Optical Angle Barcodes Enabled by a Pixelated Metasurface for Absolute Micro-Angle Measurement

Efficient and ultra-sensitive measurements of micro-angle are critical technological requirements in various fields. Traditional measurement approaches have disadvantages in terms of accuracy and system complexity. Here, a micro-angle measurement scheme based on the pixelated metasurface is reported. By utilizing the interaction between a C-band optical frequency comb (OFC) laser source and the plasmonic metasurface, precise angle encoding is achieved, enabling each meta-pixel within the pixelated metasurface to exhibit ultra-sensitive responses to angular changes. Experimental results demonstrate a resolution as low as 2.8 μrad for angle sensing. Furthermore, by controlling the dimensions of the meta-atom structural dimensions and designing specific combinations of meta-pixels, the unique angle response of individual pixels is manipulated, effectively creating an angle barcode. This technique allows for highly efficient acquisition of angle information, and based on this, it demonstrates absolute angle measurement with an average error at 7 μrad. The robustness and stability of the proposed scheme is also evaluated.     

Electromagnetic characterization of bianisotropic metasurfaces on refractive substrates: General theoretical framework

We present a general methodology for electromagnetic homogenization and characterization of bianisotropic metasurfaces formed by regular or random arrangements of small arbitrary inclusions at interfaces of two different isotropic media. The approach unites and generalizes the earlier theories developed independently by two joint research groups: that of profs. Holloway and Kuester and that of profs. Simovski and Tretyakov. We analyze the features of both formalisms and discuss their peculiarities in several example cases. Our theory can be used in the analysis and synthesis of a wide spectrum of metasurfaces.

     

The geometric phase in nonlinear frequency conversion

The geometric phase of light has been demonstrated in various platforms of the linear optical regime, raising interest both for fundamental science as well as applications, such as flat optical elements. Recently, the concept of geometric phases has been extended to nonlinear optics, following advances in engineering both bulk nonlinear photonic crystals and nonlinear metasurfaces. These new technologies offer a great promise of applications for nonlinear manipulation of light. In this review, we cover the recent theoretical and experimental advances in the field of geometric phases accompanying nonlinear frequency conversion. We first consider the case of bulk nonlinear photonic crystals, in which the interaction between propagating waves is quasi-phase-matched, with an engineerable geometric phase accumulated by the light. Nonlinear photonic crystals can offer efficient and robust frequency conversion in both the linearized and fully-nonlinear regimes of interaction, and allow for several applications including adiabatic mode conversion, electromagnetic nonreciprocity and novel topological effects for light. We then cover the rapidly-growing field of nonlinear Pancharatnam-Berry metasurfaces, which allow the simultaneous nonlinear generation and shaping of light by using ultrathin optical elements with subwavelength phase and amplitude resolution. We discuss the macroscopic selection rules that depend on the rotational symmetry of the constituent meta-atoms, the order of the harmonic generations, and the change in circular polarization. Continuous geometric phase gradients allow the steering of light beams and shaping of their spatial modes. More complex designs perform nonlinear imaging and multiplex nonlinear holograms, where the functionality is varied according to the generated harmonic order and polarization. Recent advancements in the fabrication of three dimensional nonlinear photonic crystals, as well as the pursuit of quantum light sources based on nonlinear metasurfaces, offer exciting new possibilities for novel nonlinear optical applications based on geometric phases.     

主动式液晶超表面研究进展北大核心CSCD

超表面具有亚波长尺度下精密高效的光波操控能力,但在其单独实现主动式调控方面,目前仍有诸多技术困难亟待克服。液晶与超表面的结合有望发挥各自的长处,实现一种分辨率高、衍射角大、超紧凑的新型主动式光调控器件。以液晶与超表面两部分功能设计的独立与否作为分类依据,回顾了近年来主动式液晶超表面的研究进展,具体包括液晶波片与偏振敏感超表面结合、液晶环境与共振型超表面结合、液晶与超表面光学性质互补等。最后对主动式液晶超表面所面临的挑战以及发展前景进行了讨论和展望。     

On a “structure intermediate between quasiperiodic and random”

This paper proves rigorously that the structure factor of the structure intermediate between quasiperiodic and random introduced by Aubry. Godréche, and Luck is purely singluar continuous apart from a delta function at zero for most choices of the parameters. The result is based on a proof that a flow under a steep function over an irrational circle rotation is weakly mixing for most parameters, and on the wonderland Theorem.     

声学超构表面

声学超构表面是当前声学领域的研究热点,其是一种由人工微单元构成的超薄平面结构,由于其具备平面、超薄等独特物理特性及对声波的灵活调控能力,使得其在降噪隔振、隐身技术、非接触操控物体等诸多声学领域具有重要的应用前景。文章以反射型、吸收型、透射型声学超构表面为框架,深入介绍超构表面高效调控声波的物理机制并举例展示了其构建复杂声场的能力,包括任意点反射聚焦、低频完美吸声、自弯曲声束、螺旋声波以及声能量非对称传输。     

用于相位突变界面的广义的反射定律和折射定律

考虑到位于两物质界面上的Metasurface对光线传播行为的影响, 从费马原理和边界条件连续两种角度出发, 推导了可用于相位突变界面的广义反射与折射定律. 该定律在界面对光波的相位改变量为零的情况下, 回归为通常的反射定律和折射定律. 利用广义的折射定律和反射定律讨论了介质折射率、界面上的相位梯度等因素对光传播行为的影响, 发现利用广义的折射定律和反射定律很容易实现反常反射和反常折射行为, 并给出了出现反常反射和反常折射的条件, 以此为基础可以实现对光波的随意控制. 依据广义的折射定律和反射定律分析了一维相位掩模板对光场传播行为的影响. 关键词： 超材料 相位突变界面 反射定律 折射定律     

Evidence of parameter-induced aperiodic stochastic resonance with fixed noise

Stochastic resonance (SR) is based on the cooperative effect between the stochastic dynamical system and the external forcing. As is well known, the cooperative effect is produced by adding noises. In this paper, we show the evidence that by changing the system parameters and the signal intensity, a nonlinear system in the presence of an input aperiodic signal can yield the cooperative effect, with the noise fixed. To quantify the nonlinear system output, we determine the theoretical bit error rate (BER). By numerical simulation, the validity of the theoretical derivation is checked. Besides, we show that parameter-induced SR is more realizable than SR via adding noises, especially when the noise intensity exceeds the resonance level, or when the characteristic of the noise is not known.     

Metalenses at visible wavelengths: past,present, perspectives

The so‐called ‘flat optics’ that shape the amplitude and phase of light with high spatial resolution are presently receiving considerable attention. Numerous journal publications seemingly offer hope for great promises for ultra‐flat metalenses with high efficiency, high numerical aperture, broadband operation… We temperate the expectation by referring to the current status of metalenses against their historical background, assessing the technical and scientific challenges recently solved and critically identifying those that still stand in the way.

     

On the Distribution and Gap Structure of Lee–Yang Zeros for the Ising Model: Periodic and Aperiodic Couplings

In this work, we present some results on the distribution of Lee–Yang zeros for the ferromagnetic Ising model on the rooted Cayley Tree (Bethe Lattice), assuming free boundary conditions, and in the one-dimensional lattice with periodic boundary conditions. In the case of the Cayley Tree, we derive the conditions that the interactions between spins must obey in order to ensure existence or absence of phase transition at finite temperature (T0). The results are first obtained for periodic interactions along the generations of the lattice. Then, using periodic approximants, we are also able to obtain results for aperiodic sequences generated by substitution rules acting on a finite alphabet. The particular examples of the Fibonacci and the Thue-Morse sequences are discussed. Most of the results are obtained for a Cayley Tree with arbitrary order d. We will be concerned in showing whether or not the zeros become dense in the whole unit circle of the fugacity variable. Regarding the one-dimensional Ising model, we derive a general treatment for the structure of gaps (regions free of Lee–Yang zeros) around the unit circle.