High-resolution polarization-sensitive optical coherence tomography and optical coherence tomography angiography for zebrafish skin imaging

Zebrafish is an important animal model,which is used to study development,pathology,and genetic research.The zebrafish skin model is widely used in cutaneous research,and angiogenesis is critical for cutaneous wound healing.However,limited by the penetration depth,the available optical methods are difficult to describe the internal skin structure and the connection of blood vessels between the skin and subcutaneous tissue.By a homemade high-resolution polarization-sensitive optical coherence tomography(PS-OCT)system,we imaged the polarization contrast of zebrafish skin and the zebrafish skin vasculature with optical coherence tomography angiography(OCTA).Based on these OCT images,the spatial distribution of the zebrafish skin vasculature was described.Furthermore,we monitored the healing process of zebrafish cutaneous wounds.We think the high-resolution PS-OCT system will be a promising tool in studying cutaneous models of zebrafish.

Actively tunable polarization-sensitive multiband absorber based on graphene

We design an actively tunable polarization-sensitive multiband absorber in the mid-infrared region,which consists of stacked graphene multilayers separated by dielectric layers on a metal mirror.Benefiting from the anisotropic structure,the absorber has dual absorption bands with almost perfect absorption at different wavelengths under the x and y polarizations.Analyzing the electric field amplitude distributions and the surface currents,we find that the absorption peaks under the same polarization are excited in the graphene layers independently.Therefore,more absorption bands can be achieved by increasing the graphene layers.Adjusting the Fermi energy of the graphene layers,the working wavelengths of the polarization-sensitive multiband absorbers can be tuned actively,and thus achieving a wide band regulation range.Besides,the peak number and the peak strength of the multiband absorber can be actively controlled by the polarization angle as well.We also propose a method to design an actively tunable polarization-sensitive multiband absorber,which may have potential applications in mid-infrared devices,such as polarization-sensitive filters and detectors.

High-performance polarization-sensitive photodetector based on a few-layered PdSe2 nanosheet

The extraordinary optical and electronic properties of anisotropic two-dimensional materials,such as black phosphorus,ReS2,and GeSe,enable them a promising component of polarization-sensitive photodetectors.However,these applications are significantly limited by the challenges of air-stability,response time,and linearly dichroic ratio.Interestingly,palladium diselenide(PdSe2)with high air stability is an emerging material that has robust in-plane anisotropy induced by its asymmetric pentagonal lattice structure.We have successfully prepared a few-layer PdSe2 using micromechanical exfoliation,and here we demonstrate the strong linear dichroism behavior of PdSe2 by polarization-resolved absorption spectra measurements.Such unique linear dichroism,endows the PdSe2 photodetector powerful ability to detect polarized light.The photodetector based on 5L PdSe2,as tested with polarization-dependent photocurrent mapping,exhibited competitive capability to detect polarized light,achieving a significant photocurrent on/off ratio(>10^2),the quite fast response time(<11 ms)and robust linearly dichroic ratios(/max//min≈1.9 at 532 nm).These results are essential advance in the development of polarization-sensitive photodetector,a crucial step towards opening up a new avenue for the application of 2D optoelectronic devices.

Highly aligned organic microwire crystal arrays for high-performance polarization-sensitive photodetectors and image sensors

Organic semiconductors with excellent optoelectronic properties are important building blocks for highperformance organic devices.Patterning organic crystals with high precision and accurately positioning them at the target position are major challenges for integrated devices.However,uncontrollable dewetting of the conventional solution method leads to as-prepared micro-nanocrystals with high defect-state density,low crystalline quality,and disordered distribution,which impair the uniformity of the device performance and limit integration.By regulating the solution position with a template and guiding the solution flow direction under gravity,aligned organic microwire arrays and polygonal patterns were fabricated.The polarization-sensitive photodetector exhibited responsivity up to 1234 A W^(-1),linear dynamic range of 148 dB,I_(photo)/I_(dark)of 10^(4),response time as low as 1.1 ms,and dichroic ratio up to 2.1.Given the homogeneity of microwire arrays,the device-to-device variation was reduced to 3.58%,resulting in high-quality imaging.This study provides new insights into organic micro/nanocrystal patterning and device integration.

Ultra-broadband,fast,and polarization-sensitive photoresponse of low-symmetry 2D NdSb_(2)

Broadband photodetectors with polarization-sensitive ability have received extraordinary attention for modern optoelectronic devices.Ideal photodetectors should possess high responsivity,fast response,and good stability,which are rare to meet at the same time in one low-symmetric two-dimentional(2D)material.In this work,neodymium diantimonides(RSb_(2)),a member of light rare-earth diantimonides RSb_(2)(R=La–Nd,Sm)with low-symmetry structure,is introduced as a fascinating highly anisotropic 2D material for broadband detection(532 nm to 4μm).The photodetector exhibits a responsivity of 0.49 mA·W^(−1)with 15μs response time at 532 nm and highly stable performance under ambient conditions over 8 months.Furthermore,we identify the polarization-sensitive photoresponse of the detector and demonstrate a high anisotropic factor~1.6.In addition,strong inplane anisotropy is revealed by anisotropic phonon response and the photodetection mechanism is investigated by scanning photocurrent microscopy measurements.This pioneer work on RSb_(2)paves the way for further exploration of 2D RSb_(2)for high performance polarized photodetectors with fast photothermoelectric response.

Wide-spectrum polarization-sensitive and fast-response photodetector based on 2D group Ⅳ-Ⅵ semiconductor tin selenide

Tin selenide(SnSe)has attracted considerable interest recently on account of its low-symmetry lattice structure,great compatibility with key semiconductor technology,and remarkable electrical and optical performance.SnSe-based polarization-sensitive photodetectors show promising application prospects because of their fast response and excellent photoelectric performance.Here,an in-plane anisotropic SnSe nanosheet was synthesized and reported in detail by applying angle-resolved polarized Raman spectroscopy(ARPRS),polarization-resolved optical microscopy(PROM),angle-resolved optical absorption spectroscopy(AROAS),and other crystal structure characterization methods.Moreover,SnSe crystals exhibit superior polarization detection performance with a high anisotropic photocurrent ratio(2.31 at 1064 nm)due to the structure formed by the Van der Waals superposition of covalently bonded atomic layers.Furthermore,SnSe-based photodetectors have high responsivity(9.27 A/W),high detectivity(4.08×10^(10)Jones),and fast response(in the order of nanoseconds).These results suggest a new method for fabricating 2D fast-response polarization-sensitive photodetectors in the future.

Polarization-sensitive and active controllable electromagnetically induced transparency in U-shaped terahertz metamaterials

Electromagnetically induced transparency(EIT)phenomenon is observed in simple metamaterial which consists of concentric double U-shaped resonators(USRs).The numerical and theoretical analysis reveals that EIT arises from the bright-bright mode coupling.The transmission spectra at different polarization angle of incident light shows that EIT transparency window is polarization sensitive.More interestingly,Fano resonance appears in the transmission spectrum at certain polarization angles.The sharp and asymmetric Fano lineshape is high valuable for sensing.The performance of sensor is investigated and the sensitivity is high up to 327 GHz/RIU.Furthermore,active control of EIT window is realized by incorporating photosensitive silicon.The proposed USR structure is simple and compact,which may find significant applications in tunable integrated devices such as biosensor,filters,and THz modulators.

A polarization-sensitive,self-powered,broadband and fast Ti_(3)C_(2)T_(x)MXene photodetector from visible to near-infrared driven by photogalvanic effects

Broadband,self-power,and polarization-sensitivity are desirable qualities for a photodetector.However,currently few photodetectors can fulfill these requirements simultaneously.Here,we propose a Ti_(3)C_(2)T_(x)(MXene)photodetector that is driven by the photogalvanic effect with impressive performances.A polarization-sensitive photocurrent is generated at zero bias under the illumination of linearly polarized laser light of 1064 nm,with an extinction ratio of 1.11.Meanwhile,a fast response with a 32/28 ms rise/decay time and a large on/off switching ratio of 120 are achieved.Besides,a robust zero-bias photocurrent is also generated in the photodetector under the illumination of 940 and 620 nm light,as well as the white light,showing a broadband photoresponse from the near-infrared to visible.Moreover,quantum transport simulations indicate that the photogalvanic effect plays an important role in the generation of the polarized photocurrent at zero bias due to the broken space inversion symmetry of the stacked few-layer Ti_(3)C_(2)T_(x).Our results shed light on a potential application of the Ti_(3)C_(2)T_(x)–MXene in the low-power photodetection with high performances.

Optical and electrical properties of two-dimensional anisotropic materials

Two-dimensional(2D) anisotropic materials, such as B-P, B-As, GeSe, GeAs, ReSe2, KP15 and their hybrid systems, exhibit unique crystal structures and extraordinary anisotropy. This review presents a comprehensive comparison of various 2D anisotropic crystals as well as relevant FETs and photodetectors, especially on their particular anisotropy in optical and electrical properties. First, the structure of typical 2D anisotropic crystal as well as the analysis of structural anisotropy is provided. Then, recent researches on anisotropic Raman spectra are reviewed. Particularly, a brief measurement principle of Raman spectra under three typical polarized measurement configurations is introduced. Finally, recent progress on the electrical and photoelectrical properties of FETs and polarization-sensitive photodetectors based on 2D anisotropic materials is summarized for the comparison between different 2D anisotropic materials. Beyond the high response speed, sensitivity and on/off ratio, these 2D anisotropic crystals exhibit highly conduction ratio and dichroic ratio which can be applied in terms of polarization sensors, polarization spectroscopy imaging, optical radar and remote sensing.

Terahertz endoscopic imaging for colorectal cancer detection:Current status and future perspectives

Terahertz(THz) imaging is progressing as a robust platform for myriad applications in the field of security,health,and material science.The THz regime,which comprises wavelengths spanning from microns to millimeters,is non-ionizing and has very low photon energy:Making it inherently safe for biological imaging.Colorectal cancer is one of the most common causes of death in the world,while the conventional screening and standard of care yet relies exclusively on the physician's experience.Researchers have been working on the development of a flexible THz endoscope,as a potential tool to aid in colorectal cancer screening.This involves building a single-channel THz endoscope,and profiling the THz response from colorectal tissue,and demonstrating endogenous contrast levels between normal and diseased tissue when imaging in reflection modality.The current level of contrast provided by the prototype THz endoscopic system represents a significant step towards clinical endoscopic application of THz technology for invivo colorectal cancer screening.The aim of this paper is to provide a short review of the recent advances in THz endoscopic technology and cancer imaging.In particular,the potential of single-channel THz endoscopic imaging for colonic cancer screening will be highlighted.

Polarization sensitive photodetector based on quasi-1D ZrSe_(3)

The in-plane anisotropy of transition metal trichalcogenides(MX_(3))has a significant impact on the molding of materi-als and MX_(3) is a perfect choice for polarized photodetectors.In this study,the crystal structure,optical and optoelectronic aniso-tropy of one kind of quasi-one-dimensional(1D)semiconductors,ZrSe_(3),are systematically investigated through experiments and theoretical studies.The ZrSe_(3)-based photodetector shows impressive wide spectral response from ultraviolet(UV)to near in-frared(NIR)and exhibits great optoelectrical properties with photoresponsivity of 11.9 mA·W^(-1) and detectivity of~106 at 532 nm.Moreover,the dichroic ratio of ZrSe_(3)-based polarized photodetector is around 1.1 at 808 nm.This study suggests that ZrSe_(3) has potential in optoelectronic applications and polarization detectors.

Dichroic Electro-Optical Behavior of Rhenium Sulfide Layered Crystal

Dichroic behaviors of layered ReS2 have been characterized using angular dependent polarizedabsorption and resistivity measurements in the van der Waal plane. The angular dependent optical and electrical measurements are carried out with angles ranging from θ= 0°(E || b) to θ= 90°(E ^b) with respect to the layer crystal’s b-axis. The angular de pendence of polarized energy gaps of ReS2 shows a sinusoidal variation of energies from ~1.341 eV (E ||b to ~1.391 eV (E ^ b). The experimental evidence of polarized energy gap leaves ReS2 apotential usage for fabrication of a polarized optical switch suitable for polarized optical communication in nearinfrared (NIR) region. Angular dependence of resistivities of ReS2 in?the vander Waal plane has also been evaluated. The relationship of inplane resistivities shows a sinusoidallike variation from θ= 0°(E ||b) to 90°(E ^ b) and repeated periodically to 360°. The experimental results of optical and electrical measurements indicated that ReS2 is not only an opticaldichroic layer but also an electricaldichroism material presented in the layer plane.

Tensorial tomographic Fourier ptychography with applications to muscle tissue imaging

We report tensorial tomographic Fourier ptychography(T^(2)oFu),a nonscanning label-free tomographic microscopy method for simultaneous imaging of quantitative phase and anisotropic specimen information in 3D.Built upon Fourier ptychography,a quantitative phase imaging technique,T^(2)oFu additionally highlights the vectorial nature of light.The imaging setup consists of a standard microscope equipped with an LED matrix,a polarization generator,and a polarization-sensitive camera.Permittivity tensors of anisotropic samples are computationally recovered from polarized intensity measurements across three dimensions.We demonstrate T^(2)oFu’s efficiency through volumetric reconstructions of refractive index,birefringence,and orientation for various validation samples,as well as tissue samples from muscle fibers and diseased heart tissue.Our reconstructions of healthy muscle fibers reveal their 3D fine-filament structures with consistent orientations.Additionally,we demonstrate reconstructions of a heart tissue sample that carries important polarization information for detecting cardiac amyloidosis.

Retinal nerve fiber layer (RNFL) integrity and its relations to retinal microvasculature and microcirculation in myopic eyes

Background:The aim was to determine retinal nerve fiber layer function and its relations to retinal microvasculature and microcirculation in patients with myopia.Method:Polarization-sensitive optical coherence tomography(PS-OCT)was used to measure phase retardation per unit depth(PR/UD,proportional to the birefringence)of the retinal nerve fiber layer(RNFL).Optical coherence tomography angiography(OCTA)was used to measure macular vessel density analyzed using fractal analysis.In addition,a retinal function imager(RFI)was used to measure macular blood flow velocities in arterioles and venules.Twenty-two patients with moderate myopia(MM,refraction>3 and<6 diopters),seventeen patients with high myopia(HM,≥6 D)and 29 healthy control subjects(HC,≤3.00 D)were recruited.One eye of each patient was imaged.Results:Although the average PR/UD of the RNFL in the HM group did not reach a significant level,the birefringence of the inferior quadrant was significantly lower(P<0.05)in the HM group compared to the HC group.Significant thinning of the average RNFL and focal thinning of RFNL in temporal,superior and inferior quadrants in the HM group were found,compared to the HC group(P<0.05).There were no significant differences of retinal blood flow velocities in arterioles and venules among groups(P>0.05).The macular vessel density in both superficial and deep vascular plexuses was significantly lower in the HM group than in the other two groups(P<0.05)as well as in the MM group than in the HC group(P<0.05).The average PR/UD and PR/UD in the inferior quadrant were not related to refraction,axial length,blood flow velocities and macular vessel densities(r ranged from−0.09 to 0.19,P>0.05).Conclusions:The impairment of the retinal nerve fiber birefringence in the HM group may be one of the independent features in high myopic eyes,which appeared not to relate to macular microvascular density and blood flow velocity.

Self-assembled ultrafine CsPbBr_(3) perovskite nanowires for polarized light detection

One-dimensional(1D)metal halide perovskite nanowire(NW)arrays with high absorption efficiency,emission yield and dielectric constants,as well as anisotropic optoelectronic properties have found applications in energy harvesting,flexible electronics,and biomedical imaging devices.Here,a modified two-step solvothermal method is developed for the synthesis of self-assembled cubic CsPbBr_(3) NW arrays.This method provides facile access to continuous and uniform ultrafine perovskite NWs and well-aligned pure perovskite NW arrayed architectures.Under excitation at 365 nm,the CsPbBr_(3) NWs give a strong blue emission observable to the naked eyes.The CsPbBr_(3) NWs also exhibit strong two-photon excited luminescence under the irradiation with an 800 nm pulse laser.By rotating the polarization angle of the 800 nm laser,strong polarization dependence with a polarization degree up to~0.49 is demonstrated in the selfassembled CsPbBr_(3) NW array,although the CsPbBr_(3) NWs have an isotropic cubic structure.Based on density functional theory(DFT)calculations,this polarization-dependent emission is correlated with the anisotropic charge density distribution of the perovskite NWs.These findings suggest that the ultrafine CsPbBr_(3) NWs with a well-defined self-assembled architecture could be applied as next-generation polarizationsensitive photoelectronic detection materials.

Enhanced photogalvanic effect in the two-dimensional MgCl_(2)/ZnBr_(2) vertical heterojunction by inhomogenous tensile stress

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl_(2)/ZnBr_(2) vertical van der Waals heterojunction with the noncentrosymmetric C_(3v) symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl_(2)/ZnBr_(2) vertical heterojunction in the low-power UV photodetection.

A chain-type diamine strategy towards strongly anisotropic triiodide of DMEDA·I6

Linearly bonded triiodide chains with fairly small distance between the adjacent iodine ions feature a facile electron transfer and highly anisotropic properties.Here,we demonstrate a novel strategy towards a new one-dimensional linear triiodide DMEDA·I6,using chain-type N,N'-dimethylethanediamine(DMEDA)cation to coordinate triiodine ions.This triiodide has the shortest distance between adjacent I3^- and good linearity.An estimated electronic band gap of1.36 e V indicates its semiconducting properties.100 fold differences both in polarization-sensitive absorption and effective mass were achieved by simulation,with directions parallel and perpendicular to the a-axis of DMEDA·I6.The DMEDA·I6 single crystal-based photodetectors show a good switching characteristic and a distinct polarization-sensitive photoresponse with linear dichroic photodetection ratio of about 1.9.Strongly anisotropic features and semiconducting properties of DMEDA·I6 make this triiodide system an interesting candidate for polarization related applications.

Flexible high-resolution thin micropolarizers for imaging polarimetry

More durable[with high impact force],lighter,and more compact flexible azo dye micropolarizers are attractive candidates for low-cost,simple polarization imaging systems.The liquid crystal polymer[LCP],as an emerging material developed by photo-alignment technology,is a potential material for organizing the long-range ordered structure of azo dyes.However,little research has been done on LCP aligned azo dyes.This paper points out and solves a key problem that restricts the fabrication of high-precision arrays in guest[azo dye]-host[LCP]systems:the doping of dyes leads to disorder of the LCP during curing.After solving the problem,the relationship between the thickness of the LCP and the extinction ratio of the polarizing film was investigated,which effectively improved the extinction ratio.Alignment of azo dye molecules in the range of 2μm[0°-180°]and arrays of micropolarizers[0°,45°,90°,-45°]with 8μm×8μm pixel pitch was achieved by laser direct writing technology.The bending cycle test demonstrates the mechanical stability of the ultrathin flexible polarizer.The flexible patterned polarizer with robust chemical and mechanical stabilities provides a flexible way to capture the polarization of the light and highly integrated advanced flexible optoelectronic devices.

Vapor-Induced Coating Method for Well-Aligned and Uniform Organic Semiconductor Single Crystals

Uniform and well-aligned organic semiconductor single crystals(OSSCs)are critical for high-performance electronic and optoelectronic device applications due to their long-range order and low defect density.However,it is still challenging to fabricate uniform and well-aligned OSSCs by an efficient and facile method.Here,we report a vapor-induced coating method to prepare uniform organic semiconductor stripe single crystals with well-aligned orientation.The coating velocity and solution concentration are important to control the stripe crystals’morphology,which influence the triple-phase contact line dewetting behavior and then change the mass transport of the meniscus.Insufficient solute supply causes the generation of dendritic crystals.Uniform stripe single crystals of high quality and pure orientation are prepared in the condition of a sufficient and suitable solute supply.Moreover,the electronic and optoelectronic properties are evaluated.Notably,the polarization-sensitive photodetectors based on the uniform stripe crystals exhibit high polarization sensitivity and its dichroic ratio of photocurrent is 1.98.This method is efficient for the preparation of various high-quality and uniform organic semiconductor stripe single crystals,opening an opportunity for high-performance organic functional devices.

Photonic-assisted FSK signal generation based on carrier phase-shifted double sideband modulation

An approach to generate high-speed and wideband frequency shift keying(FSK)signals based on carrier phase-shifted double sideband(CPS-DSB)modulation is proposed and experimentally validated.The core part of the scheme is a pair of cascaded polarization-sensitive LiNbO_(3) Mach–Zehnder modulators and phase modulators,whose polarization directions of the principal axes are mutually orthogonal to each other.A proof-of-concept experiment is carried out,where a 0.5 Gb/s FSK signal with the carrier frequencies of 4 and 8 GHz and a 1 Gb/s FSK signal with the carrier frequencies of 8 and 16 GHz are generated successfully.