Flat multifunctional liquid crystal elements through multi-dimensional information multiplexing

Flat optical elements have attracted enormous attentions and act as promising candidates for the next generation of optical components.As one of the most outstanding representatives,liquid crystal(LC)has been widely applied in flat panel display industries and inspires the wavefront modulation with the development of LC alignment techniques.However,most LC elements perform only one type of optical manipulation and are difficult to realize the multifunctionality and light integration.Here,flat multifunctional liquid crystal elements(FMLCEs),merely composed of anisotropic LC molecules with space-variant orientations,are presented for multichannel information manipulation by means of polarization,space and wavelength multiplexing.Specifically,benefiting from the unique light response with the change of the incident polarization,observation plane,and working wavelength,a series of FMLCEs are demonstrated to achieve distinct near-and far-field display functions.The proposed strategy takes full advantage of basic optical parameters as the decrypted keys to improve the information capacity and security,and we expect it to find potential applications in information encryption,optical anti-counterfeiting,virtual/augmented reality,etc.

Solvent-free fabrication of broadband WS2 photodetectors on paper

Paper-based devices have attracted extensive attention due to the growing demand for disposable flexible electronics.Herein,we integrate semiconducting devices on cellulose paper substrate through a simple abrasion technique that yields high-performance photodetectors.A solvent-free WS_(2) film deposited on paper favors an effective electron-hole separation and hampers recombination.The as-prepared paper-based WS2 photodetectors exhibit a sensitive photoresponse over a wide spectral range spanning from ultraviolet(365 nm)to near-infrared(940 nm).Their responsivity value reaches up to~270 mA W^(−1) at 35 V under a power density of 35 mW cm^(−2).A high performance photodetector was achieved by controlling the environmental exposure as the ambient oxygen molecules were found to decrease the photoresponse and stability of the WS_(2) photodetector.Furthermore,we have built a spectrometer using such a paperbased WS_(2) device as the photodetecting component to illustrate its potential application.The present work could promote the development of cost-effective disposable photodetection devices.

Measuring Topological Charges of Optical Vortices with Multi-Singularity Using a Cylindrical Lens

我们在场与多重奇特测量光旋涡的拓扑的费用的一个简单方法。用一个圆柱的透镜，一根旋涡横梁能与多重分开的黑暗的洞腐烂进轻地分布，谁的数，就等于输入横梁的拓扑的费用。这个结论然后与多重奇特经由实验和旋涡横梁的繁殖的数字模拟被验证。这个方法也是可靠的与奇特的不同分布测量宽带旋涡横梁的拓扑的费用，它不诉诸多重横梁 interferometric 实验。

The interaction of in-band and in-gap lattice soliton trains in optically induced two-dimensional photonic lattices

We demonstrate the coherent interactions of lattice soliton trains, including in-band solitons （IBSs） and gap soliton trains （GSTs）, in optically induced two-dimensional photonic lattices with self-defocusing nonlinearity. It is revealed that the π-staggered phase structures of the lattice soliton trains will lead to anomalous interactions. Solely by changing their initial separations, the transition between attractive and repulsive interaction forces or reversion of the energy transfer can be obtained. The ‘negative refraction＇ effect of the soliton trains on the interaction is also discussed. Moreover, two interacting IBSs can merge into one GST when attraction or energy transfer happens.

Broadband and continuous wave pumped second-harmonic generation from microfiber coated with layered GaSe crystal

The conversion-efficiency for second-harmonic(SH)in optical fibers is significantly limited by extremely weak second-order nonlinearity of fused silica,and pulse pump lasers with high peak power are widely employed.Here,we propose a simple strategy to efficiently realize the broadband and continuous wave(CW)pumped SH,by transferring a crystalline GaSe coating onto a microfiber with phase-matching diameter.In the experiment,high efficiency up to 0.08%W-1mm-1 is reached for a C-band pump laser.The high enough efficiency not only guarantees SH at a single frequency pumped by a CW laser,but also multi-frequencies mixing supported by three CW light sources.Moreover,broadband SH spectrum is also achieved under the pump of a superluminescent light-emitting diode source with a 79.3 nm bandwidth.The proposed scheme provides a beneficial method to the enhancement of various nonlinear parameter processes,development of quasi-monochromatic or broadband CW light sources at new wavelength regions.

Simulation analysis of evolution of hot-images induced by coplanar multi-scatterers

Based on the diffraction theory model for hot-image formation, the evolution of hot-images induced by multiscatterers located in the same plane perpendicular to the propagation axis is numerically simulated. The simulation results show that hot-images induced by coplanar multi-scatterers are also coplanar no matter whether they exist simultaneously or severally. However, if they exist simultaneously the peak intensity of the primary hot-images is weaker than if they exist severally. The unequal competition for energy between the scattered beams from the scatterers leads to the fact that part of the corresponding hot-images are relatively enhanced and the others are restrained. The results show that the hot-images of certain scatterers become stronger when any of these parameters, i.e. amplitude modulation coefficient, phase modulation coefficient and size of the surrounding scatterer, decrease.

Three-dimensional modulations on the states of polarization of light fields

Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.

Improved Microfluidic Coupled-Cavity Waveguides for Slow Light Transmission

我们在场基于在空中的选择液体渗入，生产的洞在夫妇洞波导减缓光的一个方法与三角形的格子在夫妇洞波导由二维的 photonic 水晶和分析组织了慢轻的繁殖。不同夫妇洞波导的组速度侧面，在波导和邻近波导的第一排洞的增加的半径在在洞之间的洞里由选择液体渗入获得了，被使用飞机波浪扩大方法和一个紧密的有约束力的模型评估。我们决定最佳的参数减少组速度。用更简单的夫妇洞波导结构，我们与大多数调查相比获得更小的组速度。

Creation of topological vortices using Pancharatnam-Berry phase liquid crystal holographic plates

Recently,physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications.Therein,topological light fields,because of their unique opportunity of combining experimental and analytical studies,are attracting more interest.Here,based on the Pancharatnam-Berry(PB)phase,we report the creation of Hopf linked and Trefoil knotted optical vortices by using phaseonly encoded liquid crystal(LC)holographic plates.Utilizing scanning measurement and the digital holographic interference method,we accurately locate the vortex singularities and map these topological nodal lines in three-dimensions.Compared with the common methods realized by the spatial light modulator(SLM),the phase-only LC plate is more efficient.Meanwhile,the smaller pixel size of the LC element reduces the imperfection induced by optical misalignment and pixellation.Moreover,we analyze the influence of the incident beam size on the topological configuration.

Coupling-induced spectral splitting for plasmonic sensing with ultra-high figure of merit

We investigate a kind of spectral splitting effect in a plasmonic multilayer system, which consists of stacked Al_2 O_3 and SiO_2 layers, a thin metal film, and a dielectric prism substrate. The results illustrate that an obvious peak appears in the center of the surface plasmon resonance（SPR）-induced reflection spectral dip in the structure with the SiO_2/Al_2 O_3/SiO_2 layers. This spectral splitting response can be regarded as an electromagnetically induced transparency（EIT） like effect,which is attributed to the coupling and interference between the SPR on the metal film and guided-mode resonance（GMR）in the Al_2 O_3 layer. The theoretical calculations agree well with the numerical simulations. It is also found that the reflection spectrum will be further split by the introduction of another Al_2 O_3 layer into the multilayer structure. The reintroduced GMR in the Al_2 O_3 layer changes the coupling and interference process between the SPR and GMR field, giving rise to the generation of ultra-narrow reflection dip. Especially, the spectral splitting can facilitate the realization of plasmonic sensors with ultra-high figure of merit（583）, which is about 5 times larger than that of traditional SPR sensors. These results will provide a new avenue to the light field manipulation and optical functionalities, especially biochemical and environmental sensing.

Graphene-empowered dynamic metasurfaces and metadevices

Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to the static metasurfaces and metadevices,where the functionalities cannot be actively tuned in situ post-fabrication.Due to the in-trinsic advantage of active tunability by external stimulus,graphene has been successively demonstrated as a favorable candidate to empower metasurfaces with remarkably dynamic tunability,and their recent advances are propelling the EM wave manipulations to a new height:from static to dynamic.Here,we review the recent progress on dynamic metasur-faces and metadevices enabled by graphene with the focus on electrically-controlled dynamic manipulation of the EM waves covering the mid-infrared,terahertz,and microwave regimes.The fundamentals of graphene,including basic ma-terial properties and plasmons,are first discussed.Then,graphene-empowered dynamic metasurfaces and met-adevices are divided into two categories,i.e.,metasurfaces with building blocks of structured graphene and hybrid metasurfaces integrated with graphene,and their recent advances in dynamic spectrum manipulation,wavefront shap-ing,polarization control,and frequency conversion in near/far fields and global/local ways are elaborated.In the end,we summarize the progress,outline the remaining challenges,and prospect the potential future developments.

High-efficiency second-order nonlinear processes in an optical microfibre assisted by few-layer GaSe

The centrosymmetric nature of silica fibre precludes the realisation of second-order nonlinear processes in optical fibre systems.Recently,the integration of 2D materials with optical fibres has opened up a great opportunity to develop allfibre active devices.Here,we demonstrate high-efficiency second-order nonlinear frequency conversions in an optical microfibre assisted with few-layer gallium selenide(GaSe)nanoflakes.Attributed to the strong evanescent field of the microfibre and ultrahigh second-order nonlinearity of the GaSe nanoflakes,second harmonic generation(SHG)and sum-frequency generation(SFG)are effectively achieved with only sub-milliwatt continuous-wave(CW)lasers in the wavelength range of 1500–1620 nm,covering the C and L telecom bands.The SHG intensity from the microfibre is enhanced by more than four orders of magnitude with the assistance of the GaSe nanoflakes on fibre nonlinear processes.Moreover,in the SFG process,the intensity transfer between different frequencies can be effectively manipulated by changing the wavelengths and powers of two pump lasers.The realised strong second-order nonlinearity in the GaSe-integrated microfibre might expand the applications of all-fibre devices in all-optical signal processing and new light source generation at awkward wavelengths.

Dynamically measuring the holo-information of light fields in three-dimensional space using a periodic polarization-structured light

Spatially structured light field has attracted great attention due to its novel properties and application potential in numerous fields.Among them,the most striking one is the polarization-structured light,known as the vector beam.Here,using a periodic polarization-structured light,we propose a method to dynamically measure the holo-information of light fields,including the amplitude,phase,and polarization distributions,in three-dimensional(3D)space.The measurement system is composed of a Mach-Zender interferometer involving a liquid crystal polarized grating in the reference arm,which is simple,stable,and easy to operate.Featuring the single-shot measurement,this method supports observing the dynamic variation of object light fields.The accuracy,3D polarimetry,and dynamic observation of this method are validated by measuring a calibrated quarter-wave plate,a vector vortex beam,a Poincarébeam,and a stressed polymethyl methacrylate sample.

High-Q resonances governed by the quasi-bound states in the continuum in all-dielectric metasurfaces

The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum(BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.

Coherent and Incoherent Interactions between Discrete-Soliton Trains in Two-Dimensional Light-Induced Photonic Lattices

在 discrete-soliton 火车之间的协调、支离破碎的相互作用数字地在导致光的二维的 photonic 格子被调查。去钻石和方形的格子的 discrete-soliton 火车的答案被 Petviashvili 重复方法获得。它为两个被发现那格子的类型，二同相(out-of-phase ) discrete-soliton 火车吸引(排斥) 对方，和中介总是伴有精力转移。当在二列支离破碎的 discrete-soliton 火车之间的相互作用力量总是是吸引人的时。

Hybrid vector beams with non-uniform orbital angular momentum density induced by designed azimuthal polarization gradient

Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.

Generation and motion control of optical multi-vortex

The generation and propagation dynamics of multiple optical vortices hosted in a Gaussian beam are experimentally demonstrated by use of the computer-generated holography. Fluid-like motions of the multi-vortex beam are observed owing to the helical phase structure. The multi-vortex beam with identical topological charge presents rotation, which can be suppressed by changing the sign of the topological charge alternately. In addition, the transverse motion control of the multi-vortex is proved by inserting an additional vortex. Finally, rotary and stationary vortex lattices with different periodic arrays are experimentally constructed. The results exhibit potential applications in inducing twisted or stable waveguide arrays and new types of optical traps.

A review of common-path off-axis digital holography:towards high stable optical instrument manufacturing

Digital holography possesses the advantages of wide-field,non-contact,precise,and dynamic measurements for the complex amplitude of object waves.Today,digital holography and its derivatives have been widely applied in interferometric measurements,three-dimensional imaging,and quantitative phase imaging,demonstrating significant potential in the material science,industry,and biomedical fields,among others.However,in conventional off-axis holographic experimental setups,the object and reference beams propagate in separated paths,resulting in low temporal stability and measurement sensitivity.By designing common-path configurations where the two interference beams share the same or similar paths,environmental disturbance to the two beams can be effectively compensated.Therefore,the temporal stability of the experimental setups for hologram recording can be significantly improved for time-lapsing measurements.In this review,we categorise the common-path models as lateral shearing,point diffraction,and other types based on the different approaches to generate the reference beam.Benefiting from compact features,common-path digital holography is extremely promising for the manufacture of highly stable optical measurement and imaging instruments in the future.

Influence of parameters on light propagation dynamics in optically induced planar waveguide arrays

The diffraction and refraction of light beam in optical periodic structures can be determined by the photonic band-gap structures of spatial frequency.In this paper,by employing the equation governing the nonlinear light propagations in photorefractive crystals,we study the photonic band-gap structures, Bloch modes,and light transmission properties of optically induced planar waveguide arrays.The relationship between the photonic band-gap structures and the light diffraction characteristics is discussed in detail.Then the influence of the parameters of planar waveguide arrays on the band-gaps structures,Bloch modes,and linear light transmissions is analyzed.It is revealed that the linear light transmission properties of waveguide arrays are tightly related to the diffraction relationships determined by band-gap structures.And the Bloch modes corresponding to different transmission bands can be excited by different excitation schemes.Both the increases of the intensity and the period of the array writing beam will lead to the broadening of the forbidden gaps and the concentration of the energy of the Bloch modes to the high-index regions.Furthermore,the broadening of the forbidden gaps will lead to separation and transition between the Bloch modes of neighboring bands around the Bragg angle.Additionally,with the increase of the intensity of the array writing beams,the influences from light intensity will tend to be steady due to the saturation of the photorefractive effect.