Keshri S, Marín-Sáez J, Naydenova I, Murphy K, Atencia J, Chemisana D, Garner S, Collados M V, Martin S
Appl Opt. 2020 Mar 10;59(8):2569-2579. doi: 10.1364/AO.383577.
A novel stacking procedure is presented for volume phase holographic gratings (VPHGs) recorded in photopolymer material using Corning Willow Glass as a flexible substrate in order to achieve broader angular and spectral selectivity in a diffractive device with high efficiency for solar and LED applications. For the first time to our knowledge, we have shown a device designed for use with a white LED that has the same input and output angles and high efficiency when illuminated by different wavelengths. In this paper, two VPHGs were designed, experimentally recorded, and tested when illuminated at normal incidence. The experimental approach is based on stacking two individual gratings in which the spatial frequency and slant have been tailored to the target wavelength and using real-time on-Bragg monitoring of the gratings in order to control the recorded refractive index modulation, thereby optimizing each grating efficiency for its design wavelength. Lamination of the two gratings together was enabled by using a flexible glass substrate (Corning Willow Glass). Recording conditions were studied in order to minimize the change in diffraction efficiency and peak diffraction angle during lamination and bleaching. The final fabricated stacked device was illuminated by a white light source, and its output was spectrally analyzed. Compared to a single grating, the stacked device demonstrated a twofold increase in angular and wavelength range. The angular and wavelength selectivity curves are in good agreement with the theoretical prediction for this design. This approach could be used to fabricate stacked lenses for white light LED or solar applications.
本文提出了一种新颖的堆叠方法，用于在以康宁柳树玻璃为柔性基板的光聚合物材料中记录的体相位全息光栅（VPHG），以便在用于太阳能和LED应用的高效衍射器件中实现更宽的角度和光谱选择性。据我们所知，我们首次展示了一种设计用于白色LED的器件，该器件在被不同波长照射时具有相同的输入和输出角度且效率很高。本文设计了两个VPHG，进行了实验记录，并在正入射照明下进行了测试。实验方法是基于堆叠两个单独的光栅，其中空间频率和倾斜度已针对目标波长进行了调整，并使用光栅的实时布拉格监测来控制记录的折射率调制，从而针对其设计波长优化每个光栅的效率。通过使用柔性玻璃基板（康宁柳树玻璃）实现了两个光栅的层压。研究了记录条件，以尽量减少层压和漂白过程中衍射效率和峰值衍射角的变化。最终制造的堆叠器件由白光源照明，并对其输出进行了光谱分析。与单个光栅相比，堆叠器件的角度和波长范围增加了两倍。角度和波长选择性曲线与该设计的理论预测吻合良好。这种方法可用于制造用于白光LED或太阳能应用的堆叠透镜。
