相位梯度界面对光传播规律的影响

Influence of gradient phased interfaces on the laws of light propagation

在两种介质分界面上引入相位梯度形成相位梯度界面,这将使该界面的出射光和入射光之间产生相移.因此,与普通分界面不同,该界面对光的传播行为有着重大影响.为深入认识梯度相位界面的光学特性,本文研究了光在该类界面上的一般性传播规律.从费马原理出发,采用稳态相位法推导了基于相位梯度界面条件下的二维和三维广义反射和折射定律,该定律表明分界面也会成为影响光传播行为的重要因素,可以作为新的波前调制工具.利用广义反射和折射定律讨论了相位梯度对光传播行为的影响规律,得出了二维和三维情形下的临界条件(全反射和全透射条件),阐明了反射角不等于入射角、异常反射和折射、非平面反射和折射等一些新颖光学现象出现的原因;提出了以相位梯度界面为光学变换核心单元,依据广义反射和折射定律进行光学设计的思路,并以平面透镜和平面轴锥镜为例进行了详细说明与实验验证,实验结果和理论值符合较好,可为拓展广义定律在平面光学设计、自由曲面光学设计以及复杂光束控制中的应用提供参考.

The gradient phased interface is characterized by a non-zero phase variation along the interface between two optical media, which could generate a phase shit between the emitted and incident light beams. Unlike common ones, gradient phased interfaces have a great influence on the laws of light propagation, including light reflection and refraction, and some novel phenomena are observed. For a comprehensive understanding the optical characteristics of those gradient surfaces, the universal laws of light propagation at gradient phased interfaces are derived and discussed in detail in this paper. According to Fermat’s principle, we use the stationary phase method to successively acquire the two-dimensional（2D） and three-dimensional（3D） generalized laws of reflection and refraction. In the 2D generalized laws, the interfacial phase gradient lies in the plane of incidence, which is coplanar with the incident, refracted and reflected light beams.But in the 3D case, the phase gradient does not lie in the plane of incidence, and the non-planar reflection and refraction phenomena are observed. These generalized reflection and refraction laws indicate that the interface between two media could be an important factor when light traverses it, and gradient phased interfaces provide new degrees of freedom for manipulating the wavefront of light beams. Based on the generalized reflection and refraction laws, we analyze the influence of phase gradient on light propagation, then obtain critical angles of incidence for reflection and refraction（i.e. the critical angles for total internal reflection and total transmission） in 2D and 3D cases, and explain the reasons for some novel phenomena, such as reflection angle unequal to incidence angle, anomalous reflection and refraction,out-of-plane reflection and refraction, etc. These analysis results show that generalized laws of reflection and refraction have important value in optical design. In addition, we propose an optical design idea based on generalized laws of reflection and refraction, in which gradient phased interfaces are used as core components of optical elements to perform optical transform. And then a flat lens and flat axicon are taken for example to illustrate this idea, the design process of the two flat optical elements are shown in detail. Moreover, we experimentally simulate the gradient surfaces of the two elements by spatial light modulator, and experimental results agree well with theoretical values. It proves that this design idea is practicable. Our research is useful to understand comprehensively the generalized reflection and refraction laws, and extend the applications of generalized laws to flat optics, freeform optics and the accurate control of complex wavefront.