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We propose a photonic crystal (PC) nanostructure that combines bound states In the continuum (BIC) with a high-quality factor up to 107 for emitting circularly polarized beams. We break the in-plane inversion symmetry of the unit cell by tilting the triangular hole of the hexagonal lattice, resulting in the conversion of a symmetrically protected BIC to a quasi-BIC. High-quality circularly polarized light is obtained efficiently by adjusting the tilt angles of the hole and the thickness of the PC layer. By changing the hole's geometry in the unit cell, the Q-factor of circularly polarized light is further improved. The quality factor can be adjusted from 6.0 × 103 to 1.7 × 107 by deliberately changing the shape of the holes. Notably, the proposed nanostructure exhibits a large bandgap, which significantly facilitates the generation of stable single-mode resonance. The proposed structure is anticipated to have practical applications in the field of laser technology, particularly in the advancement of low-threshold PC surface emitting lasers (PCSELs). [ABSTRACT FROM AUTHOR]

Summary: In energy storage systems, a voltage equalizer is always needed. The voltage equalizers often include a DC‐DC converter. In this paper, the DC‐DC converter in the voltage equalizer is saved by integrating the voltage equalization circuit into the bidirectional converter of the battery system, thus simplifying the system. The voltage equalization circuit in the integrated system is composed of a LC resonant circuit and a voltage multiplier, which has the advantages of simplicity and low complexity. This paper presents the design process based on the analysis model, which enables the equalizer to obtain the optimal parameter configuration. Test results show the proposed LC‐SVM can automatically realize voltage balance between energy storage cells without additional control. [ABSTRACT FROM AUTHOR]

Largemouth bass virus (LMBV) is a systemic viral pathogen that can cause high mortality rates in cultivated largemouth bass. However, no treatment is currently approved. Therapeutic strategies against LMBV infection are urgently needed. In this study, we investigated the antiviral activity of piperine against LMBV in vitro and in vivo. In vitro antiviral activity assay showed that 210.28 μM piperine significantly decreased LMBV major capsid protein (MCP) gene expression in epithelioma papulosum cyprinid (EPC) cells by a maximum inhibitory rate of >95%. Piperine treatment inhibited LMBV replication in a dose‐dependent manner, with the half‐maximal activity (IC50) of 34.61 μM. Moreover, piperine significantly decreased the viral titers and cytopathic effects (CPE), contributing to the protection of infected cells. With regard to the steps of piperine affecting the life cycle of viruses, piperine had a direct inactivating effect on LMBV. During the virus adsorption phase, piperine prevented the adsorption of LMBV to EPC cells. Furthermore, piperine played an antiviral role mainly in the later stages of viral infection (4–8 h). To further evaluate the antiviral activity of piperine against LMBV in vivo, largemouth bass as a model organism was carried out in relevant experiments. Intraperitoneal injection of piperine (25 mg/kg) effectively improved the survival rate of LMBV‐infected largemouth bass by 20%. In addition, RT‐qPCR results of viral replication in liver, spleen, kidney, gill and swim bladder tissues showed that piperine significantly inhibited LMBV replication in vivo, thus protecting largemouth bass from LMBV‐induced death. Together, our results suggested that piperine is a therapeutic and preventative agent against LMBV infection. [ABSTRACT FROM AUTHOR]

We propose a thin-film Ge-on-Si-on-insulator (Ge-on-SOI) photodetector with enhanced performance by exploiting induced guided mode resonance (GMR) employing Ge/SiO2 grating on Si-on-insulator (SOI). Numerically calculated results and theoretical analysis demonstrate that normal-incidence light can be coupled to the GMR and partly be converted into the spatial resonance mode which propagates along the whole properly designed grating structure. A notable absorption efficiency of higher than 70% is obtained in the photodetector with only 280 nm-thick Ge/SiO2 grating, which is about 35 times larger than that of the counterpart without the designed grating structure. Remarkable enhanced light absorption can be achieved in the device with very few grating periods, which significantly promotes a theoretical 3-dB bandwidth-efficiency product of ∼66 GHz. The result is promising for a compact Ge-on-Si photodetector design with low dark current, high-bandwidth, and high-responsivity. [ABSTRACT FROM AUTHOR]

Abstract Optical imaging through scattering layers based on the 'memory effect' (ME) always suffers from a limited field of view. Here, we present a method that employs prior information to provide indispensable support for imaging behind a scattering medium, in which case the transversal distance between the targets is beyond the limited range determined by the ME. We experimentally demonstrate that given a known target, or even a light point-source, the other unknown object beyond the ME can be determined with only a single-shot camera image, even if the information of targets are mixed in the speckle pattern. Based on the same concept, we show that our technique is also capable of imaging extended object, whose size is larger than the limited range of ME. This work may have potential in practical applications such as imaging through turbulent medium or the biomedical imaging. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging (PAI) has been widely investigated by researchers from a range of areas. According to the differences between excitation laser sources, PAI can be categorized into two main types, namely the time-domain and frequency-domain PAI. Although the frequency-domain approach is more portable and economic than the other alternative, the low intensity of excitation source may lead to a lower signal-to-noise ratio (SNR). This paper aiming to propose the suitable scheme for image reconstruction, we focus on the model-based PAI system and make great efforts to reduce the impact of noise algorithmically. Three regularization algorithms, i.e., Least Square QR-factorization, Tikhonov, and Total Variation minimization by Augmented Lagrangian and alternating direction algorithms (TVAL3) are studied. By choosing three important parameters as criteria, i.e., the peak SNR, image quality index, and time consumption during different situations, the most effective regularization algorithm amongst has been selected. Based on simulation results and detailed discussions, TVAL3 algorithm performs better than the other two for model-based signal reconstruction. The result is pivotal for effective PAI in high quality and highly efficient biomedical tomography and microimaging. [ABSTRACT FROM AUTHOR]

Optical imaging and focusing through complex samples is a challenge with important applications in many fields. The critical problem is that turbid media such as biological tissue and multimode optical fibers randomly scatter and diffuse light, preventing the formation of diffraction-limited focus and image. We demonstrate with numerical simulations that a multiple scattering can be controlled via a serial optical transmission matrix and a parallel optical transmission matrix in order to obtain an achromatic focus and image at an arbitrary position. Simulation results of three-dimensional achromatic focusing and imaging based on this approach are agreed with the theoretical analysis. A scattering diffuser can be used as functional optical elements for focusing and imaging, moreover it can be manipulated and designed for multifunctional optical elements beyond traditional design. Our method will pave a way for using scattering media as unique optical achromatic elements for various applications, as well as for guiding the light and tailoring the light field. [ABSTRACT FROM AUTHOR]

We propose a novel metamaterial structure to realize dispersionless slow light based on plasmon-induced transparency (PIT) at optical frequency. Simply by breaking the symmetry of the metamaterial structure, two electric excitation coupling to the magnetic resonance (EEMR) modes generate and interplay with each other resulting the formation of the PIT resonance. Due to the hybridization of the two EEMR modes, an ultrabroad flat-band as large as 15 THz with average group index of $\sim 5$ is obtained. The corresponding normalized delay-bandwidth product is 0.475, which indicates the prominent feature in light slowing down without distortion. The proposed metamaterial structure is promising for practical information storage, optical memory, and optical buffers design. [ABSTRACT FROM PUBLISHER]

As a newly developed biomedical imaging technology, photoacoustic imaging (PAI) has attracted great attention worldwide. Traditional frequency domain PAI modality requires tremendous calculations by involving back-projection algorithm in time domain. A pure frequency domain method referred as model-based frequency domain PAI modality based on amplitude and phase analysis was introduced recently. However, the noises in signals may distort the reconstruction images severely. Since noises are normally un-stationary and non-linear, the degree of difficulty increases for restraining the impact of noises by Fourier transform. Also, impacts of different types of noise vary hugely. Moreover, inappropriate sifting process may even aggravate image distortion. In this study, a frequency domain PAI system based on chirp modulation signals has been introduced, in which the influence introduced by two main types of noise have been analyzed by simulation to show how different types of noises may damage reconstructed image in practical and to what extent. White Gaussian noise acts as an additive noise and distort the image gradually while the stochastic noise distort the image very rapidly as the fluctuation increase. Then a new method based on the empirical mode decomposition (EMD) for signal-sifting is demonstrated. By carefully choosing the thresholds and iterative steps, the reconstructed image quality has been promoted, the relative intensity of the target and noises has increased a lot. Further discussion about this method is also made, which certifies the availability of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a multilayer terahertz absorber composed of hybrid graphene and vanadium dioxide (VO2). Based on electrical controlling of graphene and thermal tuning of VO2, three different switchable absorption states are achieved in one structure. When VO2 is in the metal phase and the Fermi level of graphene is set as 0eV, high-frequency broadband (bandwidth, 5.45THz) absorption from 4.5 to 9.95THz is demonstrated. While VO2 is switched to the insulator state, absorption states depend on the Fermi energy of graphene. As the Fermi level changes from 1eV to 0eV, the absorption can be switched from low-frequency broadband (bandwidth, 2.86THz) to dual-frequency absorption. The effect of geometric parameters and fabrication tolerance on the robustness of the absorption properties is explored. The proposed absorber has three switchable states through modulation of graphene and VO2, which is expected to realize potential applications in modulating, filtering, detecting, and other fields.

A robust method for efficient spatial separation optical imaging through scattering media regardless of the three-dimensional (3D) optical memory effect is proposed. In this method, the problems of imaging dealiasing, decomposition, and separation of speckle patterns are solved by employing independent component analysis. Multitarget imaging behind a scattering layer with diverse spatial positions is observed experimentally, for the first time, to the best of our knowledge. In this work, we demonstrate that, by knowing the number of targets and keeping each subtargets' size in the optical memory effect range while isolating them beyond this range without overlap in the axial direction, speckle dealiasing and multitarget imaging are solved effectively. The strategy provides a potentially useful means for incoherent imaging through scattering media in a wide class of fields such as optical microscopy, biomedical imaging, and astronomical imaging.

Plasmon-induced transparency (PIT) in nanostructures has been intensively investigated; however, there are no known metasurface nanostructures that exhibit all optically tunable properties, where the number of transparency windows can be tuned successively and switched to off-state. In this Letter, we theoretically investigate and demonstrate a dynamically tunable, multichannel PIT at optical frequencies. The in-plane destructive interference between bright and dark dipolar resonances in coupled plasmonic nanobar topologies is exploited to produce a tunable PIT with unique characteristics. In particular, we demonstrate a sequential polarization-selective multispectral operation whereby the number of PIT channels can be varied successively from 3 to 0. The results provide a promising route for an active manipulation of PIT and show potential applications for multifunctional dynamic nanophotonics devices.

Tracking moving targets behind a scattering medium is a challenge, and it has many important applications in various fields. Owing to the multiple scattering, instead of the object image, only a random speckle pattern can be received on the camera when light is passing through highly scattering layers. Significantly, an important feature of a speckle pattern has been found, and it showed the target information can be derived from the speckle correlation. In this work, inspired by the notions used in computer vision and deformation detection, by specific simulations and experiments, we demonstrate a simple object tracking method, in which by using the speckle correlation, the movement of a hidden object can be tracked in the lateral direction and axial direction. In addition, the rotation state of the moving target can also be recognized by utilizing the autocorrelation of a speckle. This work will be beneficial for biomedical applications in the fields of quantitative analysis of the working mechanisms of a micro-object and the acquisition of dynamical information of the micro-object motion.

We analyze the imaging of gray-scale objects through highly scattering layers. The theoretical investigation with numerical simulations shows that the contrast of the speckle autocorrelations varies regularly with the change of the gray scale of the object. Therefore, gray information is well contained in the autocorrelations of the speckle patterns, and gray-scale objects are able to be exacted from these autocorrelations via speckle correlation technology. Combined with phase retrieval via the generalized approximate message passing algorithm, recovery of the objects is realized and accurate gray-scale reconstruction is demonstrated via numerical simulations. Experiment results further demonstrate the good performance of the scheme in the imaging of gray-scale objects through scattering layers. Particularly, this work will be beneficial for applications of imaging through turbid media in biomedical and biophotonics imaging.

We analyze the design of near infrared all-optical controllable and dynamically tunable multispectral Fano resonances based on subgroup decomposition of plasmonic resonances in hybrid nanoslits antenna plasmonic system. The theoretical investigation complemented with numerical simulations show that the Fano resonance lines shape can be tailored efficiently and continuously with the nanoslits geometry and the variation of the polarization states of the incident light. The subgroup decomposition of the spectral profile and the modification of plasmonic resonances lineshape that leads to the Fano-type profile of transmission is investigated and revealed. The separate contribution from individual spectral of single-slit array subgroup is attributed to the resulting overall multispectral Fano lineshape of the proposed T-shaped slits array at their corresponding spectral peaks zone. The polarization-selective tunability of the multispectral Fano resonances in the planar hybrid plasmonic system creates new avenues for designing multi-channel multi-wavelength tunable Fano effect.

A numerical and theoretical study is presented on the exhibition of tunable narrow band coupled-induced transparency phenomenon in a hybrid waveguide-plasmon system consisting of gold twin nanowires array embedded in a slab waveguide. We show that, at slightly non-normal incidence, a properly designed splitting of transmission with narrow transparency peaks may occur at a given wavelength, depending on the angle of incidence. This leads to the wavelength-selective high quality coupled-induced transparency resonance at optical frequencies. By adjusting the gap distance of the pair gratings, the coupled-induced transparency band can be switched between on-state and off-state, which provides us possibilities to develop controllable plasmonic functional devices employing plasmonic nanostructures.