All-dielectric geometric metasurfaces for the generation and manipulation of perfect high-order Poincaré sphere beams.

A high-order Poincaré sphere (HOPS) can be used to describe high-order modes of waveguides and vector beams, since it generalizes the feature of spin and the orbital angular momentum of light. HOPS beams are such beams with polarization states on the HOPS, which have potential applications in optical manipulation and optical communication. In general, the intensity distribution of this kind of beam changes with the topological charge, which limits their practical applications. Based on the concept of perfect vortex beams (PVBs), perfect HOPS beams have been proposed to solve this problem. Here, a flexible and compact scheme based on all-dielectric metasurfaces for realizing and manipulating perfect HOPS beams at near-infrared wavelength was demonstrated. Geometric-phase-only manipulation was employed for simultaneously controlling the phase and polarization of the incident light. By varying the incident polarization, several selected polarization states on the HOPS could be realized by the proposed metasurface. Further, the single ultra-thin metasurface can also realize high quality multiplexing perfect HOPS beams that carry different topological charges. Finally, a cascaded metasurface system has been proposed for generating and manipulating multiple HOPS beams. This compact flat-optics-based scheme for perfect HOPS beam generation and manipulation demonstrated here can be used for on-chip optical manipulation and integrated optical communication in the future.

Manipulation of path state based on spatiotemporal dielectric metasurface.

In this work, a spatiotemporal metasurface is proposed to manipulate the path of photons flexibly. The spatial modulation is induced by the rectangle silicon units aligned on silica in a manner with a phase gradient only for y-polarized photons, and the temporal modulation is contributed by the pumps of constructing Kerr dynamic gratings. By quantizing designed metasurfaces, the analytical solutions of output photon states can be derived correspondingly. Reversal design could be implemented by tailoring the profile of higher harmonics to infer the intensity of pumps, size of meta-atoms, and initial state. The path-polarization entanglement and correlations of output photons are realized, and then a CNOT gate is obtained by utilizing the deflection of the photon path. This work provides a scheme to deal with the spatiotemporal metasurfaces and expands the applications of metasurfaces in the quantum realm.

Metalens for generating multi-channel polarization-wavelength multiplexing metasurface holograms.

We demonstrate multi-channel metasurface holograms, where the pixels of holographic images are represented by the focal points of metalens, leading to the nanoscale resolution. The required phase profiles are implemented by elaborately arranging the hybrid all-dielectric meta-atoms with specific orientation angles. For verification, two-channel single-color images are reconstructed on the focal plane of the metalens by polarization control. Alternatively, three-channel color holograms are exhibited by manipulating the incident wavelengths. More uniquely, the metalens can be further engineered to generate polarization-wavelength multiplexing color holograms in six channels. Our work provides an effective approach to reconstructing holographic images and enables potential applications including color display, information engineering, and optical encryption.

The impact of automated writing evaluation on second language writing skills of Chinese EFL learners: a randomized controlled trial.

Introduction: In the context of the burgeoning field of second language (L2) education, where proficient writing plays an integral role in effective language acquisition and communication, the ever-increasing technology development has influenced the trajectory of L2 writing development. Methods: To address the need for enhanced writing skills among English as a Foreign Language (EFL) learners, this study investigates the efficacy of Automated Writing Evaluation (AWE) training. A randomized controlled trial employing repeated measures was conducted, involving a participant pool of 190 Chinese EFL students. The study comprehensively assessed the effects of AWE training, utilizing the Grammarly platform-an AI-driven program-on various dimensions of writing skills, encompassing task achievement, coherence and cohesion, lexicon, and grammatical accuracy. Control variables included writing self-efficacy and global English proficiency. Writing skills were evaluated through the administration of an International English Language Testing System (IELTS) writing sample test. Results: The results unequivocally demonstrate that the experimental group consistently exhibited superior performance across all facets of writing skills compared to the control group. Furthermore, the predictive influence of pre-test scores was pronounced in task achievement, coherence and cohesion, and lexicon, highlighting the pivotal role of learners' initial proficiency levels in shaping subsequent writing outcomes. Notably, the emergence of writing self-efficacy as a significant predictor of task achievement and coherence and cohesion underscores the role of learners' beliefs and confidence in shaping their writing abilities. Discussion: These findings conclusively suggest that Artificial Intelligence-based instructional programs, specifically AWE, hold the potential to effectively enhance second language writing skills, especially among learners with lower proficiency levels. This study carries crucial implications for EFL educators and researchers, advocating for the seamless integration of AWE into pedagogical strategies to foster a marked improvement in writing competence.

Peak modulation in multicavity-coupled graphene-based waveguide system.

Plasmonically induced transparency (PIT) in a multicavity-coupled graphene-based waveguide system is investigated theoretically and numerically. By using the finite element method (FEM), the multiple mode effect can be achieved, and blue shift is exhibited by tunable altering the chemical potential of the monolayer graphene. We find that the increasing number of the graphene rectangle cavity (GRC) achieves the multiple PIT peaks. In addition, we find that the PIT peaks reduce to just one when the distance between the third cavity and the second one is 100 nm. Easily to be experimentally fabricated, this graphene-based waveguide system has many potential applications for the advancement of 3D ultra-compact, high-performance, and dynamical modulation plasmonic devices.

A graphene-based Fabry-Pérot spectrometer in mid-infrared region.

Mid-infrared spectroscopy is of great importance in many areas and its integration with thin-film technology can economically enrich the functionalities of many existing devices. In this paper we propose a graphene-based ultra-compact spectrometer (several micrometers in size) that is compatible with complementary metal-oxide-semiconductor (CMOS) processing. The proposed structure uses a monolayer graphene as a mid-infrared surface waveguide, whose optical response is spatially modulated using electric fields to form a Fabry-Pérot cavity. By varying the voltage acting on the cavity, we can control the transmitted wavelength of the spectrometer at room temperature. This design has potential applications in the graphene-silicon-based optoelectronic devices as it offers new possibilities for developing new ultra-compact spectrometers and low-cost hyperspectral imaging sensors in mid-infrared region.