Optical bistability in metal-insulator-metal plasmonic Bragg waveguides with Kerr nonlinear defects

We numerically investigate the characteristics of the defect mode and the nonlinear effect of optical bistability in metal-insulator-metal (MIM) plasmonic Bragg grating waveguides with Kerr nonlinear defects. By means of finite-difference time-domain simulations, we find that the defect mode peak exhibits a blueshift and height-rise by enlarging the width of the defect layer, and it has a redshift and height-fall with the increase of the dielectric constant of defect layer. Obvious optical bistability is obtained in our waveguides with a length of less than 2 μm. The results show that our structure could be applied to the design of all-optical switching in highly integrated optical circuits.     

Three-wave approximation for the modal field inside high-index dielectric rods of hybrid plasmonic waveguides

Abstract

An approximate three-wave model is suggested for describing the modal field inside the high-index dielectric rod of a hybrid plasmonic waveguide. An evanescent wave, an uniform wave and a propagating wave are considered along the direction perpendicular to the metal surface. The superposition of these three waves forms the modal field inside the high-index rod. Through numerical tests, we find that this model is highly valid for a large range of waveguide sizes.     

Light propagation in curved silver nanowire plasmonic waveguides

Plasmonic waveguides made of metal nanowires (NWs) possess significant potential for applications in integrated photonic and electronic devices. Energy loss induced by bending of a NW during light propagation is critical in affecting its performance as a plasmonic waveguide. We report the characterization of the pure bending loss in curved crystalline silver NW plasmonic waveguides by decoupling the energy loss caused by bending and propagation. The energy attenuation coefficiency due purely to bending was also determined, which exhibited an exponential relationship with the bending radius. Finite-difference-time-domain (FDTD) methods were utilized for theoretical simulations, which matched the experimental results well.     

Integration of photonic and silver nanowire plasmonic waveguides

Future optical data transmission modules will require the integration of more than 10,000 x 10,000 input and output channels to increase data transmission rates and capacity. This level of integration, which greatly exceeds that of a conventional diffraction-limited photonic integrated circuit, will require the use of waveguides with a mode confinement below the diffraction limit, and also the integration of these waveguides with diffraction-limited components. We propose to integrate multiple silver nanowire plasmonic waveguides with polymer optical waveguides for the nanoscale confinement and guiding of light on a chip. In our device, the nanowires lay perpendicular to the polymer waveguide with one end inside the polymer. We theoretically predict and experimentally demonstrate coupling of light into multiple nanowires from the same waveguide, and also demonstrate control over the degree of coupling by changing the light polarization.     

Driving plasmonic nanoantennas with triangular lasers and slot waveguides

Plasmonic nanoantennas can generate high-intensity electric fields in a very small area. However, being passive devices, they need to be excited by external laser sources. The excitation of nanoantennas by semiconductor lasers can be inefficient and a significant amount of light may return back to the laser source after being scattered by the nanoantenna. In this paper, it is shown that the amount of light being returned to the semiconductor laser can be reduced by using dielectric slot waveguides. These waveguides can transport the incident light to the nanoantennas, but the amount of nondirectional back-scattered light is reduced after propagation through the slot waveguide.     

Optical waveguides on polysilicon-on-insulator

Optical waveguide structures have been fabricated on polysilicon-on-insulator. Structural and optical properties of the waveguides are studied by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and transmission measurements. Reasons for the waveguide loss are discussed. It is found that surface roughness can be responsible for a waveguide loss of more than 60 dB cm^–1 and that additional loss mechanisms probably exist. Methods of smoothing the surface are discussed.     

Optical spin Hall effects in plasmonic chains

Observation of optical spin Hall effects (OSHEs) manifested by a spin-dependent momentum redirection is presented. The effect occurring solely as a result of the curvature of the coupled localized plasmonic chain is regarded as the locally isotropic OSHE, while the locally anisotropic OSHE arises from the interaction between the optical spin and the local anisotropy of the plasmonic mode rotating along the chain. A wavefront phase dislocation was observed in a circular curvature, in which the dislocation strength was enhanced by the locally anisotropic effect.     

Nanorice: a hybrid plasmonic nanostructure

We have designed and fabricated a new hybrid nanoparticle that combines the intense local fields of nanorods with the highly tunable plasmon resonances of nanoshells. This dielectric core-metallic shell prolate spheroid nanoparticle bears a remarkable resemblance to a grain of rice, inspiring the name "nanorice". This geometry possesses far greater structural tunability than either a nanorod or a nanoshell, along with much larger local field intensity enhancements and far greater sensitivity as a surface plasmon resonance (SPR) nanosensor than any dielectric-metal nanostructures reported previously. Invoking the plasmon hybridization picture allows us to understand the plasmon resonances of this geometry, as arising from a hybridization of the primitive plasmons of a solid spheroid and an ellipsoidal cavity inside a continuous metal.     

Far-infrared properties of hybrid plasmonic geometries

Plasmonic structures made of periodically arranged metallic rings integrated into subwavelength holes are investigated at the far-infrared terahertz frequencies. The emergence and the interplay of various resonances sustained by such plasmonic samples are elucidated. To reveal a coherent physical picture, relevant dimensions of the samples are modified and their impact on the resonance properties is analyzed. The experimental work is fully supported by numerical simulations. The understanding of the interplay of various resonances will foster applications which require plasmonic substrates to exhibit simultaneously resonances at well-defined frequencies and line widths.     

Optical near-field mapping of plasmonic nanoprisms

The optical local-field enhancement on nanometer length scales provides the basis for plasmonic metal nanostructures to serve as molecular sensors and as nanophotonic devices. However, particle morphology and the associated surface plasmon resonance alone do not uniquely reflect the important details of the local field distribution. Here, we use interferometric homodyne tip-scattering near-field microscopy for plasmonic near-field imaging of crystalline triangular silver nanoprisms. Strong spatial field variation on lengths scales as short as 20 nm are observed sensitively depending on structural details and environment. The poles of the dipole and quadrupole plasmon modes, as identified by phase-sensitive probing and calculations performed in the discrete dipole approximation (DDA), reflect the particle symmetry. Together with the observation that the largest enhancement is not necessarily found to be associated with the tips of the nanoprisms, our results provide critical information for the selection of particle geometries as building blocks for plasmonic device applications.     

Propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides

Abstract

In this study, we numerically analyse the propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides (TGPWs). Using the finite element method, the waveguide parameters such as modal field distribution and complex propagation constant are calculated for different geometrical parameters over a wide spectral range. Moreover, using a kind of active medium with appropriate gain, the required gains for lossless propagation are obtained. Results show that the propagation properties and dispersion characteristics of the waveguide along with the value of required gain for achieving lossless propagation can be well controlled by adjusting the geometrical parameters of the waveguide. The simulation results indicate that the calculated gain values are obtainable using the existing semiconductor technology such as InGaAsP–InGaAlAs multi-quantum well and InAs/GaAs quantum dot active medium at the wavelength of 1550 nm. The strong mode confinement of the TGPWs can be used for achieving strong nonlinear effects. Furthermore, due to optical energy confinement in nanoscale, optical nanofocusing devices based on TGPWs are attainable. TGPWs can be utilized in the field of nanotechnology to fulfil the photonic devices integration.     

All-optical control of a single plasmonic nanoantenna-ITO hybrid

We demonstrate experimentally picosecond all-optical control of a single plasmonic nanoantenna embedded in indium tin oxide (ITO). We identify a picosecond response of the antenna-ITO hybrid system, which is distinctly different from transient bleaching observed for gold antennas on a nonconducting SiO(2) substrate. Our experimental results can be explained by the large free-carrier nonlinearity of ITO, which is enhanced by plasmon-induced hot-electron injection from the gold nanoantenna into the conductive oxide. The combination of tunable antenna-ITO hybrids with nanoscale plasmonic energy transfer mechanisms, as demonstrated here, opens a path for new ultrafast devices to produce nanoplasmonic switching and control.     

Optical properties of dual-core hollow waveguides

A new type of hollow glass waveguide has been fabricated that transmits radiation from visible to infrared wavelengths with low loss. The broadband transmission is achieved with a structure consisting of two distinct core regions; a silica annulus for transmission of wavelengths from 0.3 to 2.0 μm and a hollow core for transmission from 2.0 to 12.0 μm. Losses in the silica core at 633 nm are 0.3 dB/m. Losses in the 575-μm bore hollow core at 10.6 μm are 0.6 dB/m. Bending loss is negligible for radiation transmitted in the solid silica core, whereas the hollow guide loss exhibits a 1/R dependence. The dual-core waveguide can transmit broadband radiation, is rugged and flexible, and therefore, is a good candidate for medical or sensor applications.     

Optical properties of strip-loaded Er-doped waveguides

Er-doped waveguides operating in a strip-loaded configuration combine low losses with flexibility of design and ease of fabrication. A composite waveguide was fabricated by patterning a SiON strip on a film of sputtered Er-doped filter glass. Spontaneous emission of light in 1520–1570 nm band has been observed. We have also observed up to 3 dB enhancement of transmitted signal with 45 mW of launched 975 nm pump light in a waveguide 1.2 cm long.     

Optical impedance matching using coupled plasmonic nanoparticle arrays

Silver nanoparticle arrays placed on top of a high-refractive index substrate enhance the coupling of light into the substrate over a broad spectral range. We perform a systematic numerical and experimental study of the light incoupling by arrays of Ag nanoparticle arrays in order to achieve the best impedance matching between light propagating in air and in the substrate. We identify the parameters that determine the incoupling efficiency, including the effect of Fano resonances in the scattering, interparticle coupling, as well as resonance shifts due to variations in the near-field coupling to the substrate and spacer layer. The optimal configuration studied is a square array of 200 nm wide, 125 nm high spheroidal Ag particles, at a pitch of 450 nm on a 50 nm thick Si(3)N(4) spacer layer on a Si substrate. When integrated over the AM1.5 solar spectral range from 300 to 1100 nm, this particle array shows 50% enhanced incoupling compared to a bare Si wafer, 8% higher than a standard interference antireflection coating. Experimental data show that the enhancement occurs mostly in the spectral range near the Si band gap. This study opens new perspectives for antireflection coating applications in optical devices and for light management in Si solar cells.     

Optical channel waveguides by copper ion-exchange in glass

Optical channel waveguides have been obtained by electric?field?assisted diffusion of copper films on glass substrates. The mode indices of these channel waveguides were determined with the prism?coupling technique, and the refractive?index profile of the waveguide was reconstructed from measurements of the near?field intensity distribution.     

Cylindrical hybrid plasmonic waveguide for subwavelength confinement of light

A novel cylindrical hybrid plasmonic waveguide is proposed to achieve subwavelength confinement of light. With a metal core surrounded by a silica layer and a silicon layer, the proposed cylindrical hybrid plasmonic waveguide can achieve a ring-structure mode profile at the operating wavelength (1550 nm). Most mode power locates in the silica layer with a nanoscale thickness (e.g., 50, 20, or even 5 nm), which is due to the effects of both a strong discontinuity of the normal component of the electric field at the silicon-silica interface and the exited surface plasmon wave at the silica-metal interface. Cylindrical hybrid plasmonic waveguides with different structure parameters are investigated and a relatively long propagation distance of tens of micrometers (or even hundreds of micrometers) is observed.     

Optical transduction of chemical forces

We describe a plasmonic crystal device possessing utility for optically transducing chemical forces. The device couples complex plasmonic fields to chemical changes via a chemoresponsive, surface-bound hydrogel. We find that this architecture significantly enhances the spectroscopic responses seen at visible wavelengths while enabling capacities for sensitive signal transduction, even in cases that involve essentially no change in refractive index, thus allowing analytical detection via colorimetric assays in both imaging and spectroscopic modes.     

Optical properties of small-bore hollow glass waveguides

Hollow glass waveguides with a 250-μm i.d. have been fabricated with a liquid-phase deposition technique that uses silica tubing as a base material. The losses of the 250-μm-bore guide measured at CO(2) laser wavelengths are as low as 2.0 dB/m. The straight losses for the hollow guides are in good agreement with theoretically predicted losses as a result of the nearly ideal structure of the guides. It is also shown that the guides have low bending losses, a nearly pure-mode delivery, and good high-power laser transmission. By proper design of the dielectric thickness, the guide is also able to deliver Er:YAG laser energy with a low loss of 1.2 dB/m for the 320-μm-bore waveguide. Because the hollow glass waveguide is very flexible and robust, it is quite suitable for medical applications.     

Optical biosensor based on hollow integrated waveguides

The first absorbance biosensor based on pure silicon hollow integrated waveguides is presented in this work. With the use of horseradish peroxidase (HRP) as a model recognition element, an enzymatic sensor for the measurement of hydrogen peroxide was fabricated, numerically simulated, and experimentally characterized. Waveguides with widths ranging from 50 to 80 microm, having a depth of 50 microm and lengths up to 5 mm were easily fabricated by just one photolithographic step. These were further modified by covalent immobilization of HRP using silanization chemistry. Simulation studies of the proposed approach showed a sensor linear behavior up to 300 microM H2O2 and a sensitivity of 2.7 x 10(-3) AU/microM. Experimental results were in good agreement with the simulated ones. A linear behavior between 10 and 300 microM H2O2, a sensitivity of 3 x 10(-3) AU/microM, and a signal-to-noise ratio around 20 dB were attained. Also, kinetic studies of the activity of the immobilized enzyme on the silicon waveguide surface gave an apparent Michaelis-Menten constant of 0.44 mM. The simple technology proposed in this work enables the fabrication of cost-effective, easy-to-use, miniaturized biosensor generic platforms, these being envisioned as excellent candidates for the development of lab-on-a-chip systems.