Zhengji Ni

Colored image produced with guided-mode resonance filter array

A method to reproduce colored images with a guided-mode resonance filter (GMRF) array is presented in this Letter. Because of their excellent characteristics, monochromatic light of the three primary colors with high purity can be achieved by using GMRF structures. Moreover, the primary colors are obtained without changing other GMRF parameters except the period, which could be realized easily with laser direct writing technology. The result shows that a colored image with high resolution and verisimilitude can be reproduced.

Type of tunable guided-mode resonance filter based on electro-optic characteristic of polymer-dispersed liquid crystal

A narrowband guided-mode resonance filter (GMRF) incorporating polymer-dispersed liquid crystal (PDLC) is designed. Simulating the characteristics of the filter with rigorous coupled-wave analysis, we find that the resonance wavelength of the new kind of GMRF can be tuned from 672.4 to 698.4 nm by varying the refractive index of the PDLC layer with the applied voltage. Furthermore, the resonance wavelengths vary in a linear fashion with respect to the refractive index of the PDLC layer. Therefore, the desired resonance wavelength can be conveniently selected and tuned in a tuning range of 26 nm by using the applied voltage.

A new structure of multi-layer phosphor package of white LED with high efficiency

The applications of white light-emitting diodes (LEDs) have become more and more wide recently, while the low light-extraction eciency of white LED limits its development. In this letter, a new structure of multilayer phosphor package of white LED is proposed to improve the light-extraction efficiency. It is illustrated that the thickness of phosphor layer plays an important role in improving the light-extraction efficiency of LED. The light-extraction efficiency of LED is improved by double-layer or multi-layer phosphor package structures.

Tunable and Polarization-Independent Wedged Resonance Filter With 2D Crossed Grating

In this letter, a tunable and polarization-independent guided-mode resonance filter that has two-dimensional crossed grating on a wedged waveguide layer of Ta2O5 is fabricated and analysed for the communication band. The wedged waveguide layer is etched by the ion beam etching technique with a triangle-shaped mask, and the two-dimensional grating is made by holographic exposure technique. The measured spectra show that the filter can realize the property of polarization-independence at normal incidence. By the thickness gradient of the wedged layer, the filter is tunable in a range of 1599.9-1621.5 nm over a distance of 9 mm.

Calculation of the diffraction efficiency on concave gratings based on Fresnel–Kirchhoff’s diffraction formula

Fraunhofer diffraction formula cannot be applied to calculate the diffraction wave energy distribution of concave gratings like plane gratings because their grooves are distributed on a concave spherical surface. In this paper, a method based on the Kirchhoff diffraction theory is proposed to calculate the diffraction efficiency on concave gratings by considering the curvature of the whole concave spherical surface. According to this approach, each groove surface is divided into several limited small planes, on which the Kirchhoff diffraction field distribution is calculated, and then the diffraction field of whole concave grating can be obtained by superimposition. Formulas to calculate the diffraction efficiency of Rowland-type and flat-field concave gratings are deduced from practical applications. Experimental results showed strong agreement with theoretical computations. With the proposed method, light energy can be optimized to the expected diffraction wave range while implementing aberration-corrected design of concave gratings, particularly for the concave blazed gratings.

Preparation of high laser induced damage threshold antireflection film using interrupted ion assisted deposition.

Single layers and antireflection films were deposited by electron beam evaporation, ion assisted deposition and interrupted ion assisted deposition, respectively. Antireflection film of quite high laser damage threshold (18J/cm2) deposited by interrupted ion assisted deposition were got. The electric field distribution, weak absorption, and residual stress of films and their relations to damage threshold were investigated. It was shown that the laser induced damage threshold of film was the result of competition of disadvantages and advantages, and interrupted ion assisted deposition was one of the valuable methods for preparing high laser induced damage threshold films.

Study on the excitation and propagation characteristics of THz-wave surface plasmon polaritons on the surface of semiconductor

In the paper, the excitation and propagation characteristics of terahertz (THz) wave surface plasmon polaritons (SPPs) at the interfaces of semiconductors (InAs, InP, GaAs) and air are presented. By analysing the confinement strength of surface plasmon and its propagation length with frequency changing, we demonstrate that the confinement strength of surface plasmon and its propagating length are a trade-off. Furthermore, the effect of temperature variation on the propagation characteristics of SPPs wave at the surface of intrinsic semiconductor InSb is presented. Calculations show that the surface plasma frequency goes higher with increasing temperature, corresponding to the enlargement of carrier concentration of semiconductor. The factor of confinement strength decreases while the propagation length of SPPs increases with increasing temperature under a certain excitation THz wave. This will provide a valuable reference for the design and optimisation of THz wave surface plasma devices.

The Spectrum of Quantum Dots Film for UV CCD

A new kind of UV-responsive film with quantum dots (QDs) fabricated by a spin-coating method is proposed in this paper. In a previous study, the monolayer QDs film is deposited onto fused silica slides by the spin-coating way, which has some luminous problem. The introduction of composite QDs coating which adds PEDOT:PSS and poly-TPD films to the monolayer QDs film is found to have excellent performance. The reason can be that PEDOT:PSS and poly-TPD weaken the scattering and enhance the emitting of quantum dot fluorescence. The intensity of photoluminescence (PL) for composite QDs coating is dozens of times stronger than that for monolayer QDs film. Experiment results show that this composite coating has excellent fluorescent properties and emits a blue purple glow together a wide excitation spectrum field from 190 nm to 300 nm. The spectrum of the composite coating matches accurately with the detected zone of CCD, which achieves an outstanding UV-responsive coating for conventional silicon-based image sensors.

Electric field distributions of single-layer guided-mode resonance filters

Electric field distributions inside resonant reflection filters of different mode constructed with planar single-layer periodic waveguides are investigated. The electric fields intensified by resonance effects was illustrated in this paper.

The substrate cooling effect of ion beam post treatment on ZAO films properties

ZAO thin films with low surface roughness and low sheet resistance are required in the touch panels and display panels. In this work, we investigated the substrate cooling effect of ion beam post treatment on ZAO films properties, and one new way of obtain low surface roughness and low sheet resistance same time was proposed. The more exciting find of this paper is that, comparing to the samples without cooling during the process of ion beam post treatment, samples with proper cooling voltage show a sheet resistance decrease of 26% (from 11.9 Ω/□ to 8.8 Ω/□) and a roughness decrease of 35.5% (from 13.389 nm to 8.637 nm) without transparency losing. And the viewpoint that substrate cooling has the effect of weakening the crystallization, especially for the sub-face and internal parts of samples is deduced.