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The design and development of low-cost, efficient, and stable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are desirable for rechargeable metal-air batteries. In this work, N-doped porous hollow carbon spheres encapsulated with ultrafine Fe/Fe3O4 nanoparticles (FeOx@N-PHCS) were fabricated by impregnation and subsequent pyrolysis, using melamine-formaldehyde resin spheres as self-sacrifice templates and polydopamine as N and C sources. The sufficient adsorption of Fe3+ on the polydopamine endowed the formation of Fe-Nx species upon high-temperature carbonization. The prepared FeOx@N-PHCS has advanced features of large specific surface area, porous hollow structure, high content of N dopants, sufficient Fe-Nx species and ultrafine FeOx nanoparticles. These features endow FeOx@N-PHCS with enhanced mass transfer and considerable active sites, leading to high activity and stability in catalyzing ORR and OER in alkaline electrolyte. Furthermore, the rechargeable Zn-air battery with FeOx@N-PHCS as air cathode catalyst exhibits a large peak power density, narrow charge-discharge potential gap and robust cycling stability, demonstrating the potential of the fabricated FeOx@N-PHCS as a promising electrode material for metal-air batteries. This new finding may open an avenue for rational design of bifunctional catalysts by integrating different active components within all-in-one catalyst for different electrochemical reactions.

Developing cost-efficient electrocatalysts for ambient N2-to-NH3 conversion and revealing the reaction mechanism are appealing yet challenging tasks. Some transition metal oxides have been recently used to catalyze the nitrogen reduction reaction (NRR), but their further applications are greatly impeded because of their questionable conductivity, poor dispersion, limited active sites, and so forth. Herein, three-dimensional Ni foam-supported urchin-like Al-doped Co3O4 nanospheres rich in surface oxygen vacancies (Al-Co3O4/NF) were prepared via a hydrothermal process and subsequent annealing treatment. It is shown that introducing Al atoms into Co3O4 effectively tunes the electronic properties of the catalyst, and the increased surface oxygen vacancies induced by Al doping facilitate the activation of nitrogen. What is more, this urchin-like nanostructure, demonstrating an ability to limit the coalescence of gas bubbles, enables the rapid removal of small gas bubbles and better exposure of active sites to N2, thus yielding an impressive ammonia electrosynthesis activity (NH3 yield rate: 6.48 × 10-11 mol s-1 cm-2; Faradaic efficiency: 6.25%) in 0.1 M KOH. Electrochemical-based in situ Fourier transform infrared spectroscopy was employed to study the mechanism of NRR, indicating an associative alternating pathway.

We systematically investigated graphene-based slot and multi-slot waveguides. A tri-slot waveguide which significantly enhances the light-graphene interaction was experimentally demonstrated with low insertion loss. By integrating a dual-layer graphene h-BN heterostructure on the tri-slot waveguide, a high efficiency modulator is designed, which combines the advantages of high modulation efficiency (0.376 dB/μm), low insertion loss (0.01 dB/μm), large modulation bandwidth (∼0.13 THz) and low power consumption (∼0.128 pJ/bit). Our work may promote the development of future high efficient graphene-based optical devices.

Nitrogen fixation via the electrochemical nitrogen reduction reaction under ambient conditions has the potential to disrupt the energy-intensive Haber–Bosch process with a more environmentally friendly alternative. Utilizing air as the feed stock would represent an important step towards future industrialization of green ammonia. Herein, a gold–copper nanoalloy-decorated zeolitic imidazolate framework, denoted as AuCu/ZIF-8, exhibits high NH3 yield, remarkable efficiency, long-term stability and pH independence for the electrochemical synthesis of ammonia. Making ammonia from thin air and renewable electricity speaks well for the development of sustainable ammonia refineries.

Transparent films are significant industrial components that are widely used in modern optics, microelectronics, optical engineering, and other related fields. There is an urgent need for the fast and stable thickness measurement of industrial films at the micron-grade. This paper built a miniaturized and low-cost film thickness measurement system based on confocal spectral imaging and the principle of thin-film spectral interference. The reflection interference spectrum was analyzed to extract the phase term introduced by the film thickness from the full spectrum information, where local spectral noise can be better corrected. An efficient and robust film thickness calculation algorithm was realized without any calibrating sample. The micron-grade thickness measurement system had an industrial property with a measurement range of up to 75 &mu, m with a measurement uncertainty of 0.1 &mu, m, presenting a good performance in single-layer film thickness measurement with high efficiency.

Contact force quality is one of the most critical factors for safe and effective lesion formation during cardiac ablation. The contact force and contact stability plays important roles in determining the lesion size and creating a gap-free lesion. In this paper, the contact stability of a novel magnetic resonance imaging (MRI)-actuated robotic catheter under tissue surface motion is studied. The robotic catheter is modeled using a pseudo-rigid-body model, and the contact model under surface constraint is provided. Two contact force control schemes to improve the contact stability of the catheter under heart surface motions are proposed and their performance are evaluated in simulation.

We report a highly efficient graphene-based modulator by using an edge plasmonic effect in this paper. The modulation efficiency of the proposed modulator can be as large as 1.58 dB/μm, which is several times larger than that of previous reported modulators. By enhancing the gap plasmon mode and the edge plasmonic effect in a well-designed diagonal waveguide, a wedge-to-wedge SPP mode is strongly confined in both horizontal and vertical directions in terms of a small mode area (Aef /A0

Computational study of nanopillar Si/poly (3,4-ethylene dioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) heterojunction solar cell is performed by using finite element method to solve Poisson equation, drift-diffusion equations, and current continuity equations. The depletion width around the edge of the Si nanopillar is almost the same as that of planar junction, while the depletion width around the middle of the Si nanopillar is much wider than that of planar junction. As a result, besides the enhanced light absorption due to light trapping induced by nanopillar array as in previous studies, larger depletion region, which leads to higher electron-hole separation efficiency under light illumination, is another reason for short-circuit current increase of nanopillar solar cell. The reason for less open-circuit voltage of nanopillar solar cell is also clarified by explaining the reason for large dark current of the nanopillar solar cell compared to its planar structure counterpart as follows. The kink of the potential profile along the lines around the edge nanopillar leads to much sharper potential drop in the following depletion region, and results in greater hole density slope when the solar cells are forwarded biased. Since the Si/PEDOT:PSS behaves like a pn junction rather than a Schottky junction as clarified in the previous study and the PEDOT:PSS is much highly doped, nanopillar heterojunction has larger dark current than planar junction due to the larger hole diffusion current around Si nanopillar edge.

Near-infrared photodetectors (NIRPDs) have attracted great attention because of their wide range of applications in many fields. Herein, a novel self-driven NIRPD at the wavelength of 980 nm is reported based on the graphene/GaAs heterostructure. Extraordinarily, its sensitivity to light illumination (980 nm) is far beyond the absorption limitation of GaAs (874 nm). This means that the photocurrent originates from the separation of photo-induced carriers in graphene, which is caused by the vertically built-in electric field formed through the high quality van der Waals contact between graphene and GaAs. Moreover, after introducing NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) onto the graphene/GaAs heterojunction, the responsivity increases to be as superior as 5.97 mA W-1 and the corresponding detectivity is 1.1 × 1011 cm Hz0.5 W-1 under self-driven conditions. This dramatic improvement is mainly ascribed to the radiative energy transfer from UCNPs to the graphene/GaAs heterostructure. The high-quality and self-driven UCNPs/graphene/GaAs heterostructure NIRPD holds significant potential for practical application in low-consumption and large-scale optoelectronic devices.

It is of great importance to establish a definite relationship between structure and catalytic properties for developing highly efficient single-atom catalysts (SACs); however, this remains a challenge. Herein, three single atoms anchored on a nitrogen-doped carbon matrix (M-N-C, M = Fe, Co, Ni) with a metal-pyridine N structure were prepared and investigated as catalysts for electrochemical CO2 reduction. M-N-C exhibit promising capability for CO2-to-CO conversion with the selectivity order of Ni > Co > Fe and the activity order of Co > Ni > Fe, in contrast to the previously reported performance order of Ni > Fe > Co. Among M-N-C catalysts, Ni-N-C shows superior selectivity (approximately 100% CO Faradaic efficiency from −0.66 V to −0.96 V), whereas Co-N-C exhibits high activity (CO current density = −24.24 mA cm−2 and CO turnover frequency = 7182 h−1 at −0.86 V) and capability of yielding syngas (CO/H2 = 0.5∼2.11). Density functional theory calculations support the experimental selectivity and activity orders. This study presents a new possibility for improving the catalytic performance of SACs by investigating the coordinated environments of metal atoms.

A low-profile broadband bandpass frequency selective surface (FSS) with two rapid band edges is proposed in this paper for 5G near-field applications. The overall structure consists of three metallic layers, separated by two thin substrates with a thickness of 0.07λ. In addition, some centro-symmetric miniaturized slots are introduced in the middle metallic layer to further improve its stability and reduce its physical dimensions. A corresponding equivalent circuit model (ECM) is also proposed to better analyze the principles of the proposed FSS. Finally, an FSS prototype working at the center frequency of 27.5 GHz with a relative -3 dB bandwidth of 20.5% is fabricated and measured. More than 25 dB shielding effectiveness can be obtained out of the passband for a bandwidth of 1.46 GHz in this experiment. Both 3-D full-wave simulations and ECM results are in good agreement with the experimental results, having a maximum deviation of only 2.257% in the transmission zeros and poles. These results demonstrate that the proposed FSS is a good candidate for 5G near-field EMI shielding.

An active absorber with nearly zero static power consumption is proposed based on nonvolatile floating-gate graphene structure. Such absorber has almost no static power consumption benefited from the nonvolatile design. In such design, the central graphene can capture the tunneled electrons under the positive applied voltage, but cannot release these electrons after removing the voltage since it is electrically isolated from the external electrodes. Therefore, no extra power is needed to sustain the conductivity of graphene. Moreover, our proposed absorber exhibits an extremely strong absorption capacity. Even taking the strict condition for the bandwidth where all the absorptivity inside the bandwidth are larger than 90% as criterion, the proposed absorber provides more than 60 GHz absorption bandwidth which is twice larger than previous results. Furthermore, the proposed absorber shows high tolerance against large incidence angle ( $60^\circ $ ), different polarizations and nonideal factors of graphene. The results may promote various future nonvolatile absorber designs.

A graphene-based hybrid plasmonic modulator (GHPM) is proposed by adopting the electro-absorption effect of graphene. The simulation results show that the modulation efficiency of GHPM can be as large as 0.417 dB/μm, which is more than twice as much as that of recently presented graphene-on-silicon modulator (GOSM). Then we fabricate a prototype of GHPM. The measurement results demonstrate that the GHPM can work in a broadband from 1530 nm to 1570 nm and an improved modulation efficiency of 1.08 dB (at 30 μm). At last, we have discussed the factors that influence the modulation efficiency. Our work may promote the development of on-chip graphene-based plasmonic devices.

We present an effective scheme to improve the modulation capacity in graphene-based silicon modulator by employing the double slots configuration with hybrid plasmonic effects. Two modulators, i.e., metal-insulator-metal and insulator-metal-insulator configurations have been demonstrated, showing that the double slots design can significantly improve the modulation efficiency. The obtained modulation efficiency is up to 0.525 dB/μm per graphene layer, far exceeding previous studies. It can be found that the light-graphene interaction plays a pivotal role in the modulation efficiency, whereas the height of metal has profound influence on the modulation. Our results may promote various future modulation devices based on graphene.

An all-fiber structured electro-absorption (EA) modulator based on graphene is proposed. The graphene is directly attached to the core of the fiber to ensure the coupling efficiency. Mode analysis is used to reveal the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Compared with conventional semiconductor EA modulators, it exhibits an excellent performance with the advantages such as small footprint (50.2 μm), small voltage swing (0.2 V), and broad operation bandwidth. In addition, the proposed modulator features simple structure, low optical propagation and coupling loss, and good integrated compatibility as the fiber modulator. All these edges prospect the great potentiality in future high-speed optic fiber communications, optical signal processing, and all-fiber systems.

Monolayer MoS2 photodetectors are modeled and simulated by self-consistently solving diffusive transport equations in the presence of light illumination and carrier recombination with the 2-D Poisson equation. The simulated results indicate that very high photoresponsivity (PR) of $\sim 1000$ A/W observed in others’ experiments is due to strong electrostatic effect of pile up of optically generated holes, and efficient optical absorption. It is found that the value of PR is sensitive to gate bias voltage, and the photodetector performance can be improved by decreasing hole mobility if side effects of low hole mobility, such as high recombination rate, slow response speed, and more noise, are suppressed. High quality monolayer MoS2 with large electron mobility and less Shockley–Read–Hall recombination defects is desired for achieving high performance. The PR increases as the gate insulator thickness increases. The channel length needs to be carefully designed by considering the carrier recombination behavior in monolayer MoS2. The optimization method of monolayer MoS2 photodetectors proposed here is also applicable to other monolayer transition-metal dichalcogenide materials in general.

In this work, a wide band slow light is achieved in a simple one-dimensional grating waveguide. A flat band indicating slow light with group index of 13 and bandwidth over 10nm is obtained.

A broadband and tunable absorber with nearly zero static power consumption is proposed based on non-volatile floating-gate graphene structure. Such absorber has almost no static power consumption benefited from the non-volatile design. In such design, the central graphene can capture the tunneled electrons under the positive applied voltage, but cannot release these electrons after removing the voltage since it is electrically isolated from the external electrodes. Therefore, no extra power is needed to sustain the conductivity of graphene. Moreover, our proposed absorber exhibits an extremely strong absorption capacity. Even taking the strict condition for the bandwidth where all the absorptivity inside the bandwidth are larger than 90% as criterion, the proposed absorber provides more than 60 GHz absorption bandwidth which is twice larger than previous results. Furthermore, the proposed absorber shows high tolerance against large incidence angle (60°), different polarizations. The results may promote various future non-volatile absorber designs.

We proposed a versatile polarizer independent with the polarization of the incident light by coating the graphene on the silicon waveguide. The proposed polarizer works at two operation states: TE-pass state and TM-pass state, where the variation of mode effective index is different for the two states. Therefore it is able to combine TE-pass and TM-pass polarizer into one single component. The proposed device owns a compact size of 69.65μm∗2μm, high extinction ratio 19.15dB for TE-pass polarizer and 20.68dB for TM-pass polarizer, respectively. Furthermore, this device exhibits a wide working bandwidth from 1500nm to 1800nm.

We propose a high efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency is ∼8-folds larger than that of present graphene-on-silicon modulator (GOSM) (∼0.1 dB / μm). The proposed modulator has the advantage of short modulation length ∼3.6 μm, relatively low insertion loss ∼0.32 dB and larger modulation bandwidth ∼0.48 THz. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric (TE) mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This study may promote the design of high-performance on-chip electro-optical modulator.

This letter presents a novel graphene-embedded optical ring modulator that significantly enhances the modulation efficiency and tunability. Due to the enhanced light-matter interaction of graphene-embedded design, the shift rate of the resonance peak has been improved to 1.08 nm per applied voltage, which is two orders of the magnitude higher than previous ring modulators. The narrow bandwidth of the resonant modulator has been ameliorated to 149 GHz. In addition, our proposed modulator exhibits the advantages of high extinction ratio (22.13 dB) and smaller power consumption. Furthermore, a good tolerance of temperature drift (27 K) has been demonstrated in the proposed modulator.

The power distribution network (PDN) impedance of 3-D-through silicon vias (TSVs) interposer layer is modeled by considering the metal-oxide-semiconductor (MOS) structure effects. The Lambert W function is proposed to simulate the change of depletion width with the bias voltage in the static field, and the high-frequency MOS capacitance is obtained while considering the charges at the semiconductor-insulator interface. Furthermore, based on the depletion width and the insulating dielectric layer assumption, the electrical model of power-ground TSVs pair is presented by combining the MOS capacitance with TSVs parasitic RLGC (resistance-inductance-capacitance-conductance). Finally, the PDN impedance characteristics of the 3-D-IC integrated system with multiple TSVs are performed by using the proposed multitransmission line and model reduction methods, and the importance of the capacitance is presented.

A non-contact method is proposed to characterize graphene at microwave frequency by combining Raman spectroscopy and Amphenol Precision Connector (APC-7). The CVD-grown graphene is transferred to the ring-shape Teflon substrate and characterized by Raman spectroscopy to estimate its doping density and the related Fermi energy. The graphene is then sandwiched between two APC-7 coaxial connectors and S parameters under transverse electromagnetic (TEM) mode normal incident waves are measured to extract the surface conductivity through transmission matrix, in which the de-embedding process can be avoided. By combing the Kubo formula with our proposed circuit model, the scattering rate of graphene on Teflon substrate is obtained and analyzed.

In this paper, we propose a novel double-shielded interposer design with two metal layers directly contacting to the silicon substrate surfaces for high-speed signal propagating along through silicon vias (TSVs). To enhance the shielding effects, shallow highly doped silicon is made on both sides of the silicon interposer forming ohmic contact between the metallization layer and silicon. The metallization layer is etched into meshed pattern to prevent delamination. Based on the imaging method, we derive the equivalent circuit model of the proposed double-shielded interposer, and the accuracy and efficiency of the equivalent circuit model is verified by full-wave method. The proposed design can concentrate the electromagnetic field around TSVs, so that it has a lower insertion loss than the conventional ground-signal (GS) structure without shielding. This is especially useful when the low-resistivity silicon is used for the interposer. Finally, some applied guidelines are proposed to strengthen the performance and simplify the silicon fabrication processes.

We propose a graphene-based modulator integrated into currently used communication fibers. The graphene is directly built into the core of the fiber to ensure the coupling efficiency. The fiber is deliberately side-polished to enhance the light-graphene interaction. The two-dimensional model analysis method and three-dimensional finite difference time domain method are used to rigorously disclose the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Based on such a structure, a phase modulator with an arm length of 127 μm is numerically demonstrated with enhanced modulation efficiency. A quasi-linear relation between the phase change and chemical potential of graphene is found theoretically for the first time, providing a large linear dynamic range to control the phase of optical modulation.

Graphene has shown promising perspectives in optical active components due to the large active-control of its permittivity-variation. This paper systematically reviews the recent developments of graphene-based optical modulators, including material property, different integration schemes, single-layer graphene-based modulator, multi-layer and few-layer graphene-based modulators, corresponding figure-of-merits, wavelength/temperature tolerance, and graphene-based fiber-optic modulator. The different treatments for graphene’s isotropic and anisotropic property were also discussed. The results showed graphene is an excellent material for enhancing silicon’s weak modulation capability after it is integrated into the silicon platform, and has great potentials for complementary metal oxide semiconductor (CMOS) compatible optical devices, showing significant influence on optical interconnects in future integrated optoelectronic circuits.

The investigation of few-layer graphene embedded in silicon waveguide (GESW) exhibits it has a superior performance than monolayer GESW where the effective mode index variation ( Δ n e f f ) at the given chemical potential change and the number of graphene layers N (N Δ n e f f of quadri-layer GESW can be as large as 0.047, based on which a Mach–Zehnder modulator has been proposed with the advantages of only 16.5 μm arm length, low energy consumption (8 fJ/bit), high extinction ration (31.8 dB) and small applied voltage (

The analytical model based on Poisson–Boltzmann equation in a cylindrical coordinate system is developed for simulating the electrical parameters of the three-dimensional Through Silicon Via (TSV) interconnection. Considering the effects of bias voltage, the accurate charge distribution and the high-frequency capacitance in the depletion layer of the semiconductor is obtained. Moreover, the resistance and inductance parameters of TSV are extracted by using the partial element equivalent circuit method. Finally, the full resistance–inductance–capacitance–conductance electrical model of TSV interconnection is presented first time with the semiconductor behaviour, and the transmission characteristics of signal-ground TSV structure are studied.

By embedding graphene sheet in the silicon waveguide, the overall effective mode index displays unexpected symmetry and the electrorefraction effect has been significantly enhanced near the epsilon-near-zero point. An eight-layer graphene embedded Mach-Zehnder Modulator has been theoretically demonstrated with the advantage of ultracompact footprint (4 × 2 μm2), high modulation efficiency (1.316 V·μm), ultrafast modulation speed, and large extinction ratio. Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications.

In this Letter, we report a graphene-based hybrid plasmonic modulator (GHPM) realized by employing the electro-absorption effect of graphene. The simulation results show that the modulation efficiency of GHPM, i.e., extinction ratio per length, can be as large as 0.417 dB/μm, which is more than twice as much as that of recently presented graphene-on-silicon modulator. It was found that the improvement in modulation efficiency is mainly due to the enhancement of the overlap between graphene and the mode field in GHPM. A prototype of GHPM was fabricated. The measurement results showed that the GHPM can work in a broadband from 1530 to 1570 nm and an improved modulation efficiency of 1.08 dB (at 30 μm). Finally, we have discussed the factors that influence the modulation efficiency. Our proof-of-concept design may promote the development of on-chip graphene-based plasmonic devices.

Slow light, a technology to control the optical signal by reducing the group velocity, has been widely studied to obtain enhanced nonlinearities and increased phase shifts owing to its promoting of the light–matter interaction ability. In this work, a wideband slow light is achieved in a simple one-dimensional fishbone grating waveguide. A flat band indicating slow light with a group index of 13 and bandwidth over 10 nm is obtained by the plane wave expansion calculation, and the corresponding experimental results agree well with the theoretical prediction. A step taper is designed to compensate the coupling loss. The proposed fishbone grating waveguide is a good candidate for wideband slow light devices in light communication.

We reported a novel terahertz modulator based on graphene-embedded waveguide. Comparing to previous solution, the terahertz wave-matter interaction in the modulator structure is enhanced greatly. In theory, the modulation depth can be nearly 100% as the simulation results show. Experimental characterisations are carried out through continuous terahertz wave system and the terahertz time-domain spectroscopy (TDZ) system respectively. The best experimental modulation depth is 29.53%, which is much larger than state-of-art results.

We have systematically investigated the slow light performances based on two-dimensional material graphene, giving the conclusion that graphene exhibits much larger slow light capability than other materials. A large delay-bandwidth product has been obtained in a simple yet functional graphene-based waveguide with slow down factor c / υ g at 109 and slow light bandwidth Δω at 14.5 nm, which is several orders of magnitude larger than previous results.

The energy-momentum dispersion relation is a fundamental property of plasmonic systems. In this paper, we show that the method of dispersion engineering can be used for the design of ultra-compact graphene-based superscatterers. Based on the Bohr model, the dispersion relation of the equivalent planar waveguide is engineered to enhance the scattering cross section of a dielectric cylinder. Bohr conditions with different orders are fulfilled in multiple dispersion curves at the same resonant frequency. Thus the resonance peaks from the first and second order scattering terms are overlapped in the deepsubwavelength scale by delicately tuning the gap thickness between two graphene layers. Using this ultra-compact graphene-based superscatterer, the scattering cross section of the dielectric cylinder can be enhanced by five orders of magnitude., This paper has been accepted by IEEE Journal of Selected topics in Quantum Electronics

A full-polarization arbitrary-shaped 3D metasurface cloak with preserved amplitude and phase in microwave frequencies is experimentally demonstrated. By taking the unique feature of metasurfaces, it is shown that the cloak can completely restore the polarization, amplitude, and phase of light for full polarization as if light was incident on a flat mirror.

Slow light in planar photonic structures has attracted for some years an increasing interest due to amazing physical effects it allows or reinforces and to the degrees of freedom it raises for designing new optical functions. Controlling light group velocity is achieved through the use of periodical optical media obtained by nano-structuration of semiconductor wafers at the scale of light wavelength: the so-called photonic crystals. This article reviews present achievements realized in the field of slow light photonic bandgap structures, including the physical principles of slow light to the description of the most advanced integrated optical devices relying on it. Challenges and current hot topics related to slow light are discussed to highlight the balance between the advantages and drawbacks of using slow waves in integrated photonic structures. Then, future trends are described, which is focused on the use of slow wave slot waveguides for nonlinear optics and bio-photonic applications.

An ultra-compact and low-loss transverse-electric (TE)-pass polarizer is proposed by utilizing a hybrid plasmonic ridge waveguide structure on a silicon-on-insulator platform. Since the transmission of a plasmonic polarizer is greatly influenced by the interaction between the metal and the optical field, there is a large insertion loss (IL) in the polarizer based on a hybrid plasmonic waveguide. Here, the electric field distribution and the periodic coupling between the fundamental transverse magnetic mode and plasmonic mode are taken into consideration to decrease the IL and shorten the length of the device. For a 4.2 μm-long polarizer, numerical simulations with the finite-differential-time-domain method show that it has a large extinction ratio (ER) of ∼29.5 dB with a low IL of 0.18 dB at the central wavelength 1550 nm. In addition, a more than 23 dB ER is achieved across a wide bandwidth of 100 nm.

Former study shows that the graphene-embedded modulator can only work in TE mode while cannot achieve enough extinction ratio in TM mode. However, an optical modulator which can work in both TE mode and TM mode is required by the mode multiplexing technology. By simply growing a graphene-aluminum oxide metamaterial layer on the silicon waveguide, an optical-absorption modulator which can achieve a large extinction ratio in both TE mode and TM mode is designed in this letter. In addition, our modulator can achieve a very compact footprint which is only 10 μm.

We have systematically investigated the wideband slow light in two-dimensional material graphene, revealing that graphene exhibits much larger slow light capability than other materials. The slow light performances including material dispersion, bandwidth, dynamic control ability, delay-bandwidth product, propagation loss and group-velocity dispersion are studied, proving graphene exhibits significant advantages in these performances. A large delay-bandwidth product has been obtained in a simple yet functional grating waveguide with slow down factor c/vg at 163 and slow light bandwidth Δω at 94.4 nm centered at 10.38 μm, which is several orders of magnitude larger than previous results. Physical explanation of the enhanced slow light in graphene is given. Our results indicate graphene is an excellent platform for slow light applications, promoting various future slow light devices based on graphene.

The dynamic control of wide band slow surface wave in a graphene-based grating waveguide is proposed here. The extreme large bandwidth and strongly delay has been obtained and the group index can be dynamically tuned.

We propose a highly efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency (up to 1.23 dB/μm after optimization) is ∼12-fold larger than that of the present graphene-on-silicon modulator (∼0.1 dB/μm). The proposed modulator has the advantage of a short modulation length of ∼3.6 μm, a relatively low insertion loss of ∼0.32 dB, and a larger modulation bandwidth of ∼0.48 THz. The physical insight is investigated, showing that both the slow light effect and the overlap between graphene and the mode field contribute. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This Letter may promote the design of high-performance on-chip electro-optical modulators.

Optical modulator is the key components in the optical communication, yet the low modulation efficiency limits its development. A high efficiency, ultra-compact optical modulator is proposed which the electro-refraction effect has been significantly enhanced. The different kinds of graphene schemes are compared and discussed. A graphene embedded Mach-Zender modulator has been theoretically demonstrated with the advantage of ultra-compact footprint (4×30 μm2), high modulation efficiency (20 V·μm), fast modulation speed and large extinction ratio (35dB). Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications.

Enlarged group index has been reported previously when surface plasmons propagate through the graphene sheet, yet a clear slow wave performance in graphene has not been explored. We proposed and numerically analyzed here for the first time to the best of our knowledge an extremely wideband slow surface wave in a graphene-based grating waveguide. The strongly delayed wave (120n(g)167) with extremely large bandwidth (2.7 THzΔf0.7 THz) can be dynamically controlled via the gate-voltage dependent optical properties of graphene. Our results suggest that graphene may be a very promising slow light medium, promoting future slow light devices based on graphene.

Flat band slow light in symmetric line defect photonic crystal waveguides formed by adding dielectric pillars in the air holes nearest to the waveguide core is investigated. By adjusting the radii of the new dielectric pillars, a linear band in the photonic band structure appears which denotes low group velocity dispersion. High average group index of 74.4 with 2.3-nm bandwidth is demonstrated in an optimized waveguide by finite-difference time-domain simulation.

The fascinating optical properties of graphene are usually concluded in theory under the assumption that graphene is freestanding. However, in experimentally realizable devices, graphene is usually supported by a substrate, which may influence the optical properties of the graphene. Choosing the right substrate is therefore critical for graphene electromagnetic (EM) devices. In this paper, we studied the influence of two types of two-dimensional (2D) insulating substrates, hexagonal boron nitride (h-BN) and fluorographene (FG), on the graphene optical properties at room temperature. Our work shows that both substrates can preserve well the optical properties of graphene from 0.6 eV to 3.5 eV and the FG substrate can retain graphene’s original properties much better than the h-BN substrate when the photon energy is 3.5 eV. Besides, by analyzing the Kubo formula, the relaxation time of non-freestanding graphene, which can reflect the substrate–graphene interaction, is highly dependent on the substrate type and its stacking pattern. A THz graphene surface plasmonic modulator is used to further explain the substrate effect on graphene EM device design. Our results demonstrate that the h-BN substrate may degrade or fail the performance of THz (0.2 eV) can overcome the performance degradation. Finally, the substrate effects on graphene properties are also studied by examining the electronic properties of double-layer structures. Our results on the sensitivity issue that are caused by the stacking pattern and inter-layer distance may provide a reasonable explanation on the inconsistency of substrate-induced bandgap opening in graphene/h-BN heterostructures discussed in recent experimental and theoretical studies.

We have demonstrated a novel optical parallel transmission line constructed by multi-channel surface plasmon-polariton waveguides based on cross-index-modulation mechanism, which may find application in the field of nano-optical integrated circuits.

The influence on photonic crystal waveguide properties of the fabrication-induced disorder was numerically studied. By comparing the transmission spectra obtained using 3D-FDTD for four kinds of fabrication disorders, it was shown that disorder modifies the waveguide mode properties, especially in the slow light regime. Emphasis was put on the influence of the disorder localization. Results have shown the major role played by technological fluctuations of the size, shape, and position of the two first rows of holes along PhC waveguide axis. Results have revealed that bandgap properties remain almost unaffected even for huge disorder levels provided that the two first rows of holes remain unchanged. Interestingly, 3D-simulation have also shown that sharp transmission spectrum cutoffs that characteristize slow wave modes in the two-dimensional PhC bandgap are then not suppressed by the introduction of disorder but are only blue-shifted. This point constitutes an interesting result for optical integrated devices relying on low group velocity phenomena.

We present the design of realistic annular photonic-crystal (APC) structures of finite thickness aiming to obtain a complete photonic bandgap (PBG). The APC is composed of dielectric rods and circular air holes in a triangular lattice such that each rod is centered within each hole. The optical and geometrical values of the structure are studied, and the interplay between various design parameters is highlighted. The coupled role of the inner-dielectric-rod radius, material types, and slab thickness is investigated. It is shown that the slab thickness is vital to obtain a complete photonic bandgap below the light line, and the specific value of the inner-dielectric-rod radius to sustain the maximum PBG if the hole radius is fixed at proper value is found.

Ring shaped photonic crystals on SOI slab are studied aiming to search for large complete band gap. A gap to mid-gap ratio of 7% is successfully obtained.