Nanoplasmonic Waveguides Research Articles

Coherent Visible-Light-Generation Enhancement in Silicon-Based Nanoplasmonic Waveguides via Third-Harmonic Conversion.

We report visible third-harmonic conversion at λ=517 nm in subwavelength silicon-based nanoplasmonic waveguides at an unprecedented conversion efficiency of 2.3×10^{-5}. This marks both the highest third-harmonic conversion efficiency in a silicon-based or nanoplasmonic structure and the smallest silicon waveguide structure demonstrated to date. The high conversion efficiency is attributed to tight electric field confinement and strong light-matter coupling arising from surface plasmon modes in the nanoplasmonic waveguide, enabling efficient nonlinear optical mixing over micrometer length scales. The nonresonant geometry of the waveguide enables the entire λ=1550 nm femtosecond pulse spectrum to be converted to its third harmonic, which may be easily extended to the entire visible spectrum. We envisage that third-harmonic generation in silicon-based nanoplasmonic waveguides could provide a platform for integrated, broadband visible light sources and entangled triplet photons on future hybrid electronic-silicon photonic chips.

Nanoplasmonic waveguides: towards applications in integrated nanophotonic circuits

The properties of propagating surface plasmon polaritons (SPPs) along one-dimensional metal structures have been investigated for more than 10 years and are now well understood. Because of the high confinement of electromagnetic energy, propagating SPPs have been considered to represent one of the best potential ways to construct next-generation circuits that use light to overcome the speed limit of electronics. Many basic plasmonic components have already been developed. In this review, researches on plasmonic waveguides are reviewed from the perspective of plasmonic circuits. Several circuit components are constructed to demonstrate the basic function of an optical digital circuit. In the end of this review, a prototype for an SPP-based nanochip is proposed, and the problems associated with building such plasmonic circuits are discussed. A plasmonic chip that can be practically applied is expected to become available in the near future. The prospects for creating sophisticated nanophotonic circuits by harnessing the opportunities provided by plasmonics are exciting. Yurui Fang and Mengtao Sun from the Beijing National Laboratory for Condensed Matter Physics review recent progress in the development of various components and devices for generating, manipulating and detecting surface plasmon polaritons — tightly confined waves that can be excited by light at the interface between a metal and a dielectric. Their small size offers opportunities for constructing photonic devices that are smaller than the wavelength of light, a major barrier to the miniaturization of optical integrated circuits. Fang and Sun describe how nanoscale waveguides, multiplexers, lasers, high-speed modulators, logic gates and detectors for surface plasmon polaritons are all coming to fruition. They also consider the future prospects of this technology.

Tunable pattern-free graphene nanoplasmonic waveguides on trenched silicon substrate.

Graphene has emerged as a promising material for active plasmonic devices in the mid-infrared (MIR) region owing to its fast tunability, strong mode confinement, and long-lived collective excitation. In order to realize on-chip graphene plasmonics, several types of graphene plasmonic waveguides (GPWGs) have been investigated and most of them are with graphene ribbons suffering from the pattern-caused edge effect. Here we propose a novel nanoplasmonic waveguide with a pattern-free graphene monolayer on the top of a nano-trench. It shows that our GPWG with nanoscale light confinement, relatively low loss and slowed group velocity enables a significant modulation on the phase shift as well as the propagation loss over a broad band by simply applying a single low bias voltage, which is very attractive for realizing ultra-small optical modulators and optical switches for the future ultra-dense photonic integrated circuits. The strong light-matter interaction as well as tunable slow light is also of great interest for many applications such as optical nonlinearities.

Routing of surface plasmons in silver nanowire networks controlled by polarization and coating.

Controllable propagation of electromagnetic energy in plasmonic nanowaveguides is of great importance for building nanophotonic circuits. Here, we studied the routing of surface plasmons in silver nanowire structures by combining experiments and electromagnetic simulations. The superposition of different plasmon modes results in the tunable near field patterns of surface plasmons on the nanowire. Using the quantum dot fluorescence imaging technique, we experimentally demonstrate that the near field distribution on the nanowire controls the surface plasmon transmission in the nanowire networks. By controlling the polarization of the input light or by controlling the dielectric coating on the nanowire to modulate the plasmon field distribution and guarantee the strong local field intensity at the connecting junction, the surface plasmons can be efficiently routed to the connected nanowires. Depositing a thin layer of Al2O3 film onto the nanowires can reverse the polarization dependence of the output intensity at the nanowire terminals. These results are instructive for designing functional plasmonic nanowire networks and metal-nanowire-based nanophotonic devices.

Ponderomotive electron acceleration in a silicon-based nanoplasmonic waveguide.

Ponderomotive electron acceleration is demonstrated in a semiconductor-loaded nanoplasmonic waveguide. Photogenerated free carriers are accelerated by the tightly confined nanoplasmonic fields and reach energies exceeding the threshold for impact ionization. Broadband (375 nm ≤ λ ≤ 650 nm) white light emission is observed from the nanoplasmonic waveguides. Exponential growth of visible light emission confirms the exponential growth of the electron population, demonstrating the presence of an optical-field-driven electron avalanche. Electron sweeping dynamics are visualized using pump-probe measurements, and a sweeping time of 1.98 ± 0.40 ps is measured. These findings offer a means to harness the potential of the emerging field of ultrafast nonlinear nanoplasmonics.

A special issue on Information Optoelectronics: Devices, Technologies and Applications

Information technology has entered a big-data era. The every-increasing data traffic has driven the rapid development of information optoelectronics, which is related to key devices, crucial technologies, and important applications for the generation, transmission, processing, and detection of optical data information. Recent progresses on devices, technologies and applications of information optoelectronics have led to reduced footprint, improved efficiency, enhanced flexibility and extended functionality generating, delivering/manipulating, and detecting optical data information. Lots of integrated photonic devices, such as silicon-, grapheneand plasmonassisted waveguides, lasers, modulators and detectors, speciality optical fiber, and coherent optical communications, have been widely reported, showing significant advances in devices, technologies and applications of information optoelectronics. It is believed that information optoelectronics will continue its rapid development towards integrated nanophotonic devices, more advanced technologies, flexible and multi-functional applications. It is our intention to draw great attention of the research community to those hot topics in devices, technologies and applications of information optoelectronics. In this “Special Issue on Information Optoelectronics: Devices, Technologies and Applications”, we present 8 review articles and 4 research articles focusing on relevant subjects by internationally active groups in the related fields. In the review articles, Dr. Sudharsanan Srinivasan at University of California, Santa Barbara reviewed recent results on hybrid silicon mode-locked lasers focusing on low phase noise optical pulse generation. Key results included demonstration of the longest (cavity length 9 cm) integrated on-chip mode locked laser, 14 dB reduction of Lorentzian noise on a 20 GHz radio-frequency (RF) signal, and greater than 55 dB optical supermode noise suppression using harmonically mode locked long cavity laser, 10 GHz passively mode locked laser with 15 kHz linewidth using on-chip all optical feedback stabilization. Dr. Ran Hao at Zhejiang University reviewed 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. Dr. Lai Wang at Tsinghua University reviewed recent progresses on InGaN quantum dot (QD) light emitting diodes (LEDs), including the basic physics model of the strain relaxation in self-assembled InGaN QDs, the growth of InGaN QDs with a growth interruption method by metal organic vapor phase epitaxy, the optimization of GaN barrier growth in multilayer InGaN QDs, and the green, yellow-green and red InGaN QD LEDs. Dr. Xiaowei Guan and Dr. Daoxin Dai at Zhejiang University reviewed progresses on various hybrid plasmonic waveguides as well as ultrasmall functionality devices. Ultra-sharp bending of silicon hybrid nanoplasmonic waveguides, optical couplers/splitters, ultrasmall resonators, and polarization handing devices were discussed. Dr. Jian Wang at Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology reviewed recent progress on plasmon-assisted nanophotonic devices and their wide applications, including long-range hybrid plasmonic slot (LRHPS) waveguide, ultra-compact plasmonic microresonator with efficient thermo-optic tuning, high quality (Q) factor and small mode volume, compact active hybrid plasmonic ring resonator for deep-subwavelength lasing

Transmission enhancement of sharply bent nanoplasmonic slot waveguides

The bending performance of standard nanoplasmonic slot waveguides is substantially improved by reducing the leakage loss and reflection in a systematic way. The out-of-plane power leakage is suppressed by using square metallic patches above and below the bend. The in-plane power leakage is reduced by elimination of the asymmetry between the electrical length of the inner and outer corners of the bend. The unwanted reflection is decreased by changing the shape of the outer corner of the bend. The partial reflections caused by the indentations of the modified shape destructively interfere with each other and thereby decrease the unwanted back reflection.

Volume integral method for investigation of plasmonic nanowaveguide structures and photonic crystals

A vector integral–differential equation to describe electromagnetic wave propagation in nanowaveguides and photonic crystals containing thin metal layers is developed. Exact solution of the equation is obtained with the Galerkin method, taking into account the complex dielectric permittivity of metals in the optical range. A simple method for finding complex effective refractive indices for low-loss waveguide structures is developed and proved. Surface plasmon-polariton waves are simulated in the structures under consideration.

硅基混合表面等离子体纳米光波导及集成器件

In this paper,our recent theoretical and experimental results on silicon hybrid nanoplasmonic waveguides and integrated devices are reviewed.First,we present several types of silicon hybrid nanoplasmonic waveguides,which enable the confinement of optical field within the lateral scale of 100 nm,as well as a ~ 102μm propagation distance.Second,several kinds of submicron photonic integrated devices like power splitters,ultra-compact polarization beam splitters and resonators are presented by using silicon hybrid nanoplasmonic waveguides.Finally,the coupling between silicon hybrid nanoplasmonic waveguides and silicon nanowires,as well as the loss compensation of silicon hybrid nanoplasmonic waveguides with gain mediums has also been discussed.

Efficient design of nanoplasmonic waveguide devices using the space mapping algorithm

We show that the space mapping algorithm, originally developed for microwave circuit optimization, can enable the efficient design of nanoplasmonic waveguide devices which satisfy a set of desired specifications. Space mapping utilizes a physics-based coarse model to approximate a fine model accurately describing a device. Here the fine model is a full-wave finite-difference frequency-domain (FDFD) simulation of the device, while the coarse model is based on transmission line theory. We demonstrate that simply optimizing the transmission line model of the device is not enough to obtain a device which satisfies all the required design specifications. On the other hand, when the iterative space mapping algorithm is used, it converges fast to a design which meets all the specifications. In addition, full-wave FDFD simulations of only a few candidate structures are required before the iterative process is terminated. Use of the space mapping algorithm therefore results in large reductions in the required computation time when compared to any direct optimization method of the fine FDFD model.

Design of wide-angle broadband Luneburg lens based optical couplers for plasmonic slot nano-waveguides

Gradient index (GRIN) structures have attracted great interests since their invention. Especially, the recent advance in the fields of transformation optics, plasmonics, and nanofabrication techniques has opened new directions for the applications of GRIN structures in nano-photonic devices. In this paper, we apply Luneburg lens and its transformed counterpart to realize efficient coupling to plasmonic nano-waveguides. We first briefly present the general structures of Luneburg lens and generalized Luneburg lens, as well as the design process of flattened Luneburg lens applying quasi-conformal mapping techniques. After that, we study the performance of these lenses for coupling electromagnetic signals to nano-waveguides (the metal-insulator-metal nano-waveguide). Different coupling schemes are investigated. It is found that the proposed Luneburg lens based optical couplers can be used to provide broadband light couplings to plasmonic nano-waveguides under wide incident angles.

Plasmonic materials for metal–insulator–semiconductor–insulator–metal nanoplasmonic waveguides on silicon-on-insulator platform

The use of various plasmonic metals and insulators in silicon based metal–insulator–semiconductor–insulator–metal (MISIM) nanoplasmonic waveguides are investigated for use in waveguiding applications at 1.55μm. Sputtered Au, Ag, and Cu as the metal cladding with thermally grown SiO2 and ALD grown HfO2 insulating dielectric spacer layers are examined to determine how their fabrication affects the crucial metal–dielectric interface. The experimental propagation lengths and coupling efficiencies to silicon-on-insulator waveguides are compared to theoretical values, with the Au/SiO2 MISIM nanoplasmonic waveguide showing a propagation length of 7.25μm. The effect of including an adhesion layer for Au is shown to significantly increase losses.

Silicon‐based nanoplasmonic disc resonator on CMOS platform

The first demonstration of a silicon-based metal–insulator–semiconductor (MIS) nanoplasmonic disc resonator monolithically integrated on a CMOS compatible platform is presented. The nanoplasmonic disc resonator is integrated with Au/SiO2/Si MIS nanoplasmonic waveguides and conventional silicon-on-insulator photonic waveguides. The device has a high plasmonic quality (Q) factor of 82.3, one of the highest reported for an integrated silicon-based nanoplasmonic device, with a compact device footprint of only 4 µm2.

CMOS compatible horizontal nanoplasmonic slot waveguides TE-pass polarizer on silicon-on-insulator platform

An ultra-compact broadband TE-pass polarizer was proposed and demonstrated on the silicon-on-insulator (SOI) platform, using the horizontal nanoplasmonic slot waveguide (HNSW). Detailed design principle was presented, taking advantage of the distinct confinement region of the TE and TM modes in the HNSW. TM mode cut-off could be achieved when waveguide width was below 210 nm. Proof-of-concept devices were subsequently fabricated in a CMOS-compatible process. The optimized device had an active region length of 1 μm, three orders of magnitude smaller than similar device previously demonstrated on the SOI platform. More than 16 dB polarization extinction ratio was achieved across 80 nm wavelength range, with a relatively low insertion loss of 2.2dB. The compact device size and excellent broadband performance could provide a simple yet satisfactory solution to the polarization dependent performance drawback of the silicon photonics devices on the SOI platform.

Directive antenna nanocoupler to plasmonic gap waveguides

Optical nanocouplers matching a fiber microwaveguide to a plasmonic nanowaveguide are essential components for practical applications of nanophotonic systems. In this Letter we design an efficient nanocoupler using a directive nanoantenna in the visible range λ0=0.65 μm. The antenna has been optimized both in the configuration and in the matching element in order to achieve the maximum coupling efficiency (CE). In spite of the reduced size of the nanoantenna in comparison with the impinging fiber spot size (due to the localized plasmonic resonance at such high frequency), we have shown that a good efficiency can be achieved, improving the CE by a factor of 10 with respect to the nondirective antenna nanocouplers.

表面等离激元亚波长光波导滤波器研究进展

In this paper, we review recent progress in our researches on nano-plasmonic waveguide filters based on the tooth/teeth-shaped, side coupled shaped and circuitous shaped structures. A novel plasmonic waveguide filter constructed with a metal-dielectric-metal structure engraved single rectangular tooth is firstly introduced. The structure is then extended to symmetric and asymmetric multiple-teeth structures. A subwavelength side-coupled MDM filter, a low-pass wavelength filter and a high-pass wavelength filter are finally reviewed, respectively. The finite-difference-time-domain method simulation results show that these structures are of the characteristic of wavelength filters with symmetric multiple-teeth structures exhibiting wide and sharp bandgaps, while the asymmetrical multiple-teeth structure can achieve selective narrow-band filtering function. Both analytic and simulation results show that the central wavelengths of reflective or selective filters have relationships with the depth and width of a tooth. And the cutoff wavelengths of the cutoff-type structures can be easily chosen by changing the lengths or the widths of the structures. These filters may have applications to ultrahigh nanoscale integrated photonic circuits.

A Compact Nanoplasmonics Filter and Intersection Structure Based on Utilizing a Slot Cavity and a Fabry–Perot Resonator

By combining a Fabry–Perot (FP) cavity with a slot cavity, a compact filter structure is proposed. The peak resonance wavelength is determined by applying the FP resonance condition of the FP cavity. The relationship between filtering wavelength and cavity parameters is investigated. The results show that the filtering wavelength can be manipulated by changing the nanocavities' parameters. By using the finite difference time domain method, the theoretical predictions are confirmed. An intersection structure for nanoplasmonic waveguides is proposed and designed by utilizing two perpendicular filters. In addition to having compact dimensions, the proposed arrangement provides higher throughput and low cross talk. The proposed structure can be useful for designing compact integrated nanoplasmonic circuits.

Numerical solution of nonlocal hydrodynamic Drude model for arbitrary shaped nano-plasmonic structures using Nédélec finite elements

Nonlocal material response distinctively changes the optical properties of nano-plasmonic scatterers and waveguides. It is described by the nonlocal hydrodynamic Drude model, which – in frequency domain – is given by a coupled system of equations for the electric field and an additional polarization current of the electron gas modeled analogous to a hydrodynamic flow. Recent attempt to simulate such nonlocal model using the finite difference time domain method encountered difficulties in dealing with the grad–div operator appearing in the governing equation of the hydrodynamic current. Therefore, in these studies the model has been simplified with the curl-free hydrodynamic current approximation; but this causes spurious resonances. In this paper we present a rigorous weak formulation in the Sobolev spaces H(curl) for the electric field and H(div) for the hydrodynamic current, which directly leads to a consistent discretization based on Nédélec’s finite element spaces. Comparisons with the Mie theory results agree well. We also demonstrate the capability of the method to handle any arbitrary shaped scatterer.

Exploring qubit‐qubit entanglement mediated by one‐dimensional plasmonic nanowaveguides

AbstractWe exploit the qubit‐qubit coupling induced by plasmon‐polariton modes in a one‐dimensional nanowaveguide to obtain various two‐qubit entanglement situations. Firstly, we observe three phenomena occurring when preparing the initial state of the system and leaving it freely relax: spontaneous formation of entanglement, sudden birth and revival.Then, we show that plugging a laser to each of the qubit, the system arrives to an steady state which, depending on their inter‐qubit distance, can also be entangled. For this situation, we also characterize the quantum state of the system showing the entanglement‐purity‐diagram typical for two‐qubit systems. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Components for silicon plasmonic nanocircuits based on horizontal Cu-SiO_2-Si-SiO_2-Cu nanoplasmonic waveguides

We report systematic results on the development of horizontal Cu-SiO₂-Si-SiO₂-Cu nanoplasmonic waveguide components operating at 1550-nm telecom wavelengths, including straight waveguides, sharp 90° bends, power splitters, and Mach-Zehnder interferometers (MZIs). Owing to the relatively low loss for propagating (~0.3 dB/µm) and for 90° sharply bending (~0.73 dB/turn), various ultracompact power splitters and MZIs are experimentally realized on a silicon-on-insulator (SOI) platform using standard CMOS technology. The demonstrated splitters exhibit a relatively low excess loss and the MZIs exhibit good performance such as high extinction ratio of ~18 dB and low normalized insertion loss of ~1.7 dB. The experimental results of these devices agree well with those predicted from numerical simulations with suitable Cu permittivity data.