Established diffractive optical elements (DOEs), such as Dammann gratings, whose phase profile is controlled by etching different depths into a transparent dielectric substrate, suffer from a contradiction between the complexity of fabrication procedures and the performance of such gratings. In this Letter, we combine the concept of geometric phase and phase modulation in depth, and prove by theoretical analysis and numerical simulation that nanorod arrays etched on a silicon substrate have a characteristic of strong polarization conversion between two circularly polarized states and can act as a highly efficient half-wave plate. More importantly, only by changing the orientation angles of each nanorod can the arrays control the phase of a circularly polarized light, cell by cell. With the above principle, we report the realization of nanorod-based Dammann gratings reaching diffraction efficiencies of 50%-52% in the C-band fiber telecommunications window (1530-1565 nm). In this design, uniform 4 x 4 spot arrays with an extending angle of 59 degrees x 59 degrees can be obtained in the far field. Because of these advantages of the single-step fabrication procedure, accurate phase controlling, and strong polarization conversion, nanorod-based Dammann gratings could be utilized for various practical applications in a range of fields. (C) 2015 Optical Society of America
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机译：已经建立的衍射光学元件（DOE），例如达曼光栅，其相位轮廓通过在透明介电基片中蚀刻不同的深度来控制，其制造过程的复杂性与这种光栅的性能之间存在矛盾。在这封信中，我们结合了几何相位和深度调制的概念，并通过理论分析和数值模拟证明，刻蚀在硅基板上的纳米棒阵列具有在两个圆偏振态之间进行强偏振转换的特性，并且可以充当高效的半波片。更重要的是，只有通过改变每个纳米棒的取向角，阵列才能逐个单元地控制圆偏振光的相位。利用上述原理，我们报告了在C波段光纤电信窗口（1530-1565 nm）中实现基于纳米棒的达曼光栅的衍射效率达到50％-52％的事实。在这种设计中，可以在远场中获得扩展角度为59度x 59度的均匀4 x 4点阵列。由于单步制造过程的这些优点，精确的相位控制和强偏振转换，基于纳米棒的达曼光栅可用于一系列领域中的各种实际应用。 （C）2015年美国眼镜学会
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