分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Based on point spread function (PSF) engineering and astigmatism due to a pair of cylindrical lenses, a novel compressed imaging mechanism is proposed to achieve single-shot incoherent 3D imaging. The speckle-like PSF of the imaging system is sensitive to axial shift, which makes it feasible to reconstruct a 3D image by solving an optimization problem with sparsity constraint. With the experimentally calibrated PSFs, the proposed method is demonstrated by a synthetic 3D point object and real 3D object, and the images in different axial slices can be reconstructed faithfully. Moreover, 3D multispectral compressed imaging is explored with the same system, and the result is rather satisfactory with a synthetic point object. Because of the inherent compatibility between the compression in spectral and axial dimensions, the proposed mechanism has the potential to be a unified framework for multi-dimensional compressed imaging.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The central idea of metamaterials and metaoptics is that, besides their base materials, the geometry of structures offers a broad extra dimension to explore for exotic functionalities. Here, we discover that the topology of structures fundamentally dictates the topological properties of optical near fields and offers a new dimension to exploit for optical functionalities that are irrelevant to specific material constituents or structural geometries. We find that the nontrivial topology of metal structures ensures the birth of polarization singularities (PSs) in the near field with rich morphologies and intriguing spatial evolutions including merging, bifurcation, and topological transition. By mapping the PSs to non-Hermitian exceptional points and employing homotopy theory, we extract the core invariant that governs the topological classification of the PSs and the conservation law that regulates their spatial evolutions. The results have effectively bridged three vibrant fields of singular optics, topological photonics, and non-Hermitian physics, with potential applications in chiral sensing, chiral quantum optics, and beyond photonics in other wave systems.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Modeling optical field propagation in highly scattering and birefringent medium is of important interest to many photonic research branches. Despite the existence of numerical electromagnetic simulation tools and beam propagation method frameworks, there has been a lack of an analytical model including the full tensor nature of birefringence, which is an essential forward-propagation tool for applications requiring efficiently iterative regularization and end-to-end designs. Here, we present an analytical tool for modeling field propagation in a birefringent scattering medium by including a full set of field tensor elements and multiple scattering characteristics. Birefringence-controlled field propagation experiments were successfully carried out to validate the proposed model.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Diffraction gratings with high upward diffraction efficiency and large effective length are required for chip-scale light detection and ranging. In this paper, we propose a diffraction grating based on a multilayer silicon nitride waveguide, which theoretically achieves an upward diffraction efficiency of 92$\%$, a near-field effective length of 376 $\mu m$ and a far-field divergence angle of 0.105$^{\circ}$ at a wavelength of 850 nm. The diffraction grating has a high tolerance to process variations based on Monte Carlo Analysis. When the conditions are $\pm$5$\%$ layer thickness variation, $\pm$50 nm lithographic variation and $\pm$20 nm wavelength drift, more than 71$\%$ of the grating samples have a diffraction efficiency higher than 80$\%$, and 100$\%$ of the samples have an effective length larger than 200 $\mu m$ (corresponding to a far-field divergence <0.2$ ^{\circ}$). Furthermore, the near-field effective length of the grating with an upward diffraction efficiency above 90$\%$ can be adjusted from hundreds of microns to centimeters by changing the etching layer thickness and the grating duty cycle. This diffraction grating has potential application in optical sensing and imaging from visible to near-infrared wavelengths.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The recent research of topological photonics has not only proposed and realized novel topological phenomena such as one-way broadband propagation and robust transport of light, but also designed and fabricated photonic devices with high-performance indexes which are immune to fabrication errors such as defects or disorders. Photonic crystals, which are periodic optical structures with the advantages of good light field confinement and multiple adjusting degrees of freedom, provide a powerful platform to control the flow of light. With the topology defined in the reciprocal space, photonic crystals have been widely used to reveal different topological phases of light and demonstrate topological photonic functionalities. In this review, we present the physics of topological photonic crystals with different dimensions, models and topological phases. The design methods of topological photonic crystals are introduced. Furthermore, we review the applications of topological photonic crystals in passive and active photonics. These researches pave the way of applying topological photonic crystals in practical photonic devices.
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