Flexible long-wave infrared snapshot multispectral imaging with a pixel-level spectral filter array.

This paper proposes and demonstrates a flexible long-wave infrared snapshot multispectral imaging system consisting of a simple re-imaging system and a pixel-level spectral filter array. A six-band multispectral image in the spectral range of 8-12 µm with full width at half maximum of about 0.7 µm each band is acquired in the experiment. The pixel-level multispectral filter array is placed at the primary imaging plane of the re-imaging system instead of directly encapsulated on the detector chip, which diminishes the complexity of pixel-level chip packaging. Furthermore, the proposed method possesses the merit of flexible functions switching between multispectral imaging and intensity imaging by plugging and unplugging the pixel-level spectral filter array. Our approach could be viable for various practical long-wave infrared detection applications.

Miniaturized solar-blind ultraviolet imaging system enabled by a diffractive/refractive hybrid.

In this paper, we demonstrated a miniaturized diffractive/refractive hybrid system based on a diffractive optical element and three refractive lenses to achieve solar-blind ultraviolet imaging within a range of 240-280 nm. We experimentally demonstrate the optical system has both outstanding resolution and excellent imaging capability. The experiments demonstrate that the system could distinguish the smallest line pair with a width of 16.7 µm. The modulation transfer function (MTF) at the target maximum frequency (77 lines pair/mm) is great than 0.76. The strategy provides significant guidance for the mass production of solar-blind ultraviolet imaging systems towards miniaturization and lightweight.

Optically transparent infrared selective emitter for visible-infrared compatible camouflage.

Visible-infrared compatible camouflage is significant to enhance the equipment survivability through counteracting the modern detecting and surveillance systems. However, there are still great challenges in simultaneously achieving multispectral camouflage with high transmittance in visible, low emissivity in the atmospheric windows and high emissivity in the non-atmospheric window, which can be attributed to the mutual influence and restriction within these characteristics. Here, we proposed an optically transparent infrared selective emitter (OTISE) composed of three Ag-ZnO-Ag disk sub-cells with anti-reflection layers, which can synchronously improve the visible transmittance and widen absorption bandwidth in the non-atmospheric window by enhancing and merging resonance response of multi-resonators. Test results reveal that low emissivity in infrared atmospheric windows, high emissivity in the 5-8 µm non-atmospheric window and high optical transparency have been obtained. In addition, the radiative flux of OTISE in 3-5 µm and 8-14 µm are respectively 34.2% and 9.3% of that of blackbody and the energy dissipation of OTISE is 117% of that of chromium film. Meanwhile, it keeps good optical transparency due to the ultrathin Ag film. This work provides a novel strategy to design the optically transparent selective emissive materials, implying a promising application potential in visible and infrared camouflage technology.

Generation of A Space-Variant Vector Beam with Catenary-Shaped Polarization States.

We demonstrate the generation of a space-variant vector beam with catenary-shaped polarization states based on the polarization interferometry. With a spatial light modulator and a common path interferometric configuration, two orthogonally circularly polarized beams with different phase modulation overlap each other, yielding the vector beams. In addition, the polarization states of this vector beam are scalable to the arbitrary spatial distribution because of its great flexibility and universal applicability. It is expected that this vector beam may have many potential and intriguing applications in the micro/nano material processing, liquid crystal elements fabrication and optical micro-manipulation, and so on.

Descriptions of six new species in White Cloud Mountain minnow Tanichthys albonubes complex (Cypriniformes: Tanichthyidae) in southern China.

Tanichthys albonubes is a critically endangered freshwater fish in South China and is classified as a second-class state-protected animal in China. It is also a colourful ornamental fish and has been introduced into many countries and regions around the world. Previous studies have revealed that there are seven cryptic species in the T. albonubes complex. Here, six new species of these cryptic species were diagnosed and described based on external morphology, colour patterns and osteological characteristics: Tanichthys shenzhenensis sp. nov., Tanichthys huidongensis sp. nov., Tanichthys luheensis sp. nov., Tanichthys dongxingensis sp. nov., Tanichthys guipingensis sp. nov. and Tanichthys hainanensis sp. nov. In addition, an identification key to the genus Tanichthys was provided. The key diagnosable characteristics of six new species in T. albonubes complex include the margin colour of dorsal and anal fins, the number of branched dorsal and anal fins, the relative position of the orbitosphenoid to the parasphenoid, the states of the neural complex, the states of the neural spine of the fourth vertebra and the anterior process of the innominatum. These six new species were also well supported by the phylogenetic tree and uncorrected p-distances based on Cyt b sequences. The distribution pattern of the genus Tanichthys is characterized by point-like, discontinuous distribution and geographically isolated on a large scale with narrow distribution ranges of each species. This study provides scientific data for the taxonomy, conservation status assessment and evolution of Tanichthys.

Phylogeographic structure of the dwarf snakehead (Channa gachua) around Gulf of Tonkin: Historical biogeography and pronounced effects of sea-level changes.

Geological events, landscape features, and climate fluctuations have shaped the distribution of genetic diversity and evolutionary history in freshwater fish, but little attention has been paid to that around the Gulf of Tonkin; therefore, we investigated the phylogeographic structure of the dwarf snakehead (Channa gachua) on Hainan Island and mainland China, as well as two populations in Vietnam. We attempted to elucidate the origins of freshwater fish in South Hainan by incorporating genetic data from DNA markers on both the mitochondrial cytochrome b gene (cyt b) and the nuclear recombination-activating gene 1 (RAG-1). Mitochondrial phylogenetic analysis identified two major lineages (lineages A and B), which may represent separate species. Divergence data suggested that C. gachua populations diverged between 0.516 and 2.376 myr. The divergence of the two cryptic species is congruent with sea-level rise, which subsequently isolated Hainan from the mainland. During the Pleistocene glaciations, the entire region of the Gulf of Tonkin and the Qiongzhou Strait became part of the coastal plain of the Asian continent, which might have resulted in the current distribution patterns and dispersal routes of C. gachua populations. The formation of three sublineages in lineage A indicated that the Gulf of Tonkin was a geographical barrier between Hainan Island and mainland China but not between Vietnam and Hainan Island. The results of this study may help to elucidate the origins of freshwater fish in South Hainan and the phylogeographic structure of C. gachua.

Generalized Pancharatnam-Berry Phase in Rotationally Symmetric Meta-Atoms.

Pancharatnam-Berry geometric phase has attracted enormous interest in subwavelength optics and electromagnetics during the past several decades. Traditional theory predicts that the geometric phase is equal to twice the rotation angle of anisotropic elements. Here, we show that high-order geometric phases equal to multiple times the rotation angle could be achieved by meta-atoms with highfold rotational symmetries. As a proof of concept, the broadband angular spin Hall effect of light and optical vortices is experimentally demonstrated by using plasmonic metasurfaces consisting of space-variant nanoapertures with C2, C3, and C5 rotational symmetries. The results provide a fundamentally new understanding of the geometric phase as well as light-matter interaction in nanophotonics.

Spin-decoupled metasurface for simultaneous detection of spin and orbital angular momenta via momentum transformation.

With inherent orthogonality, both the spin angular momentum (SAM) and orbital angular momentum (OAM) of photons have been utilized to expand the dimensions of quantum information, optical communications, and information processing, wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated. Here, a single azimuthal-quadratic phase metasurface-based photonic momentum transformation (PMT) is illustrated and utilized for vortex recognition. Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT, OAMs within a large mode space can be determined through a single-shot measurement. Moreover, spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting, which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase. Interestingly, our proposed method can detect vectorial vortices with both phase and polarization singularities, as well as superimposed vortices with a certain interval step. Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and prominent vortex recognition ability, our approach may underpin the development of integrated and high-dimensional optical and quantum systems.

Sex dimorphism of Yunnanilus analis and its habitat adaptation in Xingyun Lake, Yunnan, China.

Yunnanilus is a group of endemic fish inhabit in Yun-Gui Plateau and its adjacent areas. They show the characteristic of sex dimorphism, which could be an important reason for their adaptation to karst habitats. Here, we used Yunnanilus analis as the model to understand the sex dimorphism characteristics and its adaptation to the karst habitats. The sex dimorphism, female fecundity, and food specialization of Y. analis were investigated in Xingyun Lake, Jiangchuan, Yunnan. Our results showed that Y. analis exhibit sex size dimorphism (sex dimorphism index=0.23; female with larger body size). There were stains on the transverse sections at females body, but not in males. Males had dark longitudinal lines at their body sides. Morphological differences between males and females were confirmed by the results of one-way analyses of variance (ANOVA), multivariate statistical analyses, principal component analyses, discriminant analyses, and one-way analyses of similarity (ANOSIM) on total length, standard body length, fork length, head width vs. heal length, and the distance between the starting point of ventral fin to the starting point of pectoral fin vs. standard body length. Fecundity of female fish was 1364.5±489.3 (470-2430) eggs, which were positively correlated with their body size. Both female and male Y. analis mainly feed on Chironomid larvae and mayfly naiads. Their food composition was somehow similar, with significantly statistical difference. In conclusion, fecundity selection pressure and food specialization should be the main factors contributing to the evolution of Y. analis' sex dimorphism. More importantly, sex dimorphism of Y. analis is a significant adaptation to the karstic habitats.

Angular-multiplexed multichannel optical vortex arrays generators based on geometric metasurface.

Recently, metasurface-based multichannel optical vortex arrays have attracted considerable interests due to its promising applications in high-dimensional information storage and high-secure information encryption. In addition to the well-known wavelength and polarization multiplexing technologies, the diffraction angle of light is an alternative typical physical dimension for multichannel optical vortex arrays. In this paper, based on angular multiplexing, we propose and demonstrate multichannel optical vortex arrays by using ultrathin geometric metasurface. For a circularly polarized incident light, the desired optical vortex arrays are successfully constructed in different diffraction regions. Moreover, the diffraction angle of the optical vortex array can be regulated by changing the illumination angle of incident light. Capitalizing on this advantage, the angular-multiplexed recombination of optical vortex array is further investigated. The combination of the diffraction angle of light and optical vortex array may have significant potential in applications of optical display, free-space optical communication, and optical manipulation.

Switchable polarization-multiplexed super-oscillatory metasurfaces for achromatic sub-diffraction focusing.

Super-oscillation phenomenon has attracted considerable interests due to its great ability of far-field super-resolution imaging. However, most super-oscillatory lenses were limited by chromatic aberration and single functionality, hence deeply restricting the flexibility of the super-oscillatory devices in practical applications. Here, an achromatic polarization-multiplexed super-oscillatory metasurface has been proposed to realize flexible light field modulations at different colors, i.e. 473 nm (blue), 532 nm (green), and 632.8 nm (red). The super-oscillatory metasurface can achieve achromatic diffraction-limited focusing under x-polarized light illumination and achromatic sub-diffraction focusing under y-polarized light illumination. Furthermore, it can also realize multi-wavelength super-oscillatory achromatic focusing with different super-resolution abilities. The proposed method could simplify the super-resolution optical imaging system and is expected to have widespread applications in color imaging, microscopy, and machine vision.

Cryptic species in White Cloud Mountain minnow, Tanichthys albonubes: Taxonomic and conservation implications.

Cryptic species describe two or more species that had mistakenly been considered to be a single species, a phenomenon that has been found throughout the tree of life. Recognizing cryptic species is key to estimating the real biodiversity of the world and understanding evolutionary processes. Molecular methods present an unprecedented opportunity for biologists to question whether morphologically similar populations are actually cryptic species. The minnow Tanichthys albonubes is a critically endangered freshwater fish and was classified as a second-class state-protected animal in China. Previous studies have revealed highly divergent lineages with similar morphological characters in this species. Herein, we tested for cryptic species across the ranges of all known wild populations of this minnow. Using multilocus molecular (one mitochondrial gene, two nuclear genes and 13 microsatellite loci) and morphological data for 230 individuals from eight populations, we found deep genetic divergence among these populations with subtle morphological disparity. Morphological examination found variance among these populations in the number of branched anal-fin rays. Based on genetic data, we inferred eight monophyletic groups that were well supported by haplotype network and population clustering analyses. Species delimitation methods suggested eight putative species in the T. albonubes complex. Molecular dating suggested that these cryptic species diverged in the period from the Pliocene to the Pleistocene. Based on these findings, we propose the existence of seven cryptic species in the T. albonubes complex. Our results highlight the need for a taxonomic revision of Tanichthys. What is more, the conservation status of and conservation strategies for the T. albonubes complex should be reassessed as soon as possible.

Simultaneous Full-Color Printing and Holography Enabled by Centimeter-Scale Plasmonic Metasurfaces.

Optical metasurfaces enable novel ways to locally manipulate light's amplitude, phase, and polarization, underpinning a newly viable technology for applications, such as high-density optical storage, holography, and displays. Here, a high-security-level platform enabled by centimeter-scale plasmonic metasurfaces with full-color, high-purity, and enhanced-information-capacity properties is proposed. Multiple types of independent information can be embedded into a single metamark using full parameters of light, including amplitude, phase, and polarization. Under incoherent white light, the metamark appears as a polarization- and angle-encoded full-color image with flexibly controlled hue, saturation, and brightness, while switching to multiwavelength holograms under coherent laser illumination. More importantly, for actual applications, the extremely shallow functional layer makes such centimeter-scale plasmonic metamarks suitable for cost-effective mass production processes. Considering these superior performances of the presented multifunctional plasmonic metasurfaces, this work may find wide applications in anticounterfeiting, information security, high-density optical storage, and so forth.

[Ecomorphological traits explaining the competition exclusion between Oryzias and mosqui-tofish].

The theory of ecomorphology predicts that species with similar morphological traits can occupy similar ecological niche, which may cause competitive exclusion. To apply this theory into fish invasion ecology research is of significance for understanding the interaction between native and invasive species. Here, we compared the morphological difference between two native (Oryzias pectoralis, Oryzias curvinotus) and one invasive species (Gambusia affinis) to explore the competitive exclusion among them. The results showed that despite O. pectoralis and O. curvinotus were sympa-tric species, they varied in spatial distribution. Such a result supported the theory of ecomorphology, which predicts that two species with similar morphological traits might have strong competition. Moreover, their population density exhibited a significant negative relationship with that of G. affinis. The morphology of G. affinis and both Oryzias species were more similar when comparing to other fish in the assemblage. Results from the cluster analysis showed that G. affinis and Oryzias species were close in a branch, with extremely low spatial niche overlap between invasive mosquitofish and native Oryzias species. There was significant negative correlation between the population abundance of mosquitofish and Oryzias species. All the results suggested that mosquitofish led to population decline of both Oryzias species, due to the ecomorphological similarity. More studies are needed to better understand the mechanisms of G. affinis invasion in habitats of native Oryzias species.

Complete mitochondrial genome of Yunnan-Guizhou Plateau endemic fish, Discogobio macrophysallidos, in China.

The complete mitochondrial genome of Discogobio macrophysallidos was first determined and analyzed in this work. Its mitochondrial genome is 16,593 bp in length, consisting of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and a non-coding control region, and its gene order was consistent with other fishes. Phylogenetic analysis showed that D. macrophysallidos were clustered with other three species of Discogobio. The complete mitogenome of D. macrophysallidos provides new molecular data for the further phylogenetic study of the genus of Discogobio.

Polarization-controlled unidirectional excitation of surface plasmon polaritons utilizing catenary apertures.

Controlling the propagation direction of surface plasmon polaritons (SPPs) at will using planar structures has been investigated in recent years. However the realization of a high extinction ratio of a SPP directional launcher in a densely integrated and miniaturized way, especially at the wavelength scale, still remains a challenge. To the best of our knowledge, the maximum value of the extinction ratio of a unidirectional SPP launcher based on the planar metasurface in experiment is nearly 250, which relies on the combined effect of several gap-plasmon resonator blocks with a lateral dimension much larger than the incident wavelength. Here, we design and experimentally demonstrate a polarization-controlled unidirectional SPP launcher based on a single column catenary aperture array with a lateral dimension as small as 552 nm, which is even smaller than the working wavelength. Under the illumination of circularly polarized light, our designed SPP launcher exhibits a simulated extinction ratio reaching up to 495 at a wavelength of 618 nm and 283 in the experiment. The compact size and distinctive extinction ratio may pave a new way for the directional excitation of SPPs and can be useful in compact plasmonic circuits and other photonic integrated devices.

Polarization-independent broadband meta-holograms via polarization-dependent nanoholes.

Composed of ultrathin metal or dielectric nanostructures, metasurfaces can manipulate the phase, amplitude and polarization of electromagnetic waves at a subwavelength scale, which is promising for flat optical devices. In general, metasurfaces composed of space-variant anisotropic units are sensitive to the incident polarization due to the inherent polarization dependent geometric phase. Here, we implement polarization-independent broadband metasurface holograms constructed by polarization-dependent anisotropic elliptical nanoholes by elaborate design of complex amplitude holograms. The fabricated meta-hologram exhibits a polarization insensitive feature with an acceptable image quality. We verify the feasibility of the design algorithm for three-dimensional (3D) meta-holograms with simulation and the feasibility for two-dimensional (2D) meta-holograms is experimentally demonstrated at a broadband wavelength range from 405 nm to 632.8 nm. The effective polarization-independent broadband complex wavefront control with anisotropic elliptical nanoholes proposed in this paper greatly promotes the practical applications of the metasurface in technologies associated with wavefront manipulation, such as flat lens, colorful holographic displays and optical storage.

Quasi-Talbot effect of orbital angular momentum beams for generation of optical vortex arrays by multiplexing metasurface design.

The quasi-Talbot effect of orbital angular momentum (OAM) beams, in which the centers are placed in a rotationally symmetric position, is demonstrated both numerically and experimentally for the first time. Since its multiplication factor is much higher than the conventional fractional Talbot effect, the quasi-Talbot effect can be used in the generation of vortex beam arrays. A metasurface based on this theory was designed and fabricated to test the validity of this assumption. The agreement between the numerical and measured results suggests the practicability of this method to realize vortex beam arrays with high integrated levels, which can open a new door to achieve various potential uses related to optical vortex arrays in integrated optical systems for wide-ranging applications.

Ultrahigh-capacity dynamic holographic displays via anisotropic nanoholes.

For the miniaturization of optical holographic and data recording devices, large information capacity or data density is indispensable but difficult to obtain using traditional technologies. In this paper, an ultrahigh-capacity metasurface hologram is proposed by encoding information in deep-subwavelength scale nanohole arrays, which can be reconstructed via a light beam with proper designed incident angles. The imaging information capacity of the two-dimensional (2D) hologram, defined by the distortion-free region, can be increased 11.5 times, which is experimentally demonstrated by focused ion beam (FIB) milling of an ultrathin metallic film. We also prove the feasibility of a three-dimensional (3D) hologram of spiral lines designed by using the point source algorithm. Benefitting from the ultrahigh capacity of the deep-subwavelength metasurface, dynamic holographic displays can be realized by controlling the incident angle. The method proposed here can also be leveraged to achieve large capacity optical storage, colorful holographic displays, lithography technology etc.

Generation and detection of orbital angular momentum via metasurface.

Beams carrying orbital angular momentum possess a significant potential for modern optical technologies ranging from classical and quantum communication to optical manipulation. In this paper, we theoretically design and experimentally demonstrate an ultracompact array of elliptical nanoholes, which could convert the circularly polarized light into the cross-polarized vortex beam. To measure the topological charges of orbital angular momentum in a simple manner, another elliptical nanoholes array is designed to generate reference beam as a reference light. This approach may provide a new way for the generation and detection of orbital angular momentum in a compact device.