Nanoscale Optical Directional Coupler

Ultracompact optical directional coupler is one of the key elements for nanoscale optical networks and highly integrated optical circuits. Although the transverse size has been reduced down to subwavelength by exploiting plasmonic waveguides, the longitudinal size has remained yet on the micrometer-scale, which seems to be a fundamental limitation by the conventional configuration based on cross-talk coupling between two neighboring waveguides. We have proposed a novel conception of optical directional coupler based on loss-overcompensated resonant coupling between two plasmonic waveguides via an in-between gain-assisted nanocavity. The loss-overcompensated state can be achieved by adjusting pumping rate in the nanocavity. The validity of the proposed conception is confirmed by numerical simulations of a physical model with the deep-subwavelength planar footprint of 300 nm × 300 nm, THz bandwidth, and an exceptionally low energy consumption on the order of 0.1 fJ per signal pulse. To our knowledge, it is the first proposed ultrafast nanoscale four-port directional coupler.     

Combination of Surface Plasmon Polaritons and Subwavelength Grating for Polarization Beam Splitting

Plasmonics - A polarization beam splitter (PBS) based on the plasmonic subwavelength grating (PSWG) is proposed and investigated. The PBS is composed by a directional coupler with a PSWG as the...     

Polarization-Controlled Tunable Multi-focal Plasmonic Lens

A polarization-controlled tunable plasmonic lens which can generate different multi-focal combinations with exciting sources of left and right circular polarizations is proposed in this paper. Both position and intensity of each focal point can be adjusted by modulating the structure of the plasmonic lens. It is believed that the polarization-controlled tunable plasmonic multi-focal lens can be potentially used for optical switches and multi-channel couplers in future logic photonic and plasmonic systems.     

Coupling Between Silicon Waveguide and Metal-Dielectric-Metal Plasmonic Waveguide with Lens-Funnel Structure

Various photonic integrated components have been implemented by ultra-thin silicon-on-insulator (SOI) waveguides; therefore, it is desirable to couple ultra-thin SOI waveguides to plasmonic waveguides. In this paper, we present an ultra-thin SOI waveguide to a metal-dielectric-metal plasmonic waveguide based on a lens-funnel structure consisting of truncated Luneburg lens and metallic parabolic funnel. The lens is implemented by varying the guiding layer thickness. The effect of different parameters of the coupler’s geometry is studied using the finite-difference time-domain method. The 1.13-μm-long coupler improves the average coupling efficiency in the C-band from 66.4 to 82.1%. The numerical simulations indicate that the coupling efficiency is higher than 69% in the entire O, E, S, C, L, and U bands of optical communication.

     

Coherent-Controlled All-Optical Devices Based on Plasmonic Resonant Tunneling Waveguides

Plasmonics - In this study, the signal processing in three-port and four-port plasmonic coupler devices by coherently controlling the phases and amplitudes of launched surface plasmons is...     

High Transmission Efficiency of Opto-electronic Devices Using Active Hybrid Plasmonic Coupler

Plasmonics - This paper discusses modeling and optimizing the performance of hybrid plasmonic bidirectional coupler which is used as a basic building block in modeling high transmission efficiency...     

Exciting Surface Plasmons with Transformation Media

We present a way of exciting surface plasmon polaritons along non-patterned metallic surfaces by means of a flat squeezing slab designed with transformation optics. The slab changes the dispersion relation of incident light, enabling evanescent coupling to propagating surface plasmons. Unlike prism couplers, the proposed device does not introduce reflections at its input interface. Moreover, its compact geometry is suitable for integration. A feasible dielectric implementation of the coupler is suggested. Finally, we show that the angular response of the device can be engineered by using a non-uniform compression factor. As an example, we design a coupler with a half-power angular bandwidth 2.5 times higher than that of a conventional dielectric coupler.     

Plasmonic Coupler and Multiplexer/Demultiplexer Based on Nano-Groove-Arrays

Plasmonics - A novel plasmonic unidirectional coupler and its extension to a multiplexer/demultiplexer are proposed and simulated. The proposed structure can be etched adjacent to...     

A Universal Plasmonic Polarization State Analyzer

We propose a universal plasmonic polarization state analyzer consisting of rectangular holes arranged along an Archimedes spiral in silver film. The analyzer can detect different polarization states of light including linear, circular, radial and azimuthal polarizations. The theoretical analysis of its transmitted field is performed on the basis of the dipole radiations, and the analytic expressions of the electric field distributions under different polarized illuminations are provided. The numerical simulations of the near-field transmissions are also conducted to verify the analytic results. The significant differences between the field distributions predict the practicability of the universal plasmonic polarization state analyzer in determining the incident light polarization states.     

A Dielectric-Thickness-Adjusting Method for Manipulating Graphene Surface Plasmon Polariton

We propose and numerically investigate a dielectric-thickness-adjusting method to manipulate the graphene surface plasmon polariton (SPP). The dispersion relationships of graphene SPP at different dielectric thickness are derived by solving the analytic equations. In addition, the SPP effective index at cutoff dielectric thickness is obtained according to different dielectric permittivity and working frequencies. As a typical application, a plasmonic Bragg reflector is designed by alternately depositing dielectric gratings along the transverse direction of the SPP propagation. The performance of the Bragg reflector is analyzed at different grating thickness, and the effective index at cutoff thickness is verified by numerical simulation. The proposed method will have important potential prospects in designing graphene-based wave trapping and slow wave devices in future.     

Tuning Colors of Silver Nanoparticle Sheets by Multilayered Crystalline Structures on Metal Substrates

We report a new concept of tuning plasmonic colors of two-dimensional crystalline silver nanoparticle sheets with layer-by-layer structures. The multilayered crystalline sheets fabricated by the Langmuir–Schaefer method keep the localized surface plasmon resonance bands at the same position (λ _max?=?465 nm) on quartz, while they change their colors drastically on metal substrates depending on the number of layers (one to five layers). The response of the absorption spectra was absolutely nonlinear, with maximum absorption for two or three layers. The obtained results were well reproduced by the finite difference time domain simulation. The simulation confirmed that these plasmonic colors originate not only from near-field coupling of plasmon resonance but also far-field nano-optics of the multilayered silver nanoparticle sheets.     

Multiple-Wavelength Focusing and Demultiplexing Plasmonic Lens Based on Asymmetric Nanoslit Arrays

A multiple-wavelength focusing and demultiplexing plasmonic lens based on asymmetric nanoslit arrays is designed. The nanoslit arrays are perforated in a gold film and act as metal–insulator–metal plasmonic waveguides. By manipulating the widths of the slit arrays, the plasmonic lens can concentrate two incident plane wave beams to two separated focal points corresponding to their wavelengths. The full wave simulation is performed to verify the designed lens. This work provides a way to design more compact and integrated wavelength-division multiplexing plasmonic devices for nanophotonic communication and spectral imaging.     

All-Optical Plasmonic Switches Based on Coupled Nano-disk Cavity Structures Containing Nonlinear Material

All-optical plasmonic switches based on a novel coupled nano-disk cavity configuration containing nonlinear material are proposed and numerically investigated. The finite difference time domain simulation results reveal that the single-disk plasmonic structure can operate as an “on–off” switch with the presence/absence of pumping light. We also demonstrate that the proposed T-shaped plasmonic structure with two disk cavities can switch signal light from one port to another under an optical pumping light, functioning as a bidirectional switch. The proposed nano-disk cavity plasmonic switches have many advantages such as compact size, requirement of low pumping light intensity, and ultra-fast switching time at a femto-second scale, which are promising for future integrated plasmonic devices for applications such as communications, signal processing, and sensing.     

Multilayer Hybrid Plasmonic Nano Patch Antenna

This is the first report of a hybrid plasmonic nano patch antenna having metal insulator metal (HMIM) multilayer configuration. It is designed in a footprint area of 1.7 × 1.175 μm² to resonate at 1.55 μm wavelength. The proposed antenna is inset fed by an HMIM plasmonic waveguide for achieving proper impedance matching. It is observed, through electromagnetic numerical simulation, that the proposed plasmonic nano patch antenna emits a directional beam with a bandwidth, gain, and efficiency of 0.194 μm, 8.3 dB, and 96% respectively, which are significantly higher than previously reported designs. Since inset-fed antennas are suitable for developing high-gain antenna array, hence further, we examined antenna performance by designing antenna array. The proposed antenna is practically realizable and can be fabricated using standard semiconductor fabrication process. Moreover, it could be used for numerous chip scale applications such as wireless interconnects energy harvesting, photoemission, photo detection, scattering, heat transfer, spectroscopy, and optical sensing.

     

Plasmonic Lens with Multiple-Turn Spiral Nano-Structures

In this paper, we investigate the focusing properties of a plasmonic lens with multiple-turn spiral nano-structures, and analyze its field enhancement effect based on the phase matching theory and finite-difference time-domain simulation. The simulation result demonstrates that a left-hand spiral plasmonic lens can concentrate an incident right-hand circular polarization light into a focal spot with a high focal depth. The intensity of the focal spot could be controlled by altering the number of turns, the radius and the width of the spiral slot. And the focal spot is smaller and has a higher intensity compared to the incident linearly polarized light. This design can also eliminate the requirement of centering the incident beam to the plasmonic lens, making it possible to be used in plasmonic lens array, optical data storage, detection, and other applications.     

Design and Optimization of Open-cladded Plasmonic Waveguides for CMOS Integration on Si3N4 Platform

Herein, we present a design analysis and optimization of open-cladded plasmonic waveguides on a Si₃N₄ photonic waveguide platform targeting CMOS-compatible manufacturing. For this purpose, two design approaches have been followed aiming to efficiently transfer light from the hosting photonic platform to the plasmonic waveguide and vice versa: (i) an in-plane, end-fire coupling configuration based on a thin-film plasmonic structure and (ii) an out-of-plane directional coupling scheme based on a hybrid slot waveguide. A comprehensive numerical study has been conducted, initially deploying gold as the reference metal material for validating the numerical models with already published experimental results, and then aluminum and copper have been investigated for CMOS manufacturing revealing similar performance. To further enhance coupling efficiency from the photonic to the plasmonic part, implementation of plasmonic tapering schemes was examined. After thorough investigation, plasmo-photonic structures with coupling losses per single interface in the order of 1 dB or even in the sub-dB level are proposed, which additionally exhibit increased tolerance to deviations of critical geometrical parameters and enable CMOS-compatible manufacturing.

     

Modulation–Frequency Analysis of an Electrically Pumped Plasmonic Amplifier

Frequency of variations of surface plasmon intensity at the input of a plasmonic amplifier is called modulation–frequency. High modulation–frequency behavior of a Schottky junction-based plasmonic amplifier has been in the focus of this paper. Both small signal and large signal conditions have been considered. In small signal condition, an analytical solution of the rate equations of the electrons and photons has been presented which its results are in accordance with the simulation results of a harmonic balance method. For an amplifier of 100 μm length, the small signal gain has been 14.62 dB from both methods. Large signal behavior has been described by IIP2 and IIP3 in a two tone test which has been implemented by the harmonic balance method. IIP2 and IIP3 of the plasmonic amplifier of this work at 1 GHz are –21.2 and –19.95 dBm, respectively, and their values increase with frequency.     

Plasmonic Slot Waveguides with Core Nonlinearity

We analytically study the interplay between group velocity dispersion and material dispersion due to femtosecond ultrafast pulse inside plasmonic slot waveguides with nonlinear dielectric core. The analytic investigation of the role of the core nonlinearity on pulse propagation has been investigated. Interestingly, our model shows that the focusing and defocusing effects of the material can be revered if the material is confined inside the core of a plasmonic slot. We confirm our analytical results with nonlinear finite difference time domain (FDTD) simulations.     

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1?×?10³ nm/RIU and its figure of merit is as high as 2?×?10⁵ at λ?=?980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm² may find important applications in the on-chip nano-sensors.     

Glucose Level Measurement Using Photonic Crystal Fiber–based Plasmonic Sensor

In this study, we demonstrate the design of a photonic crystal fiber (PCF)-based plasmonic sensor to measure the glucose level of urine. The sensor is designed by placing a small segment of PCF between a lead-in and a lead-out single-mode fiber. We utilize the finite element method to simulate the proposed plasmonic sensor for the measurement of glucose level in urine. To offer external sensing, the cladding layer of the PCF was coated by a thin layer of gold where the gold-coated PCF was immersed in the urine sample. As a result, the urine can easily interact with the plasmonic layer of the sensor. In the outermost laser of the PCF, we considered a perfectly matched layer as a boundary condition. The simulation results confirm excellent wavelength and amplitude sensitivities where the maximum wavelength sensitivity was 2500 nm/RIU and amplitude sensitivity was 152 RIU^?1 with a sensing resolution of 4?×?10^?6. For optimization of the plasmonic sensor, we varied the physical parameters of the cladding air holes and the thickness of the gold layer during the simulation. We strongly believe that the proposed plasmonic sensor will play a significant role to pave the way for achieving a simple but effective PCF-based glucose sensor.