluorescence emission is dispersed, which brings a challenge to the collection of emission signal and the improvement of bio-sensing sensitivity. Directional fluorescence emission enhancement is crucial to solve this problem. In this work, we propose a hybrid structure consisting of a dielectric cylinder on a sharp convex gold groove to achieve highly focused fluorescence emission in both near field and far field. Due to scattering, constructive interference, guided resonance modes (cavity modes), surface plasmon mode and photonic nanojet effect, the fluorescence excitation and far-field directional fluorescence emission are enhanced obviously. In addition, the directional fluorescence enhancement is obvious for random positions of the FNPs in the designed structures and arbitrary volume of bio-solution. Such advantages are fantastic for sensitive biochemical detection and analysis.

Doubly resonant second-harmonic generation of a vortex beam from a bound state in the continuum

Second-harmonic generation in nonlinear materials can be greatly enhanced by realizing doubly resonant cavities with high quality factors. However, fulfilling such doubly resonant condition in photonic crystal (PhC) slab cavities is a long-standing challenge, because of the difficulty in engineering photonic bandgaps around both frequencies. Here, by implementing a second-harmonic bound state in the continuum (BIC) and confining it with a heterostructure design, we show the first doubly resonant PhC slab cavity with 2.4 × 10 − 2 W − 1 intrinsic conversion efficiency under continuous-wave excitation. We also report the confirmation of highly normal-direction concentrated far-field emission pattern with radial polarization at the second harmonic frequency. These results represent a solid verification of previous theoretical predictions and a cornerstone achievement, not only for nonlinear frequency conversion but also for vortex beam generation and prospective nonclassical sources of radiation.

Electromagnetic scattering, absorption and thermal emission by clusters of randomly distributed magneto-optical nanoparticles

In this work the scattering, absorption and the far-field thermal emission properties of clusters of randomly distributed magneto-optical (MO) nanoparticles are studied, considering spectral, directional and polarization state of the electromagnetic waves. We observe the Zeeman splitting effect in the scattered, absorbed and far-field emitted energy, the magnitude of which are directly influenced by the multiple scattering effect among the nanoparticles. The scattering and thermally emitted waves by the cluster have large degrees of circular polarization in directions parallel to the applied magnetic field H, but are linearly polarized in directions perpendicular to H, the effect of multiple scattering on the polarization state is much weaker. Moreover, the angular distribution of both the intensity and polarization state of the scattered and emitted waves can be effectively altered by the applied direction of H. In the multiple scattering by the MO nanoparticle cluster, we find that the MO effect can break the reciprocity of all the four Stokes parameters. In addition, we reconfirm the validity of Kirchhoff's law for the MO nanoparticle cluster considering four polarization states. Our work indicates that MO effect can be utilized to dynamically tune the apparent radiative properties of particle-dispersed systems like functional coatings, where the multiple scatterings by the dispersed particles are accompanied by the thermal emission process.

Routing valley exciton emission of a WS2 monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

The valleys of two-dimensional transition metal dichalcogenides (TMDCs) offer a new degree of freedom for information processing. To take advantage of this valley degree of freedom, on the one hand, it is feasible to control valleys by utilizing different external stimuli, such as optical and electric fields. On the other hand, nanostructures are also used to separate the valleys by near-field coupling. However, for both of the above methods, either the required low-temperature environment or low degree of coherence properties limit their further applications. Here, we demonstrate that all-dielectric photonic crystal (PhC) slabs without in-plane inversion symmetry (C2 symmetry) can separate and route valley exciton emission of a WS2 monolayer at room temperature. Coupling with circularly polarized photonic Bloch modes of such PhC slabs, valley photons emitted by a WS2 monolayer are routed directionally and are efficiently separated in the far field. In addition, far-field emissions are directionally enhanced and have long-distance spatial coherence properties.

Performance improvement of ultraviolet-A multiple quantum wells using a vertical oriented nanoporous GaN underlayer

Well-aligned, lateral and vertical oriented nanoporous GaN was fabricated using the electrochemical etching procedure and its influence on the optical characteristics of ultraviolet-A multiple quantum well (MQW) structure was investigated. We used a MQW structure with a V-defect and n-Al0.1Ga0.9 N layer, which greatly improved the uniformity of vertical electrochemical etching. Compared to the as-grown MQW structure, the lateral and vertical oriented nanoporous MQW structures have 3.8-fold and 8.1-fold photoluminescence intensity enhancement and the full width at half maximum has been narrowed from 18.4 nm to 7.9 nm and 2.8 nm, respectively. The vertical oriented nanoporous MQW structure has a rectangular far-field emission pattern with uniform forward light distribution and the view angle of 85% intensity is 50°. This study provides an effective method for improving the light output and controlling the emission angle of GaN based light emitting devices, as well as a method for preparing well-aligned nanopores in semiconductors.

Nanoscale force sensing of an ultrafast nonlinear optical response

The nonlinear optical response of a material is a sensitive probe of electronic and structural dynamics under strong light fields. The induced microscopic polarizations are usually detected via their far-field light emission, thus limiting spatial resolution. Several powerful near-field techniques circumvent this limitation by employing local nanoscale scatterers; however, their signal strength scales unfavorably as the probe volume decreases. Here, we demonstrate that time-resolved atomic force microscopy is capable of temporally and spatially resolving the microscopic, electrostatic forces arising from a nonlinear optical polarization in an insulating dielectric driven by femtosecond optical fields. The measured forces can be qualitatively explained by a second-order nonlinear interaction in the sample. The force resulting from this nonlinear interaction has frequency components below the mechanical resonance frequency of the cantilever and is thus detectable by regular atomic force microscopy methods. The capability to measure a nonlinear polarization through its electrostatic force is a powerful means to revisit nonlinear optical effects at the nanoscale, without the need for emitted photons or electrons from the surface.

Spin-Momentum-Locked Edge Mode for Topological Vortex Lasing.

Spin-momentum locking is a direct consequence of bulk topological order and provides a basic concept to control a carrier's spin and charge flow for new exotic phenomena in condensed matter physics. However, up to date the research on spin-momentum locking solely focuses on its in-plane transport properties. Here, we report an emerging out-of-plane radiation feature of spin-momentum locking in a non-Hermitian topological photonic system and demonstrate a high performance topological vortex laser based on it. We find that the gain saturation effect lifts the degeneracy of the paired counterpropagating spin-momentum-locked edge modes enabling lasing from a single topological edge mode. The near-field spin and orbital angular momentum of the topological edge mode lasing has a one-to-one far-field radiation correspondence. The methodology of probing the near-field topology feature by far-field lasing emission can be used to study other exotic phenomena. The device can lead to applications in superresolution imaging, optical tweezers, free-space optical sensing, and communication.

Differential Signaling Compromises Video Information Security Through AM and FM Leakage Emissions

Video display units (VDUs) using differential signaling technology significantly increase the risk of compromising video information security through leakage emissions. This article shows that differential signaling cables act as substantial video leakage sources. A concept is proposed that explains the video leakage principles of VDUs using differential signal cables such as the high-definition multimedia interface (HDMI) cable, digital visual interface (DVI) cable, and the low-voltage differential signaling (LVDS) cable. The emanations of the LVDS cable are closely examined by measuring simultaneously the differential video signal on the LVDS lines and its near- and far-field leakage emissions. From these measurements, several conclusions are drawn that give new insights into the video eavesdropping risk of VDUs using differential signaling methods. Furthermore, a novel video image reconstruction method is proposed that exploits the compromising emanations of a VDU by using frequency demodulation techniques. This article shows that leaked video emanations of VDUs using differential signaling cables are not only amplitude modulated (AM) but also frequency modulated (FM). This strongly implies that the possible algorithmic toolset of malicious video eavesdroppers is much larger than currently assumed. This article investigates several VDU setups at a distance of 10 m, including an ultrahigh-definition video display, three different HDMI cables and two notebooks. Additionally, the AM-based and FM-based video image reconstruction results are discussed and compared.

Metasurface Integrated Monolayer Exciton Polariton.

Monolayer transition-metal dichalcogenides (TMDs) are the first truly two-dimensional (2D) semiconductor, providing an excellent platform to investigate light-matter interaction in the 2D limit. The inherently strong excitonic response in monolayer TMDs can be further enhanced by exploiting the temporal confinement of light in nanophotonic structures. Here, we demonstrate a 2D exciton-polariton system by strongly coupling atomically thin tungsten diselenide (WSe2) monolayer to a silicon nitride (SiN) metasurface. Via energy-momentum spectroscopy of the WSe2-metasurface system, we observed the characteristic anticrossing of the polariton dispersion both in the reflection and photoluminescence spectrum. A Rabi splitting of 18 meV was observed which matched well with our numerical simulation. Moreover, we showed that the Rabi splitting, the polariton dispersion, and the far-field emission pattern could be tailored with subwavelength-scale engineering of the optical meta-atoms. Our platform thus opens the door for the future development of novel, exotic exciton-polariton devices by advanced meta-optical engineering.

Non-Lorentzian LDOS in coupled photonic crystal cavities probed by near- and far-field emission

Non-Lorentzian LDOS in coupled photonic crystal cavities probed by near- and far-field emission

Notched-elliptical polymer microdisk resonator for unidirectional emission at visible and near-infrared wavelengths

We propose the design of a doped-polymer elliptical microdisk resonator with a wavelength-size notch and characterize the ability of such a resonator to act as a unidirectional emission source. The resonator shows low beam divergence (∼4°) and high emission efficiency of 84% in near-infrared wavelength region. The effects of the deformation parameter and the notch size on the far-field emission are analyzed, to illustrate that the device is robust and reliable. It is demonstrated that the proposed device can be conveniently downscaled for unidirectional emission in visible wavelength region without sacrificing the performance.

Single-Mode Lasers (1050 nm) of Mesa-Stripe Design Based on an AlGaAs/GaAs Heterostructure with an Ultra-Narrow Waveguide

The emission characteristics of single-mode lasers based on an AlGaAs/GaAs heterostructure with an ultra-narrow waveguide are studied. It is shown that using an ultra-narrow waveguide (100 nm) and thin (70 nm) wide-gap barriers at the waveguide/cladding interface makes narrower the vertical divergence of far-field emission. The lateral and vertical divergences are 5° and 18.5°, respectively, for the narrow-stripe (5.1 μm) single-mode lasers developed in the study. The lasers demonstrate efficient single-mode operation up to a power of 200 mW. Raising the current further gives rise to higher order modes, the maximum optical power in continuous-wave lasing being limited to 550 mW by overheating. Passing to the pulsed operation mode (pulse width 200 ns) makes it possible to raise the maximum peak optical power to 1500 mW.

Scale Law of Far-Field Thermal Radiation from Plasmonic Metasurfaces.

Although metamaterials or metasurfaces consisting of patterned subwavelength structures have been widely employed for thermal emission control, the collective behavior of the emitter array in a metasurface still remains unclear. Here, based on the quasinormal mode theory, we derive a new scale law to elucidate the far-field thermal emission from a metasurface composed of densely packed plasmonic nanoemitters. The tight binding method is used to approximate the collective resonant mode of the emitter array. Because of in-phase near-field interaction, the thermal radiation from a single emitter in a metasurface is suppressed by its adjacent emitters. We find that the overall far-field thermal radiation from a metasurface can be either positively or negatively correlated with the packing density of the emitters, depending on the mode properties of the single emitter. This new scale law thus serves as a general guideline for designing metasurfaces with desired thermal emission properties.

Non-Lorentzian Local Density of States in Coupled Photonic Crystal Cavities Probed by Near- and Far-Field Emission.

Recent theories proposed a deep revision of the well-known expression for the Purcell factor, with counterintuitive effects, such as complex modal volumes and non-Lorentzian local density of states. We experimentally demonstrate these predictions in tailored coupled cavities on photonic crystal slabs with relatively low optical losses. Near-field hyperspectral imaging of quantum dot photoluminescence is proved to be a direct tool for measuring the line shape of the local density of states. The experimental results clearly evidence non-Lorentzian character, in perfect agreement with numerical and theoretical predictions. Spatial maps with deep subwavelength resolution of the real and imaginary parts of the complex mode volumes are presented. The generality of these results is confirmed by an additional set of far-field and time-resolved experiments in cavities with larger modal volume and higher quality factors.