Invisibility cloaks, a subject that usually occurs in science fiction and myths, have attracted wide interest recently because of their possible realization. The biggest challenge to true invisibility is known to be the cloaking of a macroscopic object in the broad range of wavelengths visible to the human eye. Here we experimentally solve this problem by incorporating the principle of transformation optics into a conventional optical lens fabrication with low-cost materials and simple manufacturing techniques. A transparent cloak made of two pieces of calcite is created. This cloak is able to conceal a macroscopic object with a maximum height of 2 mm, larger than 3500 free- Significant progress has been made during the exploration of invisibility cloak. The first theoretical model of a transformation-based cloak [3] required extreme values of the constitutive parameters of materials used and can only work within a very narrow frequency band [3,15]. Schurig et al. overcame the first flaw by using simplified constitutive parameters at microwaves based on metamaterial technologies [6]. To bypass the bandwidth limitation and push the working frequencies into the optical spectrum, it has been proposed that an object sitting on a flat ground plane can be made invisible under a fully dielectric gradient-refractive-index "carpet" cloak generated by quasiconformal mapping [5]. This carpet cloak model has led to a lot of subsequent experiments in both microwave [8,13] and infrared frequencies [9][10][11]14]. However, a serious limitation of carpet cloaks was recently pointed out: the quasiconformal mapping strategy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the hidden object, making the object detectable [16]. Furthermore, all previous experiments of invisibility in the optical spectrum, from infrared [9-11, 14] to visible [7,12] frequencies, were demonstrated under a microscope, hiding objects with sizes ranging from the order of 1 wavelength [7,[9][10][11]14] to approximately 100 wavelengths [12]. How to "see" the invisibility effect with the naked eye, i.e. to cloak a macroscopic object in visible light, is still a crucial challenge. In addition, most previous optical cloaks [7,[9][10][11]14] required complicated nano-or microfabrication, where the cloak, the object to be hidden, and the surrounding medium serving as the background were all fabricated in one structure. Thus they could not be easily separated from their embedded structures and transferred elsewhere to cloak other objects. These limitations, such as detectability, inadequate capacity to hide a large object, and nonportability, must be addressed before an optical cloak becomes practical. 2The above limitations boil down to two difficulties in the fabrication of cloak materialsanisotropy and inhomogeneity. The previously proposed quasiconformal mapping strategy attempted to solve anisotropy in order to facilitate metamaterial implementation [5]. However, in conventional optical lens fab...

Fluorescence microscopy with optical sectioning capabilities is extensively utilized in biological research to obtain three-dimensional structural images of volumetric samples. Tunable lenses have been applied in microscopy for axial scanning to acquire multiplane images. However, images acquired by conventional tunable lenses suffer from spherical aberration and distortions. Here, we design, fabricate, and implement a dielectric Moirémetalens for fluorescence imaging. The Moirémetalens consists of two complementary phase metasurfaces, with variable focal length, ranging from ∼10 to ∼125 mm at 532 nm by tuning mutual angles. In addition, a telecentric configuration using the Moirémetalens is designed for high-contrast multiplane fluorescence imaging. The performance of our system is evaluated by optically sectioned images obtained from HiLo illumination of fluorescently labeled beads, as well as ex vivo mice intestine tissue samples. The compact design of the varifocal metalens may find important applications in fluorescence microscopy and endoscopy for clinical purposes.

Holographic gratings formed in thick phenanthrenquinone- (PQ-) doped poly(methyl methacrylate) (PMMA) can be made to have narrowband spectral and spatial transmittance filtering properties. We present the design and performance of angle-multiplexed holographic filters formed in PQ-PMMA at 488 nm and reconstructed with a LED operated at approximately 630 nm. The dark delay time between exposure and the preillumination exposure of the polymer prior to exposure of the holographic area are varied to optimize the diffraction efficiency of multiplexed holographic filters. The resultant holographic filters can enhance the performance of four-dimensional spatial-spectral imaging systems. The optimized filters are used to simultaneously sample spatial and spectral information at five different depths separated by 50 microm within biological tissue samples.

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We demonstrate a method for single-shot quantitative phase imaging based on the transport of intensity equation (TIE) in a volume holographic microscope (VHM). The VHM system uses a multiplexed volume hologram to laterally separate images from different focal planes. This axial intensity information is then used to solve the TIE and recover object phase quantitatively. Further, we show improved phase recovery by using five multiplexed gratings in one hologram.

SKS wave splitting measurement is a powerful tool to characterize mantle deformation and study the dynamics and evolution of continents. We have made measurements of SKS wave splitting beneath the China mainland and adjacent regions. Our goal is to obtain the magnitude and orientation of upper mantle anisotropy and provide constraints for the evolution model of the crust and mantle. We use the technique of Silver and Chan to determine SKS wave splitting parameters at more than 80 three‐component broadband stations in China and neighboring regions, including the azimuths of fast polarization direction (ϕ) and delay times of split shear wave (δt). The fast wave polarization directions at most stations share a common preferred orientation in a same tectonic block. The fast axes show good correlation with the past and present‐day tectonic movement. Delay times range from 0.4s to 2.4s with an average about 1.2s. According to the splitting parameters of SKS wave, anisotropic characteristics in the study region are analyzed to investigate the dynamic process in the Earth.

A new methodology describing the effects of aperiodic and multiplexed gratings in volume holographic imaging systems (VHIS) is presented. The aperiodic gratings are treated as an ensemble of localized planar gratings using coupled wave methods in conjunction with sequential and non-sequential ray-tracing techniques to accurately predict volumetric diffraction effects in VHIS. Our approach can be applied to aperiodic, multiplexed gratings and used to theoretically predict the performance of multiplexed volume holographic gratings within a volume hologram for VHIS. We present simulation and experimental results for the aperiodic and multiplexed imaging gratings formed in PQ-PMMA at 488nm and probed with a spherical wave at 633nm. Simulation results based on our approach that can be easily implemented in ray-tracing packages such as Zemax® are confirmed with experiments and show proof of consistency and usefulness of the proposed models.

Quantitative phase imaging (QPI) has been investigated to retrieve optical phase information of an object and applied to biological microscopy and related medical studies. In recent examples, differential phase contrast (DPC) microscopy can recover phase image of thin sample under multi-axis intensity measurements in wide-field scheme. Unlike conventional DPC, based on theoretical approach under partially coherent condition, we propose a new method to achieve isotropic differential phase contrast (iDPC) with high accuracy and stability for phase recovery in simple and high-speed fashion. The iDPC is simply implemented with a partially coherent microscopy and a programmable thin-film transistor (TFT) shield to digitally modulate structured illumination patterns for QPI. In this article, simulation results show consistency of our theoretical approach for iDPC under partial coherence. In addition, we further demonstrate experiments of quantitative phase images of a standard micro-lens array, as well as label-free live human cell samples.