Holographic grating fabrication for wide angular bandwidth using polymer thin films

To increase the angular bandwidth of volume holographic grating, we fabricate holographic gratings based on grating multiplexing technique by using thin films of photopolymers and polymer dispersed liquid crystals. Experimental results confirm that the liquid crystal materials increase the refractive index modulation of the grating, enabling high diffraction efficiency with wide angular response compared to pure polymer materials. We observe that the fabricated holographic grating has near 80% of diffraction efficiency and about 18° of angular bandwidth, which can be further improved by modifying the liquid crystal/polymer mixtures and the grating multiplexing technique. The grating can be used to fabricate holographic waveguide structures for emerging applications in the near-eye display systems.     

Nonreciprocal microwave devices based on magnetic nanocomposites made of opal matrices

Microwave circulators based on magnetic nanocomposites made of opal matrices are mathematically simulated and experimentally studied. Mathematical models are based on the solution of the 3D diffraction problems using the projection method and the decomposition computational algorithm that employs autonomous units with magnetic nanoinclusions and virtual Floquet channels. The computational algorithm developed using the projection method with effective parameters of the magnetic nanocomposite is used to calculate the S parameters of the scattering matrix of the microwave Y circulator based on the opal-matrix magnetic nanocomposite. The S parameters (real loss, isolation between arms, and reflection coefficient) of the Y circulator are measured for several nanocomposites made of opal matrices with magnetic nanoparticles (Co_0.5Zn_0.5Fe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄) and compared with the parameters of the circulator based on magnesium–manganese ferrite in a frequency interval of 14–18 GHz. The simulated results are compared with the experimental dependences.     

Periodical rocking long period gratings in PANDA fibers for high temperature and refractive index sensing

We report periodical rocking long period gratings (PR-LPGs) in PANDA fibers fabricated with CO2 laser. The PR-LPGs achieve very high coupling efficiency of 19 dB with 12 periods and a 3.5° twist angle in just one scanning cycle, which is much more effective than the conventional CO2 laser fabrication technique. This type of LPGs exhibits polarization-selective resonance dips which demonstrate different sensitivities to environmental parameters. The high temperature and external refractive index sensitivities are measured simultaneously, so it can be used as a wavelength-selective polarization filter and sensor. This work has been supported by the National Natural Science Foundation of China (No.61605168), the Natural Science Foundation of Hebei Province (No.F2016203392), the College and University Natural Science Foundation of Hebei Province (No.QN2016078), the Science and Technology Project of Qinhuangdao City (No.201601B050), and the Intramural Doctoral Foundation of Yanshan Universtiy (No.B1011). E-mail:jinwa@ysu.edu.cn      

Effect of the magnetic phase transition on the charge transport in layered semiconductor ferromagnets TlCrS<Subscript>2</Subscript> and TlCrSe<Subscript>2</Subscript>

TlCrS₂ and TlCrSe₂ crystals were synthesized by solid-state reaction. X-ray diffraction analysis showed that TlCrS₂ and TlCrSe₂ compounds crystallize in the hexagonal crystal system with lattice parameters a = 3.538 Å, c = 21.962 Å, c/a ≈ 6.207, z = 3; a = 3.6999 Å, c = 22.6901 Å, c/a ≈ 6.133, z = 3; and X-ray densities ρ _x = 6.705 and 6.209 g/cm³, respectively. Magnetic and electric studies in a temperature range of 77–400 K showed that TlCrS₂ and TlCrSe₂ are semiconductor ferromagnets. Rather large deviations of the experimental effective magnetic moment of TlCrS₂ (3.26 μ_B) and TlCrSe₂ (3.05 μ_B) from the theoretical one (3.85 μ_B) are attributed to two-dimensional magnetic ordering in the paramagnetic region of strongly layered ferromagnets TlCrS₂ and TlCrSe₂. The effect of the magnetic phase’s transition on the charge transport in TlCrS₂ and TlCrSe₂ is detected.     

Magnetic field sensor based on peanut-shape structure and multimode fiber

An all fiber magnetic field sensor with peanut-shape structure based on multimode fiber (MMF) is proposed and experimentally demonstrated. The sensing structure and magnetic fluid (MF) are both encapsulated in capillary, and the effective refractive index of MF is affected by surrounding magnetic field strength. The measurement of magnetic field is realized by observing the wavelength drift of interference peak. The transmission spectrum generated by Mach-Zehnder interferometer (MZI) includes core-core mode interference and core-cladding mode interference. Experimental results demonstrate that the core-cladding mode interference is sensitive to magnetic field, and the magnetic field sensitivity is 0.047 8 nm/mT. In addition, two kinds of interference dips are sensitive to temperature, and the sensitivities are 0.060 0 nm/°C and 0.052 6 nm/°C, respectively. So the simultaneous measurement of magnetic field strength and temperature can be achieved based on sensitivity matrix. This work has been supported by the National High Technology Research and Development Program of China (No.2013AA014200), the National Natural Science Foundation of China (No.11444001), and the Municipal Natural Science Foundation of Tianjin (No.14JCYBJC16500). E-mail:13821538563@163.com      

电磁超表面与信息超表面

电磁超材料和超表面是物理、信息与材料领域的热点与前沿,带来了许多新奇的物理现象和突破性的应用. 信息超表面作为近些年来新兴的研究方向,通过数字编码的方式来调控电磁波,构建了由物理世界通往数字世界的桥梁. 本文首先全面总结了电磁超材料与超表面的起源与发展历程;其次重点介绍了可调超表面与可重构超表面、时空调制超表面与器件的发展现状;接着系统介绍了数字编码与可编程信息超表面的基本概念和主要应用,讨论了信息超表面存在的挑战与未来展望;最后简要对电磁超表面和信息超表面的发展趋势进行了总结.     

数字编码超表面:迈向电磁功能的可编程与智能调控

数字编码超表面是超材料与超表面领域的重要研究分支。通过数字编码方法替代等效媒质理论来表征超表面，不仅有效简化了超表面设计，而且建立了数字信息与超材料物理的联系。该文系统梳理数字编码超表面的发展历程，重点介绍其在可编程与智能电磁调控领域的最新研究进展。首先，详细介绍数字编码超表面的基本概念以及基于数字编码超表面的信息论研究；然后，具体介绍可编程超表面的工作原理和实现方式以及可编程超表面的不同研究方向，包括辐射式可编程超表面、多维度可编程超表面、时域数字编码超表面与新体制通信系统；接着，介绍智能超表面的最新研究进展，展示其环境感知与自适应电磁调控能力；最后，对超表面的未来发展进行讨论与展望。      

An FBG impact location system based on broadband light source and improved TDoA algorithm

When a structure material is damaged by impact events, the reliability and lifetime of the material will be severely affected. So impact location is considered as the prime approach for structural health and damage monitoring. In this study, a novel fiber Bragg grating (FBG) impact location system based on broadband light source is designed, aiming at the shortcoming of existing location systems based on FBG. An improved localization algorithm based on the time difference of arrival (TDoA) is proposed for impact location. According to this algorithm, the impact position can be accurately predicted without wave velocity. Impact planar location experiments are carried out for verification of the FBG impact location system and algorithm on a400 mm×400 mm×3 mm aluminum alloy plate. The resulted locating error shows high precision and good stability of the proposed system. This work has been supported by the National Natural Science Foundation of China (Nos.61503218, 61403233, 61573226 and 61473176), the Excellent Young and Middle-Aged Scientist Award Grant of Shandong Province of China (No.BS2013DX018), and the Natural Science Foundation of Shandong Province for Outstanding Young Talents (No.ZR2015JL021). E-mail:pangdan@163.com      

Nutation line shape for the nonstationary regime of magnetic resonance flowmeter–relaxometer

An upgrade of the structure of magnetic resonance flowmeter–relaxometer is proposed to improve the metrological characteristics. The improved structure of the magnetic resonance flowmeter–relaxometer is based on the modulation of static magnetic field Н₀ by ac magnetic field in the region of the nutation coil. The experiments show that the measurements of liquid flow q in the proposed regime make it possible to eliminate the effect of measurement errors related to variations in amplitude and phase of the NMR signal inverted by 180° under rapid variations in quantity q and increase the measurement dynamic range of quantity q by 30%.     

High strength coupling and low polarization-dependent long-period fiber gratings based on the helicoidal structure

A compact helicoidal long-period fiber grating (HLPFG) was fabricated by twisting a single mode fiber with CO₂ laser beam exposure and its characteristic was experimentally investigated. The eccentricity between the core and the cladding of a fiber is introduced from the screw-type deformation. This helically induced significant periodic index change along the fiber produces strong mode coupling between the core and the cladding of −20 dB with a short grating length of 1 cm. The novel resonance wavelength shift of a HLPFG was analyzed with co-directional or contra-directional torsion to the helix.     

Magnetic nanostructures and nanodevices with a semiconductor or dielectric spacer

Magnetic properties of nanoscale magnetic-layer systems using FeNi, Co, FeMn, Al₂O₃, and SiC layers are studied experimentally. The dependence of magnetic behavior on the system geometry and parameters is addressed. Ferromagnet-semiconductor exchange coupling subject to the amplitude of an applied magnetic field is revealed. It is found that the magnetic behavior of the nanostructures varies in a nonlinear manner with applied magnetic field. Spin-tunneling magnetoresistance is observed in magnetic-layer junctions containing an Al₂O₃ spacer. In-plane-conduction magnetic-field sensors using an Al₂O₃ or a SiC spacer are fabricated and tested.Translated from Mikroelektronika, Vol. 34, No. 1, 2005, pp. 56–64.Original Russian Text Copyright © 2005 by Kasatkin, Muravjev, Plotnikova, Pudonin, Azhaeva, Sergeeva, Khodzhaev.     

Geometric Effects in Current-Voltage Characteristics of a Cross-Shaped MDM Ni/NiO/Fe Structure

The current–voltage (I–U) characteristics of a cross-shaped metal-dielectric-metal (MDM) Ni/NiO/Fe structures with NiO layers of different thicknesses are investigated. The dependence of the sign of the differential resistance on the current flowing through the structure and on the thickness of the NiO in a four-contact measuring system of potentials is revealed. In a region 8–10 nm thick, the voltage on the structure changes sign thrice and has the form of an N-shaped curve. This dependence is explained by the geometric effect, which appears due to the competition between the vertical and lateral electron transport, when the ratio of the resistances of the dielectric interlayer and metallic leading electrodes changes under the influence of the current. The numerical calculation confirms the experimentally observed I–U dependences.     

Specific features of the charge carrier mobility in nanowires in transverse electric and magnetic fields

The effect of an electric field E orthogonal to the quantum-wire axis and a magnetic field H (H ⊥ E, H ‖ E) on conductivity is studied within the context of the parabolic potential model. It is shown that, if the interaction of charge carriers with the rough surface of the nanostructure is taken into account, the charge-carrier mobility μ as a function of increasing E is described by an unsteady oscillating curve. A physical interpretation of such behavior of μ with E is proposed. The specific features of mobility in a transverse magnetic field are discussed.     

太赫兹信息超材料与超表面

该文对信息超材料,包括数字超材料、编码超材料、以及可编程超材料的研究进展及其在太赫兹领域的应用进行了综述,从原理分析、数值仿真、样品制备、实际应用等多个角度介绍了信息超材料对电磁波全面而灵活的调控能力,着重探讨了编码超材料在太赫兹领域的发展以及应用,最后阐述了现场可编程超材料的原理及其在构建新型成像系统、新概念雷达中的应用。信息超材料与超表面对太赫兹波束的灵活调控可用于制作波束分离、低雷达散射截面等多种功能器件,为太赫兹频段电磁波的实时调控开辟了新的途径。      

Hollow‐Out Patterning Ultrathin Acoustic Metasurfaces for Multifunctionalities Using Soft fiber/Rigid Bead Networks

Acoustic metasurfaces that can manipulate and control sound waves at 2D subwavelength scales open new avenues to unusual applications, such as asymmetric transmission, super‐resolution imaging, and particle manipulation. However, the long‐standing goals of pushing frontier metamaterials research into real practice are still severely constrained by cumbersome configuration, large acoustic loss, and rigid structure of the existing metamaterials. An ultrathin metasurface (10–300 µm in thickness, up to ≈λ/650, λ the wavelength) that is capable of imparting sound wave with a nontrivial phase shift with high transmittance (>80%) in the range of 5–30 kHz is fabricated here. The metasurface is comprised of a porous network of soft polymer fiber/rigid beads that are physically equivalent to crosslinked spring‐mass resonators. Moreover, the traditional paper‐cutting art to carve the ultrathin metasurface into hollow‐out patterns is incorporated, resulting in a variety of remarkable functions, including acoustic vortex, focusing, and super‐resolution. The hollow‐out patterning approach innovates the traditional one‐step metadevice fabrication process into two separated steps: 1) fabrication of ultrathin metasurfaces; 2) hollow‐out patterning of metasurfaces. The strategy opens an avenue to mass production of acoustic metadevices, shedding light on the applications of the metamaterials in acoustic cloaking, acoustic positioning, and particle manipulation.     

Effect of annealing temperature and rate of sputtering on the magnetic properties and microstructure of the polycrystalline nickel films with (200) texture

The dependences of the magnetic properties and morphology of polycrystalline nickel (Ni) films with the (200) texture that are fabricated using the dc magnetron sputtering on the SiO₂/Si(100) substrates on sputtering rate annealing temperature T, and film thickness d are analyzed. It is demonstrated that an increase in the sputtering rate from 17 to 35 nm/min does not affect the saturation magnetization 4πM and ferromagnetic resonance line width ΔH but leads to a significant increase in the coercivity H _c for the films whose thickness d is greater than critical thickness d _cr (d > d _cr). It is also demonstrated that d _cr depends on both sputtering rate and annealing temperature. The films with the thickness d > d _cr exhibit the stripe domain structure whose period increases with increasing d and rate v. The annealing of the films with d ≥ 40 nm at T ≈ 200–400°C results in an increase in ΔH and H _c by a factor of 2–4, an increase in 4πM by 25%, an increase in grain size ξ by a factor of 20–30, and the formation of the stripe domain structure in the films that do not exhibit such structure prior to annealing and substantial strengthening of the (200) texture.     

Magnetic resonances in (CH3NH3)2MnCl4

We have studied the \(\mathop q\limits^ \to = 0\) magnetic excitations of (CH₃NH₃)₂MnCl₄ in the antiferromagnetic and in the spin-flop regimes by means of magnetic resonance in the millimeter range (60–100 GHz). Rather odd line shapes of the resonance absorption line for narrow lines are explained as interference effects between the resonant and the non-resonant circular wave in the sample. For the antiferromagnetic resonance (AFMR) and for the paramagnetic resonance (EPR, above the Néel temperature), we have also studied the line width as a function of temperature.