Silver Waveguides Research Articles

A Triangle Hybrid Plasmonic Waveguide with Long Propagation Length for Ultradeep Subwavelength Confinement

Facing the problems of ohmic loss and short propagation length, the application of plasmonic waveguides is limited. Here, a triangle hybrid plasmonic waveguide is introduced, where a cylinder silicon waveguide is separated from the triangle prism silver waveguide by a nanoscale silica gap. The process of constant optimization of waveguide structure is completed and simulation results indicate that the propagation length could reach a length of 510 μm, and the normalized mode area could reach 0.03 along with a high figure of merit 3150. This implies that longer propagation length could be simultaneously achieved along with relatively ultra-deep subwavelength mode confinement due to the hybridization between metallic plasmon polarization mode and silicon waveguide mode, compared with previous study. By an analysis of fabrication errors, it is confirmed that this waveguide is fairly stable over a wide error range. Additionally, the excellent performance of this is further proved by the comparison with other hybrid plasmonic waveguides. Our work is significant to manipulate light waves at sub-wavelength dimensions and enlarge the application fields, such as light detection and photoelectric sensors, which also benefit the improvement of the integration of optical devices.

Numerical study of an efficient light focusing nano-coupler based on C-shaped waveguides

We present an FDTD simulation study of a new design of light focusing nano-coupler consisting of a tapered succession of C-shaped silver waveguides. Its operation is based on the use of the fundamental guided mode \(TE_{10}\). Thanks to the optimization of the structural design parameters, we have demonstrated numerically that this compact coupler enables a sub-wavelength light focusing with a transmission coefficient of 65% and a coupling efficiency of 77% that have higher values than the optimized designs reported in the literature. We also show that our structure is an efficient functional coupler at multiple wavelengths when used in a periodic grating as well as an isolated device. This could pave the way for the development of a new generation of metamaterials for guidance and detection applications.

Temporal coherence of surface plasmons in silver waveguides

Surface plasmon polaritons, in spite of being lossy, are known to preserve their coherence over long distances. In this paper, we investigate the coherence of surface plasmons propagating on a silver thin film surface using free-space optical Mach–Zehnder interferometry, where they are found to maintain their temporal coherence up to 80 µm, thus setting, for the first time to the best of our knowledge, a new limit. This can be important in applications integrating plasmonics with quantum information processing, where decoherence is a major challenge.

Optical Guided Modes with Arbitrary Propagation Constants in the Plane Array of Metallic Waveguides

The optical guided modes in the plane array of metallic cylindrical waveguides are considered. The case of the arbitrary propagation constant β is studied. Thus far, only the case β = 0 has been investigated in literature. We have revealed that just for β ≠ 0, the new branch of guided modes appears. The case of silver waveguides is investigated in details. It is found that, for sufficiently small β, the dispersion curve for the guided mode is located below the transmission window. We found the conditions for which the dispersion curve with β ≠ 0 is located completely within the transmission window. The multiple scattering formalism based on the expansion in the vector cylinder harmonics is employed. The cases of copper and gold waveguides are discussed briefly.

Hybrid plasmonic graphene modulator with buried silicon waveguide

We propose a low-loss broadband modulator by combining plasmonic effect with graphene to realize highly efficient modulation on the SOI (Silicon-On-Insulator) platform. Due to a hybrid plasmonic waveguide including buried silicon waveguide and silver waveguides, the fundamental mode is mainly confined in two single-layer graphene sheets, and the electric field vector is parallel to the graphene sheets ensuring the high efficient light absorption of graphene. The specific hybrid structure makes it easy for graphene transfer. Also, non-coplanar structure of silicon waveguide and silver waveguides provides simplified fabrication process and fabrication tolerance. The simulation results demonstrated that modulation bandwidth of 346 GHz is obtained, and the 3 dB modulation length is only 9.493μm. In addition, competitively low propagation loss of 0.85 dB was realized of the hybrid modulator.

Electroless silver plating of 3D printed waveguide components by peristaltic pump driven system

V-band waveguide components operating in 57–64 GHz ISM band is presented. Consumer-grade stereolithographic 3D printer is used to print these waveguide components with black-pigmented acrylate-based polymer. Electroless deposition of silver on these microwave components is achieved using an in-house system assembled with off-the-shelf components. This system is driven by a peristaltic pump, circling plating solution between silver bath and waveguide. Metal plated WR-15, 2-inch waveguide section offers average insertion coefficient of −0.35 dB. Trough waveguide section connected to rectangular waveguide through rectangular to trough waveguide transition is metal plated and offers average insertion coefficient of −1 dB. Silver deposited using the pump operated system offers potential of achieving comparable results as conventional dip coating technique.

Theory for anomalous refraction of visible light by the plane array of metallic waveguides

The effect of anomalous or negative angle refraction in the periodic systems of silver waveguides is investigated. This effect arises solely due to the waveguide interaction and requires the system of specific geometrical configuration. It is also shown that the propagation constant provides a flexible mechanism to manipulate the anomalous refraction. We employ the multiple scattering formalism based on the exact solution of the Maxwell equations for a single waveguide problem. Also the method based on the lattice sum transformation into a fast convergent series is involved. This technique dramatically decreases the time necessary for performing the numerical simulations and increases the accuracy of the computational process. It is shown that all the directions, which the periodic system is possible to radiate, can be obtained beforehand, i.e. analytically, without numerical simulations. The latter ones are needed to determine energy the flux going into each of those directions.

Silver-based surface plasmon waveguide for terahertz quantum cascade lasers.

Terahertz-frequency quantum cascade lasers (THz QCLs) based on ridge waveguides incorporating silver waveguide layers have been investigated theoretically and experimentally, and compared with traditional gold-based devices. The threshold gain associated with silver-, gold- and copper-based devices, and the effects of titanium adhesion layers and top contact layers, in both surface-plasmon and double-metal waveguide geometries, have been analysed. Our simulations show that silver-based waveguides yield lower losses for THz QCLs across all practical operating temperatures and frequencies. Experimentally, QCLs with silver-based surface-plasmon waveguides were found to exhibit higher operating temperatures and higher output powers compared to those with identical but gold-based waveguides. Specifically, for a three-well resonant phonon active region with a scaled oscillator strength of 0.43 and doping density of 6.83 × 1015 cm-3, an increase of 5 K in the maximum operating temperature and 40% increase in the output power were demonstrated. These effects were found to be dependent on the active region design, and greater improvements were observed for QCLs with a larger radiative diagonality. Our results indicate that silver-based waveguide structures could potentially enable THz QCLs to operate at high temperatures.

Design of hybrid structure for fast and deep surface plasmon polariton modulation.

The electric and optical performance of different surface plasmon polariton (SPP) electric modulation structures have been investigated by comparing the response speed and modulation figures of merit (FoM). To overcome the capacitance limitation and improve the response speed, we proposed a novel silver-graphene-dielectric-graphene-semiconductor vertical structure. Semiconductor nano-waveguide is introduced to help reduce ohmic loss in silver waveguide and reflect the leaked optical field back, enhancing the modulation depth. Through optimization, a device with estimated modulation FoM of more than 70% and hundreds of GHz response speed and 3 dB bandwidth is designed, which may bring great improvement to previous optical modulators.

Propagating Surface Plasmon Polaritons: Towards Applications for Remote-Excitation Surface Catalytic Reactions.

Plasmonics is a well‐established field, exploiting the interaction of light and metals at the nanoscale; with the help of surface plasmon polaritons, remote‐excitation can also be observed by using silver or gold plasmonic waveguides. Recently, plasmonic catalysis was established as a new exciting platform for heterogeneous catalytic reactions. Recent reports present remote‐excitation surface catalytic reactions as a route to enhance the rate of chemical reactions, and offer a pathway to control surface catalytic reactions. In this review, we focus on recent advanced reports on silver plasmonic waveguide for remote‐excitation surface catalytic reactions. First, the synthesis methods and characterization techniques of sivelr nanowire plasmonic waveguides are summarized, and the properties and physical mechanisms of plasmonic waveguides are presented in detail. Then, the applications of plasmonic waveguides including remote excitation fluorescence and SERS are introduced, and we focus on the field of remote‐excitation surface catalytic reactions. Finally, forecasts are made for possible future applications for the remote‐excitation surface catalysis by plasmonic waveguides in living cells.

Electromagnetic Bloch-like oscillations in planar quasiperiodic metal-dielectric waveguide arrays

We investigate the spatial Bloch-like oscillations in planar double-period silver waveguide arrays. Three types of oscillation modes are obtained in the sixth-generation double-period structure at different incident position, namely positive oscillation mode, negative oscillation mode and breathing-wave–like oscillation mode. The period of the three types of oscillation modes increases when the incident wavelength is redshifted, while the period of the up-oscillation and down-oscillation of the breathing-wave–like oscillation mode decreases and increases, respectively, in the gradient sixth-generation double-period system.

Optical Gradient Waveguides in Photo-Thermo-Refractive Glass Formed by Ion Exchange Method

Photo-thermo-refractive (PTR) glasses are the class of polyfunctional materials that combine the properties of several monofunctional materials such as photo-refractive, laser, luminescent, and plasmonic ones. Based on PTR glasses, various diffractive holographic elements and photonic devices were developed in both the volume and fiber versions. In this paper, the fabrication of optical planar waveguides on PTR glass by low-temperature ion exchange is reported for the first time. Planar waveguides were fabricated through substituting the sodium ions in glass by silver, potassium, rubidium, and cesium ones from the nitrate melts. The silver waveguides were shown to have the largest depth (27 μm) and reveal no birefringence. For the silver waveguides, an increase in the refractive index is caused by differences in the polarizabilities of cations exchanged. The maximum increment of the refractive index was observed in the cesium waveguides (0.0512). An increase in the refractive index and also appearing the birefringence in potassium, rubidium, and cesium waveguides are found to be due to the compressive mechanical stresses and their relaxation. The potentialities of the ion exchange technology for fabricating, in PTR glasses, planar gradient waveguides with low losses (0.5 dB/cm) are demonstrated, the potentialities extending the application field of PTR glasses in photonics.

Design and study of nano‐plasmonic couplers using aluminium arsenide and alumina

A theoretical study of nano-plasmonic couplers constructed using aluminium arsenide (AlAs) and alumina (Al2O3) is presented. The analysis has been done using the finite difference time domain technique. The dependence of coupling efficiency on the width of the air layer of silver–air–silver waveguide has been investigated to determine the optimal width of air. Coupling efficiency with the variation in input signal wavelength, reflection coefficient and return loss have been calculated numerically in order to characterise the performance of AlAs and Al2O3 as nano-plasmonic couplers. The resonant peaks have also been obtained for both AlAs and Al2O3. The couplers provide appreciable performance at 1550 nm wavelength and have simple rectangular shape with no tapering which provides advantage in the fabrication process. It also offers broadband operation.

Terahertz wave transmission in flexible polystyrene-lined hollow metallic waveguides for the 25-5 THz band

A low-loss and low-dispersive optical-fiber-like hybrid HE₁₁ mode is developed within a wide band in metallic hollow waveguides if their inner walls are coated with a thin dielectric layer. We investigate terahertz (THz) transmission losses from 0.5 to 5.5 THz and bending losses at 2.85 THz in a polystyrene-lined silver waveguides with core diameters small enough (1 mm) to minimize the number of undesired modes and to make the waveguide flexible, while keeping the transmission loss of the HE₁₁ mode low. The experimentally measured loss is below 10 dB/m for 2 < ν < 2.85 THz (~4-4.5 dB/m at 2.85 THz) and it is estimated to be below 3 dB/m for 3 < ν < 5 THz according to the numerical calculations. At ~1.25 THz, the waveguide shows an absorption peak of ~75 dB/m related to the transition between the TM₁₁-like mode and the HE₁₁ mode. Numerical modeling reproduces the measured absorption spectrum but underestimates the losses at the absorption peak, suggesting imperfections in the waveguide walls and that the losses can be reduced further.

Focusing properties of a tapered hollow silver waveguide

We numerically demonstrate a kind of tapered hollow silver waveguide for optically guiding and focusing of light through finite-difference time-domain (FDTD) simulations. The results of numerical simulation reveal that the tapered hollow silver waveguide can efficiently guide and focus a laser light to a tiny, highly localized beam spot of 1 μm diameter. The physical mechanism of the cone-focused laser light is explored. The influence of incident angle and waveguide geometry on the focusing properties is also discussed. The results obtained here might have important reference value for applications in tapered optics, and designing the optimum cone shape for fast ignition and generating high energy charged particles.

Application of PVD silver for integrated microwave passives in silicon technology

High quality broadband passives are needed to implement MMIC/MIC in silicon. This paper discusses potential benefits of silver metallization to boost the performance of the integrated passive components. Silver is chosen because this metal offers the highest possible electrical conductivity at room temperature. A PVD process was used for silver deposition because this technique meets the requirements of high purity and surface quality. Electromigration, electrochemical migration and agglomeration are not expected to be a problem in silver microwave passives due to the coarse dimensions and low operating current densities encountered in these structures. Ag and Cu coplanar waveguides on silicon substrates were designed, fabricated and tested. Silver waveguides showed a 2–3dB/cm improvement in attenuation over copper devices at 40GHz.

Changes in electrical conductance of hydrogenated amorphous silicon deposited on optical waveguides in glass

A study of electrical conductance of hydrogenated amorphous silicon (a-Si:H) films deposited on optical waveguides in a soda-lime glass (SLG) substrate is carried out, from the viewpoint of electrical instability of a-Si:H caused by the penetration of Na ions from the glass into the film. The optical waveguides were prepared by K+–Na+ or Ag+–Na+ ion exchange using thermal or field-assisted methods. The effective thickness of optical waveguides was of several micrometers. The obtained results show that in the case of a-Si:H film deposited on silver waveguide there is a dependence of electrical conductance on measurement duration, if strongly weakened as compared with film deposited on the original SLG substrate. The a-Si:H films deposited on potassium waveguide and on Na-extracted surface are as stable, as the referent samples with Corning 7059 (Na-free) glass substrate.

Analysis of Mode Conversion at Discontinuities between K+–Na+ and Ag+–Na+ Ion-Exchanged Waveguides in Glass

The analysis of mode conversion caused by discontinuity between K+–Na+ and Ag+–Na+ ion-exchanged waveguides in glass is carried out. The experimentally obtained refractive index profiles of the waveguide regions are considered. Structures consisting of single-mode potassium and 2-, 5-, or 11-mode silver waveguides are studied using the least squares boundary residual method. The power coefficients of light propagation through the interface between the two waveguide regions are evaluated. In the case of structure consisting of a single-mode potassium waveguide and 11-mode silver one, the power transmittance coefficient for the lowest-order transverse electric mode reaches a value of 98.9%.

Bending losses and beam profiles of zinc selenide-coated silver waveguides for carbon dioxide laser light

Circular hollow waveguides with an interior silver layer and an inner coating of zinc selenide are fabricated. The fabrication process for rf sputtering of zinc-selenide and silver, electroplating of nickel, and etching of a polyimide mandrel is described in detail. As a result of the measurements of transmission losses, the waveguides show a remarkably low-loss property when they are bent. Further, output beam profiles of the straight and the bent waveguide are investigated, and it is shown that the waveguide with a smaller diameter exhibits a well-shaped beam profile without sacrificing the low-loss property.

Development of tapered glass coupling waveguides for source radiation input into multichannel LiNbO/sub 3/ modulator arrays

The investigation shows that a tapered glass optical waveguide provides an effective coupling device for introducing and directing radiation from a semiconductor laser source (e.g., GaAs) into a multichannel Ti:LiNbO/sub 3/ optical array modulator. A tapered planar waveguide was produced by RF sputter depositing Corning 7059 glass on Corning 2947 microscope slides which were used as substrates. The waveguide thickness tapers from 2 to 1 mu m over a waveguide propagation distance of 1 cm. In addition, graded index silver indiffused waveguides suitable for couplers were also produced in this investigation by indiffusing silver ions into Corning 2947 microscope slides. An inverse WKB analysis of these graded index waveguides was used to explore the refractive index profile. Microprobe X-ray wavelength-dispersive analysis measurements of the silver concentration profile show that the deep multimode silver guides have an index profile that is more parabolic in shape than Gaussian. Shallow, single-mode, or two-mode silver waveguides appear to have a complementary error function index profile.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>