Nanodisk Resonator Research Articles

Plasmon induced transparency and refractive index sensing in two nanocavities and double nanodisk resonators

Two novel implementations for plasmon-induced transparency (PIT) based on two rectangular nanocavities coupled to a bus waveguide and two nanodisk resonators have been studied and simulated with Finite Difference Time Domain (FDTD) method with Perfectly Matched Layer (PML) boundary conditions. It is shown that the wavelength, transmission and width of the PIT peaks can be tuned by changing the radii of the nanodisk resonators and the gap width. Benefitting from the narrow-appeared transparency windows, the proposed PIT-structures can act as nanosensors with refractive index sensitivity and a figure of merit equal to 800 nm. RIU−1 and 61.55 RIU−1, respectively. The proposed devices have potential nanophotonic applications due to simple geometry, compactness and their resistance to the oxidation.

Tunable triple-band graphene refractive index sensor with good angle-polarization tolerance

Abstract In this article, we design a triple-band graphene refractive index sensor with good angle-polarization tolerance, which is composed of graphene elliptic–circular nanodisk resonators periodically arranged on a dielectric substrate. The numerical results indicate that the resonant wavelengths of three modes of graphene resonators show consecutively linear tunability when the refractive index of the surrounding medium varies, and the sensitivity is up to 11. 56 μ m /RIU. The sensing range can be further adjusted by controlling the doping level of graphene. In addition, the proposed graphene sensor maintains polarization insensitivity over a wide angular range (0–60°), showing very good angle-polarization tolerance. This work enables us to achieve a tunable triple-band sensor and provides potential value for label-free biomedical sensing.

Double and triple-wavelength plasmonic demultiplexers based on improved circular nanodisk resonators

Plasmonic demultiplexers using improved circular nanodisk resonators (CNRs) and metal-insulator-metal waveguides have been designed. The proposed structures use air and silver as insulator and metal layers, respectively. The relative permittivity of silver has been characterized by Drude, Palik, and Drude–Lorentz models in our finite-difference time-domain simulations. To obtain demultiplexers, first two filters based on improved CNRs are designed. One of the most outstanding features of a CNR is that the resonance wavelength can be tuned by changing its radius. It is shown that increasing the CNRs radii for the single-mode bandpass filter increases the resonance wavelength, linearly. Accordingly, double and triple-wavelength demultiplexers (DeMuxes) have been proposed for the wavelength range of 600 to 2000 nm. Due to their small area, the proposed demultiplexers can be applied in integrated optical circuits for optical communication purposes.

Tunable plasmon-induced reflection based on graphene nanoribbon Fabry-Perot resonator and nanodisks

The proposed structure shows the tunable plasmon-induced reflection (PIR) effect within the mid-infrared region. The destructive interference between a graphene nanoribbon as the bright mode resonator and two graphene nanodisk resonators (NDRs) as the dark mode resonators is responsible for the PIR window formation. The structure is simulated numerically by the 3D-FDTD method, and the results show that the PIR window can be simply tuned by the design parameters as well as the dynamic change in the Fermi energy of the NDRs. The formation of the double PIR effect is possible when the NDRs are displaced in opposite directions. The simplicity of the structure, from both the design and the implementation point of view, which is due to the possibility of the realization of the device in one single spatial plane and the straightforward parameter tuning makes it appropriate for various applications including multi-channel filters, sensors, and fast-light-based devices.

Novel High-Sensitivity Racetrack Surface Plasmon Resonance Sensor Modified by Graphene.

In order to overcome the existing challenges presented by conventional sensors, including their large size, a complicated preparation process, and difficulties filling the sensing media, a novel high-sensitivity plasmonic resonator sensor which is composed of two graphene-modified straight waveguides, two metallic layers, and a racetrack nanodisk resonator is proposed in this study. The transmission characteristics, which were calculated by the finite element theory, were used to further analyze the sensing properties. The results of quantitative analysis show that the proposed plasmonic sensor generates two resonance peaks for the different incident wavelengths, and both resonance peaks can be tuned by temperature. In addition, after optimizing the structural parameters of the resonator, the Q value and the refractive sensitivity reached 21.5 and 1666.67 nmRIU−1, respectively. Compared with other studies, these values translate to a better performance. Furthermore, a temperature sensitivity of 2.33 nm/5 °C was achieved, which allows the sensor to be easily applied to practical detection. The results of this study can broaden the useful range for a nanometer-scale temperature sensor with ultrafast real-time detection and resistance to electromagnetic interference.

Realization of single-mode plasmonic bandpass filters using improved nanodisk resonators

In this paper, symmetric and asymmetric plasmonic bandpass filter (BPF) topologies based on the metal–insulator–metal (MIM) configuration are proposed. These filters are numerically investigated using finite difference time domain (FDTD) method. The metal and dielectric used for the realization of the filters are silver and air, respectively. The real and imaginary parts of silver’s permittivity used in numerical simulation are based on the Drude–Lorentz and Palik models. Both structures are composed of two waveguides, a nanodisk, and parenthesis-shaped adjunctions. The inclusion of symmetrical and nonsymmetrical adjunctions results in single mode filters with higher transmission peaks compared to the original nanodisk-based filter. To provide better physical insight, various structural parameters of the filter are changed and their effects on filter’s response are presented. It is observed that the resonance mode of proposed BPFs can be tuned by changing the nanodisk resonator radius. Such structures can be employed in various plasmonic devices such as multiplexers and demultiplexers for optical communication purposes.

Surface plasmon polariton nanocavity with ultrasmall mode volume

We present a plasmonic nanocavity structure, consisting of a gallium phosphide (GaP) cylinder penetrating into a rectangular silver plate, and study its properties using a finite element method (FEM). An ultrasmall mode volume of is achieved, which is more than 200 times smaller than the previous ultrasmall mode volume plasmonic nanodisk resonators. Meanwhile, the quality factor of the plasmonic nanocavity is about 38.2 and is over two times greater than the ultrasmall mode volume plasmonic nanodisk resonators. Compared to the aforementioned plasmonic nanodisk resonators, a more than one-order of magnitude larger Purcell factor of is achieved. We determined the resonant modes of our plasmonic nanocavity are dipolar plasmon modes by analyzing the electric field properties. In addition, we investigate the dependence of the optical properties on the refractive index of the cavity material and discuss the effect of including the silica (SiO2) substrate. Our work provides an alternative approach to achieve ultrasmall plasmonic nanocavity of interest in applications to many areas of research, including device physics, nonlinear optics and quantum optics.

Polarization independent high transmission large numerical aperture laser beam focusing and deflection by dielectric Huygens’ metasurfaces

In this letter, we propose all-dielectric Huygens’ metasurface structures to construct high numerical aperture flat lenses and beam deflecting devices. The designed metasurface consists of two-dimensional array of all-dielectric nanodisk resonators with spatially varying radii, thereby introducing judiciously designed phase shift to the propagating light. Owing to the overlap of Mie-type magnetic and electric resonances, high transmission was achieved with rigorous design analysis. The designed flat lenses have numerical aperture value of 0.85 and transmission values around 80%. It also offers easy fabrication and compatibility with available semiconductor technology. This spectrally and physically scalable, versatile design could implement efficient wavefront manipulation or beam shaping for high power laser beams, as well as various optical microscopy applications without requiring plasmonic structures that are susceptible to ohmic loss of metals and sensitive to the polarization of light.

Multifunctional Sensors and Switch in MDM Waveguide With Symmetric Dual Side-Coupled Nanodisks

A multirole waveguide with symmetric dual side-coupled nanodisk resonators, which can act as refractive index sensor, temperature sensor, and optical switch, is proposed and investigated numerically. By the finite-difference time-domain simulations, it is demonstrated that the value of the refractive index sensitivity of the nano-sensor can reach 1333 nm/RIU. And with ethanol fully filled in the resonators, it can act as a temperature sensor with temperature sensitivity of 0.52 nm/°C. Furthermore, by filling with liquid crystal material, the transmittance of the optical switch is up to 73.6% at the wavelength of 1310 nm. This letter may pave a way for multifunctional applications in the on-chip nano-sensing area.

Plasmonically Induced Absorption and Transparency Based on Stub Waveguide with Nanodisk and Fabry-Perot Resonator

A novel metal-insulator-metal (MIM) plasmonic waveguides structure, which is composed by stub waveguide with nanodisk and Fabry-Perot (F-P) resonator, has been proposed and numerically simulated with the finite-difference time-domain (FDTD). Based on the three-level system, the extreme destructive interference between bright and dark resonators gives rise to the distinct plasmonically induced absorption (PIA) response with the abnormal dispersion and novel fast-light feature. Simultaneously, the dramatic double plasmonically induced transparency (PIT) effect with slow-light characteristic can also be achieved in the system. The relationship between the transmission characteristics and the geometric parameters is studied in detail. By optimum design, the modulation depth of the PIA transmission spectrum of 90 % with 0.145 and 0.14 ps fast-light effect can be gained simultaneously, and the peak transmissivity of the double PIT system of 75.2 and 72.8 % with −0.38 ps slow light-effect can be achieved. The simulated transmission features are in agreement with the temporal-coupled mode theory (CMT). The characteristics of the system indicate an important potential application in integrated optical circuits such as slow-light and fast-light devices, high-performance filter, and optical storage.

The effects of silver slabs in nanodisk resonator of plasmonic tunable band-pass filter

A novel and simple method to meliorate nanodisk resonator using silver slabs is proposed. In this regard, we numerically and theoretically compared the meliorated resonator with the nanodisk resonator without silver slabs at the plasmonic tunable band-pass filter. It was found that configuration of the proposed resonator leads to reduction of the plasmonic filter dimensions. Also, we calculated the amount of this reduction based on the disk-shaped nanocavity resonant theory and the meliorated resonator simulation results. Therefore, the resonance wavelengths depend on the relative permittivity and nanocavity radius which were consistent with the outcomes achieved by the simulations of FDTD (Finite-Difference Time-Domain). The FDTD simulations shown transmission spectra were tunable by changing of structure parameters. Through this method, it was revealed that simple plasmonic devices can be designed with smaller dimension for highly integrated optical devices.

Enhanced plasmonic band-pass filter with symmetric dual side-coupled nanodisk resonators

A plasmonic band-pass filter with symmetric dual side-coupled nanodisk resonators in metal-insulator-metal system is proposed. Compared with the single side-coupled nanodisk resonator structure, the new structure has better transmission response due to the superposition of the outgoing-wave fields' amplitudes of the two resonators. The accurate transmission expression is provided based on the temporal coupled mode theory, and the dynamic transmission response is studied by finite difference time domain method. It is indicated that the transmission characteristics of the symmetric dual nanodisk resonator structure is sensitive to the refractive index of the nanodisk resonators and geometrical parameters. Moreover, the optimum transmission at the wavelengths of 1310 nm and 1550 nm can reach up to 90.8% and 86.2%, with the relative full width at half-maximum of 35 nm and 42 nm, which are better than the results reported in recent literatures. The filter we proposed has important potential applications on plasmonic nanostructures in highly integrated optical circuits and optical information processing.

Plasmonic-Induced Transparency and Slow-Light Effect Based on Stub Waveguide with Nanodisk Resonator

A compact plasmonic system based on a stub metal-insulator-metal (MIM) waveguide coupled with a nanodisk resonator for plasmonic-induced transparency (PIT) has been proposed and numerically simulated by employing the finite-difference time-domain (FDTD). A reasonable analysis of the transmission features based on the temporal coupled-mode theory is given and is in good agreement with the FDTD simulation. In addition, the relationship between the transmission characteristics and the geometric parameters including the radius of the nanodisk, the coupling distance, and the deviation length between the stub and the nanodisk is studied in a step further. By optimum designing, the transmission of the PIT system can reach to as high as 90 %, as well as the group index can be over 88. The characteristics of our plasmonic system indicate an important potential application in integrated optical circuits such as optical storage, ultrafast plasmonic switch, highly performance filter and slow-light devices.

Zinc Oxide Based Plasmonic Multilayer Resonator: Localized and Gap Surface Plasmon in the Infrared

Using alternative plasmonic materials, we experimentally demonstrate gap plasmon resonances in metal–insulator–metal nanostructures in the near- and mid-infrared wavelength regions utilizing gallium doped zinc oxide as the metallic component and undoped zinc oxide as the dielectric. We show that similar to metal–insulator–metal resonators previously demonstrated with noble metals, the layered transparent conducting oxide nanodisks support gap surface plasmon resonances characterized by highly confined electromagnetic fields in the dielectric gap. Such resonances can be tailored to desired values by varying the dielectric-layer thickness. Utilizing these observed gap plasmon resonance, we examine the potential of our structure for sensing applications by measuring the surface enhanced infrared absorption of an octadecanethiol layer. The layered nanostructure can detect very weak absorption resonances in nanoscale volumes of absorbing material deposited over the nanodisk resonator.

A High-Sensitivity Refractive-Index Sensor Based on Plasmonic Waveguides Asymmetrically Coupled with a Nanodisk Resonator**Supported by the National Natural Science Foundation of China under Grant No 61275059.

A high-sensitivity plasmonic refractive-index sensor based on the asymmetrical coupling of two metal-insulator-metal waveguides with a nanodisk resonator is proposed and simulated in the finite-difference time domain. Both analytic and simulated results show that the resonance wavelengths of the sensor have an approximate linear relationship with the refractive index of the materials which are filled into the slit waveguides and the disk-shaped resonator. The working mechanism of this sensor is exactly due to the linear relationship, based on which the refractive index of the materials unknown can be obtained from the detection of the resonance wavelength. The measurement sensitivity can reach as high as 6.45 × 10−7, which is nearly five times higher than the results reported in the recent literature [Opt. Commun. 300 (2013) 265]. With an optimum design, the sensing value can be further improved, and it can be widely applied into the biological sensing. The sensor working for temperature sensing is also analyzed.

Low-power, ultrafast, and dynamic all-optical tunable plasmonic analog to electromagnetically induced transparency in two resonators side-coupled with a waveguide system

We theoretically and numerically investigate a low-power, ultrafast, and dynamic all-optical tunable plasmonic analog to electromagnetically induced transparency (EIT) in two nanodisk resonators side-coupled to a metal-insulator-metal plasmonic waveguide system. The optical Kerr effect is enhanced by the slow light effect of the plasmonic EIT-like effect and the plasmonic waveguide based on graphene-Ag composite material structures with giant effective Kerr nonlinear coefficient. The optical Kerr effect modulation method is applied to improve tuning rate with response time of subpicoseconds or even femtoseconds. With dynamically tuning the propagation phase of the plasmonic waveguide, π-phase shift of the transmission spectrum in the plasmonic EIT-like system is achieved under excitation of a pump light with an intensity as low as 5.85 MW/cm2. The group delay is controlled between 0.09 and 0.4 ps. All observed schemes are analyzed rigorously through finite-difference time-domain simulations and coupled-mode formalism. Results show a new direction toward the low power consumption and ultrafast responses of integration plasmonic photonic devices and all-optical dynamical storage of light devices in optical communication and quantum information processing.

Realizing Fano-like resonance in a one terminal closed T-shaped waveguide

We obtain a special Fano-like resonance in a semi-closed T-shaped waveguide with nanodisk resonator, in which only two bright plasmon modes work. It is found that the transmission spectrum occurs a red-shift by increasing either length of the nanoslot or radius of the nanodisk. Moreover, when the length of the nanoslot and radius of the nanodisk reach to some particular values at the same time, the transmission spectrum will show an inverse line shape or the Fano-like resonance will disappear. Meanwhile, the classical figure of merit obtained by calculation is as high as 199 with a sizable classical sensitivity value reaches to 1114 nm/RIU. The generalized figure of merit also comes to an impressive value of 7961 nm/RIU. Besides, it is worth noting that the maximums of these two kinds of FOM lie in the dips of different linewidth, which can be utilized in diverse types of sensors. Our studies further provide a guidance for fabricating planar devices in near-infrared region.

The Line Shape of Double-Sided Tooth-Disk Waveguide Filters Based on Plasmon-Induced Transparency**Supported by the National Natural Science Foundation of China under Grant Nos 11374041 and 11404030, and the Fund of State Key Laboratory of Information Photonics and Optical Communications of Beijing University of Posts and Telecommunications of China.

We numerically investigate a coupled-resonator structure consisting of a stub resonator and a nanodisk resonator using a two-dimensional finite element method. Simulation results show that plasmon-induced transparency (PIT) occurs in the transmission spectra, and the sharp asymmetric Fano lines increase the sensitivity to 1.4 × 103 nm/RIU. We also analyze the properties of the structure with different radii of the nanodisk and the length of the tooth cavity. Moreover, we find that the PIT only happens when the staggered system is around a fixed location with different separate distances, which is not similar to the previous researches. Our model may be important to photonic-integrated circuits and the sensitivity in sensors.

Plasmon-Induced Optical Anisotropy in Hybrid Graphene–Metal Nanoparticle Systems

Hybrid plasmonic metal-graphene systems are emerging as a class of optical metamaterials that facilitate strong light-matter interactions and are of potential importance for hot carrier graphene-based light harvesting and active plasmonic applications. Here we use femtosecond pump-probe measurements to study the near-field interaction between graphene and plasmonic gold nanodisk resonators. By selectively probing the plasmon-induced hot carrier dynamics in samples with tailored graphene-gold interfaces, we show that plasmon-induced hot carrier generation in the graphene is dominated by direct photoexcitation with minimal contribution from charge transfer from the gold. The strong near-field interaction manifests as an unexpected and long-lived extrinsic optical anisotropy. The observations are explained by the action of highly localized plasmon-induced hot carriers in the graphene on the subresonant polarizability of the disk resonator. Because localized hot carrier generation in graphene can be exploited to drive electrical currents, plasmonic metal-graphene nanostructures present opportunities for novel hot carrier device concepts.

Theoretical investigation of a plasmonic sensor based on a metal–insulator–metal waveguide with a side-coupled nanodisk resonator

A plasmonic sensor based on a metal–insulator–metal waveguide with a side-coupled nanodisk resonator is proposed and numerically investigated using a finite-difference time-domain method. The numerical simulation results indicate that more than one sharp resonance dip appears in the transmission spectrum in the telecommunication regime, and each resonance wavelength has a linear relationship with the refractive index of the dielectric in the resonator. In addition, the sensing characteristics of the structure and the influence of its structural parameters are analyzed in detail by investigating the transmission spectra. As a refractive-index sensor, its sensitivity can reach as high as 1150 nm per refractive index unit near the resonance wavelength of 1550 nm, and its sensing resolution can reach 10−6 for a wavelength resolution of 0.01 nm. Furthermore, by employing the relationship between the temperature and the refractive index, the temperature-sensing characteristics of the structure are also discussed. Near the resonance wavelength of 1550 nm, the temperature sensitivity can reach 0.45 nm/°C. The sensor has a compact and simple structure and may find many potential and important applications in optical networks-on-chip and on-chip nanosensors.