Plasmonic Waveguide Research Articles

Plasmonic modulators based on enhanced interaction between graphene and localized transverse-electric plasmonic mode

Active plasmonic modulators with high modulation depth, low energy consumption, ultra-fast speed, and small footprint are of interest and particular significance for nanophotonics and integrated optics. Here by constructing a transverse-electric (TE) plasmonic mode and maximizing the in-plane component localized on the graphene surface, we propose a high-performing plasmonic modulator based on a graphene/split ring-like plasmonic waveguide (SRPW) system with a record high modulation depth (20.46 dB/µm) and suppressed insertion loss (0.248 dB/µm) at telecom wavelength 1310 nm, simultaneously possessing pronounced advantage in broadband ability (800-1650 nm) and superior electrical performance with energy consumption of 0.43 fJ/bit and modulation speed of 200 GHz. This innovative design provides a novel approach and idea for enhancing the interaction between light and matter in the waveguide system and will certainly inspire new schemes for the development of on-chip integrated optoelectronic devices.

Plasmonic Waveguide based Filter Design with Demultiplexing and Slow Light Capabilities

Plasmonic Waveguide based Filter Design with Demultiplexing and Slow Light Capabilities

Ultracompact polarization beam splitter based on hybrid plasmonic waveguide

A compact polarization beam splitter (PBS) based on a three-waveguide plasmonic directional coupler was proposed and modeled. The directional coupler comprised two common silicon-on-insulator (SOI) ridge waveguides, with a metal-capped plasmonic SOI waveguide sandwiched between them. The geometrical structure of the three-waveguide directional coupled waveguide was optimized, realizing the phase matching of transverse magnetic (TM) modes but not of transverse electric (TE) modes. The structure and performance of the PBS was optimized using a finite-difference time-domain method. Simulation results showed that the birefringence comparison of TE and TM modes in a hybrid plasmonic waveguide was enhanced using a dielectric loading waveguide to obtain an ultra-compact structure; the final optimized coupling length of the device was 6.1 µm. At the center wavelength of 1.55 µm, the polarization extinction ratio of the TE and TM modes was 34.57 dB and 23.24 dB, and the insertion loss was 0.01 dB and 0.13 dB, respectively.

Plasmonic devices – equivalent circuit representations

An equivalent circuit model for plasmonic slot waveguide-based devices is presented. Taking advantage of the high mode confinement provided by this waveguide geometry, we express plasmonic waveguide geometries using transmission line parameters and express T-junctions using lumped equivalent circuit elements. By combining these fundamental building blocks, we subsequently introduce equivalent circuit models for stub filters and branch-line couplers. We show that plasmonic circuits, if designed with sharp discontinuities, feature low losses that are comparable to losses from RF circuits and even the corresponding photonic circuits. The framework presented here gives insight into the design of novel microwave-inspired plasmonic devices and circuits and significantly speeds up the design time, as a large part of the geometry optimization can be performed in the equivalent circuit domain. For instance, we use this framework in a follow-up paper to design ultra-compact plasmonic hybrids, such as those needed for coherent detection.

Sodium-based plasmonic waveguides with high confinement factors and ultra-low gain thresholds.

The noble metal-based hybrid plasmon mode features low loss and strong field localization, making it widely applicable in the field of nanophotonic devices. However, due to the high loss of noble metals, the gain threshold is unacceptably high, usually larger than 0.1 µm-1. Here we present a hybrid plasmonic waveguide consisting of a SiO2 layer coated Na nanowire and a hexagonal semiconductor nanowire. Based on the high performance of the proposed waveguide, the Purcell factor exceeding 120 and a confinement factor above 90% are achieved, leading to an ultra-low gain threshold of 0.02117 µm-1. In addition, the proposed waveguide exhibits an extremely low cross talk, making it highly suitable for applications in compact photonic integrated devices. The proposed waveguide may contribute to the development of low-threshold nano-lasers and promote other applications in nanophotonics.

Terahertz Metal-Graphene Composite Plasmon Waveguides Combining Strong Field Confinement with Low Cross-Talk: A FEM Study

Terahertz Metal-Graphene Composite Plasmon Waveguides Combining Strong Field Confinement with Low Cross-Talk: A FEM Study

Ultrafast Silicon/Graphene Optical Nonlinear Activator for Neuromorphic Computing

AbstractOptical neural networks (ONNs) have shown great promise in overcoming the speed and efficiency bottlenecks of artificial neural networks. However, the absence of high‐speed, energy‐efficient nonlinear activators significantly impedes the advancement of ONNs and their extension to ultrafast application scenarios like real‐time intelligent signal processing. In this work, a novel silicon/graphene ultrafast all‐optical nonlinear activator, leveraging the hybrid integration of silicon slot waveguides, plasmonic slot waveguides, and monolayer graphene is demonstrated. Exploiting the exceptional picosecond‐scale photogenerated carrier relaxation time of graphene, the response time of the activator is markedly reduced to ≈93.6 ps, establishing all‐optical activator as the fastest known in silicon photonics to knowledge. Moreover, the all‐optical nonlinear activator holds a low threshold power of 5.49 mW and a corresponding power consumption per activation of 0.51 pJ. Its feasibility and capability for use in ONNs, manifesting performance comparable with commonly used activation functions are experimentally confirmed. This breakthrough in speed and energy efficiency of all‐optical nonlinear activators opens the door to significant improvements in the performance and applicability of ONNs.

Nano-strip Engineering for Coupling Length Enhancement in Pattern-Free Suspended Graphene-based Plasmonic Waveguides

Nano-strip Engineering for Coupling Length Enhancement in Pattern-Free Suspended Graphene-based Plasmonic Waveguides

1 × 2 Graphene Surface Plasmon Waveguide Beam Splitter Based on Self-Imaging.

Based on the principle of self-imaging, a 1 × 2 graphene waveguide beam splitter is proposed in this work, which can split the graphene surface plasmons excited by far-infrared light. The multimode interference process in the graphene waveguide is analyzed by guided-mode propagation analysis (MPA), and then the imaging position is calculated. The simulation results show that the incident beam can be obviously divided into two parts by the self-imaging of the graphene surface plasmon. In addition, the influences of the excited light wavelength, Fermi level, dielectric environment on the transmission efficiency are studied, which provide a reference for the research of graphene waveguide related devices.

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

Plasmon scattering at a junction in double-layer two-dimensional electron gas plasmonic waveguide

Abstract The scattering of plasmons at a junction within a double-layer two-dimensional electron gas plasmonic waveguide is studied via a full electromagnetic method. The dispersion relation is derived by utilizing the transfer matrix method and can be extended to the situation of an arbitrary number of layers. By numerically solving the dispersion equations, both the acoustic and optical plasmon modes are identified in this double layer system, and the unstable plasmon modes arising from plasmon coupling in different layers are discussed elaborately. Subsequently, the total fields are expanded with eigenmodes and matched at the interface to analyze the scattering characteristics at the junction. The results indicate that the total power of the plasmon mode is amplified when the electron fluid flows from a high concentration region to a low concentration region, and the amplification is more evident at a higher drift velocity. Additionally, we address the scattering of unstable plasmons caused by the two-stream instability and find that the transmitted plasmons are excited intensively at the incidence of the growing plasmon, leading to the plasmon amplification. The detailed examination of plasmon scattering at junction is the prerequisite for studying more complex structures of terahertz plasmonic devices and comprehending the corresponding amplification mechanism.

Enhanced Plasmonic Trapping and Fluorescent Emission of Nitrogen-Vacancy Nanodiamonds Using a High-Efficiency Nanofocusing Device.

Fluorescent nanodiamonds (FNDs) with nitrogen-vacancy centers are pivotal for advancing quantum photonics and imaging through deterministic quantum state manipulation. However, deterministic integration of quantum emitters into photonic devices remains a challenge due to the need for high coupling efficiency and Purcell enhancement. We report a deterministic FND-integrated nanofocusing device achieved by assembling FNDs at a plasmonic waveguide tip through plasmonic-enhanced optical trapping. This technique not only increases the emission rate by 58.6 times compared to isolated FNDs but also preferentially directs radiation into the waveguide at a rate 5.3 times higher than that into free space, achieving an exceptional figure-of-merit of ∼3000 for efficient energy transfer. Our findings represent a significant step toward deterministic integration in quantum imaging and communication, opening new avenues for quantum technology advancements.

Dispersion Properties in Uniaxial Chiral–Graphene–Uniaxial Chiral Plasmonic Waveguides

Dispersion Properties in Uniaxial Chiral–Graphene–Uniaxial Chiral Plasmonic Waveguides

Compact and broadband polarization beam splitter based on a bridged hybrid plasmonic waveguide coupler on a thin-film lithium niobate.

We propose a compact and broadband polarization beam splitter (PBS) based on a thin-film lithium niobate. The hybrid plasmonic waveguide (HPW) is used as a bridge in a three-waveguide coupler to achieve large birefringence. A degree of phase-matching is introduced for optimization. The proposed PBS exhibits a 125-nm bandwidth (1495-1620 nm) of polarization extinction ratio (PER) over 20 dB or an 85-nm bandwidth (1515-1600 nm) of PER over 25 dB, with a device length of only 81 μm. An ultra-low insertion loss of 0.04 dB is achieved around the wavelength of 1550 nm. In addition, the proposed device exhibits high robustness of the fabrication tolerance.

Enhancement of nonlinear optic effect of the second harmonic generation in plasmonic waveguide using graphene and pyramid-shape gold nanoparticles

Enhancement of nonlinear optic effect of the second harmonic generation in plasmonic waveguide using graphene and pyramid-shape gold nanoparticles

Polarized and Evanescent Guided Wave Surface-Enhanced Raman Spectroscopy of Ligand Interactions on a Plasmonic Nanoparticle Optical Chemical Bench.

This study examined applications of polarized evanescent guided wave surface-enhanced Raman spectroscopy to determine the binding and orientation of small molecules and ligand-modified nanoparticles, and the relevance of this technique to lab-on-a-chip, surface plasmon polariton and other types of field enhancement techniques relevant to Raman biosensing. A simplified tutorial on guided-wave Raman spectroscopy is provided that introduces the notion of plasmonic nanoparticle field enhancements to magnify the otherwise weak TE- and TM-polarized evanescent fields for Raman scattering on a simple plasmonic nanoparticle slab waveguide substrate. The waveguide construct is called an optical chemical bench (OCB) to emphasize its adaptability to different kinds of surface chemistries that can be envisaged to prepare optical biosensors. The OCB forms a complete spectroscopy platform when integrated into a custom-built Raman spectrograph. Plasmonic enhancement of the evanescent field is achieved by attaching porous carpets of Au@Ag core shell nanoparticles to the surface of a multi-mode glass waveguide substrate. We calibrated the OCB by establishing the dependence of SER spectra of adsorbed 4-mercaptopyridine and 4-aminobenzoic acid on the TE/TM polarization state of the evanescent field. We contrasted the OCB construct with more elaborate photonic chip devices that also benefit from enhanced evanescent fields, but without the use of plasmonics. We assemble hierarchies of matter to show that the OCB can resolve the binding of Fe2+ ions from water at the nanoscale interface of the OCB by following the changes in the SER spectra of 4MPy as it coordinates the cation. A brief introduction to magnetoplasmonics sets the stage for a study that resolves the 4ABA ligand interface between guest magnetite nanoparticles adsorbed onto host plasmonic Au@Ag nanoparticles bound to the OCB. In some cases, the evanescent wave TM polarization was strongly attenuated, most likely due to damping by inertial charge carriers that favor optical loss for this polarization state in the presence of dense assemblies of plasmonic nanoparticles. The OCB offers an approach that provides vibrational and orientational information for (bio)sensing at interfaces that may supplement the information content of evanescent wave methods that rely on perturbations in the refractive index in the region of the evanescent wave.

Past, present, and future of hybrid plasmonic waveguides for photonics integrated circuits

This article addresses the past, present, and future status of hybrid plasmonic waveguides (HPWs). It presents a comprehensive review of HPW-based photonic integrated circuits (PICs), covering both passive and active devices, as well as potential application of on-chip HPW-based devices. HPW-based integrated circuits (HPWICs) are compatible with complementary metal oxide semiconductor technology, and their matched refractive indices enables the adaptation of existing fabrication processes for silicon-on-insulator designs. HPWs combine plasmonic and photonic waveguide components to provide strong confinement with longer propagation length Lp of HP modes with nominal losses. These HPWs are able to make a trade-off between low loss and longer Lp, which is not possible with independent plasmonic and photonic waveguide components owing to their inability to simultaneously achieve low propagation loss with rapid and effective all-optical functionality. With HPWs, it is possible to overcome challenges such as high Ohmic losses and enhance the functional performance of PICs through the use of multiple discrete components. HPWs have been employed not only to guide transverse magnetic modes but also for optical beam manipulation, wireless optical communication, filtering, computation, sensing of bending, optical signal emission, and splitting. They also have the potential to play a pivotal role in optical communication systems for quantum computing and within data centers. At present, HPW-based PICs are poised to transform wireless chip-to-chip communication, a number of areas of biomedical science, machine learning, and artificial intelligence, as well as enabling the creation of densely integrated circuits and highly compact photonic devices.

Formation mechanism of the U-shaped spectrum based on a simple plasma–dielectric–plasma (PDP) waveguide

Manipulating electromagnetic (EM) waves by plasma–dielectric–plasma (PDP) waveguides or plasma array structures presents significant potential in microwave signal processing, such as filtering, signal delay, and EM enhancement or shielding. Owing to the simple structure and easy fabrication, the waveguide with a tooth-shaped resonator has been a strong candidate as a filtering device. Based on our previous work focusing on U-shaped filtering excited by PDP waveguides with a double-teeth structure, in this work, the formation mechanism of a U-shape filtering spectrum is systematically explored by transmission line theory (TLT) with proper field distributions. The results indicate that the U-shape spectrum consists of boundary edges and a filtering stopband. The boundary edges are attributed to Fano-type resonance, and the enhanced destructive interference from double teeth is responsible for the stopband. Such an approach shows a specific and clear mechanism for the generated U-shaped spectrum. In addition, the theoretical analysis of double teeth without Fano-type resonances is rigorously demonstrated using TLT, which significantly contributes to bandwidth modulation of stopband filtering in theory. These results contribute to the understanding of the formation mechanism of a U-shaped spectrum from a gap plasmon waveguide (such as PDP or metal–insulator–metal (MIM)) with tooth-shaped resonators, offering a feasible direction for the optimization of filtering properties, as well as offering significant parameters for subsequent experimental design.

Evanescent field engineering to reduce cross-talk in pattern-free suspended graphene-based plasmonic waveguides using nano-strips

Suppression of the cross-talk between neighboring photonic components has been considered one of the most efficient methods for increasing the packing density of photonic integrated circuits. In this study, an effective cross-talk reduction approach is developed for plasmonic waveguides. Firstly, the mode characteristics of the waveguide are investigated, and then two silicon strips are placed beside the two adjacent waveguides. The mechanism of the cross-talk suppression method highly relies on the evanescent waves. The designed strips in this study manipulate the wave vectors of surface plasmon polaritons. The tangential component of the wave vector is conserved along the interface, while the perpendicular component in the surroundings can be equal to zero or imaginary, leading to evanescent waves. Placing the strips increases the perpendicular component of the wave vector in the surroundings, resulting in less cross-talk. So, the coupling length of the waveguide with the strips at the wavelength of 10 μm increases up to 345 μm which is 25 times longer than that in its non-strip counterpart. Also, the figure-of-merit and loss of the designed structure are up to 1000 and 0.13 dB/μm at a chemical potential of 0.8 eV and a wavelength of 10 μm, respectively. So, high figure-of-merit and low loss along with long coupling length are the interesting features of the designed plasmonic waveguide which propose promising structures with high performance in the near-infrared.

Design and Simulation of a Three-Channel Plasmonic Demultiplexer in an MIM Waveguide

This study proposes a structure for optical plasmonic demultiplexers based on nanodisk/nanoring resonators in metal-insulator-metal (MIM) plasmonic waveguides. The proposed structure can transmit the desired wavelength spectra, including telecommunication and visible waves. It consists of a bus waveguide, several nanodisks and nanorings, and three drop waveguides, consisting of several filters that can be extended to N×1 channels. The FWHM of the designed structure was calculated to be approximately 18 nm. The transmission spectrum of each demultiplexer channel can be easily adjusted by changing the geometric parameters and refractive index. As the waveguide refractive index increases, the transmission spectrum shifts to higher wavelengths, and its amplitude decreases due to internal structural losses. Therefore, the differences between the waveguide and metal refractive indices gradually decrease, and the light confinement decreases in the waveguide, leading to an increase in FWHM. The outputs of each channel have two sharp resonance modes, resulting from the coupling of two interacting cavities (ring and disk) due to the Fano resonance phenomenon. This study employed a two-dimensional (2D) finite difference time domain (FDTD) numerical method and simulation by FDTD Lumerical software to evaluate the transmission properties.