分类: 光学 >> 光学设计与制造 提交时间: 2022-10-19 合作期刊: 《桂林电子科技大学学报》
摘要: 为了更好地选择一个合适的的辅助物镜,基于辅助物镜的工作原理,从理论推导和实验仿真两方面出发,对常见双胶合形式的辅助物镜进行了结构优化设计。根据设计要求,合理选择辅助物镜的初始结构,并从理论上推导了各类像差。基于初始结构和优化目标,利用光学设计软件OSLO对2种形式的辅助物镜进行了结构优化和像差分析。之后对于创新型双胶合-厚弯月型辅助物镜进行设计优化,以文献中相似透镜的结构参数为该设计的初始结构,利用OSLO光学软件及设计经验,对其进行结构优化、像差分析及矫正。对2种形式的辅助物镜进行对比分析的结果表明,2种结构形式的辅助物镜经过优化后,其参数均能满足设计要求,但双胶合-厚弯月型的辅助物镜更适用于大像面的光学系统。
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Fourier single-pixel imaging (FSI) is a branch of single-pixel imaging techniques. It uses Fourier basis patterns as structured patterns for spatial information acquisition in the Fourier domain. However, the spatial resolution of the image reconstructed by FSI mainly depends on the number of Fourier coefficients sampled. The reconstruction of a high-resolution image typically requires a number of Fourier coefficients to be sampled, and therefore takes a long data acquisition time. Here we propose a new sampling strategy for FSI. It allows FSI to reconstruct a clear and sharp image with a reduced number of measurements. The core of the proposed sampling strategy is to perform a variable density sampling in the Fourier space and, more importantly, the density with respect to the importance of Fourier coefficients is subject to a one-dimensional Gaussian function. Combined with compressive sensing, the proposed sampling strategy enables better reconstruction quality than conventional sampling strategies, especially when the sampling ratio is low. We experimentally demonstrate compressive FSI combined with the proposed sampling strategy is able to reconstruct a sharp and clear image of 256-by-256 pixels with a sampling ratio of 10%. The proposed method enables fast single-pixel imaging and provides a new approach for efficient spatial information acquisition.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The recent discovery of higher-order topology has largely enriched the classification of topological materials. Theoretical and experimental studies have unveiled various higher-order topological insulators that exhibit topologically protected corner or hinge states. More recently, higher-order topology has been introduced to topological semimetals. Thus far, realistic models and experimental verifications on higher-order topological semimetals are still very limited. Here, we design and demonstrate a three-dimensional photonic crystal that realizes a higher-order Dirac semimetal phase. Numerical results on the band structure show that the designed three-dimensional photonic crystal is able to host two four-fold Dirac points, the momentum-space projections of which at an edge are connected by higher-order hinge states. The higher-order topology can be characterised with the calculation of the \chi(6) topological invariant at different values of k_z. An experiment at microwave frequencies is also presented to measure the hinge state dispersion. Our work demonstrates the physical realization of a higher-order Dirac semimetal phase and paves the way to exploring higher-order topological semimetals phases in three-dimensional photonic systems.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Resonance coupling in non-Hermitian systems can lead to exotic features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been widely employed to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineering spatial wavefronts have remained elusive. Here, we show that, by operating a suitably tailored metagrating around a BIC and EPs, it is possible to achieve an extreme degree of control over coupling to different diffraction orders in metasurfaces. We stack subwavelength metallic slit arrays on a metal-insulator-metal waveguide, enabling a careful control of the coupling between localized and guided modes. By periodically tuning the coupling strength from weak to strong, we largely tailor the overall spectrum and enable the emergence of singular features, like BICs and EPs. Perfect unitary diffraction efficiency with large spectrum selectivity is achieved around these singular features, with promising applications for arbitrary wavefront shaping combined with filtering and sensing.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: A recent work [PRL, 126, 208002 (2021)] has explored how thermal noise-induced randomness in a self-assembled photonic crystal affects photonic band gaps (PBGs). For the system of a two-dimensional photonic crystal composed of a self-assembled array of rods with square cross sections, it was found that its PBGs can exist over an extensive range of packing densities. Counterintuitively, at intermediate packing densities, the transverse magnetic (TM) band gap of the self-assembled system can be larger than that of its corresponding perfect system (rods arranged in a perfect square lattice and having identical orientations). Due to shape anisotropicity, the randomness in the self-assembled system contains two kinds of randomness, i.e., positional and orientational randomness of the particles. In this work, we further investigate how PBGs are influenced solely by positional or orientational randomness. We find that compared to the perfect situation, the introduction of only orientational randomness decreases the transverse electric (TE) band gap while having no obvious effects on the transverse magnetic (TM) band gap. In contrast, the introduction of only positional randomness decreases the TE band gap significantly, while it can widen or narrow the TM band gap, depending on the parameter range. We also discuss the thermal (i.e., self-assembled) system where two kinds of randomness are present. Our study contributes to a better understanding of the role orientational randomness and positional randomness play on PBGs, and may benefit the PBG engineering of photonic crystals through self-assembly approaches.