Hybrid Plasmonic Waveguide Research Articles

Hybrid plasmonic optical modulator based on multi-layer graphene

Hybrid plasmonic waveguide provided high confinement of the propagating light and it is compatible with silicon on insulator technology. Graphene with unique optical properties has been used in optical modulator to give a high extinction ratio, broadband operation, and small footprint. In this paper, we used graphene as an absorber layer in a hybrid plasmonic waveguide structure to get sub-wavelength field confinement and better interaction between the graphene and the propagating light to reach maximum absorption of the graphene. We studied the effects of a different number (2–6) of the graphene layers on the extinction ratio, bandwidth, and energy consumption. The modulation extinction ratio is as high as 36 dB/μm and it has a flat response in a wide range of wavelength. The power consumption is about 14 fJ/bit. This modulator has a good response in all communication bands.

Ultra-compact, low-loss terahertz waveguide based on graphene plasmonic technology

In order to meet the demand for highly integrated terahertz chips with ultra-low transmission loss, a novel hybrid graphene plasmonic waveguide is proposed, wherein low-index insulators are embedded between a slot-rib (covered by graphene) structure and a high-index dielectric waveguide. This designed waveguide combines the plasmonic response of graphene, energy distribution mechanism of materials with large refractive index difference, and modal properties of hybrid plasmonic waveguide to yield superior waveguiding performance. We achieved 50 times stronger mode confinement along with five times smaller propagation loss, as compared to the traditional graphene hybrid plasmonic waveguide operating at 3 THz. Investigation on the influence of modal properties on chemical potential of graphene revealed an active approach to control mode confinement or propagation distance. In addition, owing to the ultra-strong energy confinement of modes, the crosstalk caused by coupling between two parallel waveguides is negligible, which paves the way for realizing ultra-compact, chip-level terahertz devices.

Enhancing Propagation Length of Surface Plasmon Polaritons by Using Metallic Double-Layer Structure

In this paper, we propose to use a wedge-shaped plasmonic waveguide with a metallic double-layer structure for improving the propagation length of surface plasmon polaritons. The wedge silicon waveguide is covered by a first layer of Ag and by a second layer of Au outermost in which the former has a good lightwave guiding property but unstable to the operating medium and the latter is more stable to the operating medium. Numerically investigated results show that the propagation length of surface plasmon polaritons using the Au/Ag double-layer structure with an appropriate thickness of the Au covering layer can be increased by a factor of 2.5 compared to that of using the only Au metallic structure at the same propagation mode area. The advantage of the proposed metallic double-layer structure is also preserved in hybrid plasmonic waveguides.

Two-dimensional plasmonic waveguides for nanolasing and four-wave mixing

Plasmonic waveguides are an essential element of nanoscale coherent sources, including nanolasers and four-wave mixing (FWM) devices. Here we report how the design of the plasmonic waveguide needs to be guided by the ultimate application. This contrasts with traditional approaches in which the waveguide is considered in isolation. We find that hybrid plasmonic waveguides, with a nonlinear material sandwiched between the metal substrate and a high-index layer, are best suited for FWM applications, whereas metallic wedges are preferred in nanolasers. We also find that in plasmonic nanolasers high-index buffer layers perform better than more traditional low-index buffers.

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.

In-plane electric field confinement engineering in graphene-based hybrid plasmonic waveguides.

Surface plasmon polaritons (SPPs) are surface modes confined to metal-dielectric interfaces. This confinement enhances the electromagnetic field and therefore, SPPs are sensitive to surface conditions. The properties of two dimensional materials such as graphene thus can be enhanced and used to engineer nanoscale components for optical communications. However, SPPs are transverse magnetic modes with electric fields out-of-plane that limit flexibility. In this contribution, we numerically analyze the confinement and in-plane enhancement in graphene-based hybrid plasmonic waveguides. We find that plasmonic modes supported by metal nanoparticle chain waveguides provide higher in-plane enhancement compared to those supported by nano-strip and slot hybrid plasmonic waveguides. Our results contribute to the performance improvement of graphene light absorption devices, including electro-optic modulators and photodetectors.

A circularly polarized hybrid plasmonic nanoantenna

AbstractIn this article, a waveguide fed circularly polarized hybrid plasmonic nanoantenna (CP‐HPNA) is proposed for nanophotonic applications, at 1550 nm wavelength telecommunication window. Here, the concept of hybrid plasmonic waveguide (HPWG) in conjunction with transmission line model is well incorporated in terms of electromagnetics. The proposed antenna geometry is an L‐hexagonal shaped patch fed by HPWG. The FDTD computational technique through CST microwave studio is used for design, simulation and characterization of CP‐HPNA. The proposed antenna exhibits an impedance bandwidth of 4.07 THz (S11 ≤ −10 dB) and prior to that, complete circular polarization is achieved, with an axial bandwidth of 5.49 THz (AR ≤ 3 dB). It shows broadside pattern with realized gain of 4.64 dB, directivity of 8.10 dBi and antenna efficiency of 63.98% at 1550 nm wavelength. With observed outcomes, the proposed antenna model finds its way‐out for many nanophotonic applications, ranging from the fields of optical sensing to lidars and in wireless optical communications from interconnects to intraconnects of chips. In correspondence to its utility, this research article, can significantly be treated as a link for visualizing the concepts of optical through classical electromagnetism.

Record Purcell factors in ultracompact hybrid plasmonic ring resonators.

For integrated optical devices and traveling-wave resonators, realistic use of the superior wave-matter interaction offered by plasmonics is impeded by ohmic loss, which increases rapidly with mode volume reduction. In this work, we report composite hybrid plasmonic waveguides (CHPWs) that are not only capable of guiding subwavelength optical mode with long-range propagation but also unrestricted by stringent requirements in structural, material, or modal symmetry. In these asymmetric CHPWs, the versatility afforded by coupling dissimilar plasmonic modes provides improved fabrication tolerance and more degrees of device design optimization. Experimental realization of CHPWs demonstrates propagation loss and mode area of 0.03 dB/μm and 0.002 μm2, corresponding to the smallest combination among long-range plasmonic structures reported to date. CHPW ring resonators with 2.5-μm radius were realized with record Purcell factor compared with existing plasmonic and dielectric resonators of similar radii.

LSPR Excitation on Au Nanorings From Integrated Hybrid Plasmonic Aperture Waveguide and Its Application in Methanol Detection in the IR-Band

The presented work deals with an infra-red (IR)-band methanol sensor, which has been realized in an integrated device having hybrid plasmonic aperture waveguide and Au-nanoring array over broad wall of it covered by porous silicon clad. Through modeling and numerical simulations, we have shown that suitable synthesized aperture in the waveguide can excite localized surface plasmon resonance (LSPR) on the nanorings of suitable diameter via radiative field coupling, whereas LSPR can be tuned with the received methanol by the porous silicon clad. Thus, by contrasting the power available at the sense port of the waveguide with null and finite methanol doses, we have determined sensitivity (STM) and figure of merit (FOM) of the sensor, and our further analyses suggest that the sensor response can be tailored by diameter of aperture and ring, and by the porosity of the silicon cladding medium. In this respect, we have found that, for 20%-45% clad porosity, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sub> = 77.95-66.66 nm/RIU and FOM = 17.51-7.66/RIU can be achieved during methanol detection.

Sub-Femtojoule Hybrid Plasmonic Optical Modulator

A highly compact optical modulator is proposed and analyzed. The modulator is based on the hybrid plasmonic waveguide platform. The structure of the modulator is built from silicon, silver, and electro-optical polymer layers. Hybrid plasmonic modes of symmetric and asymmetric natures excited in the structure were investigated. The symmetric mode is characterized by its lower propagation loss, so it was selected for the excitation of the device. The modulator's operation mechanism is based on the racetrack resonator configuration. Full three-dimensional electromagnetic analysis was performed around the 1.55-μm telecommunication wavelength. Different parameters such as the power coupling to the bus waveguide, the bend loss, the propagation loss, and the Q-factor of the resonances were studied in order to optimize the racetrack resonator design. The modulator is characterized by its extremely low energy consumption of 0.5 fJ/bit, high modulation depth of 10.5 dB, while the insertion losses were limited to 0.5 dB.

Hybrid plasmonic waveguide coupling of photons from a single molecule

We demonstrate the emission of photons from a single molecule into a hybrid gap plasmon waveguide. Crystals of anthracene, doped with dibenzoterrylene (DBT), are grown on top of the waveguides. We investigate a single DBT molecule coupled to the plasmonic region of one of the guides and determine its in-plane orientation, excited state lifetime, and saturation intensity. The molecule emits light into the guide, which is remotely out-coupled by a grating. The second-order autocorrelation and cross-correlation functions show that the emitter is a single molecule and that the light emerging from the grating comes from that molecule. The coupling efficiency is found to be βWG = 11.6(1.5)%. This type of structure is promising for building new functionality into quantum-photonic circuits, where localized regions of strong emitter-guide coupling can be interconnected by low-loss dielectric guides.

Highly confined long range transmission of a surface plasmon polariton mode in a novel design of metallic slit-groove nanostructures

In this paper a novel metallic slit-groove nanostructure is proposed for long range unidirectional transmission of light from a subwavelength slit. This nanostructure utilizes a metallic slit-groove nanostructure coupled with a hybrid Plasmon waveguide to travel the surface plasmon polariton (SPP) beam with a high intensity in long travel distances. The new design takes advantage of both unidirectional excitation of SPP mode in metallic slit-groove nanostructures and highly confined mode in hybrid plasmonic waveguides. The coupling strength between metallic gratings with hybrid plasmonic waveguide is dominated by the geometric parameters of the nanostructure. The simulation results show that our proposed structure has higher mode intensity and longer propagation length compared to that of conventional metallic slit-groove nanostructure.

Nanophotonic on-chip hybrid plasmonic electro-optic modulator with phase change materials

A vertical hybrid plasmonic waveguide (HPWG) modulator incorporating Au nano-rings and operating in the near-infrared (NIR) band is proposed using phase change chalcogenide thin film (Ge2Sb2Te5, commonly known as GST). It is shown that with amorphous to crystalline phase transition of GST, significant modulation depths can be achieved in the optical C-band. Further, localized surface plasmon resonance (LSPR) excitations from the Au nano-ring embedded in the low-indexed slot region is used to enhance the overall performance of the reported GST based electro-optic modulator. In addition, significant wavelength shifts, and improved extinction ratio (ER) is obtained by varying Au nano-ring radius and other geometrical parameters. Our finite element method based 3D-COMSOL numerical simulations reveal that 12.24dB/μm (9.3dB/μm) extinction ratio per unit length can be achieved with (without) Au nano-rings considering r=80 nm; L=500 nm; and λ=1.56 um, respectively.

Temperature Sensor of MoS2 Based on Hybrid Plasmonic Waveguides

In order to overcome the challenge of traditional sensors, including large size, complex preparation process, and difficult filling and sensing media, a long-range dielectric-loaded hybrid plasmonic waveguide (LRDLHPW) based on MoS2 is proposed and numerically studied. The propagation length is as high as 4.85 cm, and the corresponding mode width is 981 nm. A near-infrared plasmonic sensor based on the hybrid plasmonic waveguide-nanocavity system achieves a refractive index sensitivity of 787.5 nm/RIU and line width and figure of merit of 30 nm and 26.3, respectively; at the same time, the temperature sensitivity is as high as 2.775 nm/ ° C. Compared with other researches, the sensor proposed in this paper improves the adaptability and sensitivity of the device, and the ultracompact structure combined with the planar waveguide structure makes it easy to integrate to chip. In addition, the device can also be used as an adjustable surface plasmon polaritons band-pass filter. Note that increasing sensitivity is accompanied by decreasing resolution, and vice versa. The trade-off between sensitivity and resolution is important in order to achieve a larger figure of merit. In general, the structure designed by us achieves good optical and sensing characteristics and is widely used in nanophotonic circuits, environmental monitoring, and even drug research.

Excitation of Hybrid Plasmonic Waveguide Modes by Colloidal Quantum Dots

Quantum information technologies will greatly benefit from efficiently coupled quantum emitter–waveguide systems. Hybrid plasmonic waveguide modes are relatively low-loss confined modes, which prov...

Compact general interference hybrid-plasmonic multimode interferometers used for optical hybrid.

We propose three general interference multimode interferometers (MMIs) based on hybrid plasmonic waveguides (HPWs). Among them, the general 2×2 and 4×4 MMIs are designed for a 90° optical hybrid, while the 3×3 MMI is for a 120° optical hybrid. First, by considering the mode interference characteristics inside the multimode HPWs, a compromise between the number of guided modes and the device length is obtained at a determined height of the SiO2 interlayer of the HPW. Also, by analyzing the characteristics of multimode propagation in the HPW-MMI, it is found that the optimal positions of self-images would shift from their theoretical ones. In addition, tapered HPW sections are implemented to improve the coupling efficiencies for lights coupled into/out of the multimode section. Therefore, by optimizing the width and length of the multimode section, and especially the position of the input and output single-mode waveguides, the appropriate structure parameters of three HPW-MMIs are obtained, where the footprints of the 2×2, 3×3, and 4×4 HPW-MMIs are only 1.96×5.4 μm2, 2.18×12.0 μm2, and 2.52×11.5 μm2, respectively. The simulation results show that, at the wavelength of 1550nm, the 2×2 HPW-MMI exhibits a transmission of 75.6%, a maximum transmissions imbalance of 0.55dB, and a phase error of 3.68°; the 3×3 HPW-MMI exhibits a transmission of 69.2%, a maximum transmissions imbalance of 0.43dB, and a phase error of 4.66°; and the 4×4 HPW-MMI exhibits a transmission of 68.5%, a maximum transmissions imbalance of 0.91dB, and a phase error of 4.81°. All these performances meet the standard industry requirements.

Low loss semi‐MIM hybrid plasmonic waveguide with high electric field confinement

AbstractAmong different types of plasmonic waveguides that support surface‐plasmon‐polariton (SPP) mode, metal‐insulator‐metal (MIM) waveguides have the best electric field confinement in expense of high propagation loss. On the other hand, hybrid plasmonic waveguides (HPWGs) are represented as low loss plasmonic waveguides with moderate confinement. In this work, a new design of HPWG is proposed with higher electric field confinement compare with conventional HPWG by adding lossy spacer layer to the designed HPWG. This modification causes the proposed design be more similar to metal‐insulator‐metal (MIM) waveguides but with less propagation loss. The proposed design is called semi‐MIM HPWG and its structure is studied analytically and numerically. Dimensions of the proposed semi‐MIM HPWG is optimized to work at 193.5 THz and the proper stepped taper transition is designed to feed the waveguide by photonic feed lines.

Compact and broadband silicon-based mode-division (de)multiplexer using an asymmetrical directional coupler

We have proposed an ultracompact mode-division (de)multiplexer ((de)MDMUX) based on an asymmetrical directional coupler (ADC) with SiO2 top cladding, where a taper-etched silicon wire and a hybrid plasmonic waveguide (HPW) are used. By carefully selecting the structural dimensions, TE0 mode from the input port 1 (I1) is gradually coupled into the wide multimode waveguide (MMW) and then transformed to TE1 mode while that from the input port 2 (I2) just passes through the bar branch and outputs directly, forming an efficient two-mode (de)multiplexer. With the aid of the HPW as well as the taper-etched wire, coupling length is reduced and fabrication tolerance is enlarged to some extent. From the results, such device has a total length of only 17.1μm with a short coupling length of 4.1μm, and it provides a low crosstalk (CT) of -25.6 (-27.7) dB and a low insertion loss (IL) of 0.51 (0.04) dB at the wavelength of 1.55μm when TE0 mode is input in the I1 (I2).

Subpicosecond flat-top pulse shaping using a hybrid plasmonic microring-based temporal differentiator

Design of a fractional-order photonic temporal differentiator, based on the silicon hybrid plasmonic add-drop microring resonators, is proposed. Because of the strong light confinement in the hybrid plasmonic waveguides, the overall footprint of the differentiator is significantly reduced. The numerical simulation results show that the differentiator can reach considerably wide 3 dB bandwidth of about 2.5 THz (20 nm) with the microring radius of 1.2 μm. It is also shown that the differentiation order and the 3 dB bandwidth of the proposed structure can be tuned in the range of [0.6 1.0] and [1.74 2.5] THz ([14 20] nm), respectively, by modifying the geometrical parameters of the differentiator. Mentioned bandwidth is higher than the previously reported values for microring-based photonic differentiators. Furthermore, the wide bandwidth and the tunable differentiation order of the structure along with its compact footprint make it a promising choice for the processing of ultrashort optical pulses. Generation of short flat-top pulses from input Gaussian pulses is then considered as an example of such applications. It is shown through three-dimensional finite-difference time-domain simulations that the proposed differentiator can be used to generate a flat-top pulse with the flat duration of 330 fs and the FWHM of ∼1 ps, from an ultrashort Gaussian input pulse, with the FWHM of 490 fs.

Modifying the figure of merit in hybrid plasmonic waveguide for Kerr nonlinear effect

Hybrid plasmonic waveguide (HPW) has offered the promise to combine long propagation lengths and strong modal confinement at sub-wavelength scale. All-optical signal processing can be achieved by relying on nonlinear optical interactions such as Kerr nonlinear effect. It is essential to provide sufficient information in order to characterize the nonlinear optical performance of nonlinear HPW (NLHPW). In this study, a figure of merit (FoM) was proposed for the description of the performance of the nonlinear optical waveguide characterized by its material damage threshold, propagation length, nonlinear coefficient, and confinement factor. In this paper, SOI-based and InP-based NLHPW were simulated using finite element method, and they were evaluated with regards to proposed FoM at telecom wavelength of 1550 nm.