波状结构二维光子晶体近场亚波长成像的研究

Near-Field Subwavelength Imaging in Wave-Like Two-Dimensional Photonic Crystal

研究了波状结构二维光子晶体(2DPC)在红外波段的负折射近场成像,对其等频面进行了分析,指出波状结构二维光子晶体无法实现负折射远场成像的原因在于缺少与入射介质等频面相匹配的光子晶体圆形等频面,所用的矩形等频面使波状膜层二维光子晶体不可避免地具有各向异性特征,进而将成像限制在近场范围内。采用时域有限差分(时域有限差分)方法模拟了不同厚度的波状结构二维光子晶体近场成像效果,当厚度为两倍栅格常量时,单光源的成像分辨力为0.28λ,达到亚波长分辨效果。分辨力随着光源逐渐远离近场范围而降低,而像点的位置基本不随光源距离和光子晶体厚度的变化而改变。双光源的成像模拟进一步验证了波状结构二维光子晶体的近场亚波长成像能力,分辨力达到0.35λ,但成像质量受光子晶体厚度变化的影响较大。

Near-field subwavelength imaging based on negative refraction in wave-like two-dimensional photonic crystals within infared band. The adopted rectangular iso-frequency surface results in the inhomogereity of wave-like two-dimensional photonic crystal unavoidably, so the imaging is confined in the near-field region. For the lack of the circular-shaped iso-frequency surface in photonic crystal matching that of the incident medium, far-field imaging based on negative refraction is unavailable in wave-like two-dimensional photonic crystal. The finite-difference timedomain method is used to simulate the near-field imaging in wave-like two-dimensional photonic crystal of different thickness. The resolution of 0.28λ is achieved for single point source when the thickness of photonic crystal is twice of lattice constant. The resolution will gradually degrade as the source moves beyond the near-field domain. Meanwhile, the image is strongly confined in the near-field region on the other side of photonic crystal in spite of the change of source position and photonic crystal thickness. In order to further demonstrate the subwavelength imaging ability of wave-like two-dimensional photonic crystal, double sources are used. Resolution of 0.35λ is obtained, but the imaging quality depends on the thickness of photonic crystal greatelv.