Plasmonic Waveguide Research Articles

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.

Broadband Enhancement of Magneto-Optical Effects in Hybrid Waveguide-Plasmonic Surfaces for Sensing.

Conventional magnetophotonic nanostructures typically function within narrow wavelength and incident angle ranges, where resonance is observed and magneto-optical (MO) effects are amplified. Expanding these operational ranges may allow for improved applications, including in (bio)sensing devices. In this study, we describe a hybrid magnetoplasmonic waveguide grating (HMPWG) in which the coupling of plasmonic resonances and waveguide modes leads to enhanced MO effects and sensitivity, according to full-wave electromagnetic simulations. High transverse magneto-optical Kerr effect (TMOKE) signals were observed for the full range of wavelengths and angles investigated, i.e., for θinc ≥ 1° and 500 nm ≤ λ ≤ 850 nm. As a proof-of-concept we verified that using the HMPWG nanostructure with an aqueous solution as superstrate one may obtain a sensitivity in variation of the refractive index unit (RIU) of S = 166°/RIU and S = 230 nm/RIU in angle and wavelength interrogation modes, respectively. Upon comparing with conventional magnetoplasmonic gratings, which only enable excitation of plasmonic resonances, we demonstrate that HMPWG nanostructures can be further optimized to reach not only high sensitivity but also high resolution in sensing and biosensing.

Room-temperature quantum nanoplasmonic coherent perfect absorption

Light-matter superposition states obtained via strong coupling play a decisive role in quantum information processing, but the deleterious effects of material dissipation and environment-induced decoherence inevitably destroy coherent light-matter polaritons over time. Here, we propose the use of coherent perfect absorption under near-field driving to prepare and protect the polaritonic states of a single quantum emitter interacting with a plasmonic nanocavity at room temperature. Our scheme of quantum nanoplasmonic coherent perfect absorption leverages an inherent frequency specificity to selectively initialize the coupled system in a chosen plasmon-emitter dressed state, while the coherent, unidirectional and non-perturbing near-field energy transfer from a proximal plasmonic waveguide can in principle render the dressed state robust against dynamic dissipation under ambient conditions. Our study establishes a previously unexplored paradigm for quantum state preparation and coherence preservation in plasmonic cavity quantum electrodynamics, offering compelling prospects for elevating quantum nanophotonic technologies to ambient temperatures.

Hybrid Si-Au plasmonic sensor on the end-facet of a dual-core optical fiber enhanced by hotspots: a theoretical study

We propose an efficient hybrid Si-Au sensor on the end-facet of a dual-core single-mode optical fiber. The design incorporates slanted Si grating couplers on the two cores, interconnected by a plasmonic waveguide bearing subwavelength corrugations. The corrugations enhance the surface sensitivity by creating regions of strongly enhanced fields - plasmonic hotspots. Unlike conventional Si waveguide grating couplers, we employ slanted slits for unidirectional coupling/decoupling between TM-polarized core light and surface plasmon polaritons. Our structure results in about 3% core-to-core (TM-to-TM) coupling efficiency, while also providing high bulk and surface sensitivities of about 1000 nm RIU−1 and 1.66 nm nm−1, respectively. The sensor can be interrogated remotely in a transmission arrangement. The sensing medium can be probed by dipping the fiber tip directly therein. Potential applications include remote sensing, brain studies, or in-vivo biosensing.

Mid-Infrared Wavelength Light Transmission in a Suspended Cylindrical Nanowire Hybrid Plasmonic Waveguide

Mid-Infrared Wavelength Light Transmission in a Suspended Cylindrical Nanowire Hybrid Plasmonic Waveguide

Design of $$2\times 4$$ optical decoder based on IMI plasmonic waveguide with slot

Design of $$2\times 4$$ optical decoder based on IMI plasmonic waveguide with slot

Design of a nano-scale optical 2-bit analog to digital converter based on artificial intelligence

A novel, to our knowledge, optical 2-bit analog to digital converter (ADC) plasmonic waveguide was proposed using a metal–insulator–metal (MIM) with a circular disk resonator. A mutual cooperation between the finite element method of COMSOL software and MATLAB with the aid of artificial intelligence (AI) presented by the multi-layer perceptron (MLP) has been proposed for implementing the main structure. The phase shift difference between the input and the control ports is the basic principle used to select the outcomes on the output port. The transmission threshold (Tthreshold) is selected to be 0.5, resonance wavelength is 1040 nm, and the footprint of the design is 1200×2500nm. Several criteria like full width at half maximum (FWHM), contrast ratio (CR), modulation depth (MD), insertion loss (IL), and curves covering a complete wavelength range from 800 to 2000 nm versus transmission value (Tv) are simulated to evaluate the plasmonic system performance. The FWHM is 17 nm, CR is equal to 10.8 dB, MD and IL are 98.17% and −1dB, respectively, and the quality factor (Q-factor) for a single segment of the design reached 61.17.

All-optical multichannel switch and slow light based on dynamically tunable plasmon-induced transparency

The triple plasmon-induced transparency (PIT) effect based on a metal–insulator–metal waveguide structure comprising two groups of big and small disk resonators (BSDRs) is investigated theoretically and numerically. As a tool employed to explain the PIT, N-order coupled mode theory (CMT), is established, and the calculated results of the triple-PIT effect exhibit excellent consistency with finite-difference time-domain simulations. The influence of the separation between the small disk resonators on the triple-PIT response is discussed in detail through the dynamical equation. Further research shows that the central wavelengths of the triple-PIT transmission window can be adjusted with extremely low pump intensity and ultrafast optical response when monolayer graphene covers the surface of the BSDRs. Meaningfully, light traveling at resonant wavelengths can be effectively slowed down, with the highest group index reaching 368. Based on the PIT effect, a low-power and ultrafast switch is realized with a modulation amplitude of more than 93% at the corresponding wavelengths of the eight depressions. Thus, not only do the insights put forward new ideas, to the best of our knowledge, for highly tunable optoelectronic devices, but the results from the N-order CMT also offer new theory progress and references in the plasmonic waveguide structures.

Recent Progress in Light Polarization Control Schemes for Silicon Integrated Photonics

AbstractLight polarization control is a target in photonics, and this paper provides a comprehensive review of research from various groups on the silicon‐on‐insulator (SOI) platform. It draws comparisons between devices such as polarization splitters (PS), polarizers, and polarization splitters/rotators (PSR). These devices are fabricated using various technologies, including silicon nanowires, ridge waveguides, hybrid plasmonic waveguides, and subwavelength grating (SWG) waveguides. A detailed review of polarizers used as cleanup filters in splitters is initiated. Subsequently, various polarization splitters utilizing asymmetric directional couplers (ADCs), which typically exhibiting low extinction ratios (ERs), are delved. To enhance ERs, a detailed comparison of methods outlined in the literature is provided. One notable method includes integrating on‐chip polarizers at both ports to eliminate unwanted light fractions and achieve exceptionally high ERs. Furthermore, SWG‐based polarizers and splitters commonly face issues with Bragg reflections that can affect other photonic devices and lasers and ways to minimize unwanted polarization back reflections in SWG‐designed polarization control devices are examined. Finally, emerging applications in mid‐infrared (MIR) sensing are explored, highlighting the necessity of polarization rotators for on‐chip transverse electric (TE) operation, since quantum cascade lasers, the primary sources in this range, emitting radiation in the (TM) mode.

Study on mode properties of GaAs-based hybrid plasmonic terahertz waveguides

Terahertz (THz) fields are increasingly being used to address the critical challenges associated with achieving high data rates and rapid communication. In this study, a hybrid plasmonic THz waveguide is designed and analysed operating in the 2.5–3.5 THz frequency range. The waveguide is constructed using gallium arsenide as the high-refractive-index core, surrounded by aluminium arsenide and silver placed on a high-density polyethylene (HDPE) substrate. Graphene is strategically positioned between the HDPE layers to enhance light confinement. The mode properties of the proposed waveguide are simulated with Comol Multiphysics using the finite-element method and show unique characteristics. Observation of the simulated results at 2.5–3.5 THz reveals a high effective refractive index of 3.79, a maximum effective mode area of 1.88 mm2, a high birefringence of 0.2, a low dispersion of 0.10 ps THz−1 cm−1, a high mode field diameter of 15.8 mm, a high beat length of 123 mm and a low confinement loss of 1.79 × 10−9 mm−1. These features make the proposed waveguide suitable for applications in photonic integrated circuits for THz communications.

Spoof surface plasmons spawning pencil-beam antennas of subwavelength profile.

Slot-array antennas based on metallic waveguides have been widely used to generate pencil-beams, attracting attention due to their design simplicity and compact size. However, current slot-array antennas possess wavelength-scale profiles, which do not align optimally with the low-profile requisites of contemporary integrated communication and radar systems. Here, we propose a low-profile slot-array antenna designed specifically for the pencil-beam generation. Constructed with the two-dimensional-array (2D-array) slots situated on a sub-wavelength domino plasmon waveguide, the pencil-beam is generated with a peak gain of up to 21.6 dBi. Moreover, the generated pencil-beam allows for a wide scanning range of over 73.6° by adjusting the operating frequency from 45 to 65 GHz. Our research shows great potential for enhancing millimeter-wave radar capabilities and advancing communication systems.

Optimized hybrid plasmonic waveguide-based ring resonator for advanced refractive index sensing

In this study, we conducted a comprehensive numerical analysis employing the finite element method to explore the characteristics of a hybrid plasmonic waveguide (HPWG)-based ring resonator (RR) structure. Our investigation reveals that the device’s sensitivity can be significantly augmented through strategic geometric modifications. The device exhibits sensitivities of approximately 176 nm RIU−1 and 238 nm RIU−1 when utilizing WG widths of 300 nm and 270 nm, respectively, in forming the ring structure. Through optimization efforts aimed at enhancing the overlap between the dielectric and plasmonic modes, the device’s sensitivity reaches an optimized level of around 316 nm RIU−1 by reducing the ring width to 250 nm. Overall, our findings underscore the potential for leveraging geometric adjustments to enhance the sensitivity and functionality of HPWG-based RRs, thereby advancing their utility in diverse sensing applications.

Theoretical and Experimental Analysis of Single-Arm Bimodal Plasmo-Photonic Refractive Index Sensors.

In this paper, we study both theoretically and experimentally the sensitivity of bimodal interferometric sensors where interference occurs between two plasmonic modes with different properties propagating in the same physical waveguide. In contrast to the well-known Mach-Zehnder interferometric (MZI) sensor, we show for the first time that the sensitivity of the bimodal sensor is independent of the sensing area length. This is validated by applying the theory to an integrated plasmo-photonic bimodal sensor that comprises an aluminum (Al) plasmonic stripe waveguide co-integrated between two accessible SU-8 photonic waveguides. A series of such bimodal sensors utilizing plasmonic stripes of different lengths were numerically simulated, demonstrating bulk refractive index (RI) sensitivities around 5700 nm/RIU for all sensor variants, confirming the theoretical results. The theoretical and numerical results were also validated experimentally through chip-level RI sensing experiments on three fabricated SU-8/Al bimodal sensors with plasmonic sensing lengths of 50, 75, and 100 μm. The obtained experimental RI sensitivities were found to be very close and equal to 4464, 4386, and 4362 nm/RIU, respectively, confirming that the sensing length has no effect on the bimodal sensor sensitivity. The above outcome alleviates the design and optical loss constraints, paving the way for more compact and powerful sensors that can achieve high sensitivity values at ultra-short sensing lengths.

Compact unidirectional waveguide grating emitter with enhanced wavelength sensitivity based on the hybrid plasmonic mode

Waveguide grating antennas are widely adopted in beam-steering devices, typically enabling the beam steering in longitudinal direction within a two-dimensional scanning optical array by changing the input wavelength. However, traditional waveguide grating antennas suffer from limited tuning range due to low dispersion of the gratings. In this paper, a compact silicon grating waveguide antenna array is proposed with enhanced wavelength sensitivity by introducing a periodically modulated hybrid plasmonic mode. The hybrid plasmonic mode is supported by the hybrid plasmonic waveguides (HPWs) composed of silicon waveguides and periodic subwavelength silver strips. In order to convert the guided waves to the radiated waves, a series of silicon emitting segments are deposited above the HPWs. Additionally, the horizontally arranged array of HPWs also acts as a reflector of the downward radiation, resulting in an effective unidirectional emission. Through the optimization of physical parameters, the proposed antenna array achieves a wavelength-length tuning efficiency up to 0.3°/nm within the wavelength range of 1500∼1600 nm, exhibiting a significant improvement compared with traditional ones. Moreover, an average upward emissivity exceeding 80% with a maximum value of 89% within the 100 nm bandwidth is demonstrated through the numerical simulations. The proposed compact antenna array provides an alternative solution in realizing large-scale integrated high-tuning-efficiency optical beam-steering devices.

Hybrid Plasmonic Waveguides with Tunable ENZ Phenomenon Supported by 3D Dirac Semimetals

AbstractBy depositing a dielectric fiber on top of 3D Dirac semi‐metal (DSM) and Au layers, the tunable propagation properties of hybrid modes are systematically investigated in the mid‐infrared regime, including the effects of the temperatures, the Fermi levels, and rotation angles. Interestingly, due to the importance of inter‐band transition in the mid‐infrared spectral regime, a strong temperature related epsilon‐near‐zero (ENZ) phenomenon has manifested near the transition frequency. Namely, below room temperature, the real part of the effective refractive index (propagation length) shows a peak (valley). Particularly, at 77 K, the according abruption ratio (ratio of maximum to minimum in ENZ region) is 9.71 (204.1). Additionally, the propagation properties are also closely associated with the Fermi level. When the Fermi level varies in the range of 0.08–0.15 eV, the peak position of the real part of the effective refractive index shifts blue from 21.3 to 38.2 THz, and the according abruption ratio of the propagation length can be modulated in the range of 3.81–45.3. These results are very useful for designing tunable plasmonic devices, such as cutting‐edge modulator, filter, and resonators.

Enhancing modulation performance by design of hybrid plasmonic optical modulator integrating multi-layer graphene and TiO2 on silicon waveguides

A novel way to enhance modulation performance is through the design of a hybrid plasmonic optical modulator that integrates multi-layer graphene and TiO2 on silicon waveguides. In this article, a design is presented of a proposed modulator based on the use of the two-dimensional finite difference eigenmode solver, the three-dimensional eigenmode expansion solver, and the CHARGE solver. Leveraging inherent graphene properties and utilizing the subwavelength confinement capabilities of hybrid plasmonic waveguides (HPWs), we achieved a modulator design that is both compact and highly efficient. The electrical bandwidth f 3dB is at 460.42 GHz and it reduces energy consumption to 12.17 fJ/bit with a modulator that functions at a wavelength of 1.55 μm. According to our simulation results, our innovation was the optimization of the third dielectric layer’s thickness, setting the stage to achieve greater modulation depths. This synergy between graphene and HPWs not only augments subwavelength confinement, but also optimizes light–graphene interaction, culminating in a markedly enhanced modulation efficiency. As a result, our modulator presents a high extinction ratio and minimized insertion loss. Furthermore, it exhibits polarization insensitivity and a greater bandwidth. Our work sets a new benchmark in optical communication systems, emphasizing the potential for the next generation of chip-scale with high-efficiency optical modulators that significantly outpace conventional graphene-based designs.

Compact, low-loss, and high-polarized-extinction ratio terahertz TM-pass polarizer based on a hybrid plasmonic waveguide with a graphene ridge

A compact, low-loss, and high-polarized-extinction ratio TM-pass polarizer based on a graphene hybrid plasmonic waveguide (GHPW) has been demonstrated for the terahertz band. A ridge coated by a graphene layer and the hollow HPW with a semiround arch (SRA) Si core is introduced to improve structural compactness and suppress the loss. Based on this, a TM-pass polarizer has been designed that can effectively cut off the unwanted TE mode, and the TM mode passes with negligible loss. By optimizing the angle of the ridge, the height of the ridge, air gap height, and the length of the tapered mode converter, an optimum performance with a high polarization extinction ratio of 30.28 dB and a low insert loss of 0.4 dB is achieved in the 3 THz band. This work provides a scheme for the design and optimization of polarizers in the THz band, which has potential application value in integrated terahertz systems.

Miniaturized leaky-wave antenna with backward-to-forward beam scanning and suppressed open stop-band based on substrate-integrated plasmonic waveguide

This work presents a theoretical design and experimental demonstration of a novel miniaturized leaky-wave antenna (LWA) using composite waveguide based on substrate-integrated plasmonic waveguide (SIPW). The SIPW is designed by embedding hybrid dual spoof surface plasmon polariton (SSPP) structure into a three-layer substrate integrated waveguide (SIW). Due to the slow-wave effect of SIPW, the proposed miniaturized composite waveguide forms slowed phase velocity and decreased lower cutoff frequency. To excite backward-to-forward beam scanning mode and suppress the open stop-band, an asymmetric sinusoidal modulated structure is introduced to the surface of the composite waveguide. The experimental results indicate that the proposed SIPW-based LWA can achieve continuous beam scanning from the backward to the forward direction within the bandwidth of 10.6-13.7 GHz, passing through the broadside at 11.6 GHz.