Modeling graphene based surface plasmon waveguides and devices

To optimize the performance of organic light-emission devices (OLEDs), optical simulation or electrical simulation is often used to help designing the device structures. However, employing electrical or optical simulation separately to optimize the device might lead to incorrect conclusions. A few researches have combined optical and electrical simulations to design OLED structures by merely inserting the maximum carrier recombination rate calculated from electrical simulation into optical simulation programs, which is still insufficient for optimization of OLEDs due to lack of considering the influence of optical interference positions. In this paper, we investigate the OLED performance by using three simulation methods, pure optical, pure electrical, or combination of both, to design the devices. Using the models incorporating both electrical and optical simulations, we found that the optimal emission position occurs neither at the place with the best optical interference nor at the point where carrier recombination rate is the maximum. In order to verify the simulation results, we design the testing devices, red fluorescence OLEDs of bi-layer structures, with various positions of recombination emission. It is found that the position of recombination emission has major impact on the device performance of OLEDs, which lead to some important design rules. With integration of electrical and optical simulations, the real emission position could be predicted with excellent agreements to the experimental results. Applying this method to design the red fluorescent bi-layer OLEDs, the device with very high efficiency of 8.44 cd/A was achieved.

A fully integrated efficient surface plasmon coupler composed of a non-tapered waveguide is designed for the infrared through rigorous numerical and theoretical studies. To study such structures, a general methodology to study rigorously discontinuities in open waveguides is used. It relies on a full vector description given by Maxwell’s equations in the framework of the finite element method. In our case, the discontinuities are provided by the graphene patches that are modelled as 2D conductivity pieces. The leaky modes of the invariant structure are first computed and then injected as incident fields in the full structure with the graphene patches and sheet using a scattered field approach. This method we recently published allows to compute all the field and energy quantities needed to characterize the investigated couplers. These couplers are designed to work on the far infrared regime. TAS, a special chalcogenide glass is considered for the guiding layer. The studied waveguide is a rib waveguide. The input part of the studied device is the bare rib waveguide. Following the propagation axis, the device is composed of the coupler region, made of a finite number of graphene patches located just above the core guiding layer. The role of this coupler is to generate electromagnetic fields in the next continuous graphene sheet (also located on the top of the core layer) where the surface plasmon polariton part of the field is propagating. The graphene properties are the ones provided by the Kubo formula. The studied device is fully integrated and no out of plane waves have to be considered, only electromagnetic fields propagating inside the structures are considered. Parametric numerical studies as a function of the waveguide thickness and of the duty cycle parameter describing the coupling patches have been conducted in order to maximize the plasmonic part of the generated field near the graphene layer. Several waveguide and coupler configurations with realistic parameter have been obtained proving a highly efficient and fully integrated coupler. Among these configurations, one where the mode coupling between the main mode and higher orders modes is minimized is of particular interest for practical applications.

In conventional LEDs, a mesa-structure is usually used and it causes the current to be overcrowded in a specific region. We propose a novel structure of GaN-based LED to overcome this problem. In order to distribute the current in an active region, a spreading pad is inserted at the p-type region in the GaN based LED device. The inserted spreading pad helps the current flow because it is more conductive than the p-type GaN layer. By performing electrical and optical simulations, the effects of the spreading pad insertion are confirmed. The results of electrical simulation show that the current spreads more uniformly and more radiative recombination is produced as well. Moreover, from the optical simulation, it is revealed that the ITO is less absorptive material than p-GaN if the condition of specific wavelength sources is satisfied. Considering all of the results, we can conclude that the luminescent power is enhanced by the spreading pad.

Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution‐processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series‐connected multi‐junction organic solar cells (OSCs). Drying at 80 °C in air is sufficient for this solution‐processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage (Voc) of 0.56 V is obtained for single‐junction OSCs based on a low band‐gap polymer, while multi‐junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive Voc as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi‐junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution‐processed IML. The demonstration of this efficient, solution‐processed IML represents a convenient way for facilitating fabrication of multi‐junction OSCs to achieve high power conversion efficiency.

We have systematically investigated the localized surface plasmon resonance (LSPR) of the silver nanoparticles by using electron energy loss spectroscopy (EELS) and optical simulation based on boundary element methods with respect to the diameter and the impact parameter variations. The both peaks of EELS and optical curve were occurred from 3.2 to 3.8 eV. Interestingly, we found two types of plasmon modes. At the impact parameter from 0 to R, the plasmon showed the properties as bulk plasmon, while at the greater value than R it showed the surface plasmon mode. This result showed the EELS simulation was better to observe a high-order of LSPR spectra than optical simulation. High-order was originated from a higher multipolar mode and weak interaction in surface plasmon phenomenon. As shown above, the EELS measurement can detect a high-order mode of LSPR than the optical measurement.

A radio over fiber is one solution to broaden RF signal, a combination between wireless and wireline. An effective conversion between both signals is another way to enhanced this technology toward 5G. A compact design of integrated antenna and electro optic modulation can have dual functions, an antenna and an electro optic modulation. It uses several optical materials to give electro optic effect. The simulation uses a gold patch antenna and copper ground design as the integrated device. This paper purpose a 4 GHz bowtie antenna integrated with optical modulator. The integration is designed by inserting an optical material in a gap between two arms of bowtie antenna. It has optical crystals layer as a modified bowtie antenna to enlarge the electrical field on the antenna. The electrical field is compared and analyzed using a formula based on the simulation results. The impact of impedance mismatch in the integrated antenna gives a minimized formula that can give one and 2.7 times better electrical field for electro optic alteration. The simulation gives better bandwidth 115,83% but smaller gain 73.3 % than the conventional.

This study presents a novel high-efficiency electro-optic (EO) light modulator whose operation is based on the attenuated total reflec- tion effect, in which the surface plasmon wave is excited by an incident waveguide light wave. The EO light modulator is fabricated using a non- linear optical polymer material that is a side-chain EO polyimide with 2-(N-ethyl-4-(tricyanovinyl)anilino)ethanol chromophore. The modulator is characterized, and its performance tested, in terms of the thickness and dielectric constant of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic re- sponse of the EO light modulator is fully investigated and discussed. © 2005 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1868775) Subject terms: surface plasmon resonance; attenuated total reflection; electro- optic polymer; waveguide-coupled; nonlinear optical.

Dielectric thin films on a metal surface are an efficient means in terms of effective index contrast to realize optical elements for surface plasmon (SPs). We show that laterally structured thin films can on one hand be applied as SP lenses or prisms. On the other hand, they can be applied as SP waveguides, including bends and couplers.

In this chapter, the authors put forward and optimize the surface plasmonic metal waveguide geometry for the recently proposed terahertz (THz) injection laser based on resonant radiative transitions between tunnel-coupled graphene layers. They find an optimal number of active graphene layer pairs corresponding to the maximum net modal gain. The authors introduce a scheme of THz laser based on resonant photon-assisted transitions in multiple graphene layer structure embedded in a surface plasmonic waveguide enhancing the light-matter interactions. They find the ultimate modal gain and threshold length for lasing, and show that a seemingly simple solution to increase the number of active graphene layer pairs does not always lead to the gain enhancement. The authors find the corresponding upper limit of the modal gain in the THz lasers based on the multiple tunnel-coupled GLs. Our findings support the possibility of creating ultracompact graphene-based THz lasers.

In this paper, the design of CMOSAPD in standard 0.35 µm CMOS technology is presented;Simulation and Comparison between two CMOS avalanche photodiode (APDs) modes are performed. Electrical and Optical Simulations are carried out using SILVACO ATLAS © Suite. Two modes of Electrical Simulation have been presented. The performances of APDs in both modes have been compared in terms of responsively, noise and gain. Both structures present interesting characteristics.Monolithic integration of sensors and circuits in CMOS processes result in tremendous advantages in terms of dimensions shrink, low power consumption, low cost etc.

Graphene absorption from the visible to infrared spectrum has great potential and broad applications in miniature of modern optoelectronic biosensors and photodetectors. However, graphene has zero bandgap energy, which limits its absorption to 2.3% in the visible and infrared spectrums. Here, we propose a metastructure to optimize graphene absorption in the visible to near-infrared frequency regions. The metastructure, comprising an array of aluminum square blocks (Al-SBs) on a graphene layer, a silica spacer, and an Al reflector, is investigated for absorption enhancement. This work deciphers the effect of the periodicity of decorated Al-SBs on the evolution of dual-band absorption in single-layer graphene under normal incidence. The electromagnetic signatures of two excited modes indicate that surface plasmons and magnetic dipole plasmons are mediators of absorption. The investigation into the impact of geometrical parameters illustrates that the coexisting phenomena of a relative broad peak and a relative sharp peak have been achieved simultaneously with high efficiency. The dynamic manipulation of surface plasmons and magnetic dipole plasmons presents great potential for a diverse range of applications, such as sensing and imaging. By controlling the periodicity of Al-SBs, it is possible to achieve active control of surface plasmon resonance, and a detection range of 300 nm is observed. Dynamic control of the magnetic dipole plasmon is successfully achieved by modifying the electrical environment of the graphene layer, which is realized by altering the underlying spacer material. Collectively, the findings of this study demonstrate the significant potential of the suggested metastructure for its prospective applications in optoelectronic devices, including biosensors, photovoltaics, and photodetectors that rely on the dynamic control of surface and magnetic plasmon resonances.

A graphene-based surface plasmon (SP) waveguide switch is designed at near infrared frequencies. First, graphene is modeled in electronic and electromagnetic solvers, in order to use graphene strips for designing the waveguide. Because of finite size of these strips, propagating surface plasmon polaritons (SPPs) along them exhibit spatial dispersion. By considering this and shifting interband losses to higher frequencies (by doping the graphene strips), the waveguide switch is designed to operate at 30 THz. In this paper, chemical potential in the graphene strips is controlled through applying back and top gate voltages which provide a reconfigurable waveguide switch and the chemical potentials of the strips are changed so that ultra-confinement and extremely low-loss propagation are achieved. The designed switch provides extremely low return loss and ultra-bandwidth in 30--40 THz frequency range. Due to the spatial dispersion in the graphene strips, new procedures are proposed to calculate the return and insertion losses of the switch and also absorbed power in the graphene strips.

Performance improvement of thin-film silicon solar cells using transversal and longitudinal titanium nitride plasmonic nanogratings

A statistical methodology used to judge optical material interpolation models is presented in this paper. A quality- of-fit criterion related to probable performance impact in lens design is used. This treatment was developed as a way to judge the acceptability in lens design of low and medium precision data so that material model developed from this type of data could be used to some level of confidence in a wide assortment of lens designs--in other words, judging whether the material model is universally applicable. The results will show that a universal acceptability criterion is very demanding on the statistics of the data. However, the method developed lends itself to a wider use in judging material models for less demanding lens designs, too. Therefore, the initial criteria goal may rule out some fit models for universal utility in lens design, but the same material models may be usable for less demanding lens design performance situations.

Mask line roughness contribution in EUV lithography