A Tunable Slow Light Device with Multiple Channels Based on Plasmon-Induced Transparency

Slow light devices with buffering capability play a critical role in all-optical signal processing. In this paper, multiple slow light phenomena are implemented based on plasmon-induced transparency (PIT) in our device. The device mainly consists of dual tooth cavities coupled with stub resonators, respectively. Temporal coupled-mode theory model illustrates that the triple PIT phenomena can be achieved based on different formation mechanisms. The simulation results calculated by the finite-difference time-domain method reveal that significant slow light response occurs at two wavelength regions. In addition, the parameters of structure have an important influence on PIT response and slow light characteristics. Moreover, the separate manipulation of wavelength, transmission and group index at transparency peak can be achieved in different slow light channels by adjusting the structural parameters. This plasmonic device is of great significance for the design of optical networks on chips.

     

Broadband Plasmon-Induced Transparency in Plasmonic Metasurfaces Based on Bright-Dark-Bright Mode Coupling

Plasmon-induced transparency (PIT), an analog of electromagnetically induced transparency, originates from destructive interference of plasmonic resonators with different quality factors and brings about the extreme dispersion within the narrow transparency window, promising remarkable potential for slow light, nonlinear optics and biochemical sensors. However, sometimes a broad transmission frequency band is more desirable for other applications such as bandpass filters. In general, strong coupling between bright and dark plasmon modes in coupled resonant systems leads to wide transparency bandwidth at the PIT resonance. Based on multi-oscillator coupling theory, a metasurface structure consisting of three perpendicularly connected metallic nanobars is purposefully designed and numerically demonstrated to support broadband PIT spectral response. The near-field patterns indicate that the broadening of the transparent band results from the constructive interference of dual excitations of the single non-radiative (dark) resonator by the two radiative (bright) antennas. These results show that this scheme of bright-dark-bright mode coupling is significantly beneficial for designing filters operating over a broad frequency range.

     

Investigating the Characteristics of a Double Circular Ring Resonators Slow Light Device Based on the Plasmonics-Induced Transparency Coupled with Metal-Dielectric-Metal Waveguide System

We have numerically investigated an analog of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) waveguide bend. The geometry consists of two asymmetrical stubs extending parallel to an arm of a straight MDM waveguide bend. Finite-difference time-domain simulations show that a transparent window is located at 1550 nm, which is the phenomenon of plasmonic-induced transparency (PIT). Signal wavelength is assumed to be 820 nm. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. Multiple-peak plasmon-induced transparency can be realized by cascading multiple cavities with different lengths and suitable cavity-cavity separations. Large group index up to 73 can be obtained at the PIT window. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends. In addition, the relationship between the transmission characteristics and the geometric parameters including the radius of the nano-ring, the coupling distance, and the deviation length between the stub and the nano-ring is studied in a step further. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. For indirect coupling, formation of transparency window is determined by resonance detuning, but, evolution of transparency is mainly attributed to the change of the coupling distance. Theoretical results may provide a guideline for control of light in highly integrated optical circuits. The characteristics of our plasmonic system indicate a significant potential application in integrated optical circuits such as optical storage, ultrafast plasmonic switch, highly performance filter, and slow light devices.     

Systematic Theoretical Analysis of Selective-Mode Plasmonic Filter Based on Aperture-Side-Coupled Slot Cavity

By taking the aperture as a resonator, we propose an analytical model to describe the dynamic transmission in metal-dielectric-metal (MDM) waveguide aperture-side-coupled with slot cavity. The theoretical results and the finite-difference time-domain (FDTD) simulations agree well with each other, and both demonstrate the mode selectivity and filtering tunability of the plasmonic structure. By adjusting the phase shifts in slot cavity or resonance frequency determined by the aperture, one can realize the required transmission spectra and slow light effect. The theoretical analysis may open up avenues for the control of light in highly integrated optical circuits.     

Ultracompact Slow Surface Plasmon Polaritons Superlattice with Broad Bandwidth and Super-High Normalized Delay-Bandwidth Product

In this paper, we propose an ultracompact low-loss plasmonic superlattice for slow surface plasmon polaritons. The superlattice consists of a two-dimensional metal gap waveguide (Ag-SiO₂-Ag) inserted with thin metal films working as coupled reflectors. Theoretical calculations indicate that the device is working on a broad bandwidth of 37 THz including the two telecom wavelengths of 1,310 and 1,550 nm and with mean group refractive index of 3.5 and mean transmission of 60 %. As the total geometric thickness is only 1.6 μm, the normalized delay-bandwidth product of the superlattice is as high as 0.44. All the theoretical prediction based upon the transfer matrix method is validated by the finite-difference time-domain numerical simulation on surface plasmon polaritons propagating in the superlattice.     

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

Plasmonics - 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...     

Tunable Plasmon-Induced Transparency Effect in MIM Side-Coupled Isosceles Trapezoid Cavities System

We propose a plasmonic structure based on the metal-insulator-metal waveguide with the side-coupled isosceles trapezoid cavities. Both of the structures based on the side-coupled trapezoid cavities separated or connected with waveguides can realize the plasmon-induced transparency (PIT). By adjusting the structure parameters, the off-to-on PIT response can be tunably achieved. The coupled mode theory (CMT) method is used to study the PIT phenomenon and explain the transmission characteristics. This work may provide a potential way for designing highly integrated photonic devices.

     

Improvement on the Performance of InP/CdS Solar Cells with the Inclusion of Plasmonic Layer of Silver Nanoparticles

The effect of nano-Ag (n-Ag) plasmonic layer in InP/CdS solar cell structure was examined. An enhancement of short circuit current improving the overall cell efficiency was observed in InP/n-Ag/CdS cells. Location of the plasmonic layer in the above cell structure has been analyzed critically. The effect of introducing plasmonic layer on the overall performance of the cell has been studied in terms of the morphology, particle size distribution, optical absorption, I–V, C–V characteristics, and lifetime of the photo-generated carriers. Secondary ion mass spectroscopy (SIMS) studies were carried out for investigating possible interface alloying.     

Plasmon-Induced Transparency and Refractive Index Sensing Based on a Trapezoid Cavity Coupled with a Hexagonal Resonator

Plasmonics - Tunable plasmon-induced transparency (PIT) effect is studied in a plasmonic device on the basis of the metal-insulator-metal (MIM) structure which consists of trapezoid and hexagonal...     

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.     

A Novel Terahertz Semiconductor Metamaterial for Slow Light Device and Dual-Band Modulator Applications

In this paper, we propose a novel planar semiconductor metamaterial which consists of two H-shape structures which are nested together and composed of InSb deposited on a thin quartz substrate. The two H-shape structures serve as the bright modes and are exited strongly by the incident wave and interact with each other. This coupling leads to a powerful plasmonically induced transparency (PIT) effect at terahertz frequencies. This scheme provides a way to achieve slow light, and the corresponding group index can reach a value of 1300. We calculated group velocity dispersion (GVD) and saw this structure was a low group velocity dispersion (LGVD) system. Therefore, the proposed structure will be useful in designing slow-light devices, optical buffers, delay lines, and ultra-sensitive sensors. We also showed that the proposed design is tunable, namely changes in geometric parameters and type of semiconductor can largely change the group index. In addition, we considered another application for our design that is a thermal dual-band terahertz metamaterial modulator and numerically obtained frequency and amplitude modulation depth, tunability bandwidth, and loss for this device. We obtained an amplitude modulator depth of 99.7 % and a frequency modulator depth of 47 % that verified this structure can be used in wireless communication and encode information systems in the THz regime.     

Electromagnetically Induced Transparency and Refractive Index Sensing for a Plasmonic Waveguide with a Stub Coupled Ring Resonator

A plasmonic refractive index sensor based on electromagnetically induced transparency (EIT) composed of a metal-insulator-metal (MIM) waveguide with stub resonators and a ring resonator is presented. The transmission properties and the refractive index sensitivity are numerically studied with the finite element method (FEM). The results revealed an EIT-like transmission spectrum with an asymmetric line profile and a refractive index sensitivity of 1057 nm/RIU are obtained. The coupled mode theory (CMT) based on transmission line theory is adopted to illustrate the EIT-like phenomenon. Multiple EIT-like peaks are observed in the transmission spectrum of the derived structures based on the MIM waveguide with stub resonator coupled ring resonator. To analyze the multiple EIT-like modes of the derived structures, the H _z field distribution is calculated. In addition, the effect of the structural parameters on the EIT-like effect is also studied. These results provide a new method for the dynamic control of light in the nanoscale.     

Dynamically Switchable Multispectral Plasmon-Induced Transparency in Stretchable Metamaterials

We propose dynamically switchable multispectral plasmon-induced transparency (PIT) with high modulation depth in a three-dimensional metamaterial standing on a flexible substrate. The proposed metamaterial is composed of a pair of metal–insulator–metal (MIM) nano-cut-wires and a pair of insulator–metal–insulator (IMI) nano-cut-wires. Results show that two PIT windows can be achieved because of the near-field coupling between the dipole supported by the IMI nano-cut-wire and two quadrupoles supported by the MIM structures. These two PIT windows can be blue-shifted or even flipped over by stretching the substrate along one direction, or be switched off by stretching along the other direction. A classical coupled oscillator model is developed to quantitatively describe and explain these results. We expect this work will find promising applications in multispectral sensors, slow light devices and nonlinear optical devices.

     

Realization of Graphene-Based Tunable Plasmon-Induced Transparency by the Dipole-Dipole Coupling

A numerical and theoretical study is presented on the realization of tunable plasmon-induced transparency (PIT) phenomenon in the three-dimensional patterned graphene nanostrips. The simulation results reveal that the PIT effect is generated due to the excitation of dark mode which can be considered a dipole. The three-level plasmonic system is employed to explain the physical mechanism of the PIT effect. Different from previous reported form (dipole-quadrupole coupling), the proposed is attributed to the dipole-dipole coupling. The PIT effect can be tuned by changing the coupling length between bright and dark mode as well as the Fermi energy of graphene. Our studies provide guidance for fabricating ultra-compact devices in practical application.     

Λ-Type and V-Type Plasmon-Induced Transparency in Plasmonic Waveguide Systems

Plasmonics - We present bright-dark-bright mode, dark-bright-bright mode, and bright-dark-bright-dark mode plasmonic waveguide structures. And the typical plasmon-induced transparency (PIT) spectra...     

Coupled Mode Demonstration of Slow-Light Plasmonic Sensor Based on Metasurface at Near-Infrared Region

In this paper, we theoretically and numerically reported a dual plasmon-induced transparency and the relevant sensing property in a multi-cross metasurface by the coupled mode analysis. A phase coupling model was established to characterize the optical response of this plasmonic sensor. It was found that the transparency windows were sensitive to the resonance mode of each metal strip, which was well demonstrated by the theoretical model. Both the sensing property and the slow light in this structure were discussed. A high figure of merit of 223 and sensitivity of 850 nm/RIU were achieved. In addition, the 1170-nm near-infrared light can be slowed down by nearly two order of magnitude with group delay of 0.45 ps in this sensor. These results may provide guidance for light-matter interaction-enhanced slow-light sensor and integrated optical circuit design.

     

Does light spectral quality affect survival and regeneration of potato (Solanum tuberosum L.) shoot tips after cryopreservation?

Cryopreservation, the storage of germplasm at ultra-low temperature is the most reliable tool for long-term preservation of plant genetic resources. Cryopreservation techniques are widely applied but the effect of light spectra on plant recovery after cryopreservation is largely unknown. Therefore, we investigated the effect of different light spectral qualities on survival and regeneration of shoot tips of potato (Solanum tuberosum L.) cultivars Agrie Dzeltenie, Maret, Bintje, Désirée and Anti cryopreserved by the DMSO-droplet method. Prior to cryopreservation, the plants were stored under cool white fluorescent light (CW). Post-cryopreservation, the plants were allowed to regenerate under six different light qualities: CW, warm white light (HQI), blue LEDs (B), red LEDs (R), red with 10 % of blue (RB) and RBF - red with 10 % of blue with addition of 20 % of far-red LEDs. The light spectral quality had a significant effect on the survival and regeneration of potato shoot tips after cryopreservation. The combination of red light with 10 % of blue (RB) doubled the regeneration percentage of all cultivars, whereas red light (R) was not suitable for regeneration after cryopreservation. Specifically, the regeneration percentages were increased in RB compared to CW from 25.5 to 52.6 % for ‘Agrie Dzeltenie’, 25.0–43.6 % for ‘Maret’, 8.1–26.1 % for ‘Bintje’, 0.0–17.1 % for ‘Anti’ and 18.2–36.6 % for ‘Désirée‘. Therefore, the modification of light spectra during the recovery phase is a promising tool for increasing the regeneration of potato shoot tips after cryopreservation.     

Tunable Plasmonically Induced Transparency with Asymmetric Multi-rectangle Resonators

Plasmonically induced transparency (PIT) effect in a metal–insulator–metal waveguide coupled to asymmetric multi-rectangle resonators is investigated numerically. By adjusting parameters of resonators, we cannot only realize single, double, or treble PIT peaks in the compact structure, but also induce an off-to-on PIT optical response. Numerical simulation by finite element method was conducted to verify our designs. This proposed structure, hence has potential applications for ultra-compact optoelectronic devices at communication band.

     

Modification of a Silver Substrate for Advanced Spectro-Electrochemical Applications of SERR Spectroscopy

A substrate for surface-enhanced resonance Raman spectroscopy (SERRS) in the near-ultraviolet (UV) range is presented, extending the potential window for electrochemical applications. Silver nanoparticles were synthesized exhibiting a localized surface plasmon resonance at the excitation wavelength and adsorbed onto a template-stripped silver substrate, whereby the number of particles per unit area was controlled by the adsorption time. Any attempt to employ spectro-electrochemistry on these surfaces, however, was hampered by the anodic dissolution of silver at potentials higher than 300 mV vs. standard hydrogen electrode (SHE). In order to extend the potential window for electrochemistry and still being able to use the resonance effect from silver nanoparticles, a 5-nm thick gold layer was sputtered on top of the Ag/AgNPs substrate. Cyclic voltammetry measurements of cytochrome c (cc) were carried out showing that the electrochemical behavior of gold can extend the potential range of the composite surface significantly. Furthermore, a potentiostatic titration of cc on this substrate by SERRS demonstrated that the resonance Raman effect of silver nanoparticles with the Soret band of the heme had been maintained in the presence of the gold adlayer. The positions of the plasmon resonances measured by reflection spectroscopy method were confirmed by finite-difference time-domain simulations. Gold is the optimal substrate for electrochemistry, whereas silver is the optimal material for plasmonic applications. Combining both metals gives us a surface with good performance for electrochemical applications as well as an enhancement effect sufficient to study redox-active biomacromolecules such as cc.