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.

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.

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.

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.

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.

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.

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.

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.

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.

用于偏振光探测的自组装超细CsPbBr_(3)钙钛矿纳米线

一维金属卤化物钙钛矿纳米线因具有较高的吸收和发射效率、较大的介电常数以及各向异性的光电特性等优势而在能源收集、柔性电子和生物成像设备等领域展现出潜在的应用价值.本论文提出了一种改进的两步溶剂热法用于制备自组装的立方相CsPbBr_(3)纳米线阵列,为获得连续均匀的超细钙钛矿纳米线和有序排列的纯钙钛矿纳米线阵列提供了一个更为简便的方法.在365 nm紫外光的激发下,肉眼可见地观测到来自CsPbBr_(3)纳米线的蓝光发射.同时,在800 nm脉冲激光的激发下,CsPbBr_(3)纳米线也表现出较强的双光子发射.改变800 nm脉冲激光的偏振方向,可以发现,CsPbBr_(3)纳米线虽然具有各向同性的立方结构,但其自组装的纳米线阵列仍表现出较强的偏振依赖性,偏振度达到0.49.基于密度泛函理论计算,CsPbBr_(3)纳米线阵列的偏振依赖发射与其各向异性的电荷密度分布有关.上述结果表明具有良好自组装特性的超细CsPbBr_(3)钙钛矿纳米线有望用于下一代偏振敏感光电探测器件.

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.

高度对齐有机微线晶体阵列用于高性能偏振敏感光电探测器和图像传感器

有机微纳晶体的图案化对于实现高度集成的有机光电子器件具有重要意义.然而在溶液法制备有机微纳晶体过程中,溶液流动的无序性会导致所制备的微纳晶体分布和排列具有高度无序性和不可控性,从而导致所制备的器件阵列中器件与器件之间的性能差异显著,不利于实现微纳器件的集成化.因此,本文提出一种模板控制溶液流动的方法,实现了有机微米线晶体可控图案化.基于有序排列的微米线晶体图案阵列,所制备的光电探测器不仅具有高性能,且器件-器件差异低至3.58%.结合微米线高度的结构各向异性,所制备的光电探测器阵列成功实现了偏振敏感成像功能.

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.

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.