Enhancement of electroluminescent properties of organic optoelectronic integrated device by doping phosphorescent dye

Organic optoelectronic integrated devices（OIDs） with ultraviolet（UV） photodetectivity and different color emitting were constructed by using a thermally activated delayed fluorescence（TADF） material 4, 5-bis（carbazol-9-yl）-1, 2-dicyanobenzene（2 CzPN） as host. The OIDs doping with typical red phosphorescent dye [tris（1-phenylisoquinoline）iridium（Ⅲ）, Ir（piq）3], orange phosphorescent dye {bis[2-（4-tertbutylphenyl）benzothiazolato-N,C-（2＇）]iridium（acetylacetonate）,（tbt）2 Ir（acac）}, and blue phosphorescent dye [bis（2, 4-di-fluorophenylpyridinato）-tetrakis（1-pyrazolyl）borate iridium（Ⅲ）, FIr6] were investigated and compared. The（tbt）2 Ir（acac）-doped orange device showed better performance than those of red and blue devices, which was ascribed to more effective energy transfer. Meanwhile, at a low dopant concentration of 3 wt.%, the（tbt）2 Ir（acac）-doped OIDs showed the maximum luminance, current efficiency, power efficiency of 70786 cd/m^2, 39.55 cd/A, and 23.92 lm/W, respectively, and a decent detectivity of 1.07 × 10^11 Jones at a bias of -2 V under the UV-350 nm illumination. This work may arouse widespread interest in constructing high efficiency and luminance OIDs based on doping phosphorescent dye.

Study of nanocrystalline VO_2 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70 ℃, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction （XRD） and atomic force microscope （AFM）, respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy （XPS） results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, Eopt2p-3d ： 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.

Theoretical study and optimization of a high power mid-infrared erbium-doped ZBLAN fibre laser

Based on the rate equations describing the erbium-doped fluoride glass （ZBLAN） fibre lasers with different pumping configurations being taken into account, this paper presents theoretical calculations related to the dynamic population density and the operation performance of a high power mid-infrared all-fibre erbium-doped ZBLAN fibre laser. It shows that the ground-state absorption, excited-state absorption and energy-transfer-upconversion processes co-exist and produce a population balance, causing the laser to operate stably at a continuous wave state. A good agreement between the theoretical results and recent experimental measurement is obtained. Furthermore, the laser structure parameters including fibre length, reflectance of output fibre Bragg grating and pumping configurations are quantitatively optimised to achieve the best performance. The results show, as expected, that the slope efficiency of the fibre laser can be improved significantly through optimisation, which then provides an important guide for the design of high-performance mid-infrared erbium-doped ZBLAN fibre lasers.

Film thickness effect on the performance of small molecular solar cell

An efficient organic photovoltaic （OPV） cell with an indium-tin-oxide/CuPc/C60/Ag structure has been investigated by changing the film thickness of organic layers. A high olin-circuit voltage （Yoc） of 0.5 V, a short-circuit current density （Jsc） of 5.81 mA/cm^2, and a high power conversion efficiency （ηp） of 1.2% were achieved at an optimum film thickness. The results demonstrate that material thickness is an important factor to cell optimization, especially for maximizing the absorption rate as will as reducing the cell resistance. Experimental results also indicate that the power conversion efficiency increases from 1.2% to 1.54% as a BCP exciton blocking layer of 10 nm is introduced.

High performance pentacene organic field-effect transistors consisting of biocompatible PMMA/silk fibroin bilayer dielectric

Pentacene organic field-effect transistors （OFETs） based on single- or double-layer biocompatible dielectrics of poly（methyl methacrylate） （PMMA） and/or silk fibroin （SF） are fabricated. Compared with those devices based on sin- gle PMMA or SF dielectric or SF/PMMA bilayer dielectric, the OFETs with biocompatible PMMA/SF bilayer dielectric exhibit optimal performance with a high field-effect mobility of 0.21 cm2/Vs and a current on/off ratio of 1.5 × 104. By investigating the surface morphology of the pentacene active layer through atom force microscopy and analyzing the elec- trical properties, the performance enhancement is mainly attributed to the crystallization improvement of the pentacene and the smaller interface trap density at the dielectric/organic interface. Meanwhile, a low contact resistance also indicates that a good electrode/organic contact is formed, thereby assisting the performance improvement of the OFET.

Effects of deposition temperature on optical properties of MgF2 over-coated Al mirrors in the VUV

Both long-term environmental durability and high reflectance of protected-Al mirrors are of great importance for developing the optical instruments in the vacuum ultraviolet(VUV) applications. In this paper, the dependence of spectral property and environmental durability of MgF2 over-coated Al mirrors using a 3-step method on deposition temperature of the outermost MgF2 layer are investigated in detail. Optics(reflectance), structure(surface morphology and crystalline), and environmental durability(humidity test) are characterized and discussed. The results show that both optical and moistureresistant properties of MgF2 over-coated Al mirrors are dependent on MgF2 deposition temperature, and the optimal deposition temperature for the outermost MgF2 layer should be between 250℃ and 300℃ for MgF2 over-coated Al mirrors to have both reasonably high reflectance in the VUV spectral range and high moisture resistance for long lifetime applications.

High-precision measurement of low reflectivity specular object based on phase measuring deflectometry

Phase measuring deflectometry(PMD)is a robust,noncoherent technique for the characterization of specular surface.For measuring high specular reflectivity surface,PMD can deliver micron radian range local gradient.However,when the measured surface has low specular reflectivity,the accuracy of the measured gradient is low since the captured fringe pattern shows low signal to noise ratio.The phase error characteristics in PMD system when testing low reflectivity surfaces are analyzed.The analysis illustrates that the random phase error increases rapidly while the nonlinear error drops slowly with the decreasing of the tested surface reflectivity.In order to attain high precision measurement of low reflectivity specular surface,a robust error reduction method based on wavelet de-noising is proposed to reduce the phase error.This error reduction method is compared with several other normally used methods in both simulation and experiment work.The method based on the wavelet de-noising shows better performance when measuring the low reflectivity specular surface.

Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO_3 bulk:Effects of annealing temperatures

Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400 ℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400 ℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400 ℃. After annealing at 400 ℃, the film becomes almost transparent. Increasing annealing time at 400 ℃ can lead to a small blue shift of the optical gap of the film.

Numerical model of multilayer organic light-emitting devices

A numerical model of multilayer organic light-emitting devices is presented in this article. This model is based on the drift-diffusion equations which include charge injection, transport, space charge effects, trapping, heterojunction interface and recombination process. The device structure in the simulation is ITO/CuPc （20 nm）/NPD （40 nm）/Alq3 （60 nm）/LiF/Al. There are two heterojunctions which should be dealt with in the simulation. The I-V characteristics, carrier distribution and recombination rate of a device are calculated. The simulation results and measured data are in good agreement.

Detection of Insider Selective Forwarding Attack Based on Monitor Node and Trust Mechanism in WSN

The security problems of wireless sensor networks (WSN) have attracted people’s wide attention. In this paper, after we have summarized the existing security problems and solutions in WSN, we find that the insider attack to WSN is hard to solve. Insider attack is different from outsider attack, because it can’t be solved by the traditional encryption and message authentication. Therefore, a reliable secure routing protocol should be proposed in order to defense the insider attack. In this paper, we focus on insider selective forwarding attack. The existing detection mechanisms, such as watchdog, multipath retreat, neighbor-based monitoring and so on, have both advantages and disadvantages. According to their characteristics, we proposed a secure routing protocol based on monitor node and trust mechanism. The reputation value is made up with packet forwarding rate and node’s residual energy. So this detection and routing mechanism is universal because it can take account of both the safety and lifetime of network. Finally, we use OPNET simulation to verify the performance of our algorithm.

Enhancement of Frster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence（TADF） layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone（DMAC-DPS） and an ultrathin non-doped yellow phosphorescence layer employing bis[2-（4-tertbutylphenyl）benzothiazolato-N,C2＇]iridium（acetylacetonate）（（tbt）_2Ir（acac））.Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline（Bphen） and 1,3,5-tris（2-Nphenylbenzimidazolyl） benzene（TPBi） are selected as the electron transporting layer（ETL）,and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l＇Eclairage（CIE） coordinates variation of（0.017,0.009） at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency（EQE）,current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer（FRET）from DMAC-DPS to（tbt）_2Ir（acac） is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

Demodulated method of optical fiber Stokes temperature sensors

Based on the Stokes signals of the spontaneous Raman backscattering,a demodulated method for the simultaneous distributed temperature measurement in an optical fiber is presented to improve the sensitivity of the sensor.The experimental system of Stokes temperature sensor is set up and 2 km of operating length,1 m of distance resolution ,accuracy of ±0.1℃ are obtained.

Optimal design of a multi-mode interference splitter based on SOI

In this paper, the multimode waveguide lengths and the output port locations of a SOI （silicon on insulator） material-based 1×4 MMI （multimode interference） optical splitter are optimized by means of FD-BPM （finite difference - beam propagation method）. An improved 1×4 MMI optical splitter is designed. Compared with an usual optical splitter, a smaller loss 0. 12dB and a better output port power uniformity 0.11dB are achieved for the optical signal transmission.

Structure optimization of polymeric Mach-Zehnder rib waveguide

A systematic analysis of the polymeric Mach-Zehnder rib waveguide is presented based on the calculation and optimization. The simulation is carried out with the Effective Index Method (EIM) and two-dimensional (2-D) Finite Difference Beam Propagation Method (FD-BPM). The large refractive index step between the consecutive polymer layers is reduced by using EIM and thus the precision of the calculation is ensured. The important param- eters of the waveguide such as Y-junction angle and the separation gap are discussed and their relationships with the optical power propagation and the loss characteristics are investigated in this paper. The total loss of the opti- mized structure is 0.258 dB.

Swept Frequency Measurement of Electrooptic Phase Modulators Using Dispersive Fibers

A novel method based on the use of dispersive fibers is proposed and experimentally demonstrated for measuring the high-frequency modulation index,as well as the half-wave voltage,of electro-optic phase modulators.Fiber dispersion causes the phase modulated signal to become intensity modulated,which allows for the high resolution swept frequency measurement of phase modulators,using a vector network analyzer.The proposed method holds without the restriction of small-signal approximation,which is applicable for the measurement at different driving levels and operating wavelengths.

Design of Novel Compact Electromagnetic Bandgap Structures with Enhanced Bandwidth

Two kinds of compact electromagnetic band gap （EBG） structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Because of its significantly enlarged equivalent inductor and capacitance, the period of the lattice is approximately 4.5% of the free space wavelength. By insetting several narrow slits in the ground plane, the bandwidth of the main bandgap is enhanced by nearly 19%. Further effort has been made for designing a three layer compact EBG structure. Simulation results show that its period is reduced by about 26% compared to that of proposed two layer EBG structure, and the bandwidth of the main bandgap is about 3 times as that of the proposed two layer EBG structure. The detailed designs including a two layer compact 3×7 EBG array with and without defect ground plane and the three layer EBG array are given and simulation results are presented.

Modeling and experiments of N-doped vanadium oxide prepared by a reactive sputtering process

An original numerical model, based on the standard Berg model, is used to simulate the growth mechanism of Ndoped VOx deposited with changing oxygen flow in the reactive gas mixture. In order to compare with the numerical model, N-doped VOx films are prepared by reactive magnetron sputtering from a metallic vanadium target immersed in a reactive gas mixture of Ar＋O2＋N2. Both experimental and numerical results show that the addition of N2 to the process alleviates the hysteresis effect with respect to the oxygen supply. Film compositions obtained from the XPS analysis are compared to the numerical results and the agreement is satisfactory. The results also show that the compound of VN is only found at very low O concentration because of the replacement reaction of VN by O2 atoms with higher oxygen flow rate.

Development of Digital-Controlled Measuring Instrument for Hearing

A digital-controlled measuring instrument for hearing, which is mainly composed of STC11F16EX, AD9833, ISD400416MS and LM1972, is introduced in this paper. It may output highly accurate and purified sine signal whose frequency and amplitude are controlled by digital data. Specially, the displaying number of decibel is equal to actual number of decibel because that frequency response of earphone is corrected through software of microcontroller. Additionally, touching buttons, which is simple and convenience to use, is selected. Hence this instrument is convenient to measure and teach about hearing specially, research and study on frequency characteristic of human ear and impedance characteristic of human body in medical science.

Characteristics of photonic nanojets from two-layer dielectric hemisphere

The properties of the photonic nanojet generated by a two-layer dielectric microsphere are studied. Simulation results indicate that this novel structure can generate a photonic nanojet outside its volume when the refractive index contrast relative to the background medium is higher than 2：1 in the condition of plane wave incidence. When the refractive index is smaller than 2, we show that an ultralong nanojet generated by the two-layer hemisphere has an extension of 28.2 wavelengths, and compared with the homogeneous dielectric hemisphere, it has superior performance in jet length and focal distance. Its dependence on the configuration and refractive index is investigated numerically. According to the simulation of the two-layer dielectric microsphere, a photonic nanojet with a full width at half maximum（FWHM） less than 1/2 wavelength is obtained and the tunable behaviors of the photonic nanojet are demonstrated by changing the reflective indices of the material or radius contrast ratio.

A Nonlinear Mirror Structure to Improve the Performance of the Distributed Fiber Temperature Sensor Based on Raman Backscattering

A novel nonlinear mirror structure which can increase the optical signal-to-noise ratio of a distributed fiber Raman temperature sensor is proposed, and 6 dB improvement of the optical signal-to-noise ratio is obtained. With the assistance of the nonlinear mirror, we demonstrate that the spatial resolution of the sensor is improved from 3 m to 1 m, and the temperature accuracy is improved from ±0.6℃ to ±0.2℃. The theoretical analysis and the experimental data are in good agreement.