Luminance behaviour of PLEDs with integration of nanomaterials

Incorporation of nanomaterials in device structure is the key to enhance performance of polymer light emitting diodes (PLEDs). The major challenges that impede competence of PLEDs, for application in display technology, are (i) non-availability of stable low work function metals to act as cathode, (ii) presence of charge trapping centers in the polymer chains and (iii) total internal reflection of light at ITO/glass and glass/air interfaces. The foremost problem leads to increase in turn ON voltage of the device and reduction in electron injection from cathode. Low injection and high trapping probability of electrons lead to charge imbalance in the emissive layer and shifting of recombination zone towards cathode. This immensely constrains the formation and radiative decay of excitons in the emissive layer and declines the luminosity of the device. In this review, experimental studies on the integration of nanomaterials in PLED structures to enhance device luminance are presented. The diverse impact of their geometric features, ionization potential, electrical conductivity and refractive index on the carrier transport and light extraction in PLEDs is discussed and a perspective on this evolving research path is provided.     

Indium tin oxide anode modification for enhanced polymer light‐emitting devices

Abstract— Effort has been focused on exploring indium tin oxide (ITO) anode modification for enhanced performance of polymer light‐emitting diodes (PLEDs). It was found that oxidative treatment, e.g., a commonly used oxygen plasma, modifies ITO surface effectively to produce a low‐conductivity oxygen‐rich region. As a consequence, oxygen plasma‐treated ITO behaves somewhat similarly to specimens where there is an ultra‐thin insulating layer on its surface. It shows that the presence of such an ultra‐thin insulating interlayer between the ITO and the polymer layer favors the efficient operation of the PLEDs. The result of this effort provides an insight to better understand optimal anode contact for enhanced PLED performance.     

基于FDTD二维光子晶体器件设计软件的开发

介绍了一个基于时域有限差分法（FDTD）的二维光子晶体器件设计软件PCCAD,所用的核心算法是时域有限差分法。与同类FDTD商业软件相比,特点在于其具有多种光子晶体结构编辑模板,多种点源、线源,先进的边界吸收技术及多种参数优化扫描等功能。快速傅里叶变换及Pade算法在软件设计中的应用使模拟更加精确、快速。软件适用于各种平面光子晶体的仿真设计,探索新的器件结构。最后,利用此软件设计了直波导、T型波导等二维平面光子晶体器件。     

A research on the CN-ICCG–FDTD algorithm of plasma photonic crystals and the transmission coefficient of electromagnetic wave

The general FDTD method cannot calculate a complex object because of limit of the CFL conditions. CN-FDTD is an improvement on the FDTD method, and it can get rid of the CFL conditions and become wholly unconditional stable form. The advantage of the ICCG method for solving large sparse matrix will be taken in the CN-FDTD equation solving. ICCG method can accelerate iteration for numerical calculation, reduce memory overhead and be easy to be programmed at the same time. CN-ICCG–FDTD method researches the object model of plasma photonic crystals. Plasma photo crystals have unique properties. They can show mainly characteristics of plasma, or have the main properties of photonic crystals. Combination of plasma and photonic crystals makes it possible to adjust the plasma parameters to control the properties of photonic crystals. In this paper, it calculates characteristic parameters of plasma photonic crystals under different conditions, such as the reflection electric field, the transmission electric field, the transmission coefficient, to verify accuracy of CN-ICCG–FDTD method. The results of this paper prove the method is accurate, performs stably, and has certain advantages.     

基于Matlab的光子晶体波导仿真研究

本文首先介绍了光子晶体波导的原理,然后分析时域有限差分法微分方程及边界条件,最后运用matlab语言实现二维光子晶体波导的仿真。     

Epsilon-near-zero or mu-near-zero materials composed of dielectric photonic crystals

We theoretically demonstrate that at certain frequencies two-dimensional dielectric photonic crystals （PCs） may be regarded as either epsilon-near-zero or mu-near-zero materials. We show that the transmission through a slab of such materials upon normal incidence is normally non-unity and decays with slab thickness. However, when the incident angle increases slightly, the transmittance experiences a dramatic increase due to the Brewster effect. The combination of the tunneling and resonance effects makes such materials good candidates for almost perfect bending waveguides and cloaking in waveguides. The zero index also enables applications of focusing and directive emission. At last, the distinction between the single-zero and double-zero media is discussed. In all of the above results, the numerical simulations perfectly match with theoretical predictions from the effective medium analysis.     

Energy‐efficient liquid‐crystal displays (e2‐LCDs) using a photonic‐crystal backlight system

Abstract— Cholesteric liquid crystals automatically form one‐dimensional photonic crystals. For a photonic crystal in which light‐emitting moieties are embedded, unique properties such as microcavity effects and simultaneous light emission and light reflection can be expected. Three primary‐color photonic‐crystal films were prepared based on cholesteric liquid crystal in which fluorescent dye is incorporated. Microcavity effects, i.e., emission enhancement and spectrum narrowing, were observed. Two types of demonstration liquid‐crystal displays (LCDs) were fabricated using the prepared photonic‐crystal films in a backlight system. One is an area‐color LCD in which a single photonic‐crystal layer is used for each color pixel and the other is a full‐color TFT‐LCD in which three stacked photonic‐crystal layers are used as light‐conversion layers. The area‐color LCD was excited by using 365‐nm UV light, and the full‐color TFT‐LCD was excited by using 470‐nm blue LED light. Because of the photonic crystal's unique features that allow it to work as light‐emitting and light‐reflecting layers simultaneously, both LCDs demonstrate clear readable images even under strong ambient light, such as direct‐sunlight conditions, under which conventional displays including LCDs and OLED displays cannot demonstrate clear images. In particular, an area‐color LCD, which eliminated color filters, gives clear images under bright ambient light conditions even without backlight illumination. This fact suggests that a backlight system using novel photonic‐crystal layers will be suitable for energy‐efficient LCDs (e²‐LCDs), especially for displays designed for outdoor usage.     

光子晶体并行Matlab仿真研究与实现

由于Madab软件的网络通信局限,使得在并行时域有限差分(FDTD)计算仿真中,难以实现子域间的消息发送与接收操作.针对这个问题,提出一种新的基于磁盘-内存互逆映射的解决方法,在简化并行FDTD算法实现的同时,显著提高了算法执行性能.作为算法实现的应用,对光子晶体光波导的电磁耦合效应进行了数值仿真研究,结果证实:波导耦合区域内不同半径比介质柱所导致的结构变化将造成耦合长度的改变,且其耦合关系曲线具有平稳区与迅变区两类不同特性的变化范围区间.     

Multifunctional glassy liquid crystals for photonics

Abstract— As an emerging class of photonic materials, morphologically stable glassy liquid crystals, were developed following a versatile molecular design approach. Glassy cholesteric liquid crystals with elevated phase‐transition temperatures and capability for selective‐wavelength reflection and circular polarization were synthesized via deterministic synthesis strategies. Potential applications of glassy cholesteric liquid crystals include high‐performance polarizers, optical notch filters and reflectors, and circularly polarized photoluminescence. A glassy nematic liquid crystal comprising a dithienylethene core was also synthesized for the demonstration of nondestructive rewritable optical memory and photonic switching in the solid state.     

Pitch Angle Control of Unmanned Air Vehicle with Uncertain System Parameters

In this paper a new algorithm of trajectory tracking based on closest radius solution of the interval equations system is proposed. The design procedure is given and applied to the pitch angle control of unmanned testing rocket with uncertain parameters. The proposed algorithm gives a framework to design a control for a wide range of different linear time-invariant processes with uncertain parameters and can be implemented also in the case of non-convex problems. The algorithm gives the analytical way of finding the nearly optimal solution of model reference trajectory tracking in the case of general time-invariant systems with uncertain parameters and can be used when optimization method fails due to the complexity of the problem.     

Single-objective optimization framework for designing photonic crystal filters

This work presents a single-objective optimization framework for designing complex photonic crystal (PhC) filters. As a case study, a super defect PhC filter with five rods is considered. Due to the large number of structural parameters and complexity of designing process, the problem is formulated and optimized by using a recent optimization algorithm called multi-verse optimizer (MVO). Six optimal super defect filters are obtained by MVO with respect to the WDM standard, which is defined by ITU-T Recommendation G.694.2. The designed super defect filters are then placed side by side to implement WDM. The results of FDTD simulation of the designed WDM show that the magnitude of output spectral transmission is higher than that of the current works in the literature. In addition, the high-quality factor and low crosstalk value (−32.9 dB) are the other advantages of the designed WDM with optimal super defect filters.

     

Optimizing angular placements of the LEDs in a LCD backlight module for maximizing optical efficiency

This study aims to optimize angular placements of the LEDs with novel cone-shaped caps for achieving high optical efficiency in an ultra-thin, directly-lit RGB LED backlight unit (BLU) for large-sized LCD-TVs. This novel lens cap is used as a diffuser with the purpose to gain higher efficiency and provide satisfactory uniformity over a display panel. To this aim, the outer surface of the novel lens is coated with aluminum for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, finally to the output plane. Since the emitted white light from LEDs result from color-mixing of three individual RGB chips in a LED package, the addition of the LED cap however deteriorates the aforementioned expected color mixing. The optimal design on angular placements of LEDs presented in this study for satisfactory color-mixing and emission uniformity is achieved by necessary optics simulations via TracePro, followed by utilizing an intelligent numerical optimization technique, genetic algorithm (GA). The design parameters for GA optimization are different combinations of LED placement angles in a backlight module. Favorable color balance is shown achievable in terms of high low color difference resulted. Finally, experiments are conducted, which successfully validate the expected performance of color balance and emission uniformity for a novel cone-shaped LED lens with optimized angular placements in a large-area backlight module.     

Lattice-parameter effects on diffracted transmission of GaN two-dimensional square-lattice photonic crystals

The lattice-parameter effects on the diffracted transmission of GaN square-lattice photonic crystals (2PhC) at the wavelength of 460 nm were studied by using a rigorous coupled wave analysis (RCWA). The impacts of lattice parameters on the diffracted transmission are calculated in the ranges for lattice pitch from 100 nm to 2000 nm,fill factor from 0.1 to 0.9 and grating height from 100 nm to 1000 nm,respectively. Our simulation results confirm that the lattice pitch is the dominant factor of the diffractio...     

Fabrication of silicon-based two-dimensional photonic crystals

Both triangular lattice and square lattice photonic crystals with lattice constant 400 nm and the radius 200 nm of the air pores in the silicon substrate have been designed, fabricated and realized. The processes of the fabrication of the two-dimensional photonic crystals, based on silicon, including mask making, electron-beam lithography, and inductively coupled plasma etching are introduced.     

Design and simulation of MEMS optical switch using photonic bandgap crystal

This paper details the novel design of a non-blocking in-plane microelectromechanical systems (MEMS) optical cross connect (OXC) designed and simulated with a new class of material known as the photonic bandgap (PBG) crystal for integration of device technology in optical switching and telecommunication applications. Particularly, silicon is the material of choice being investigated for the PBG MEMS device designed to address the objectives of achieving high optical performance with strategic exploitation for potential applications. Based on the physical and mathematical theories, the PBG and MEMS structures are studied and modelled. Simulations were carried out based on the plane wave method (PWM) and the finite difference time domain (FDTD) method to explore the benefits of integrating photonic crystals with MEMS technology to improve the performance of OXC devices.     

新型光子晶体THz滤波器

提出了一种新型基于光子晶体的太赫兹滤波器,该滤波器在线缺陷中设计了由三个点缺陷构成的谐振腔,能够实现双波长的高效滤波功能。文中使用平面波展开法(PWM)分析了正方晶格光子晶体的带隙结构,并利用时域有限差分法(FDTD)研究了滤波器的一些性能指标。仿真结果表明,该新型滤波器能够把频率为3.413 THz和3.222 THz的太赫兹波滤出,并且具有滤波带宽窄、体积小等优点。     

发射功率可变的无线传感器网络能量级别选取

针对一种无线传感器网络节点的发射功率可变,其最大发射半径是最小能量发射半径r的k倍,即kr的传感器网络,研究节点最佳能量发射半径ir的设计问题。通过数学分析得到能量消耗公式,给出最优的能量发射级别k的计算方法。采用优化的发射功率相比采用固定功率的发射方法能够大幅度地提高网络寿命,对传感器网络的优化具有较好的指导作用。     

Design of phononic crystals for self-collimation of elastic waves using topology optimization method

Self-collimating phononic crystals (PCs) are periodic structures that enable self-collimation of waves. While various design parameters such as material property, period, lattice symmetry, and material distribution in a unit cell affect wave scattering inside a PC, this work aims to find an optimal material distribution in a unit cell that exhibits the desired self-collimation properties. While earlier studies were mainly focused on the arrangement of self-collimating PCs or shape changes of inclusions in a unit cell having a specific topological layout, we present a topology optimization formulation to find a desired material distribution. Specifically, a finite element based formulation is set up to find the matrix and inclusion material distribution that can make elastic shear-horizontal bulk waves propagate along a desired target direction. The proposed topology optimization formulation newly employs the geometric properties of equi-frequency contours (EFCs) in the wave vector space as essential elements in forming objective and constraint functions. The sensitivities of these functions with respect to design variables are explicitly derived to utilize a gradient-based optimizer. To show the effectiveness of the formulation, several case studies are considered.     

Fabrication of silicon-based two-dimensional photonic crystals

Both triangular lattice and square lattice photonic crystals with lattice constant 400 nm and the radius 200 nm of the air pores in the silicon substrate have been designed, fabricated and realized. The processes of the fabrication of the two-dimensional photonic crystals, based on silicon, including mask making, electron-beam lithography, and inductively coupled plasma etching are introduced.

     

Process Parameters Optimization: A Design Study for TiO$_{2}$ Thin Film of Vacuum Sputtering Process

This paper proposes a procedure for process parameters design by combining both modeling and optimization methods. The proposed procedure integrates the Taguchi method, the artificial neural network (ANN), and the genetic algorithm (GA). First, the Taguchi method is applied to minimize experimental numbers and to collect experimental data representing the quality performances of a system. Next, the ANN is used to build a system model based on the data from the Taguchi experimental method. Then, the GA is employed to search for the optimal process parameters. A process parameters design for a titanium dioxide (TiO₂) thin film in the vacuum sputtering process is studied in this paper. The quality objective is to form a smaller water contact angle on the TiO₂ thin-film surface. The water contact angle is 4° obtained from the system model of the proposed procedure. The process parameters obtained from the proposed procedure were used to conduct the experiment in the vacuum sputtering process for the TiO₂ thin film. The water contact angle given from the practical experiment is 3.93°. The difference percent is 1.75% between 4° and 3.93°. The result obtained from the system model of the proposed procedure is promising. Hence, we can conclude that the proposed procedure is a very good approach in solving the problem of the process parameters design.