Long-range Plasmon Waveguide Research Articles

Design of long-range hybrid plasmonic waveguides with graphene-based electrical tuning of propagation length

Design of long-range hybrid plasmonic waveguides with graphene-based electrical tuning of propagation length

Ultracompact temporal integrator using graphene-based long-range hybrid plasmonic waveguides.

A microdisk-resonator add-drop temporal integrator, composed of a long-range hybrid plasmonic waveguide, with graphene as the central layer, is proposed for the first time, to the best of our knowledge. The integrator benefits from a considerable integration time of ∼5.55ps, which is about 11 times longer than our previously proposed plasmonic integrator, and also is fairly comparable with the integration time of a microring-based integrator with a ring radius of 47.5 µm. Based on 3D-finite-difference time-domain simulations, the integrator, with a significantly compact footprint of ∼4µm×3µm, shows the FWHM of 53 GHz. The presented graphene-based temporal integrator, with a highly miniaturized footprint and satisfactory integration time, may find applications in ultrafast plasmonic-based signal processing systems.

Quarter-Millimeter Propagating Plasmons in Thin-Gold-Film-Based Waveguides for Visible Spectral Range

A series of long-range plasmonic waveguides based on a thin three-layer Al2O3/gold/Al2O3 film operating in the visible spectral range have been studied experimentally and theoretically. For long-range plasmonic waveguides having identical structure but different lengths, the propagation length of plasmonic waves was determined to be $\text{250} \pm \text{15} \mu {\text{m}}$ at $\lambda = \text{765} {\text{nm}}$ and was in a very good agreement with the theoretical value obtained through numerical modeling. The demonstrated propagation length is the highest one for the gold film-based plasmonic waveguides described in the literature for a uniform (non-photonic-crystal) substrate in the UV, visible, and near IR (up to $\text{1} \mu {\text{m}}$ ) spectral ranges, which is due to high technological quality of the fabricated waveguides and optimized three-layer structure. The proposed waveguides could find applications in optical interconnects and guided-wave optical sensors.

Characterization of long-range plasmonic waveguides at visible to near-infrared regime

Long-range surface plasmon polariton waveguides composed with thin gold stripes embedded in SU-8 polymer cladding with various stripe widths were fabricated. Material properties of the polymer cladding layer, gold thin film, and the device structures were discussed. Optical properties based on modal propagation were characterized at visible to near-infrared wavelengths. The measured propagation losses of waveguide widths from 3 to 9 μm at 633, 785, and 1550 nm are 7.5-18.8, 6.8-12.5, and 1.9-3.9 dB/mm, respectively. Guiding mode properties such as overlap integrals between the simulated and the measured fields and the polarization extinction ratios of the waveguides with different stripe widths were investigated at the telecommunication wavelength. Good accordance between the measurement and simulation results was presented.

Long-range all-dielectric plasmonic waveguide in mid-infrared

In this paper, we introduce the modal analysis of hybrid plasmonic waveguides in the mid-infrared region. In our plasmonic waveguide, the metal is replaced by doped silicon allowing for low-loss, subwavelength confinement of optical modes that can be easily integrated with standard silicon technology. In addition, our waveguide characteristics can be easily tuned along the wavelength by changing the doping concentration of the doped silicon layer. Manipulating the dimensions of the waveguide, we can effectively change the propagation distance and the mode confinement. The simulation results show a maximum propagation distance of 220 µm and modal area of 5–500 times smaller than the diffraction limit area. Moreover, the wavelength dependence of the effective indices of the hybrid structures modes around the doped silicon resonance was investigated. Our results showed that our structures exhibit anomalous dispersion and can support slow and fast light. Also, a comparison has been made between our hybrid structure and the conventional insulator–metal–insulator (IMI) waveguide with metal replaced by our doped silicon. This comparison shows that our hybrid structure is a compromise between the modal area and the propagation distance of the IMI structures.

Magnetoplasmonic RF mixing and nonlinear frequency generation

We present the design of a magnetoplasmonic Mach-Zehnder interferometer (MZI) modulator facilitating radio-frequency (RF) mixing and nonlinear frequency generation. This is achieved by forming the MZI arms from long-range dielectric-loaded plasmonic waveguides containing bismuth-substituted yttrium iron garnet (Bi:YIG). The magnetization of the Bi:YIG can be driven in the nonlinear regime by RF magnetic fields produced around adjacent transmission lines. Correspondingly, the nonlinear temporal dynamics of the transverse magnetization component are mapped onto the nonreciprocal phase shift in the MZI arms, and onto the output optical intensity signal. We show that this tunable mechanism can generate harmonics, frequency splitting, and frequency down-conversion with a single RF excitation, as well as RF mixing when driven by two RF signals. This magnetoplasmonic component can reduce the number of electrical sources required to generate distinct optical modulation frequencies and is anticipated to satisfy important applications in integrated optics.

Long-range plasmonic waveguides with hyperbolic cladding.

We study plasmonic waveguides with dielectric cores and hyperbolic multilayer claddings. The proposed design provides better performance in terms of propagation length and mode confinement in comparison to conventional designs, such as metal-insulator-metal and insulator-metal-insulator plasmonic waveguides. We show that the proposed structures support long-range surface plasmon modes, which exist when the permittivity of the core matches the transverse effective permittivity component of the metamaterial cladding. In this regime, the surface plasmon polaritons of each cladding layer are strongly coupled, and the propagation length can be on the order of a millimeter.

CMOS-Compatible Long-Range Dielectric-Loaded Plasmonic Waveguides

CMOS-compatible long-range dielectric-loaded plasmonic waveguides featuring long propagation lengths and strong mode confinements are designed and studied using the finite-element method. The waveguide composition includes a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ridge on the top of a thin metal stripe deposited on a silicon-on-insulator (SOI) wafer with a thin top SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer produced by thermal oxidation. All the materials chosen in the design are compatible with complementary metal-oxide-semiconductor technology and can be integrated with plasmonic, electronic and photonic components. Influence of various waveguide parameters on the waveguide characteristics is analyzed, including the thicknesses of the Si layer and the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers, the dimension of the ridge, as well as the parameters of the metal stripe. It is found that, at the telecom wavelength of 1.55 μm, the propagation length of CMOS-plasmonic waveguides can reach 1.07 mm with a lateral mode confinement of ~1.18 μm and 4.43 mm with a lateral mode width of ~2.32 μm. The bending loss and coupling length are both calculated to evaluate the applicability of the proposed device for high density integration and a figure of merit is proposed to show the tradeoff between the propagation length and the lateral mode width in the application of plasmonic devices.

Enhanced Optical Forces by Hybrid Long-Range Plasmonic Waveguides

Compared with optical resonant structures, current plasmonic waveguides have the advantage of enhancing optical forces in a broad range of wavelengths, but the enhancement can only be maintained for several dozens of microns at 1.55 μm. Here, a hybrid long-range plasmonic waveguide, consisting of two identical dielectric nanowires symmetrically placed on each side of a thin metal film, is proposed for optical forces. Strong optical coupling between the dielectric waveguide mode and long-range plasmonic mode leads to enhanced optical forces on the dielectric nanowire at low input optical power due to the deep subwavelength optical energy confinement. The enhancement can be maintained for distances of 1~2 orders of magnitude larger than that of previous plasmonic waveguides. The deep subwavelength optical confinement as well as enhanced field gradient also allows efficient trapping of single nanoscale particle, while the smaller propagation loss ensures a much larger trapping region at the same input optical power. The present results enable the potential applications of precisely controlling the positions of dielectric nanowires as well as manipulating a single nanoparticle such as a biomolecule and one quantum dot.

Coupling Characteristic of a Novel Hybrid Long-Range Plasmonic Waveguide Including Bends

In this paper, the modal analysis of a novel design of a hybrid long-range plasmonic waveguide is introduced and analyzed using the full-vectorial finite difference method. The suggested design has high index material as a cap to reduce the propagation loss and optimum bending radius as well. The analyzed parameters are the real effective index and propagation loss. In addition, the bending analysis of the reported design is introduced. The coupling is performed between three different waveguides: straight dielectric waveguide, straight hybrid long-range plasmon waveguide, and uniformly bent hybrid one.

Directional coupling in long-range dielectric-loaded plasmonic waveguides

Directional couplers (DCs) based on long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) operating at telecom wavelengths are studied both numerically and experimentally. The investigated LR-DLSPPWs are formed by ~1.2-µm-high and 1-µm-wide polymer ridges fabricated atop of 15-nm-thick and 500-nm-wide gold stripes supported by a 288-nm-thick Ormoclear polymer deposited on a low-index (n(s) ≈1.34) layer of Cytop. DC structures consisting of sine-shaped S-bends (having an offset of ~10 µm over a distance of ~20 µm) and ~100-µm-long parallel LR-DLSPPWs with a center-to-center separation of 2 µm are characterized using scanning near-field microscopy. The experimentally obtained values of the propagation length (~400 µm), S-bend loss (~4 dB) and coupling length (~100 µm) are found in good agreement with the numerical simulations, indicating a significant potential of LR-DLSPPWs for the realization of various plasmonic components.

Long-Range Hybrid Plasmonic Slot Waveguide

We propose and design a silicon-based long-range hybrid plasmonic slot (LRHPS) waveguide. The waveguide structure consists of a thin metal film (silver) inserted into a vertical low-index slot [filled with silicon nanocrystal (Si-nc)] between two high-index dielectrics (silicon), forming two nanoscale low-index Si-nc slot regions. The modes are confined within the two vertical regions. The designed LRHPS waveguide takes advantages of both traditional long-range surface plasmon polariton waveguide and hybrid plasmonic waveguide. The combined effects of long-range surface plasmon polaritons and discontinuity of electric field at the interface between two dielectrics with high-contrast refractive index enable a millimeter-scale propagation range together with a subwavelength mode confinement for potential high-density nanophotonic integration. The resultant quasi-TE mode properties of LRHPS waveguide, including long-range hybrid (LRH) mode and short-range hybrid (SRH) mode, are analyzed, showing a long propagation length up to 14.55 mm (corresponding to a low loss of $3\times 10^{-4} \hbox{dB}/\mu\hbox{m}$ ) with a slot size of 150 nm $\times$ 200 nm. Normalized power and intensity are also calculated, indicating tight mode confinement within subwavelength low-index slot regions. Moreover, nonlinearity and chromatic dispersion are also studied. Due to the design freedom of double-slot structure, a high nonlinearity of $7.82 \times 10^{6} \hbox{W}^{-1}\hbox{km}^{-1}$ and a low chromatic dispersion of $-$ 28.29 ps/nm/km at 1550 nm are achieved, implying possible applications in efficient nonlinear optical signal processing.

An efficient directional coupling from dielectric waveguide to hybrid long-range plasmonic waveguide on a silicon platform

The silicon-based three-dimensional hybrid long-range plasmonic waveguide not only supports long-range propagation distance (~mm) but also has an ultra-small modal area (~10−2 μm2) at 1.55 μm. Here, we propose a directional coupler for effective coupling from a dielectric slab-waveguide to the hybrid plasmonic waveguide on a silicon platform. Our simulation results show that the coupler is able to excite hybrid long-range plasmonic mode with short coupling length, low insertion loss, and high extinction ratio. With the arm separation of 0.3 μm, the coupling length can be made 5.2 % of the propagation length of the hybrid plasmonic waveguide, while the insertion loss and extinction ratio are −0.12 and 22.4 dB, respectively. This coupler offers the potential applications in signal routing between the hybrid long-range plasmonic waveguide and dielectric waveguide in the photonic integrated circuits.

A hybrid long-range plasmonic waveguide with sub-wavelength confinement

A symmetric three dielectric layer stack with a low–high–low dielectric constant distribution is proposed to replace the conventional single dielectric layer on both sides of the thin metal layer to guide the long range surface plasmonic polaritons. Our simulation result shows that the new design is capable of providing more compact modal confinement as well as low loss transmission due to the coupling between the plasmonic and dielectric waveguide modes.

A Silicon-Based 3-D Hybrid Long-Range Plasmonic Waveguide for Nanophotonic Integration

Decreasing the widths and thicknesses of thin metal stripes can effectively increase the propagation distance of long-range surface plasmon polaritons, but at the cost of significant reduction on the overall mode confinement, which fundamentally limits the packing density in nanophotonic integration. By utilizing the coupling between the dielectric waveguide and plasmonic modes, we propose a silicon-based 3-D hybrid long-range plasmonic waveguide that not only supports long-range propagation, but also has compact modal size. Our simulation result shows that a propagation distance of 696 μm with an ultrasmall modal area of 0.0013 μm2 can be simultaneously achieved at 1.55 μ m.

Simulation of complex plasmonic circuits including bends

Using a finite-element, full-wave modeling approach, we present a flexible method of analyzing and simulating dielectric and plasmonic waveguide structures as well as their mode coupling. This method is applied to an integrated plasmonic circuit where a straight dielectric waveguide couples through a straight hybrid long-range plasmon waveguide to a uniformly bent hybrid one. The hybrid waveguide comprises a thin metal core embedded in a two-dimensional dielectric waveguide. The performance of such plasmonic circuits in terms of insertion losses is discussed.

Theoretical Analysis of Long-Range Dielectric-Loaded Surface Plasmon Polariton Waveguides

A structure for guiding surface plasmon polaritons (SPPs) over millimeter distances with tight mode confinement is presented and analyzed in detail using the finite element method. The proposed long-range plasmonic waveguide consists of a dielectric ridge deposited on a narrow metal stripe supported by a dielectric buffer layer covering a low-index substrate. It is shown that such an asymmetric waveguide structure can be designed to support a long-range symmetric SPP mode, featuring a propagation length of ≈ 3.1 mm and lateral mode width of ≈ 1.6nμ m at telecom wavelengths of ~ 1.55 μm. Our analysis covers a broad spectrum of parameters: ridge dimensions, buffer layer parameters (refractive index and thickness), as well as metal stripe width, considering in detail the underlying mechanisms of SPP waveguiding in this configuration. The suggested configuration offers easy connection to electrodes enabling, e.g., thermo-optic or electro-optic control, and is technologically simple, making fabrication possible using only a few lithography steps. Additionally, a new figure of merit is introduced, which is related to a number of plasmonic components allowed for a given mode confinement and propagation loss, aiming thereby at the evaluation of the application potential of plasmonic waveguides.

Directional coupling between dielectric and long-range plasmon waveguides

We have designed, fabricated and characterized integrated directional couplers capable of converting the mode of an optical dielectric waveguide into a long-range plasmon propagating along a thin metal stripe. We demonstrate that the coupling between the two types of waveguides is generally very weak unless specific conditions are met. This sensitivity could be potentially exploited in sensing applications or for developing novel active photonic components.