Application of Davidenko's Method to a Lossy Nonlinear Waveguide

Davidenko's method is implemented for determining the complex propagation constants (Modal index and attenuation coefficient) of nonlinear TE waves guided by an asymmetrical lossy nonlinear dielectric wave-guide. The waveguide structure has a generalized nonlinear substrate with a permittivity of the form ? ～ | E |^δand an absorbing cover making the propagation constant to be complex. Davidenko's method shows to be a fast and accurate analysis in finding the complex propagation constants. The effects of initial condition parameter on the propagation characteristics are investigated, analyzed and discussed.     

Te-waves guided by arbitrary nonlinear dielectrics bounded by linear media

Considerable interest is currently being devoted to nonlinear propagation in dielectric slab waveguides for integrated optics and millimetric applications. Much of the current work is based on Kerr-like (∈ ～E ²) nonlinear media and numerically discussed. We present a exact solution of TE-waves for arbitrary nonlinear dielectric (∈ ～ |E| ^δ ). We applicate this solution to the planar nonlinear optic waveguides and the dispersion relations are given. The results show that the propagation constants are a function of the field magnitude.     

The nonlinear self-defocusing electromagnetic surface waves in a metalised ferrite film

The dispersion relations for TE s-polarized nonlinear electromagnetic surface waves guided by a metallised ferrite film, surrounded by a nonlinear self-defocusing dielectric cover with intensity dependent refractive indices have been computed. Numerical results are also illustrated to show the propagation characteristics for different values of the film thickness, and at a fixed value of the dielectric-ferrite interface nonlinearity. It has been found that the surface waves exist in both directions of propagation, where the external field is applied. The propagation of these waves is non-reciprocal, and has a resonant interaction in the reverse direction. The power flow carried by the structure has also been calculated for different values of the slab thickness. The non-reciprocity has also been obsorved, and the power flow level can been controlled by the film thickness. of semi-infinite gyromagnetic and nonlinear media². If we increase the operating frequency, the power flow level changes at a fixed film thickness, forβ ≥ 0 and forβ ≤0 as in Figs.4. There exist a limited eigenvalues (solutions) with f=17.8GHz forβ ≥ 0, and for different values of the operating frequency forβ ≤ 0. So the eigenvalues and the power flow level can be varied as the operating frequency is tunned. At f=17.8GHz forβ ≥ 0, as in fig.4b, to some value of the power flow there correspond two propagation wave index, which are being related to bistable states of nonlinear surface. All the above mentioned behaviours exhibit the characteristics of microwave switches, isolators, and limiters and could be used in some experimental applications in Microwave Engineering Technology. The other parameters effects as the magnetic field, magnetization, types of ferrite etc. on the dispersion characteristics and the power flow are now under consideration.     

Stability of black, gray, and bright nonlinear guided waves in athin film bounded by a self-defocusing medium

Stability of nonlinear guided waves trapped in a thin linear film bounded by an infinite self-defocusing nonlinear medium is investigated. In addition to the trapped black and gray nonlinear guided waves, the existence of a novel class of bright nonlinear guided waves (with nonzero intensity background) is demonstrated. The gray and fundamental bright nonlinear guided waves are found stable whereas the black nonlinear guided waves are unstable to an asymmetric perturbation (but stable to a symmetric perturbation). The instability of the black nonlinear guided waves is shown to develop into various states, including stable gray and bright nonlinear guided waves, depending on initial excitations     

TM waves in nonlinear saturable thin films: a multilayered approach

The dispersion of guided TM (transverse magnetic)-polarized waves in a thin nonlinear saturable film bounded by linear media is investigated. The film is assumed to be isotropic with both of the electric field components contributing to its dielectric function. The variation of the wave effective index with the guided power and also with the surface magnetic field intensity is obtained. Different mechanisms giving rise to the nonlinearity of the film are shown to result only in small quantitative differences in the dispersion behavior. A recursive scheme for solving the nonlinear wave equation within the film is fully described. The scheme relates to the saturable dielectric function used and its based on the stratification of the film region into a large number of linear sublayers     

Angular behavior of the absorption limit in thin film silicon solar cells

We investigate the angular behavior of the upper bound of absorption provided by the guided modes in thin film solar cells. We show that the 4n² limit can be potentially exceeded in a wide angular and wavelength range using two‐dimensional periodic thin film structures. Two models are used to estimate the absorption enhancement; in the first one, we apply the periodicity condition along the thickness of the thin film structure, but in the second one, we consider imperfect confinement of the wave to the device. To extract the guided modes, we use an automatized procedure that is established in this work. Through examples, we show that from the optical point of view, thin film structures have a high potential to be improved by changing their shape. Also, we discuss the nature of different optical resonances that can be potentially used to enhance light trapping in the solar cell. We investigate the two different polarization directions for one‐dimensional gratings, and we show that the transverse magnetic polarization can provide higher values of absorption enhancement. We also propose a way to reduce the angular dependence of the solar cell efficiency by the appropriate choice of periodic pattern. Finally, to obtain more practical values for the absorption enhancement, we consider the effect of parasitic loss that can significantly reduce the enhancement factor. Copyright © 2013 John Wiley & Sons, Ltd.     

对称非线性薄膜波导TE模的色散特性

用均匀（重整化）微扰方法分析Ｋｅｒｒ型非线性薄膜两侧为折射率相等的包层与衬底情形ＴＥ模的传播特性，传播常数用表征非线性的功率密度极值作为参数来表示。在微扰法失效情况下，用数值积分法求解。本文方法简便，节省机时，对典型实例的计算结果与精确数值计算结果十分符合。     

基于人工神经网络激光烧蚀制备PDPhSM基纳米复合薄膜聚合效率的预测

为有效缩短脉冲激光烧蚀制备有机硅聚合物聚二苯基硅亚甲基硅烷(PDPhSM)基纳米复合薄膜工艺中繁琐的实验过程,分别采用多层前馈(BP)神经网络和径向基函数(RBF)神经网络对PDPhSM基纳米复合薄膜的制备工艺与聚合效率之间的关系进行建模,并将其运用到聚合效率的预测中去,讨论了激光能量密度、环境压强、靶衬距离、沉积时间和聚合效率之间的关系。克服了以往单因素实验法不能正确反映制备工艺和聚合效率之间复杂的非线性关系的弱点。预测和验证结果均表明实验值和网络预测值之间相对误差都在10%以内,但径向基函数神经网络较多层前馈神经网络能够更精确、更可靠地逼近它们之间的非线性关系。该方法为有效、快捷、经济地开发研制PDPhSM基纳米复合薄膜提供了新的思路和有效手段。     

基于纳米多孔薄膜的对称平面光波导湿度传感器

通过在对称平面玻璃光波导上下表面各制备一层纳米多孔TiO2薄膜,形成了一种简单新颖的光学湿度传感器。其原理为,导波光在平面对称光波导中的传播损失依赖于纳米多孔Ti02薄膜的平均折射率,后者依赖于薄膜内部的水分子吸附量,而薄膜的水分子吸附量随着周围相对湿度的变化而变化,通过实时测量导波光传播损失的变化就能够感知外围的相对...     

Synthesis and optical characterization of Ag nanoparticles

The results of chemical synthesis and optical behavior of silver nanoparticles with sizes ranging from 2-10 nm which were obtained by reduction of Ag⁺ are reported. The material morphology was examined by transmission electron microscopy (TEM) and physical properties were studied by photoluminescence in the range of 400-550 nm using two different excitation wavelengths (320 and 380 nm). The signature provided by the silver plasmon is readily noticed in the silver nanoparticles. The nonlinear optical properties were obtained using a Z-scan setup and agree with previous results obtained by other methods and preparation of samples. In particular, a positive nonlinear refractive index of 5.0115×10⁻¹⁰ m²/W was obtained for a broad sample of silver nanoparticles between 2 and 10 nm. The agreement between the properties of the thin film sample and the nanoparticles give emphasis to the Z-scan technique for nonlinearity measurements of much more complex metal-dielectric structures.     

Self-switching in hollow waveguides with a Kerrlike nonlinearpermittivity

The dispersion relations, stability, and excitation of the stationary nonlinear transverse electric (TE) waves guided by a nonlinear hollow waveguide are examined numerically. This waveguide consists of a self-focusing nonlinear film bounded by two identical linear claddings of the higher refractive index. Since a minimum power for guidance of the stationary waves always exists, the nonlinear hollow waveguide acts as a lower threshold device. A stability analysis using the beam propagation method shows that all the stationary TE_n modes, including the asymmetric TE₀ mode, are stable on the positively sloped branch (dP/dβ>0) of the nonlinear dispersion curve. The lower threshold device using the nonlinear hollow waveguide exhibits very sharp power-switching characteristics, and the required device length is fairly short     

Striking effects of cobalt (III) nuclearity in fused salphen complexes on their electroconductivity and thin film transistor activity

Dinuclear and trinuclear cobalt (III) complexes were prepared using fused salphen ligands that have the same number of benzene rings along the major axis of the molecules. The two compounds were used as organic thin film formed on a glass or a SiO₂/n-Si substrate for investigating electronic conductivity and transistor characteristics, respectively. The conductivity of di- and trinuclear complexes were 8.5 × 10⁻⁵ and 5.8 × 10⁻³ S cm⁻¹, meaning that the increment of the nuclearity from two to three resulted in multiplication of 70 times. The thin film of the trinuclear complex showed a faint transistor activity, where the thin film act as n-type semiconductor. In contrast, the dinuclear complex did not afford a detectable response to the gate voltage.     

脉冲激光扫描淀积类金刚石薄膜

采用能量密度为1.178×109W/cm2的XeCl准分子激光直接辐照高纯度的石墨靶,并同时采用辅助放电,在1×10-5Torr的真空环境中,于温度为80℃的Si(100)的基片上淀积出类金刚石薄膜,Raman光谱显示在1330cm-1处出现较强的散射峰值;对薄膜红外光谱进行测试,其光谱在2900cm-1处有吸收峰,表明所淀积的类金刚石薄膜含有C-H键,其H元素与C元素的比为45%.薄膜的电阻率为1.89×106Ω/cm,通过光吸收测得的该薄膜的能隙为1.55eV.     

Thermally deposited Ag-doped CdS thin film transistors with high-k rare-earth oxide Nd2O3 as gate dielectric

The performance of thermally deposited CdS thin film transistors doped with Ag has been reported. Ag-doped CdS thin films have been prepared using chemical method. High dielectric constant rare earth oxide Nd₂O₃ has been used as gate insulator. The thin film trasistors are fabricated in coplanar electrode structure on ultrasonically cleaned glass substrates with a channel length of 50 μm. The thin film transistors exhibit a high mobility of 4.3 cm² V^?1 s^?1 and low threshold voltage of 1 V. The ON-OFF ratio of the thin film transistors is found as 10⁵. The TFTs also exhibit good transconductance and gain band-width product of 1.15 × 10^?3 mho and 71 kHz respectively.     

Optical absorptive response of platinum doped TiO2 transparent thin films with Au nanoparticles

In this paper different optical absorption bands associated to the surface plasmon of resonance of a nanoparticle containing sample were achieved by a sol–gel processing route. We study the linear and nonlinear optical absorptive properties of a titanium dioxide thin film with superficial Au nanoparticles. A chaotic behavior related with modification of the optical absorption by a multi-wave mixing interaction was investigated. A characteristic Mandelbrot group tendency was used to describe the possibility of a resulting absorptive response. The analysis of the observations showed that an excitation at 488 nm wavelength in the nanocomposite can originate a measurable change in the absorptive properties for the propagation of optical beams at 532 nm and at 650 nm. However, the inhibition of this condition exhibited by the film can be obtained by the shift of its plasmonic response. It is considered that the near resonance participation of the Au nanoparticles is mainly responsible for avoiding the photodarkening contribution to the optical absorptive response of the sol–gel TiO₂ film with embedded Au nanoparticles. Potential applications of the samples are proposed for development of optical sensors or transparent thin films for filtering functions.     

Fabrication of suspended thin film resonator for application of RF bandpass filter

Characteristics of AlN thin film and thin film resonator for RF bandpass filter have been studied. AlN thin films were deposited by RF magnetron sputter system. Deposition parameters such as N₂ contents, Ar and N₂ partial pressures, and the distance between metal target and substrate were found to affect the piezoelectric response. To fabricate the suspended thin film resonator (STFR) using the piezoelectric AlN thin film, the etching of AlN and the surface micromachining process were conducted. The thickness of AlN film and membrane for the STFR are 2 and 15 μm, respectively. This membrane was fabricated by SOI technology. The device with the dimension of 160 × 160 μm² has a resonant frequency of 1.653 GHz, a K_eff² of 2.4%, a bandwidth of 17 MHz, and a quality factor of 91.7. The device with the dimension of 200 × 200 μm² has a resonant frequency of 1.641 GHz, a K_eff² of 1.2%, and a bandwidth of 9 MHz, and a quality factor of 50.2.     

Low-voltage organic ferroelectric field effect transistors using Langmuir–Schaefer films of poly(vinylidene fluoride-trifluororethylene)

Langmuir–Schaefer transfer was used to fabricate ultrathin films of ferroelectric copolymer, poly(vinylidene fluoride-trifluoroethylene) (70–30 mol%), for non-volatile memory application at low operating voltage. Increasing the number of transferred monolayers up to 10 led to improved film crystallinity in the “in-plane” direction, which reduced surface roughness of the semicrystalline film. Treatment of the substrate surface by plasma results in different film coverage which was subsequently found to be governed by interaction of the deposited film and surface condition. Localized ferroelectric switching was substantially attained using piezo-force tip at 10 V on 10-monolayer films. Integrating this film as a dielectric layer into organic capacitor and field effect transistor yields a reasonably good leakage current (<10^?7 A/cm²) with hysteresis in capacitance and drain current with ON/OFF ratio of 10³ for organic ferroelectric memory application at significantly reduced operating voltage of |15| V.     

Full-wave characterization of high-Tcsuperconducting transmission lines

A full-wave numerical analysis is applied to accurately characterize superconducting transmission lines embedded in a layered dielectric medium. A volume integral equation formulation is developed by using a spectral domain dyadic Green's function for stratified media. Galerkin's method with rooftop basis functions for the electric field distribution inside the superconductor is then employed to solve the complex propagation constant. The thickness of the superconducting film is arbitrary in this analysis, and the formulation rigorously accounts for the anisotropy of the superconducting film. The propagation characteristics of a superconducting microstrip transmission line with a thin dielectric buffer layer are investigated. A superconducting stripline configuration with an air gap is also studied     

High-performance C60 and picene thin film field-effect transistors with conducting polymer electrodes in bottom contact structure

C₆₀ and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C₆₀ thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility μ value of 0.41 cm² V^?1 s^?1, while the picene thin film FET showed p-channel enhancement-type characteristics with the μ of 0.61 cm² V^?1 s^?1. The μ values recorded for C₆₀ and picene thin film FETs are comparable to those for C₆₀ and picene thin film FETs with Au electrodes.     

High Optical Gain of Solution-Processed Mixed-Cation CsPbBr3 Thin Films towards Enhanced Amplified Spontaneous Emission

A solution-processed thin film made of all-inorganic CsPbBr₃ perovskite is a promising candidate for low-cost and flexible green-color lasers. However, the amplified spontaneous emission (ASE) of solution-processed CsPbBr₃ films still experiences a high threshold owing to poor morphology and insufficient optical gain. Here, a multiple-cation doping strategy is demonstrated to develop compact, smooth thin films of Cs_0.87(FAMA)_0.13PbBr₃/(NMA)₂PbBr₄ (FA: formamidinium; MA: methylammonium; NMA: naphthylmethylammonium) with a record high net modal optical gain of ≈ 3030 cm⁻¹ and low propagation loss of 1.0 cm⁻¹. The FA and MA cations improve the crystallization kinetics to form continuous films, and the NMA cations reduce the grain dimension, increase film dispersibility/uniformity, and enhance spatial confinement to promote optical gain. Room-temperature ASE is demonstrated under a low threshold of ≈ 3.8  µ J cm⁻² without degradation after four months of storage in glove box or excitation by 3 × 10⁷ laser pulses. These findings provide insights into enhancing the optical gain and lowering the threshold of perovskite lasers in terms of molecular synthesis and microstructure engineering.