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Tunable mode converter is a key component of channel switching and routing for optical communication system by adopting mode-division multiplexing. Traditional mode converter hardly implements high-order mode conversion and dynamic tunability simultaneously. In this study, we design a tunable mode converter filled with liquid crystal, which can convert fundamental mode into multiple high-order modes (TE0, TE1, and TE2) with a good performance and low intrinsic loss. For this multiple-objective task, we propose an inverse design framework based on the adjoint method. To experimentally prove our design, a tunable mode converter filled with air or water and a mode demultiplexer are fabricated to implement dynamic routing. The experimental results agree well with the simulation and reveal the crosstalk only around −7 dB. With its performance and efficiency, our proposed design flow can be a powerful tool for multifunction device design.

Whether cities can attain a win-win situation with simultaneous environmental protection and economic growth is a compelling issue in current urban development. It will be of great practical significance to comprehensively evaluate the implementation effect of the multi-dimensional goals of an urban development from the perspective of a green total factor productivity (GTFP) evaluation. The paper places pollution reduction and carbon reduction into the research framework of GTFP, introduces the SBM-DDF model to evaluate the urban GTFP of 58 cities in the Yellow River Basin (YRB) from 2006 to 2020, and employs the panel regression model to empirically study the factors influencing the urban GTFP of the region. The results are obtained as follows: (1) from the perspective of time range, the urban GTFP in the basin displays an evolutionary trend of first declining and then mounting, demonstrating the highest GTFP in the downstream, the second-highest in the midstream and the lowest in the upstream; (2) regarding the spatial distribution characteristics, the urban GTFP in the basin presents obvious spatial differences, showing the regional differences by increasing from the upstream to the downstream; (3) from the perspective of the whole basin, the advancement of economic development, urbanization processes, environmental regulations and the ecological background have significantly positive effects in improving the urban GTFP, while the improvement of the industrial structure, opening-up and energy intensity affects the urban GTFP of the basin negatively; and (4) from the perspective of the regional heterogeneity of the effects of the various influencing factors, the improvement of the opening-up and industrial structure expedites the growth of the urban GTFP of the downstream, the advancement of urbanization process restrains the urban GTFP in the upstream and the impact of the ecological background on the urban GTFP in different regions is relatively complex. This study is of great importance to improve the urban GTFP and boost the high-quality development of the cities in the basin.

Public participation in the context of the river chief system is not only beneficial for long-term river and lake governance (RLG), but it also is an important supplement to the existing governance mode led by the government. On the basis of the integrated model of TPB-NAM, this paper discusses the influencing factors and driving mechanisms of public participation in river and lake governance in the context of the river chief system from aspects of self-interest and altruism. Through the investigation of residents, 508 sample data points were obtained and analyzed by the structural equation model (SEM). The results were as follows: (1) the explanatory power of the TPB-NAM model (R2 = 60.7%) was superior to that of the extended TPB model (R2 = 60.0%) and NAM model (R2 = 50.0%). (2) From the perspective of individual rationality, the intention for public participation in RLG had a significant positive influence on behavior, and behavior attitudes and subjective norms could predict their intentions. However, the roles were different; from the perspective of social rationality, awareness of negative consequences could actively affect positive personal norms through the ascription of responsibility, and positive personal norms could promote public participation in RLG. (3) Government norms were another important factor driving public participating in RLG. The results are of great theoretical significance for further exploring the public intention and behavior related to participation in RLG.

Metasurfaces are promising platforms for integrated compact optical systems. Traditional metasurface holography design algorithms are limited to information capacity due to finite spatial bandwidth production, which is insufficient for the growing demand for big data storage and encryption. Here, we propose and demonstrate deep learning empowered ultra-dense complex-amplitude holography using step-moving cascaded metasurfaces. Using deep learning artificial intelligence optimization strategy, the barriers of traditional algorithms can be conquered to meet diverse practical requirements. Two metasurfaces are cascaded to form the desired holography. One of them can move to switch the reconstruction images due to diffraction propagation accumulated during the cascaded path. The diffraction pattern from the first metasurface propagates at a different distance and meets with the second metasurface, reconstructing the target holographic reconstructions in the far-field. Such a technique can provide a new solution for multi-dimensional beam shaping, optical encryption, camouflage, integrated on-chip ultra-high-density storage, etc.

In this paper, we report all-optical manipulation of magnetization in ferromagnetic Co/Pt thin films enhanced by plasmonic resonances. By annealing a thin Au layer, we fabricate large-area Au nanoislands on top of the Co/Pt magnetic thin films, which show plasmonic resonances around the wavelength of 606 nm. Using a customized magneto-optical Kerr effect setup, we experimentally observe an 18.5% decrease in the minimum laser power required to manipulate the magnetization, comparing the on- and off-resonance conditions. The results are in very good agreement with numerical simulations. Our research findings demonstrate the possibility to achieve an all-optical magnetic recording with low energy consumption, low cost, and high areal density by integrating plasmonic nanostructures with magnetic media.

Optical geometric-phase metasurfaces provide a robust and efficient means for light wave control by simply manipulating the spatial orientations of the in-plane anisotropic meta-atoms, where polarization conversion plays a vital role. However, the concept of acoustic geometric-phase modulation for acoustic field control remains unexplored because airborne acoustic waves lack a similar optical polarization conversion process. In this work, a new type of acoustic meta-atom with deep-subwavelength feature size is theoretically investigated and further applied to acoustic field engineering based on the emerged concept of acoustic geometric phase. Herein, tunable acoustic geometric-phase modulation of designated order is obtained via the near-field coupled orbital angular momentum transfer process, and the topological charge-multiplexed acoustic geometric phase endows our meta-arrays with multiple functionalities. Our work extends the capacity of the acoustic geometric-phase meta-arrays in high-quality acoustic field reconstruction and offers new possibilities in multifunctional acoustic meta-holograms.

The economic system is an irreversible entropy increase process which is constructed by many elements and is far away from the equilibrium point; and affected by various parameters change, it is quite common that its motion state appears chaotic phenomenon due to instability. The extremely complex and not completely random aperiodic motion form of chaotic phenomenon is strongly sensitive to initial conditions. The development of nonlinear science, especially the emergence and development of chaos and fractal theory, has gradually become a powerful tool for economists to study the complexity, uncertainty and nonlinearity of social economic systems; and some visionary economists began to apply the research results of nonlinear science to economics, which has produced nonlinear economics. On the basis of summarizing and analyzing previous research works, this paper first obtains the non-degenerate equilibrium point of some typical fractional-order chaotic economic systems and transforms the equilibrium points of those systems to the origin through coordinate transformation, and then analyzes the Jacobi matrixes of new systems obtained through coordinate translation, and the parameter conditions of bifurcation in the economic systems are finally given and the numerical simulation of the fractional-order chaotic economic system evolution is carried out through bifurcation diagram, phase diagram and time series diagram. The study results of this paper provide a reference for the further study of the evolution of fractional-order chaotic economic systems with non-degenerate equilibrium points.

Smith-Purcell radiation results from charged particles that move closely to a periodic structure. In this work, we report the on-demand control of Smith-Purcell radiation by rationally designed gra...

Weyl points, which are the degenerate points in three-dimensional momentum space, have been widely studied in the photonic system, and show some intriguing phenomena such as topologically protected surface states and chiral anomalies. Type-I Weyl systems possess a complete bandgap, and topologically protected surface states can be excited without disturbing the bulk states. In this work, we investigate the influence of the sign of coupling coefficient on the topological property of the system and find that type-I Weyl points can be realized by introducing a negative coupling between the stacking layers of the designed photonic crystal. We propose a new strategy to construct a type-I Weyl system by stacking the hexagonal photonic lattice. Different from the topological nontrivial photonic system with a positive coefficient, the negative couplings in the photonic system are realized by adding another resonating site between stacking layers. We theoretically demonstrate that the effective coupling between the resonating sites in adjacent layers sign-flips through the judicious design of the nearest coupling strength and eigenfrequency of the additional sites. The surface states at opposite boundaries of the proposed system have opposite group velocities, which is the feature of type-I Weyl points. Our study provides a new method of exploring topologically protected photonic systems and developing possible topological devices.

Metasurfaces based on geometric phase acquired from the conversion of the optical spin states provide a robust control over the wavefront of light, and have been widely employed for construction of various types of functional metasurface devices. However, this powerful approach cannot be readily transferred to the manipulation of acoustic waves because acoustic waves do not possess the spin degree of freedom. Here, we propose the concept of acoustic geometric-phase meta-array by leveraging the conversion of orbital angular momentum of acoustic waves, where well-defined geometric-phases can be attained through versatile topological charge conversion processes. This work extends the concept of geometric-phase metasurface from optics to acoustics, and provides a new route for acoustic wave control., Comment: 14 pages, 4 figures

Su, Z.X.; Zhang, G.X., and Xu, L., 2020. Water environment management evaluation approach based on IFPWA operator under intuitionistic fuzzy environment. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 229–233. Coconut Creek (Florida), ISSN 0749-0208.Water environment problem has great effect on sustainable development. Considering the fuzziness of mankind thinking as well as the complicacy of the objective world, this study establishes evaluation method under intuitionistic fuzzy environment. Firstly, by using IFPWA Operator, the evaluation information of all evaluation indexes is aggregated. Secondly, intuitionistic fuzzy entropy is applied for calculating the weights of every index. Thirdly, an evaluation method of water environment management is established by using IFPWA Operator with intuitionistic fuzzy information, where a transfer equation introduced to transform the intuitionistic fuzzy number to score is proposed. Finally, a practical example for rural water environment performance evaluation is applied to certify the feasibility and effectiveness of the method that has been proposed.

Because of the strong inherent resonances, the giant optical activity obtained via chiral metamaterials generally suffers from high dispersion, which has been a big stumbling block to broadband applications. In this paper, we propose a type of planar chiral metamaterial consisting of interconnected metal helix slat structures with four-fold symmetry, which exhibits nonresonant Drude-like response and can therefore avoid the highly dispersive optical activity resulting from resonances. It shows that the well-designed chiral metamaterial can achieve nondispersive and pure optical activity with high transmittance in a broadband frequency range. And the optical activity of multi-layer chiral metamaterials is proportional to the layer numbers of single-layer chiral metamaterial. Most remarkably, the broadband behaviors of nondispersive optical activity and high transmission are insensitive to the incident angles of electromagnetic waves and permittivity of dielectric substrate, thereby enabling more flexibility in polarization manipulation.

We proposed a novel strategy to design a deep subwavelength metasurface with full 2π transmission phase modulation and high transmission efficiency by applying resonators with interfering Fano resonance. Theoretical investigation demonstrates that the transmission efficiency of the resonators depends on the direct transmission coefficient, direct reflection coefficient, and Q factor. When an impedance layer is added in the resonators, the direct transmission and direct reflection coefficients can be facilely manipulated so that the span of the transmission phase around the resonance frequency can be extended to 2π. As a result, we can continuously adjust the transmission phase from 0 to 2π through changing the geometric parameters of the resonators and construct a deep subwavelength metasurface with the resonators to manipulate the transmission wave with high efficiency. We also find that a layer of grating can be used as the impedance layer to change direct transmission and direct reflection in the actual design of the metasurface. The proposed strategy may provide effective guidance to design a deep subwavelength metasurface for controlling a transmitted wave with high efficiency.

In this paper, we have designed a metasurface based on electrically tunable Mie-type resonators and theoretically demonstrated its tunable response to electromagnetic waves with varying frequency. The metasurface consists of disk-like ferroelectric resonators arrayed on a metal film and the upper surface of resonators is covered by ion gel film which is transparent for incident electromagnetic wave. Using the metal film and ion gel film as electrodes, the permittivity of the resonators can be adjusted by an external electric field and, as a result, the reflection phase of the resonators can be dynamically adjusted in a relatively wide range. By programmable controlling the electric field strength applied on resonators of metasurface, a 2π phase ramp can be realized and, thereby, the arbitrary reflection behavior of incident waves with varied frequency is obtained. Because of the tunability, this metasurface can also be used to design adaptive metasurface lens and carpet cloak.

We theoretically investigate optical refraction behavior in a fluid system which contains silica-coated gold nanorods dispersed in silicone oil under an external electric field. Because of the formation of a chain-like or lattice-like structure of dispersed nanorods along the electric field, the fluid shows a hyperbolic equifrequency contour characteristic and, as a result, all-angle broadband optical negative refraction for transverse magnetic wave propagation can be realized. We calculate the effective permittivity tensor of the fluid and verify the analysis using finite element simulations. We also find that the negative refractive index can vary with the electric field strength and external field distribution. Under a non-uniform external field, the gradient refraction behavior can be realized.

We design a tunable terahertz metasurface, which consists of two different trapezoid graphene ribbons patterned in opposite directions on a gold film, separated by a thin dielectric spacer. The two kinds of graphene ribbons can cover a nearly 2π phase shift with high reflection efficiency in different spectral regions so that the metasurface can reflect different frequency waves to totally different directions. By changing the Fermi level of the graphene ribbons, the response frequency of the proposed metasurface can be adjusted, and as a result, tunable spectrum splitting can be realized. The present metasurface provides a powerful way to control terahertz waves and has potential applications in wide-angle beam splitters.

We design a soft infrared metamaterial absorber based on gold nanorods dispersed in liquid crystal (LC) placed on a gold film and theoretically investigate its total absorption character. Because the nanorods align with the LC molecule, the gold nanorods/LC hybrid exhibits different permittivity as a function of tilt angle of LC. At a certain tilt angle, the absorber shows an omnidirectional total absorption effect. By changing the tilt angle of LC by an external electric field, the total absorption character can be adjusted. The total absorption character also depends on the concentration, geometric dimension of nanorods and defect of nanorod arrangement in LC. When the LC contains different size of gold nanorods, a broadband absorption can be easily realized. The characteristics including flexibility, omnidirectional, broadband and tunablility make the infrared metamaterial absorber possess potential use in smart metamaterial devices.

We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF(2) multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF(2) multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect.

We propose a planar composite chiral metamaterial (CCMM) by symmetrically inserting a metallic mesh between two layers of conjugated gammadion resonators. As the elaborate CCMM operates at off-resonance frequencies, it therefore presents low-loss and low-dispersion polarization rotation features. The results show that the proposed CCMM can achieve pure and dispersionless polarization rotation with efficient transmission for a linearly polarized wave within a broad bandwidth. This off-resonance CCMM overcomes the drawbacks of high transmission losses and highly dispersive polarization rotation that exist in the previous resonance-type chiral metamaterials and also exhibits more simplicity of fabrication than the three-dimensional CMMs. The intriguing properties greatly improve the performance of chiral metamaterials in controlling the polarization state of electromagnetic waves.

We propose an electrically controllable soft optical cloak based on a fluid system containing gold nanorods, which can be transformed from isotropic to anisotropic epsilon-near-zero (ENZ) state at a certain incident optical frequency due to the orientation of gold nanorods under an external electric field stimulus. Both effective medium theory and 3D finite element simulation demonstrate that, at the ENZ point, the scattering from arbitrary-shaped objects can be nearly perfect suppressed. The loss and aspect ratio of gold nanorods have an effect on the ENZ point and scattering suppression behavior. When different aspect ratio of gold nanorods is employed, the fluid has multi ENZ points and exhibits perfect suppression of scattering from objects at multiple incident optical frequencies. Because the orientation of gold nanorods depends on the strength of applied external electric field, the permittivity of fluid can be adjusted by external electric field and, as a result, the ENZ state and scattering suppression of objects can be controlled. The flexible, controllable, and multi-frequency responsive characteristics make the optical cloak possess potential use in soft smart metamaterial devices.