Polarization is crucial in various fields such as imaging, sensing, and substance detection. A compact, fast, and accurate polarization detection device is vital for these applications. Herein, we demonstrate a multifocus metalens for terahertz polarization detection that requires only a single measurement to obtain complete polarization parameters and reconstruct the polarization state of the incident field. The individual subarrays of this metalens convert each of the six polarized components into the same polarization, which in turn links the Stokes parameters to these six foci. The incident linear polarizations and elliptical polarizations are characterized by Stokes parameters and polarization ellipses. Simulations and experimental results show that the scheme can accurately detect the incident polarization with a single measurement. The proposed metasurface polarimetry may find applications in the fields of real-time terahertz detection and integrated optics. 

Full-Stokes Metasurface Polarimetry: Requiring Only a Single Measurement


 The linear electro-optic effect offers a valuable means to control light properties via an external electric field. Lithium niobate (LN), with its high electro-optic coefficients and broad optical transparency ranges, stands out as a prominent material for efficient electro-optic modulators. The recent advent of lithium niobate-on-insulator (LNOI) wafers has sparked renewed interest in LN for compact photonic devices. In this study, we present an electro-optic modulator utilizing a thin LN film sandwiched between top and bottom gold (Au) film electrodes, forming a Fabry–Pérot (F–P) resonator. This resonator exhibits spectral resonance shifts under an applied electric field, enabling efficient modulation of reflected light strength. The modulator achieved a 2.3 % modulation amplitude under ±10 V alternating voltage. Our approach not only presents a simpler fabrication process but also offers larger modulation amplitudes compared to previously reported metasurface based LN electro-optic modulators. Our results open up new opportunities for compact electro-optic modulators with applications in beam steering devices, dynamic holograms, and spatial light modulators, and more.

Lithium niobate thin film electro-optic modulator

The lithium niobate on insulator devices confine the light field to submicron size in monocrystalline lithium niobate, to achieve ultra-strong electro-optical interaction and nonlinear optical interaction, and thus extend the frontiers of the photonic research in the past decade. Such devices are manufactured using nano-fabrication technology over the thin-film lithium niobate wafer, which usually stands on a silica insulator layer above the substrate material, including low-loss waveguides, electro-optical modulators, domain engineered structures, high-Q microring resonators and electrical filters etc., and lead to breakthroughs in optical communication, microwave photonics and quantum integration. 

Recent development in integrated Lithium niobate photonics

This paper investigates the impact of e-commerce participation on household development resilience using a sample of 1229 households in the Shandong and Shaanxi provinces of China in 2022. It constructs the developmental resilience index of farm households from three dimensions of economy, society and culture using the entropy method, and establishes a counterfactual framework using the Propensity Score Matching (PSM) method. The results suggest that participation in e-commerce has a significant and positive impact on farming household development resilience. The PSM method estimates that participation in e-commerce increases the developmental resilience of farming households by 9.63% compared to non-participation, with economic, social, and cultural resilience increasing by 9.29%, 9.84%, and 9.92%, respectively. The robustness test results confirm the findings. Further analysis reveals that participation in e-commerce enhances farm household development resilience through three mechanisms: improving economic efficiency, network relationship linkage, and risk appetite. Heterogeneity analysis shows that the impact of e-commerce participation on household development resilience varies among farmers with different endowment constraints. In particular, farmers with more years of education and cooperative members benefit more from e-commerce participation, especially live and platform e-commerce. 

Impact of Rural E-Commerce Participation on Farmers’ Household Development Resilience: Evidence from 1229 Farmers in China

Abstract Photonic devices based on ferroelectric domain engineering in thin film lithium niobate are key components for both classical and quantum information processing. Periodic poling of ridge waveguide can avoid the selective etching effect of lithium niobate, however, the fabrication of high-quality ferroelectric domain is still a challenge. In this work, we optimized the applied electric field distribution, and rectangular inverted domain structure was obtained in the ridge waveguide which is beneficial for efficient nonlinear frequency conversions. Second harmonic confocal microscope, piezoresponse force microscopy, and chemical selective etching were used to characterize the inverted domain in the ridge waveguide. In addition, the performance of nonlinear frequency conversion of the periodically poled nano-waveguide was investigated through second harmonic generation, and the normalized conversion efficiency was measured to be 1,720 % W −1 cm −2 , which is close to 60 % that of the theoretical value. The fabrication technique described in this work will pave the way for the development of high-efficiency, low-loss lithium niobate nonlinear photonic devices. 

pdf/high-efficiency-nonlinear-frequency-conversion-enabled-by-2z90fov1ns.pdf

High-efficiency nonlinear frequency conversion enabled by optimizing the ferroelectric domain structure in x-cut LNOI ridge waveguide

In certain developing countries, the e-commerce industries of rural areas are subjected to clustering, which provides an entry point through which the following can be observed: the influence of information and communications technology and the digital economy on spatial connections in rural settlements. Hence, Zhejiang Province, China's leading rural e-commerce province, is selected as the study site. The spatial correlation between e-commerce and the spatial landscape pattern of rural settlements and their network connections is analysed. Moreover, with regard to the spatial network of rural settlements, the driving factors of e-commerce are explored. The research findings demonstrate that: (1) e-commerce cluster areas are primarily distributed where the in-degree is higher than the out-degree, and the betweenness centrality is also significant. (2) E-commerce fosters the expansion and integration of land use in rural settlements and enhances the spatial network connections between rural settlements. (3) In regional economies, e-commerce enhances the connectivity and resource circulation efficiency of spatial networks in rural settlements through scale effects, traffic and informatisation levels, and the logistics development environment. The aforementioned findings contribute to the enrichment of the policy toolbox for rural planning and spatial governance, and the exploration of the market potential of e-commerce development in rural areas. 

Driving spatial network connections in rural settlements: The role of e-commerce

Polarimeters, which measure the polarization states of light directly, are essentially desired in many areas of science and technology. In our previous work, we have constructed a polarimeter based on a rotating-metasurface, and the polarization Stokes parameters of the light were measured with the known Mueller elements of the metasurface. Here, we further perform the error analysis of the metasurface polarimeter. The errors in the measured Stokes parameters have been formulated for the errors in Mueller elements of the metasurface. This analysis can be used to evaluate and minimize the errors of the metasurface polarimeter.

Error analysis of a rotating-metasurface polarimeter.

Beam Shaping by Stacked Nonlinear Moiré Metasurfaces.

Despite various successes in lithium niobate (LN) integrated photonic devices (e.g., light sources, waveguides, modulators, etc.), LN photodetectors (PD) that converts light into electrical signals have received less research attention. Here, fast LN PDs are demonstrated. Defect energy states are used within the forbidden band of the LN as electron donor centers to generate free carriers in the conduction band under optical excitation in the visible range. Compared with previous pyroelectric LN PDs whose response speeds are normally limited to the order of 100 Hz, these LN PDs show faster responses up to 10 kHz. The dependences of the PDs' performances on the electrode gap, external driving voltage, illumination power, and impurity dopants are also studied. This work provides a step toward high‐performance LN PDs for constructing monolithic full‐functional integrated LN photonic chips.

Fast Lithium Niobate Photodetector

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