Surface Plasmon Waveguide Research Articles

Spoof surface plasmonic waveguide and its band-rejection filter based on H-shaped slot units

To reduce the transverse width of the SSPP (spoof surface plasmon polaritons) waveguide, the complementary structure of the SSPP waveguide based on the H-shaped conductor periodic unit is used. In this structure, periodic H-shaped slots are cut in the conductor film on the substrate interface. Fed by the coplanar waveguide with flared ground planes, this SSPP waveguide with a small width can achieve broadband transmission characteristics below 10 GHz. Inserting small H-shaped conductor units inside the slot can form the complementary split ring resonators, and the band-stop filter is realized without increasing the lateral dimension of the original SSPP waveguide. The experimental results show that the notch frequency of the proposed filter can be effectively regulated by the height of embedded H-shaped conductor units.

A planar strongly confined spoof surface plasmonic waveguide with compact cells

ABSTRACTA new planar waveguide structure, based on spoof surface plasmon polaritons (SSPPs), is proposed featuring compact size, low loss, and good subwavelength field confinement. Compared with the rectangular- and trapezoidal-type cells in the conventional spoof surface plasmonic waveguides (SSPWs), the proposed cell has 50.7% and 27.8% size reduction at the same cut-off frequency, respectively. Moreover, the simulated electrical field distributions show that there are good improvements in the field enhancement and subwavelength confinement. To further validate the transmission characteristics of the proposed waveguide, coplanar waveguide (CPW) and corresponding transition structures are used to get a high efficient mode conversion. A CPW-SSPW-CPW structure on a dielectric board is designed, fabricated, and measured in the microwave region. Good agreement is achieved between the simulated and measured results. The last results show that the proposed waveguide has low insertion loss and flat group delay in an ultra-wideband from 2.4 to 10.3 GHz.

Corrugated organic light-emitting diodes to effectively extract internal modes.

We report a corrugated structure to effectively extract the surface plasmon polaritons (SPP) and waveguiding modes in organic light-emitting diodes (OLEDs). This structure is formed by nano-imprint of blazed gratings. To study the optimum extraction condition in terms of grating pitches, we compare the light extraction efficiency of corrugated OLEDs with three kinds of pitches, showing a 42.00% external quantum efficiency (EQE) enhancement ratio with this internal structure. Due to the transfer of SPP and waveguiding modes into substrate mode, the EQE enhancement ratio can be further pushed to 103.02% by attaching a macrolens. The simulation verifies the experimental results and shows the extraction mechanism of the corrugated structure towards transverse electric (TE) and transverse magnetic (TM) waves. We foresee that this method is able to enhance the optical efficiency of devices for both mass-production OLED lighting and display in a cost-effective way.

Spatial modulation of the electromagnetic energy transfer by excitation of graphene waveguide surface plasmons

We theoretically study the electromagnetic energy transfer between donor and acceptor molecules near a graphene waveguide (WG). The surface plasmons (SPs) supported by the structure provide decay channels which lead to an improvement in the energy transfer rate when the donor and acceptor are localized on the same side or even on opposite sides of the WG. The modification of the energy transfer rate compared to its value in absence of the WG are calculated by deforming the integration path into a suitable path in the complex plane. Our results show that this modification is dramatically enhanced when the symmetric and antisymmetric SPs are excited. Notable effects on the spatial dependence of the energy transfer due to the coherent interference between these SP channels, which can be tuned by chemical potential variations, are highlighted and discussed in terms of SP propagation characteristics.

Hybrid surface plasmon waveguide based on CdS nanowires and metal ridges

In this study, a novel hybrid surface plasmon waveguide structure based on CdS nanowires and metal ridges was designed. The waveguide structure was simulated and analysed at a working wavelength of 490 nm based on the finite element method. The electric field distribution, mode characteristics, transmission length and quality factor of the waveguide were studied with geometric parameters. Results show that the comprehensive performance of the waveguide can be significantly optimised by appropriately adjusting the geometric parameters of the structure. Through the optimal parameter design, the effective mode field area reaches 0.008 λ2, the transmission length is 21,289 nm, and the quality factor is 702.12. This waveguide structure has great potential in the fields of optoelectronic communication and optical sensing technology.

Tunable MoS2 modified hybrid surface plasmon waveguides

The tunable propagation properties of MoS2 supported hybrid surface plasmon waveguides based on dielectric fiber-gap-metal substrate structures have been investigated by using the finite element method, including the effects of structural parameters, the dielectric fiber shape and carrier concentration of the MoS2 layer. The results reveal that as the dielectric fiber radius increases, the confinement of the hybrid mode increases, and the losses show a peak. The shape of the dielectric fiber affects the propagation properties obviously, with an optimum structural parameter (a large value of the elliptical parameter) the confinement and figure of merits increase, and the dissipation decreases simultaneously. In addition, as the carrier concentration of the MoS2 layer increases, the modulation depth of absorption reaches more than 40%, and the propagation constants manifest obvious double peaks at wavelengths of 610 nm (2.03 eV) and 660 nm (1.88 eV), coming from the excitons’ absorption of the MoS2 layer. The results are very useful in helping one to understand the tunable mechanisms of hybrid mode waveguide structures and for the design of novel surface plasmonic devices in the future, e.g. absorbers, modulators, lasers, and resonators.

Angular dependent strong coupling between localized waveguide resonance and surface plasmon resonance in complementary metamaterials

We give direct evidence of both surface plasmon resonance (SPR) and localized waveguide resonance (LWR) contribution to the extraordinary optical transmission in complementary metamaterials. Strong coupling between SPR and LWR are also observed with clear evidence of Rabi splitting and anti-crossing phenomena. The splitting introduces sharp phase shift, which in turn enhances group velocity delay by the incident angle without geometric parameter change. The results not only clarify SPR and LWR effects in the extraordinary optical transmission, but also provide a novel route to control light-metamaterial interaction by angular modulation for on-chip slow light devices.

Lateral dimension tuned ultra-low loss effective surface plasmonic waveguide

Recent theoretical and experimental works demonstrate that effective surface plasmon polaritons (ESPPs) induced by structural dispersion in bounded waveguide are perfect low-frequency counterparts of optical SPPs both for the double-layered and multi-layered systems. In all these efforts, the lateral dimension of each layer was assumed to be the same and the dispersion of the ESPPs was only tuned by the dielectric permittivity in each layer. Inevitably, the dielectric loss will deteriorate the transmission performance of ESPPs due to the huge field confinement and enhancement. In this work, we propose a simple but robust scheme to dramatically enhance the transmission efficiency of ESPPs by introducing a double-layered air-filled plasmonic waveguide with different lateral dimensions. Simulation and experimental results demonstrate that an ultra-low loss plasmonic waveguide with tunable bandwidth can be easily built by changing the lateral dimension of the upper air layer. This work provides valuable guidance for flexible design of low-loss plasmonic devices and systems at microwave and terahertz frequencies.

Integrated Mode Composite Transmission Line

In this paper, a novel integrated mode composite transmission line (IMCTL) is proposed, which consists of inner and outer transmission lines. The proposed IMCTL takes full advantages of both substrate integrated waveguide (SIW) and spoof surface Plasmon polaritons (SSPPs) transmission line and supports high-frequency transmission in the inner transmission line and low-frequency transmission in the outer surface transmission line with different propagation modes. The dispersion characteristics of the inner and outer surface IMCTL are studied. The electromagnetic field (EM) distributions and propagation modes of the inner and outer surface IMCTL are examined. The circuit models of the inner and outer surface IMCTL are discussed and analyzed. In order to achieve the transmission of inner and outer surface IMCTL with different propagation modes, two simple high-efficiency conversion structures are utilized to convert the guided waves to the proposed IMCTL. The inner and outer surface IMCTL are designed and simulated, which show good transmission performance. The ohmic losses and dielectric losses of the inner and outer surface IMCTL are simulated and compared with typical transmission lines. The measured data of the proposed IMCTL show a very good agreement with the simulated results. The measured insertion losses of inner IMCTL are within 1.77 ± 0.64 dB from 5.5 to 10.0 GHz and the measured insertion losses of outer surface IMCTL are within 3.21 ± 1.22 dB from 2.0 to 6.0 GHz. The proposed IMCTL will play an important role in the integrated high-performance multiband microwave and wireless communication systems.

Optimization of angle-pixel resolution for angular plasmonic biosensors

An angular plasmonic sensor based on optimized angle-pixel resolution to detect antibody-antigen binding process is presented. Owing to discrete resonance curves by the CCD pixels, the pixel sensitivity and detection noise of the plasmonic sensors need to be balanced. The angle-pixel resolution is adjusted by changing the distance between the sensor chip and the CCD to obtain the optimal refractive index (RI) resolution for three plasmonic sensors, which are surface plasmon resonance (SPR), long range surface plasmon resonance (LRSPR) and plasmon waveguide resonance (PWR) sensors. Each plasmonic sensor can achieve its optimal RI resolution at the optimal distance, and the LRSPR sensor has the best RI resolution. Attributing to the reference channel and temperature control module in the sensor system, the RI resolution can achieve 4.37 × 10−7 RIU at Normal mode and 1.13 × 10-7 RIU at a slow response Extreme mode. The Protein A-IgG binding reaction experiment indicates that the plasmonic sensor has linear response to IgG concentration in a wide range and the limit of detection (LOD) is 5.45 pM at Extreme mode. The procedure and result of this work are helpful to the optimization of other angular plasmonic sensors.

Wideband Polarization Conversion with the Synergy of Waveguide and Spoof Surface Plasmon Polariton Modes

The ability to freely control the polarization of electromagnetic waves is of great significance, and state-of-the-art challenges include achieving efficient, wide-band polarization control with a relatively thin device in transmission geometry. To meet the challenge, this study combines slow waves (from spoof surface plasmon polariton modes) with fast waves (from waveguide modes) to handle orthogonal polarization components. Such a system can be quite thin, due to the strong dispersion between these two types of modes, with cancellation of the two nonlinearly dispersive modes yielding high-efficiency polarization conversion over a wide frequency range.

Flexibly designed spoof surface plasmon waveguide array for topological zero-mode realization.

We propose a flexibly designed photonic system based on ultrathin corrugated metallic "H-bar" waveguide that supports spoof surface plasmon polariton (SPP) at microwave frequencies. Five designs were presented, in order to demonstrate flexibility according to varying height, period, core width, rotation, and shifting on the "H-bar" unit of the waveguide. The propagation constant between two hybrid designs of period and height structure was then shown in order to study the coupling effect. Next, we constructed a coupled waveguide array that followed the Su-Schrieffer-Heeger (SSH) model. This model was constructed by a hybrid design with the identical propagation constant of each waveguide, except it had dimerized spacing. The propagation feature of topological zero mode was then observed as theoretically expected in the dimerized array. Our proposed spoof SPP waveguide array has great flexibility to be used as a powerful experiment platform, particularly in photonic simulation of the quantum or topological phenomena described by Schrödinger equation in condensed matters.

Adiabatic transfer of surface plasmons in non-Hermitian graphene waveguides

We investigate the energy transfer of surface plasmon polaritons (SPPs) based on adiabatic passage in a non-Hermitian waveguide composed of three coupled graphene sheets. The SPPs can completely transfer between two outer waveguides via the adiabatic dark mode as the waveguides are lossless and the coupling length is long enough. However, the loss of graphene can lead to breakdown of adiabatic transfer schemes. By utilizing the coupled mode theory, we propose three approaches to cancel the nonadiabatic coupling by adding certain gain or loss in respect waveguides. Moreover, the coupling length of waveguide is remarkably decreased. The study may find interesting application in optical switches on a deep-subwavelength scale.

Multichannel Long-Range Surface Plasmon Waveguides for Parallel Biosensing

Two multichannel long-range surface plasmon waveguide structures are presented for parallel biosensing applications. The required ancillary passive optical elements are modeled and validated via comparisons with measurements to find good designs for the multichannel structures. The structures were fabricated as gold stripes embedded in CYTOP claddings with the fluidic channels defined via etching. The two multichannel structures are enabled using either a triple coupler or a corporate feed in cascade with an array of sensing waveguides. We demonstrate bulk and protein sensing for each channel comparable in performance to a single straight waveguide biosensor. Multiple channels are useful for parallel sensing, referencing, and common noise rejection.

Enhanced dielectric waveguide mode from the coupling of surface plasmon polaritons excited by a parallel electron beam

Abstract The coherent, power enhanced and mode selected light radiation from the coupling of surface plasmon polaritons (SPPs) and waveguide modes is presented here. The results of theoretical analysis show that this coupling occurs in the structure of a thin metal film with finite thickness dielectric medium loading excited by free electrons at certain beam energies, referred to as the coupling points. The research of particle-in-cell simulation is also carried out, and results agree well that of theoretical analyses. Because of the coupling, the power intensity of the coherent radiation is extremely enhanced up to 32 times compared with that transformed from SPPs by Cherenkov radiation directly in the infinite medium. And even at the non-coupling points, there is also a 5 times enhancement of the radiation power. The results also show that the main mode of the loading medium is changed from the zero order waveguide mode to the mode whose operating frequency is near to that of asymmetric SPPs mode. Accordingly, the results presented here is of great significance of developing miniature, integratable, high-power-density light radiation sources from visible light to ultra-violet rays at room temperature.

Fabrication of 4.4 THz quantum cascade laser and its demonstration in high-resolution digital holographic imaging

Abstract In this work, we present our research on the fabrication of high power terahertz quantum cascade laser (THz QCL) with frequency at 4.4 THz and its demonstration in digital holographic imaging. The lasers described in this work are based upon the resonant-phonon active region design and semi-insulating surface-plasmon waveguide. The peak power varies with the size of the ridge and the maximum output power of 95 mW at 10 K in pulsed mode is obtained. The maximum working temperature is 80 K. Interestingly, by changing the injection current, the transverse mode of the laser can be switched between TM00 mode and TM01 mode. With such THz QCL as the light source, the lateral resolution of a home-built digital holographic imaging system can reach 80 μm.

Experimental observation of Ag nanowire scattering illuminated by evanescent wave

Ag nanowires are not only a good surface plasmon waveguide, but also a fabulous converter to transfer a propagating wave into a bonded surface wave and vice versa. In this paper, we investigate the scattering properties of single Ag nanowire illuminated by evanescent wave. Since the Ag nanowire can be regarded as a dipole radiator chain in p-polarized evanescent illumination, the wide-field microscopic image of the scattering field can be well explained by diffraction integration in the deep Fresnel region. Moreover, the scattering of a v-shaped Ag nanowire is also investigated in evanescent wave illumination. Because of the orientation-dependent scattering of the Ag nanowire, the scattering field beneath the nanowire can either intercross or not, depending on the propagating direction of the incident evanescent wave, which is observed by a scanning confocal microscope in the z-scanning mode. The interference between the intercrossing scattering waves result in a non-diffracted beam and the direction of the generated non-diffracted beam can be controlled as well.

Finite-difference time-domain analysis of hydrogenated amorphous silicon and aluminum surface plasmon waveguides

The large majority of surface plasmon resonance (SPR)-based devices use noble metals, namely gold or silver, in their manufacturing process. These metals present low resistivity, which leads to low optical losses in the visible and near-infrared spectrum ranges. Gold shows high environmental stability, which is essential for long-term operation, and the lower stability of silver can be overcome through the deposition of an alumina layer, for instance. However, their high cost is a limiting factor if the intended target is large-scale manufacturing. This work considers a cost-effective approach through the selection of aluminum as the plasmonic material and hydrogenated amorphous silicon instead of its crystalline counterpart. This SPR structure relies on Fano resonance to improve its response to refractive index deviations of the surrounding environment. Fano resonance is highly sensitive to slight changes of the medium, hence the reason we incorporated this interference phenomenon in the proposed sensing structure. We report the results obtained when conducting finite-difference time-domain algorithm-based simulations on this metal–dielectric–metal structure when the active metal is aluminum, gold, and silver. Then, we evaluate their sensitivity, detection accuracy, and resolution. The obtained results for our proposed sensing structure show good linearity and similar parameter performance as the ones obtained when using gold or silver as plasmonic materials.

Low detection limits using sandwich and inhibition assays on long-range surface plasmon waveguide biosensors

A long-range surface plasmon polariton waveguide composed of a gold stripe embedded in CYTOP with an etched microfluidic channel has been used as a label-free real-time biosensor to demonstrate enhanced assay formats capable of very low detection limits. Specifically, sandwich and inhibition (competitive) assays were developed and demonstrated using Bovine Serum Albumin (BSA) and anti-BSA produced in rabbit as a model bio-specific pair. Carbodiimide coupling to a self-assembled COOH-terminated alkanethiol monolayer on the gold stripe was used to immobilize biomaterial to its surface. The optical output power from the biosensor was measured continuously over time and converted into surface mass density. Titration curves were extracted for both immunoassays. We demonstrate that protein concentrations in solution of 10 pg/ml can be detected with a signal-to-noise ratio of 20 using this new optical biosensor technology.

Design and Optimization of a Graphene Modulator Based on Hybrid Plasmonic Waveguide with Double Low-Index Slots

Graphene modulators based on surface plasmonic waveguides enable a strong interaction between light and graphene because great electric field enhancement occurs in the sub-wavelength region. However, a tight field confinement will cause a large metal absorption of light. Thus, graphene modulator base on hybrid plasmonic waveguide has a tradeoff between the propagation loss and the modulation depth. Here, we achieved a good balance between them by designing and optimizing an electro-optic modulator based on hybrid plasmonic waveguide with four graphene layers. The structure of the waveguide is metal/insulator/Si/insulator/metal. The modulation depth and the propagation loss of the modulator are 0.524 and 0.05 dB/μm respectively, which make a relatively high figure of merit about 10.5. Also the obtained modulation bandwidth and power consumption are 150 GHz and 0.607 pJ/bit, respectively.