Baghdasaryan Tigran, Geernaert Thomas, Chah Karima, Caucheteur Christophe, Schuster Kay, Kobelke Jens, Thienpont Hugo, Berghmans Francis
Vrije Universiteit Brussel (VUB), Department of Applied Physics and Photonics (TONA), Brussels Photonics (B-PHOT), Pleinlaan 2, B-1050, Brussels, Belgium.
University of Mons, Electromagnetism and Telecom Department, B-7000, Mons, Belgium.
Sci Rep. 2018 Apr 3;8(1):5470. doi: 10.1038/s41598-018-23867-5.
It is common belief that photonic crystals behave similarly to isotropic and transparent media only when their feature sizes are much smaller than the wavelength of light. Here, we counter that belief and we report on photonic crystals that are transparent for anomalously high normalized frequencies up to 0.9, where the crystal's feature sizes are comparable with the free space wavelength. Using traditional photonic band theory, we demonstrate that the isofrequency curves can be circular in the region above the first stop band for triangular lattice photonic crystals. In addition, by simulating how efficiently a tightly focused Gaussian beam propagates through the photonic crystal slab, we judge on the photonic crystal's transparency rather than on isotropy only. Using this approach, we identified a wide range of photonic crystal parameters that provide anomalous transparency. Our findings indicate the possibility to scale up the features of photonic crystals and to extend their operational wavelength range for applications including optical cloaking and graded index guiding. We applied our result in the domain of femtosecond laser micromachining, by demonstrating what we believe to be the first point-by-point grating inscribed in a multi-ring photonic crystal fiber.
人们普遍认为，只有当光子晶体的特征尺寸远小于光的波长时，它们的行为才类似于各向同性的透明介质。在此，我们反驳这一观点，并报告了一种光子晶体，它对于高达0.9的异常高归一化频率是透明的，此时晶体的特征尺寸与自由空间波长相当。利用传统的光子带理论，我们证明了对于三角晶格光子晶体，在第一禁带以上的区域等频率曲线可以是圆形的。此外，通过模拟紧聚焦高斯光束在光子晶体平板中传播的效率，我们判断光子晶体的透明度，而不仅仅是各向同性。使用这种方法，我们确定了提供异常透明度的广泛光子晶体参数范围。我们的研究结果表明，扩大光子晶体的特征尺寸并扩展其工作波长范围以用于包括光学隐身和渐变折射率引导在内的应用是有可能的。我们将我们的结果应用于飞秒激光微加工领域，通过展示我们认为是在多环光子晶体光纤中写入的第一个逐点光栅。
