Baicheng Li

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.

Real-Time Angular Sensitivity Compensation of Guided-Mode Resonance Filter

Guided-mode resonant filters (GMRFs) are promising narrowband filters with high peak efficiency, but their practical applications have been restricted by their natural high angular sensitivity. We investigated the influence of incident angle and azimuthal angle on the spectral response of GMRF, and found that the resonant peaks are mainly influenced by the incident angle. A polymer-dispersed liquid crystal layer was introduced to compensate the shift of resonant wavelength through applying proper voltage in real time, and numerical results show that a large angular compensation range of about ±4.2° can be obtained while maintaining high performance of the spectral response.

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.

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.