Abstract:We demonstrate that the directionality of far-field second harmonic (SH) emission generated from individual gold nanosphere can be flexibly engineered by manipulating three-dimensional (3D) focal polarization orientation of the excitation field, which is explained by the coherent interference between SH dipolar and quadrupolar emission modes. The SH dipolar emission mode is independent of the polarization direction of the fundamental field whereas the evolution of the focal polarization orientation can dramatically modify the quadrupolar emission pattern. Therefore, the resultant SH emission pattern has a polarization-dependent behavior and side scattering almost perpendicular to the propagation direction of the incident light can be observed under a specific condition. Our findings provide a novel degree of freedom for all-optical control of directional nonlinear scattering from single nanoantenna, thereby opening new possibilities for future potential applications. This work has been supported by the Key Program of the Natural Science Foundation of Tianjin (No.19JCZDJC32700), and the Science and Technology Support Program of Tianjin (No.17YFZCSY00740). E-mail:wangxianghui@nankai.edu.cn

Abstract:By spin-coating silver nanowires (AgNWs) and polymethyl methacrylate (PMMA), applying pressure imprint and plasma treatment, we obtained flat AgNW thin film with a sheet resistance of 20 Ω/sq and a transmittance of 78% at 550 nm with low surface roughness. No significant change in sheet resistance was observed after cyclic bending (bending radius is 5 mm) test and tape test. After 1 000 bending tests, the change rate of sheet resistance was only 8.3%. The organic light-emitting devices (OLEDs) were prepared by using such AgNW electrodes and a maximum brightness of 5 090 cd/m2 was obtained. Compared with the AgNWs electrode without any treatment, the present AgNW electrodes have lower sheet resistance and better hole injection. Our results show spin-coated with flat layers, embossed and plasma-treated AgNW electrodes are suitable for manufacturing flexible organic optoelectronic devices. E-mail:jthu@hfut.edu.cn

Abstract:NaTaO3/ZnO composites were synthesized via a two-step hydrothermal method. Then ultraviolet detectors based on pure NaTaO3, ZnO and their composites with different mole ratio were fabricated. Among all the devices, the 1:1 NaTaO3/ZnO possessed a high photo-to-dark current ratio and stable periodic photoresponse. The photoresponse is facilitated by the synergistic effect between different components and the improved ZnO morphology in the composites, the reduced dimensionality in which provides a straight electron conduction pathway. Additionally, the 1:1 NaTaO3/ZnO detector also exhibits a low dark current less than 1 nA at 5 V bias, which benefits a lot to the low power dissipation and high sensitivity of devices. These results reveal that NaTaO3/ZnO composites are good candidates for the fabrication of ultraviolet detectors.

Abstract:Ag nanoparticles (NPs) were introduced into Er3+/Tm3+ codoped tellurite glasses prepared using melt-quenching and heat-treated techniques. The glass samples were characterized by the differential scanning calorimeter (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence to reveal the Ag NPs induced broadband near-infrared band emission enhancement of Er3+/Tm3+ ions. The studied glasses possessed good thermal stability with larger than 137 ℃. For glass sample heat-treated at 360 ℃ for 6 h, the nucleated Ag NPs in near-spherical shape with an average diameter about 6.5 nm dispersed in the glass matrix. Under the excitation of 808 nm laser diode (LD), the broadband near-infrared fluorescence emission extending from 1 350 nm to 1 620 nm, owing to the combined contributions from the 3H4→3F4 transition of Tm3+ at 1.47 µm band and the 4I13/2→4I15/2 transition of Er3+ at 1.53 µm band, improved significantly with the introduction of Ag NPs, which is mainly attributed to the increased local electric field. The present results indicate that Er3+/Tm3+/Ag NPs codoped tellurite glass with good thermal stability is a promising glass material for broadband fiber amplifiers of WDM transmission systems.

Abstract:Nowadays, multi-functional materials are desperately required for adapting the complex environment, which urges us to take more factors into consideration. Here, we proposed a broadband microwave absorber with multi-functionality such as optically transparent, thermal insulating and soundproof properties. Using indium tin oxide (ITO) based metamaterial, the device can achieve above 90% microwave absorption from 5.6 GHz to 23 GHz (cover X and Ku band). Moreover, with designed vacuum structure inside, the device is thermal insulating and soundproof. These multi-functional advantages give the absorber more flexibility in electromagnetic shielding and stealth application, which can be potentially applied in windows related industry.

Abstract:Laser communication is essential part of maritime-terrestrial-air intelligent communication/sensor network. Among them, different modulation formats would play a unique role in specific applications. Based on Rytov theory, we discussed system performance of the maritime laser communication with repeated coding technology in several modulation schemes. The closed-form expression of average bit error rate (BER) from weak to moderate atmospheric turbulence described by log-normal distribution is given. Differential phase shift keying (DPSK) modulation, as a potential solution for future maritime laser communication, has attracted a lot of attention. We analyzed the effects of atmospheric turbulence parameters (visibility, refractive index structure coefficient, non-Kolmogorov spectral power-law exponent, turbulence inner scale) and DPSK system parameters (receiver aperture diameter, repeat time) on average BER in detail. Compared with the aperture-averaging effects, the system BER can be well suppressed through increasing repeat time. This work is anticipated to provide a theoretical reference for maritime laser communication systems.

Abstract:The asymmetric dual-core fiber (ADCF) is proposed to obtain large group velocity dispersion (GVD) because of the coupling effects between the fundamental modes of the central core and high-order modes of the side core. The supermodes of the ADCF can provide anomalous- and normal-GVD profiles with large peak values at the maximum dispersion wavelengths. The maximum dispersion wavelengths can be shifted in the wavelength window of 1 550 nm by properly tuning the refractive indexes and diameters of the cores or spacing between the two cores. Furthermore, the numerical results show that the ADCF with the normal-GVD supermode 1 can be employed in the pulse broadening, where the broadening factor can reach more than 30 without pulse distortion from nonlinear effects.

Abstract:This letter deliberates bridging of overall electricity power requirements of the optical network unit (ONU) with the entropy noted through the ONU state transition models considered in ethernet passive optical network (EPON). The entropy depends on the steady state and transition probabilities of data. On the other hand, the power requirements (consumption) of ONUs depend on the steady sate probability of ONUs. The potential relation derived between the entropy and electrical power reveals that they related exponentially but for their logarithmic reliance. Also, the relation is validated through the numerical simulation. The deduced relation has its importance to understand the nuances of one entity given the other.

Abstract:In order to realize the rapid detection of three-dimensional defects of connectors, this paper proposes a method for detecting connector defects based on structured light. This method combines structured light with binocular stereo vision to obtain three-dimensional data for the connector. Point cloud registration is used to identify defects and decision trees are used to classify defects. The accuracy of the 3D reconstruction results in this paper is 0.01 mm, the registration accuracy of the point cloud reaches the sub-millimeter level, and the final defect classification accuracy is 94%. The experimental results prove the effectiveness of the proposed three-dimensional connector defect detection method in connector defect detection and classification.

Abstract: Detecting prohibited item based on convolutional neural networks (CNNs) is of great significance to ensure public safety. However, the natural occurrence of such prohibited items is a small-probability event, collecting enough datasets to support CNN training is a big challenge. In this paper, we propose a new method for synthesizing X-ray security image with multiple prohibited items from semantic label images basing on Generative Adversarial Networks (GANs). Theoretically, we can use it to synthesize as many X-ray images as needed. A new generator architecture with Res2Net is presented, which is more effective in learning multi-scale features of different prohibited items images. This method is extended by establishing the semantic label library which contains 14 000 images. So we totally synthesize 14 000 X-ray security images. The experimental results show the super performance (Fréchet Inception Distance (FID) score of 30.55). And we achieve 0.825 of mean average precision (mAP) with Single Shot MultiBox Detector (SSD) for object detection, demonstrating the effectiveness of our approach.

Abstract:In this paper, a method is proposed to obtain the analytical solutions of Bloch equations with phase term by using the elementary matrix transform. The effect of the initial phase on the components of Bloch vector is discussed. The result shows that by considering the initial phase of the input pulse, the amplitudes of the in-phase component and the in-quadrature component can be dynamically controlled, meanwhile the population inversion is almost immune to the initial phase. Additionally, the signal electric field expressions of the phase effect of two-pulse photon echo (2PE) is derived, which is also modulated by the initial phase.

Abstract:Spectral shifts and spectral intensities of partially coherent chirped Airy pulsed (PCCAP) beams propagating through oceanic turbulence are studied, where spectral properties of partially coherent chirped Gaussian pulsed (PCCGP) beams are also compared. The effects of optical parameters and oceanic turbulence parameters on spectral shifts at different observation positions are mainly discussed. It is shown that the spectral shift of PCCAP beam is richer than that of PCCGP beam, and there exists some critical positions for PCCAP beams where the spectral red-shift reaches its maximum. The spectral red-shift increases with increasing chirped parameter, correlation length or decreasing pulse duration. However, the increasing of spectral red-shift is accompanied by increasing dissipation rate of turbulence kinetic energy in unit mass liquid or decreasing relative intensity of temperature and salinity fluctuations, mean square temperature dissipation rate. A physical explanation of rapid spectral transition is also made. This work has been supported by the Sichuan Science and Technology Program (No.2020YJ0431). E-mail:ck@cuit.edu.cn