Plasmonic Beam Research Articles

Quantum plasmonic sensing by Hong–Ou–Mandel interferometry

We propose a quantum plasmonic sensor using Hong–Ou–Mandel (HOM) interferometry that measures the refractive index of an analyte, embedded in a plasmonic beam splitter composed of a dual-Kretschmann configuration, which serves as a frustrated total internal reflection beamsplitter (BS). The sensing performance of the HOM interferometry, combined with single-photon detectors, is evaluated through Fisher information for estimation of the refractive index of the analyte. This is subsequently compared with the classical benchmark that considers the injection of a coherent state of light into the plasmonic BS. By varying the wavelength of the single photons and the refractive index of the analyte, we identify a wide range where a 50% quantum enhancement is achieved and discuss the observed behaviors in comparison with the classical benchmark. We expect this study to provide a useful insight into the advancement of quantum-enhanced sensing technologies, with direct implications for a wide range of nanophotonic BS structures.

On-chip terahertz orbital angular momentum demultiplexer

The terahertz regime is widely recognized as a fundamental domain with significant potential to address the demands of next-generation wireless communications. In parallel, mode division multiplexing based on orbital angular momentum (OAM) shows promise in enhancing bandwidth utilization, thereby expanding the overall communication channel capacity. In this study, we present both theoretical and experimental demonstrations of an on-chip terahertz OAM demultiplexer. This device effectively couples and steers seven incident terahertz vortex beams into distinct high-quality focusing surface plasmonic beams, and the focusing directions can be arbitrarily designated. The proposed design strategy integrates space-to-chip mode conversion, OAM recognition, and on-chip routing in a compact space with subwavelength thickness, exhibiting versatility and superior performance.

Tunable Multiple Surface Plasmonic Bending Beams into Single One by Changing Incident Light Wavelength

Controllable surface plasmonic bending beams (SPBs) with propagating along bending curves have a wide range of applications in the fields of fiber sensors, optical trapping, and micro-nano manipulations. In terms of designing and optimizing controllable SPB generators, there is great significance in realizing conversion between multiple SPBs and single SPB without rebuilding metasurface structures. In this study, a SPB generator, composed of an X-shaped nanohole array, is proposed to realize conversion between multiple SPBs and a single one by changing the incident light wavelength. The Fabry–Pérot (F–P) resonance effect of SPPs in nanoholes and localized surface plasmonic (LSP) resonance of the nanohole are utilized to explain this conversion. It turns out that the relationship between the electric field intensities of SPBs and the polarization angle of incident light satisfies the sine distribution, which is consistent with dipole radiation theory. In addition, we also find that the electric field intensities of SPBs rely on the width, length, and angle of the X-shaped nanohole. These findings could help in designing and optimizing controllable and multi-functions SPBs converters.

Plasmonic Molybdenum Dioxide Ultrathin Nanowire Bundles for Highly Sensitive, Stable, and Reproducible Surface-Enhanced Raman Spectroscopy

In surface-enhanced Raman spectroscopy (SERS) detection, it is important to improve the sensitivity, stability, and reproducibility of semiconductor surface-enhanced Raman scattering (SERS) substrates. Here, a simple chemical method was used to synthesize molybdenum dioxide ultrathin nanowire bundles. The ultrathin nanowire bundles of molybdenum dioxide demonstrate distinct and robust surface plasmon resonance (SPR) effects within the visible light range. As a low-cost SERS substrate, the plasmonic molybdenum dioxide nanowire beams exhibit a Raman enhancement factor of 2.9 × 107 and a minimum detection limit of 1.0 × 10–11 mol L–1 for Rhodamine 6G. In addition, these SERS substrates based on molybdenum dioxide ultrathin nanowires exhibit good chemical stability and can resist corrosion by strong acids and bases over time. The molybdenum dioxide ultrathin nanowire bundles have a high potential to become an ideal metal-oxide-based SERS substrate material.

Detecting the Topological Charge of Optical Vortex Beams Using a Focused Surface Plasmonic Beam Generator

Detecting the Topological Charge of Optical Vortex Beams Using a Focused Surface Plasmonic Beam Generator

Modulation of Surface Plasmonic Bending Beam via Nanoslit Interactions

The discussion of resonance mechanisms for artificial structural units has always been a key to producing highly efficient, active and tunable meta-devices in the fields of controlling surface plasmon polaritons (SPPs) to generate surface plasmonic bending beams (SPBs). In this study, an array of 20 antisymmetric double V-shaped structures was designed to generate an SPB. The arms of the double V-shaped structures were panned to control the electric field intensity distributions of the SPB. The influence of the polarization states (such as polarization angles, linearly polarized (LP), left-circularly polarized (LCP) and right-circularly polarized (RCP) light) of the incident light on electric field intensity of SPB is discussed. These results can be well explained by the theory of dipole radiation. The numerical simulation results are in good agreement with the theoretical analysis. It is hoped that these results will help guide subsequent work in optimizing SPB generators.

Tailorable Polarization‐Dependent Directional Coupling of Surface Plasmons

AbstractCoupling free‐space light into surface plasmons (SPs) has traditionally faced challenges in arbitrarily controlling the directionality of the SPs with respect to the incident polarization. Recently reported polarization‐dependent directional coupling of SPs using metasurfaces has attracted enormous attention for its promise in developing innovative and on‐demand plasmonic devices. However, further progress has been hampered by the limitation in designating the directional coupling with tailorable polarization‐dependent feature and compatible ability to incidence of complex polarization distribution. Here, a directional coupling strategy is introduced to overcome these limits. It is demonstrated that, by utilizing the interference between two pairs of slit resonators with different resonance responses, the directional SP coupling can be expanded to arbitrary group of polarized incidence by simply varying their relative distance, and the SP coupling direction will reverse under the corresponding orthogonally polarized incidence without affecting the efficiency. To exhibit the versatile design capability of the strategy, it is further utilized to construct several polarization‐dependent plasmonic devices for controlling SP propagations, including two SP metalenses and a plasmonic Airy beam launcher, in which it is shown that the device can even be designed to work for non‐uniformly polarized incidence. The strategy paves a reliable route towards many practical on‐chip applications.

Plasmonic loss-mitigating broadband adiabatic polarizing beam splitter.

The intriguing analogy between quantum physics and optics has inspired the design of unconventional integrated photonics devices. In this paper, we numerically demonstrate a broadband integrated polarization beam splitter (PBS) by implementing the stimulated Raman adiabatic passage (STIRAP) technique in a three-waveguide plasmonic system. Our proposed PBS exhibits >250 nm transverse-magnetic (TM) bandwidth with <-40 dB extinction and >150 nm transverse-electric (TE) bandwidth with <-20 dB extinction, covering the entire S-, C-, and L-bands and part of the E-band. Moreover, near-lossless light transfer is achieved in our system despite the incorporation of a plasmonic hybrid waveguide because of the unique loss mitigating feature of the STIRAP scheme. Through this approach, various broadband integrated devices that were previously impossible can be realized, which will allow innovation in integrated optics.

Monolayer NaW2O2Br6: a gate tunable near-infrared hyperbolic plasmonic surface.

Electrically tunable hyperbolic polaritons in two dimensional (2D) materials can offer unexplored opportunities in integrating photonics and nano-optoelectronics into a single chip. Here, we suggest that monolayer NaW2O2Br6 can host electrically tunable hyperbolic plasmon polaritons for infrared light via first-principles calculations. 2D monolayer NaW2O2Br6 exhibits an extremely anisotropic metallic property: conducting for one direction but almost insulating for the other direction, which could be considered as a 2D analogue of metal/dielectric multilayers, a typical structure for hyperbolic metamaterials. More interestingly, we also demonstrate that the hyperbolic properties in the near-infrared range, including the hyperbolic windows, figure of merit, and propagation directions of plasmon beams, can be effectively modulated by carrier doping at the order of 1013 cm−2, which even can be accessed by solid-gated field effect transistors. Thus, it is anticipated that monolayer NaW2O2Br6 has a great potential in constructing field programmable polariton nanodevices for emerging and diverse photonic applications.

Spatio-temporal propagation dynamics of Airy plasmon pulses.

We investigate numerically the evolution of a particular type of non-diffracting pulsed plasmonic beam called Airy plasmon pulses. A suitable diffraction grating is obtained by optimizing a grating (e.g., [Phys. Rev. Lett.107, 116802 (2011)10.1103/PhysRevLett.107.116802]) for maximum generation bandwidth and efficiency to excite ultrashort Airy plasmon pulses. The optimization process is based on Airy and non-Airy plasmons contributions from the diffraction grating. The time-averaged Airy plasmon pulse generated from the grating shows a bent trajectory and quasi non-diffracting properties similar to CW excited Airy plasmons. A design-parameter-dependent geometrical model is developed to explain the spatio-temporal dynamics of the Airy plasmon pulses, which predicts the pulse broadening in Airy plasmon pulses due to non-Airy plasmons emerging from the grating. This model provides a parametric design control for the potential engineering of temporally focused 2D non-diffracting pulsed plasmonic beams.

Structured plasmonic beam: in-plane manipulation of light at the nanoscale

The brief review on recent approaches on the formation of a new class of subwavelength scale localized structured surface plasmon polaritons (SPP) beams is discussed. For the Janus-like particle (including the geometrically symmetric particles with different dielectrics) the morphology of the field localization area and its properties depends on the particle shape and material. Plasmonic hook (PH) beam does not propagate along straight line but instead follow curved self-bending trajectory. Wavefront analysis behind of such symmetric and asymmetric mesoscale rectangle structure reveals that the unequal phase of the transmitted plane wave results in the irregularly concave deformation of the wavefront inside the dielectric which later leads to creation of the PH. Such dielectric structures placed on metal film enable the realization of new ultracompact wavelength-selective and wavelength-scaled in-plane nanophotonic components. SPP have potential to overcome the constrains on the speed of modern digital integrated devices limitation due to the metallic interconnects and increase the operating speed of future digital circuits.

All-optical modulation based on MoS2-Plasmonic nanoslit hybrid structures

Abstract Two-dimensional (2D) materials with excellent optical properties and complementary metal-oxide-semiconductor (CMOS) compatibility have promising application prospects for developing highly efficient, small-scale all-optical modulators. However, due to the weak nonlinear light-material interaction, high power density and large contact area are usually required, resulting in low light modulation efficiency. In addition, the use of such large-band-gap materials limits the modulation wavelength. In this study, we propose an all-optical modulator integrated Si waveguide and single-layer MoS2 with a plasmonic nanoslit, wherein modulation and signal light beams are converted into plasmon through nanoslit confinement and together are strongly coupled to 2D MoS2. This enables MoS2 to absorb signal light with photon energies less than the bandgap, thereby achieving high-efficiency amplitude modulation at 1550 nm. As a result, the modulation efficiency of the device is up to 0.41 dB μm−1, and the effective size is only 9.7 µm. Compared with other 2D material-based all-optical modulators, this fabricated device exhibits excellent light modulation efficiency with a micron-level size, which is potential in small-scale optical modulators and chip-integration applications. Moreover, the MoS2-plasmonic nanoslit modulator also provides an opportunity for TMDs in the application of infrared optoelectronics.

Infrared diffraction radiation from twin circular dielectric rods covered with graphene: plasmon resonances and beam position sensing

This work considers the near-infrared range diffraction radiation (DR) from a modulated beam of particles passing between two identical dielectric circular nanowires covered with graphene. The resistive boundary conditions are set on the zero-thickness graphene covers with the electron conductivity determined from the Kubo formalism. Assuming that the beam velocity is fixed, we use the separation of variables in local coordinates and the addition theorems for cylindrical functions and cast the DR problem to a Fredholm second-kind matrix equation. This allows us to compute both near- and far-field characteristics with controlled accuracy. The analysis reveals that a shift of the beam trajectory from the central-symmetric position enables the excitation of additional resonances on the modes, which remain “dark” otherwise. Ignition of these resonances can be considered as a tool for noninvasive beam position monitoring with microscale devices.

Experimental verification of a plasmonic hook in a dielectric Janus particle

We report on the experimental observation of the curved plasmonic beam, a plasmonic hook (PH), for surface plasmon-polariton (SPP) waves. The SPP PH effect could be obtained with a cuboid particle with broken shape symmetry fabricated with a relatively simple routine. This has a pronounced difference with fabrication of the structure for generation of the Airy SPPs, which require complex techniques to compensate the wave vector mismatch. We confirmed the existence of SPP PH by amplitude scattering scanning near-field optical microscopy. The experimental results agree well with our predictions. Importantly, the SPP PH demonstrates the smallest curvature of the beam ever recorded for SPPs compared to that for the Airy-family plasmonic beams, which potentially can strongly impact many useful applications from nanoparticle manipulation to nanoscale bio-sensing.

Coherent amplification and inversion less lasing of surface plasmon polaritons in a negative index metamaterial with a resonant atomic medium

Surface plasmon polaritons (SPPs) lasing requires population inversion, it is inefficient and possesses poor spectral properties. We develop an inversion-less concept for a quantum plasmonic waveguide that exploits unidirectional superradiant SPP (SSPP) emission of radiation to produce intense coherent surface plasmon beams. Our scheme includes a resonantly driven cold atomic medium in a lossless dielectric situated above an ultra-low loss negative index metamaterial (NIMM) layer. We propose generating unidirectional superradiant radiation of the plasmonic field within an atomic medium and a NIMM layer interface and achieve amplified SPPs by introducing phase-match between the superradiant SPP wave and coupled laser fields. We also establish a parametric resonance between the weak modulated plasmonic field and the collective oscillations of the atomic ensemble, thereby suppressing decoherence of the stably amplified directional polaritonic mode. Our method incorporates the quantum gain of the atomic medium to obtain sufficient conditions for coherent amplification of superradiant SPP waves, and we explore this method to quantum dynamics of the atomic medium being coupled with the weak polaritonic waves. Our waveguide configuration acts as a surface plasmon laser and quantum plasmonic transistor and opens prospects for designing controllable nano-scale lasers for quantum and nano-photonic applications.

Nonlinear Self-Confined Plasmonic Beams: Experimental Proof

Controlling low power light beam self-confinement with ultrafast response time opens up opportunities for the development of signal processing in microdevices. The combination of highly nonlinear m...

Interaction between spoof localized surface plasmon and terahertz vortex beam

We theoretically and experimentally investigate a method of exciting multipole plasmons, including terahertz dark spoof localized surface plasmon (Spoof-LSP) modes, by using normally incident terahertz vortex beam. The vortex beam with angular intensity profile and phase singularities, has well-defined angular momentum which can be decomposed into the polarization-state-related spin angular momentum (SAM) for characterizing the spin feature of photon, and the helical-wavefront-related orbital angular momentum (OAM) that is characterized by an integer &lt;inline-formula&gt;&lt;tex-math id="Z-20200915102424-1"&gt;\begin{document}$ (l) $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20200695_Z-20200915102424-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, called the topological charge. By illuminating terahertz vortex beam on the metallic disk with periodic subwavelength grooves normally, we find that the terahertz dark multipole plasmons can be excited by the terahertz vortex beam carrying different OAM and SAM. We analyze the correspondence between the spin and orbital angular momentum of vortex beam and the excited dark multipolar plasmon modes. In the experiment, a terahertz stepped spiral phase plate (SPP) with high transmission and low dispersion based on the Tsurupica olefin polymer is developed and the stepped SPP can generate a terahertz vortex beam having a topological charge of 1. Then, we further study the excitation of dark multipolar Spoof-LSPs by utilizing the stepped SPP in combination with the near-field scanning terahertz microscopy. The collimated terahertz wave, which is radiated from a 100 fs (&lt;i&gt;λ&lt;/i&gt; = 780 nm) laser pulse pumped photoconductive antenna emitter, is converted into terahertz circular polarized light (CPL) which can carry SAM by the combination of the quarter wave plate and the polarizer, and then terahertz CPL impinges on the stepped SPP, producing the terahertz vortex beam which can carry OAM. The spatial two-dimensional electric field distribution is collected in steps of 0.02 mm along the &lt;i&gt;x&lt;/i&gt;-direction and &lt;i&gt;y&lt;/i&gt;-direction by a commercial terahertz near-field probe which is located close (≈ 10 μm) to the one side of polyimide film by three-dimensional electric translation stage and a microscope (FORTUNE TECHPLOGY FT-FH1080). The experimental results are in good agreement with simulations. We believe that our method will open the way for detailed research on the terahertz physics, plasma and imaging fields.

A Compound Phase-Modulated Beam Splitter to Distinguish Both Spin and Orbital Angular Momentum

Based on a phase-modulated metallic nanoslit array, an angular momentum (AM) beam splitter has been demonstrated to distinguish both spin and orbital components carried by the light beam. With such a device, the AM modes could be coupled into nondiffracting surface plasmonic beams propagating toward different directions. According to the experimental results, the extinction ratio for spin AM beam splitting is larger than 10 and the spatial interval of adjacent orbital AM modes (with a topological charge interval of 2) is more than 1.1 μm. We believe that such a device would have great potential to achieve a highly compact photonic integrated circuit with the plasmonic beam.

Compact and ultra-efficient broadband plasmonic terahertz field detector

Terahertz sources and detectors have enabled numerous new applications from medical to communications. Yet, most efficient terahertz detection schemes rely on complex free-space optics and typically require high-power lasers as local oscillators. Here, we demonstrate a fiber-coupled, monolithic plasmonic terahertz field detector on a silicon-photonics platform featuring a detection bandwidth of 2.5 THz with a 65 dB dynamical range. The terahertz wave is measured through its nonlinear mixing with an optical probe pulse with an average power of only 63 nW. The high efficiency of the scheme relies on the extreme confinement of the terahertz field to a small volume of 10−8(λTHz/2)3. Additionally, on-chip guided plasmonic probe beams sample the terahertz signal efficiently in this volume. The approach results in an extremely short interaction length of only 5 μm, which eliminates the need for phase matching and shows the highest conversion efficiency per unit length up to date.

Curved space plasmonic optical elements.

We have designed and experimentally studied non-planar curved space plasmonic optical elements. Three different smooth curved space plasmonic structures were studied: a dome that acts either as a focusing element or as a deflector for plasmonic beams, a cone that acts as a plasmonic prism, and a tapered book cover that alters the size of a plasmonic guided wave. The functional mechanism of these elements relies purely on the curvature-induced effective potential and does not require any additional dielectric layer for shaping the plasmonic beams. The curved space plasmonic elements open exciting new possibilities for guiding, focusing, deflecting, and controlling the propagation of plasmonic beams in a compact manner.