Underwater dynamic polarization imaging without dependence on the background region.

Active-polarization imaging holds significant promise for achieving clear underwater vision. However, only static targets were considered in previous studies, and a background region was required for image restoration. To address these issues, this study proposes an underwater dynamic polarization imaging method based on image pyramid decomposition and reconstruction. During the decomposition process, the polarized image is downsampled to generate an image pyramid. Subsequently, the spatial distribution of the polarization characteristics of the backscattered light is reconstructed by upsampling, which recovered the clear scene. The proposed method avoids dependence on the background region and is suitable for moving targets with varying polarization properties. The experimental results demonstrate effective elimination of backscattered light while sufficiently preserving the target details. In particular, for dynamic targets, processing times that fulfill practical requirements and yield superior recovery effects are simultaneously obtained.

A strategy to build a library of oil tracers by oleophilic silica-encapsulated DNA nanoparticles.

Artificially synthesized DNA is involved in the construction of a library of oil tracers due to their unlimited number and no-biological toxicity. The strategy of the construction is proposed by oleophilic Silica-encapsulated DNA nanoparticles, which offers fresh thinking in developing novel tracers, sensors, and molecular machines in engineering & applied sciences based on artificially synthesized DNA blocks.

Influence mechanism of the particle size on underwater active polarization imaging of reflective targets.

Underwater active polarization imaging is a promising imaging method, however, it is ineffective in some scenarios. In this work, the influence of the particle size from isotropic (Rayleigh regime) to forward-scattering on polarization imaging is investigated by both Monte Carlo simulation and quantitative experiments. The results show the non-monotonic law of imaging contrast with the particle size of scatterers. Furthermore, through polarization-tracking program, the polarization evolution of backscattered light and target diffuse light are detailed quantitatively with Poincaré sphere. The findings indicate that the noise light's polarization and intensity scattering field change significantly with the particle size. Based on this, the influence mechanism of the particle size on underwater active polarization imaging of reflective targets is revealed for the first time. Moreover, the adapted principle of scatterer particle scale is also provided for different polarization imaging methods.

Underwater active polarization descattering based on a single polarized image.

Active polarization imaging techniques have tremendous potential for a variety of underwater applications. However, multiple polarization images as input are necessary for almost all methods, thereby limiting the range of applicable scenarios. In this paper, via taking full advantage of the polarization feature of target reflective light, the cross-polarized backscatter image is reconstructed via introducing an exponential function for the first time, only based on mapping relations of co-polarized image. Compared with rotating the polarizer, the result performs a more uniform and continuous distribution of grayscale. Furthermore, the relationship of degree of polarization (DOP) between the whole scene and backscattered light is established. This leads to an accurate estimation of backscattered noise and high-contrast restored images. Besides, single-input greatly simplifies the experimental process and upgrades efficiency. Experimental results demonstrate the advancement of the proposed method for objects with high polarization under various turbidities.

Visibility enhancement of underwater images based on polarization common-mode rejection of a highly polarized target signal.

Underwater active polarization imaging is promising due to its effect of significantly descattering. Polarization-difference is commonly used to filter out backscattered noise. However, the polarization common-mode rejection of target signal has rarely been utilized. In this paper, via taking full advantage of this feature of Stokes vectors S2 which ably avoids interference from target light, the spatial variation of the degree of polarization of backscattered light is accurately estimated, and the whole scene intensity distribution of background is reconstructed by Gaussian surface fitting based on least square. Meanwhile, the underwater image quality measure is applied as optimization feedback, through iterative computations, not only sufficiently suppresses backscattered noise but also better highlights the details of the target. Experimental results demonstrate the effectiveness of the proposed method for highly polarized target in strongly scattering water.

Design of a high-Q dark hollow beam cavity based on a one-dimensional topological photonic crystal.

Dark hollow beams (DHBs) possess great potential for material processing, holography, and vortex beams, and thus designing a high-Q DHB cavity is significant for these applications. In this Letter, a method of designing and optimizing a high-Q DHB cavity based on a one-dimensional topological photonic crystal (TPhC) is proposed. Furthermore, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method (FEM) simulation. According to the simulation results, the Q factor of the designed cavity can reach the order of 105 with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The design method proposed in this Letter may not only help designers of future DHB lasers but also promote the applications of DHBs in various fields.

Ring focus reflector design for topological charge multiplexing based on a perfect vortex beam.

A ring focus reflector is proposed for transmitting a perfect vortex (PV) beam, and the transmission characteristics of the PV beam with different topological charges in free space after passing through the reflector are studied. The reflector parameters can be determined by fitting the structural formula, and PV beams of different orders transmit with small spot sizes at the same time. The transmission trajectory calculated by the diffraction formula is consistent with the ray tracing results. The research results show that the reflector can achieve a high level of transmission efficiency of beams with different topological charges, which is conducive to the multiplexing of PV beams.

A Novel Preparation Method of Composite Bolted T-Joint with High Bending Performance Based on the Prepreg-RTM Co-Curing Process.

A co-curing resin system consisting of 9368 epoxy resin for prepreg and 6808 epoxy resin for resin transfer molding (RTM) was developed. A corresponding preparation method for a novel polymer composite bolted T-joint with internal skeleton and external skin was proposed based on the prepreg-RTM co-curing process, and novel T-joints were fabricated. A series of conventional configuration T-joints based on the RTM process and T-joints made of 2A12 aluminum alloy were prepared simultaneously. Bending performances were studied on these T-joints experimentally. The results indicate that 9368 epoxy resin and 6808 epoxy resin exhibit good compatibility in rheological and thermophysical properties. The novel T-joints prepared with the prepreg-RTM co-curing process show no obvious fiber local winding or resin-rich regions inside, and the interface quality between the internal skeleton and the external skin is excellent. The main failure modes of the novel T-joint under bending load include the separation of the skin and skeleton and the fracture along the thickness on the base panel; the skeleton carries the main bending load, but there is still load transfer between external skin and internal skeleton through their interface. The internal damages of the novel T-joint are highly consistent with surface damages observed visually, facilitating the detection and timely discovery of damages. The initial stiffness, damage initiation load, and ultimate load of the novel T-joint are 1.65 times, 5.89 times, and 3.45 times that of the conventional T-joint, respectively. When considering the influence of the density, the relative initial stiffness and relative ultimate load of the novel T-joint are 1.44 times and 2.07 times that of the aluminum alloy T-joint, respectively.