JOURNAL OF SYNTHETIC CRYSTALS

Long-Lived Lithium Niobate: History and Progress

GAO Bofeng, REN Mengxin, ZHENG Dahuai, WU Wei, CAI Wei, SUN Jun, KONG Yongfa, XU Jingjun

2021, 50(7): 1183-1199.

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Lithium niobate is considered as a model crystal of nonlinear optics, which combines piezoelectric, frequency doubling, electro-optic and photorefractive properties, and has shown great practical utility. Nearly a hundred years since the birth of lithium niobate, it has played an indispensable role in the fields of national security, medical detection, high-energy physics and industrial detection. With the development of micro-nano technology, the study of new optical effects in the microstructure of lithium niobate has become one of international frontier hotspots in recent years, and the related research plays an important role in promoting the generation of new micro-nano photonic devices. This paper summarizes the history of lithium niobate around its optical properties, and introduces its recent research progress particularly in the field of nano-optics, furthermore gives prospects for future developments.

Planar Diffractive Lenses with Artificial Micro/Nano-Structures

HE Jun, HUANG Kun, ZHUANG Jicheng

2021, 50(7): 1200-1221.

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Traditional objective lenses based on the refraction of light in modern microscopy are restricted by Rayleigh diffraction limit, and its resolution is insufficient in various applications such as biological imaging, materials science and nanolithography. The existing methods to overcome this limit can be categorized into near-field (e.g., scanning near-field optical microscopy, superlens and microsphere lens) and far-field (e.g., stimulated emission depletion microscopy, photoactivated localization microscopy and stochastic optical reconstruction microscopy) approaches. However, the former operates in the challenging near-field mode using the nanoprobe to scatter the evanescent wave existing in a wavelength range of the object surface, and the latter have a selective dependence on fluorescent specimen that needs labeling in advance, which might damage the sample. Recently, through manipulating the diffraction of light with artificial micro/nano structure such as zone plate, photon-sieve and gradient metasurfaces, some miniaturized and planar lenses have been reported with intriguing functionalities such as ultrahigh numerical aperture, large depth of focus, and sub-diffraction-limit focusing at far field, thereby allowing a viable solution for the label-free super-resolution imaging. Here, recent advances in planar diffractive lenses (PDLs) are reviewed from a united theoretical account on diffraction-based focusing optics, and the underlying physics of nanofocusing via controlling interference of light is revealed. Design principle, optical performance of PDLs and their dependence on the micro-/nano-structures and materials will be presented. Optical aberration such as off-axis and chromatic aberration is introduced together with consistent efforts for aberration correction. Furthermore, a detailed tutorial about applying these planar lenses integrated in confocal scanning microscopy for nanoimaging is provided, meanwhile the applications in nanolithography and photoelectron spectrometer is introduced. Finally, the conclusion and outlook regarding future development toward practical applications is presented.

Research Progress of Sound Insulation Metamaterials

CHEN Yinghang, CHEN Jian, XU Chi, ZHONG Yuhao, HUANG Weichun, LU Minghui

2021, 50(7): 1222-1233.

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The concept of acoustic metamaterials originated from local resonance phononic crystals. As a new type of composite artificial materials, acoustic metamaterials have excellent special properties. For example, compared with conventional sound insulation materials, they can manipulate sound waves flexibly and accurately, and use small and lightweight structure to solve broadband low-frequency sound insulation. In this paper, the latest research progresses of acoustic metamaterials in sound insulation and noise reduction are reviewed. Based on bandgap theory and equivalent parameters, the sound insulation mechanism is discussed, and the related work is introduced in detail, including Helmholtz, membrane, space-coiling and composite sound insulation metamaterials. Finally, the application of this new field is predicted.

Review of Acoustic Control and Underwater Application of Bionic Acoustic Metamaterials

WANG Zhaohong, LUO Yikun, CHU Yangyang

2021, 50(7): 1234-1247.

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Acoustic metamaterials are a kind of artificial structures, and it has some special physical properties such as negative mass, negative stiffness, etc. Compared with traditional acoustic materials, acoustic metamaterials have the advantages of flexible design and expansibility. Acoustic metamaterials with small size and light weight can be used for low frequency vibration and noise reductions, low frequency broadband acoustic controls, etc. By using biological principles, bionic acoustic metamaterials have been investigate extensively. In this paper, aerodynamic noise reduction, low frequency acoustic wave control and underwater applications of bioinspired acoustic metamaterials in the past decades are reviewed. It is expected that biomimetic acoustic metamaterials will play greater roles in low-frequency acoustic wave control and underwater applications.

Research Progress on Photonic Quasicrystals

CHE Zhiyuan, SHI Lei

2021, 50(7): 1248-1258.

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Quasicrystals have unique structures with long-range order without periodicity. Photonic quasicrystals have been widely studied because of their excellent ability to control electromagnetic waves and broad application prospects. Photonic quasicrystals not only have general characteristics such as complete bandgap, localization states, negative refraction and near-zero refractive index, but also have advantages in laser and nonlinear frequency conversion due to their unique rotational symmetry. In this paper, the development of photonic quasicrystals in recent years is briefly reviewed, and the main research directions of photonic quasicrystals are introduced from two aspects, theoretical researches, and application ones. At last, the future development trend of photonic quasicrystals is prospected.

Energy Band Structure Control in One Dimensional Plasmonic Lattice

CAO Fengzhao, LYU Bokun, DING Yufeng, SHI Jinwei

2021, 50(7): 1259-1274.

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Due to its ability to concentrate electromagnetic waves into deep sub-wavelength volume, surface plasmons have been widely used in nanophotonics. Generally, surface plasmons can be divided into two categories: surface plasmon polaritons (SPPs) propagating along the interface between metal and medium, and localized surface plasmon resonance (LSPRs) bound to metal surface. There is an obvious momentum mismatch between SPPs and the corresponding free space electromagnetic wave. Grating, i.e. one-dimensional plasmonic lattice, is often used to compensate for this momentum mismatch and launch SPPs from free space. LSPRs refer to the surface plasmon localized around a single nanostructure under external light field excitation. When LSPRs are launched, the near-field enhancement effect can greatly increase the absorption and scattering of the incident light. In fact, one dimensional plasmon lattice supports both SPPs and LSPRs, which is an excellent foundamental structure for studying surface plasmon and its optical properties. Due to the coexistence of LSPR, there are much richer energy band structures in plasmonic lattice than in photonic crystals. In this review, we focus on one-dimensional plasmon lattice, and discuss the novel properties of metal plasmon from four aspects: band control, surface lattice resonance, bound states in continuum and Bose-Einstein condensation. These properties are of great significance to further promote the application of surface plasmon.

Inelastic Electron Tunneling-Based Excitation of Surface Plasmons

ZHENG Junsheng, LIU Lufang, PAN Chenxinyu, GUO Xin, TONG Limin, WANG Pan

2021, 50(7): 1275-1286.

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Surface plasmons are highly confined electromagnetic modes coherently coupled to collective oscillations of free carriers at metal (or doped semiconductor) interfaces, which can greatly enhance light-matter interaction at the nanoscale and have found valuable applications in areas such as waveguiding, biochemical sensing, ultrafast modulation, detection and nonlinear optics. They are usually excited by diffraction-limited optical approaches with the use of bulky optical components (prisms, gratings,etc), which greatly limit the miniaturization of plasmonic devices and their chip-scale high-density integration. By integrating a plasmonic nanostructure with a quantum tunnel junction, low-energy inelastically tunneled electrons can directly excite plasmonic modes in the nanostructure with advantages such as ultra-small footprint and ultra-fast speed. In this paper, recent research progress in the inelastic tunneling-based electric excitation of localized and propagating surface plasmons is overviewed.

Multilayer Thin Film Based Structural Color Filters: Principle, Fabrication and Applications

WANG Danyan, LI Moxin, LU Rusi, ZHANG Cheng

2021, 50(7): 1287-1306.

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Multilayer thin film based structural color filters have potential applications in various fields including displaying, color printing, aesthetic decoration and photovoltaics, thanks to their advantages of high purity, high brightness and long-term stability. In addition, by their simple structure, these planar multilayer thin films are compatible with mass production. This review summarizes recent progress of color filters based on multilayer thin films. Two typical device designs and their underlying working principles are elaborated. Different fabrication techniques including magnetron sputtering, electron beam evaporation, and electrochemical deposition, as well as various applications in colored solar cells, color printing, reflective displays are surveyed in detail. We conclude the review by discussing the prospects of multilayer thin film based structural color filters.

Design and Construction of Carbon-Based Crystal Materials with Pressure Response

CHEN Desi, DONG Jiajun, ZHAI Chunguang, YAO Mingguang, LIU Bingbing

2021, 50(7): 1307-1313.

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Materials that exhibit obvious pressure responses upon compression, such as hardening, compressibility and optical properties change, and so on, which have been explored as an important way to design new functional materials with desired mechanical properties and luminescent properties. Here, we will introduce some recent progress on the research of new pressure responsive functional crystalline materials with novel properties. A new strategy has been developed to design and construct new functional materials by application of high pressure to the designed co-crystals. The co-crystals have been designed based on carbon and carbon-based molecules and studied by high pressure technique. A series of new materials with potentially superhard properties, negative volume compressibility and anomalous pressure response in luminescence has been obtained.

Research Progress of Porous Silicon-Au/Ag Dendritic Composite Materials

GE Daohan, NI Chao, DING Jie, ZHANG Liqiang, ZHU Shining

2021, 50(7): 1314-1326.

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Porous silicon-Au/Ag dendritic composites have gradually demonstrated their advantages as SERS substrates since the discovery of surface-enhanced raman scattering (SERS) in the 20th century. They have found widespread application in biology, chemistry, medical treatment, and other fields. The advantage of SERS substrate porous silicon, focusing on Ag/Au in preparing the porous silicon substrate method, was examined over recent years. The porous silicon substrate with a metal coating is cost-effective to fabricate and offers a high detecting capability. This paper illustrates the application in the morphology of dendritic structures under different conditions of preparation and detection. A short analysis carried out on the future evolution of the porous silicon-Ag/Au dendritic composite structure as a SERS substrate.

Photovoltaic Microfluidic Manipulation Based on Lithium Niobate

ZHANG Xiong, GAO Zuoxuan, GAO Kaifang, SHI Lihong, LI Feifei, FAN Bolin, CHEN Lipin, ZAN Zhitao, CHEN Hongjian, YAN Wenbo

2021, 50(7): 1327-1339.

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Photovoltaic microfluidic manipulation utilizes electrostatic interaction of a non-uniform photovoltaic electrostatic field on microfluidic targets to achieve non-contact manipulation. Recently, photovoltaic microfluidic manipulation based on lithium niobate (LN) has been paid a lot of attention, and is considered as a key technology for LN-based biophotonic chips. Compared with traditional electrical and optical manipulation, photovoltaic microfluidic manipulation, using only low-power laser beams but being valid for mass of targets in a wide range, doesn’t require external power sources and fabrication of complex electrode structures, and therefore can avoid external pollution and interference to internal biological environment. In this paper, theoretical basis of photovoltaic microfluidic manipulation based on LN is introduced and the recent achievements in this field is reviewed.

Topological Origin of π Interface Modes Induced by Floquet Gauge Transition

SONG Wange, ZHU Shining, LI Tao

2021, 50(7): 1340-1347.

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Topological insulator is a kind of phase of matter that is internally insulated and can conduct electricity on the surface. The energy band of a topological insulator has non-trivial topological characteristics, which supports a boundary state that can propagate in one direction. The appearance of topological states usually depends on the topological phase transition at the interface or boundary. Recently, a new topological π mode induced by gauge transitions has been successfully observed experimentally in Floquet systems, despite the same topological order across the whole lattices. In this paper, the origin of the topological π mode induced by the gauge field transition are discussed. The Hamiltonian of two Floquet systems with different gauges has opposite π gap mass terms due to gauge transition, thus leads to the emergence of interface states, which is similar to the Jackiw-Rebbi model. The research of this paper provides a theoretical basis for the generation of topological states from gauge transitions, and deepen the understanding of the Floquet gauge.

Mode Responses of Microwave Plasmonic Resonator by Exploiting Group Representation Theory

YANG Jie, WANG Jiafu, JIA Yuxiang, CHEN Wei, QU Shaobo

2021, 50(7): 1348-1355.

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As the counterpart in the lower frequencies of localized surface plasmon (LSP) in the optical regime, spoof LSP has attracted great interest among researchers due to its notable properties such as deep-subwavelength field localization and high-Q-value resonance. Microwave plasmonic resonators (MPRs) that hold several geometric symmetries are a typical device to generate spoof LSP modes. Several methodologies have been developed to study the mode responses of the MPRs, such as effective medium theory and equivalent dispersion theory. However, both of the theories are based on the assumptions that do not properly consider the geometric symmetries held by the MPRs, resulting in which they cannot completely reveal the mode properties of the MPRs. In this paper, a methodology based on group representation theory is proposed to analyze how the geometric symmetries affect the mode responses of the MPRs. By employing symmetry arguments, it is found that the azimuthal orders of the spoof LSP modes are totally determined by the irreducible representations (irreps) of the group composed by the geometric symmetries of the MPRs. The number of the irreps is equal to the number of the spoof LSP modes. A MPR holding C_7v group symmetry is taken as an example to explain our methodology. The C_7v group only has five irreps (three doubly-degenerate and two nondegenerate irreps). Therefore, the MPR can only support five spoof LSP modes with different azimuthal orders, i.e., zero-order mode (also known as magnetic dipole), dipole, quadrupole, hexapole and quattuordecpole. The dipole, quadrupole and hexapole modes are related to three doubly-degenerate irreps implying that the three modes are doubly degenerate. The zero-order and quattuordecpole modes correspond to the two nondegenerate irreps respectively and thus are nondegenerate. The MPR with C_7v group symmetry cannot support more spoof LPS modes limited by its geometric symmetries. A MPR prototype with C_7v group symmetry is designed and simulated. The full-wave simulation results well demonstrate our methodology. Although proposed to analyze the mode responses of the MPRs, our methodology is widely applicable and can also be used to analyze the mode responses of the plasmonic resonators working in other frequency bands like the optical band.

Nonlinear Antennas with Tunable Radiation Patterns in Near Infrared

CHENG Lin, ZHANG Lei

2021, 50(7): 1356-1361.

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Various optical antennas have been proposed to control the radiation pattern in a linear manner. Furthermore, the larger nonlinearity will play a vital role, and will change the refractive index of the antenna, thereby changing the radiation pattern. By modifying the effective mass of electrons in Drude model, it can be obtained that the refractive index of ITO film changes with the optical field intensity, and provides the nonlinear refractive index as a function of frequency and intensity. Nanoantennas made of indium tin oxide (ITO) will exhibit strong Kerr effect. The linear and nonlinear responses of ITO antennas was studied, the Kerr effect of ITO was used to control the radiation pattern of the antenna. Based on this model, a nonlinear optical antenna was designed to achieve tunable radiation pattern covering a broad near infrared band (1 000 nm to 1 650 nm). Moreover, a hybrid nonlinear antenna was demonstrated, composed of ITO and silicon (Si), which can control the radiation pattern more efficiency. This work breaks through the limitation that the strong nonlinear refractive index coefficient of nonlinear material only occurs at specific resonance frequency or the zero refractive index point. Our study provides a novel approach toward ultrafast dynamical control of metamaterials, for applications such as beam steering and optical modulation.

Asymmetric Beam Splitting of Acoustic Metasurface

SONG Ailing, SUN Chaoyu, CHEN Tianning, XIANG Yanxun, XUAN Fuzhen

2021, 50(7): 1362-1370.

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Asymmetric beam splitting metasurface is a two-dimensional planar structure constructed by artificial micro-unit structures in a specific sequence, which can split the normally incident wave into two transmitted beams with freely modulated propagation direction and splitting ratio. It has broad application prospects in acoustic function device design and acoustic communication field. In this paper, the design theory and implementation method for realizing asymmetric beam splitting were systematically studied. Based on the local power conservation condition, the design theory, the impedance matrix distribution, the normal intensity distribution, and the sound pressure field distribution were investigated. The parameters of four-resonator structures are optimized by Genetic algorithm to realize the required impedance matrix distribution. The sound pressure fields indicate that the surface waves with same amplitude, same attenuation coefficients, and opposite propagation directions are excited at the incident side to match the incident and transmitted local power. The transmitted waves are divided into two beams, the refracted angles and transmission coefficients are in good agreement with the theoretical values, which demonstrate the correctness and feasibility of the design theory and realization method. The research results can provide theoretical references, design methods, and technical support for new asymmetric beam splitting device design, and promote their potential engineering applications.

Self-Collimation Effect of Wave Propagation in Phononic Crystals

ZHANG Zhao, ZHANG Lei, GUO Jiangchuan, LI Jiarui, WANG Yifei

2021, 50(7): 1371-1377.

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The wave transmission in different arrayed structures with different media and different frequency domain was calculated. It is found that the self-collimation effect of wave can be found in the designed arrayed structure phononic crystals being similar to the self-collimation of light in photonic crystals. Further computations show that the wave self-collimation can be related to the designed media and the material properties in the arrayed structures. Moreover, this phenomenon can be also affected by the geometrical property of the cross section of the metal pillar in the arrayed structures. The frequency domain for the self-collimation effect of wave increases initilally and then decreases with the increase of the specific modulus, and it is decreased with the increase of the specific density. The optimal designs on specific modulus, specific density and the geometrical properties are the key factors to realize the controlling of frequency domain of the wave self-collimation effect in the arrayed structures. Equi-frequency contour is the key criterion for the design of the self-collimation effect of wave in the periodic arrayed structures.

Characteristic Research of Low Frequency Band Gaps and Structural Improvement in Single-Sided Column Local Resonance Phononic Crystals

SUN Xiangyang, YAN Qun, GUO Xiangying

2021, 50(7): 1378-1385.

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Based on the finite element method, the band gap of the phononic crystal in single-sided cylinder local resonance was analyzed, and the influence of structural parameters on the phononic crystal was studied. The results show that the initial frequency of the first complete band gap decreases and the bandwidth increases with the increase of the height of the scatterer. With the increase of the thickness of the substrate, the initial frequency of the single-sided cylindrical phononic crystal increases gradually, the cut-off frequency first increases and then decreases. In addition, based on the classical single-sided cylindrical phononic crystal, two new ternary single-sided cylindrical phononic crystal structures are combined: embedded single-sided cylindrical phononic crystal (Hereinafter referred to as structure Ⅰ) and bonded single-sided cylindrical phononic crystal (Hereinafter referred to as structure Ⅱ). Through the analysis of the band gap characteristics, it is concluded that the two new structures have lower frequency band gap compared with the classical single-sided cylindrical phononic crystals, which is very beneficial for low-frequency vibration and noise reduction. The results of this paper will provide some theoretical guidance for practical engineering application.

Frequency Doubled/Tripled Dual Wavelength Laser Based on Cascaded PPMgLN Crystal

SUN Jie, CHEN Huaixi, ZHANG Xinbin, FENG Xinkai, LI Guangwei, LIANG Wanguo

2021, 50(7): 1386-1390.

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In this paper, a compact green and near-infrared two-color continuous wave laser source with emission wavelengths at 516 nm and 775 nm are demonstrated, respectively. A cascaded periodically poled Mg doped lithium niobate crystal is designed and fabricated for simultaneous conversion of second harmonic generation(SHG) and third harmonic generation(THG) of communication wavelength, the output of green and near-infrared laser can be obtained at the same temperature. By set up a single pass laser measurement system, 0.15 mW green light at 516 nm and 1.19 mW light at 775 nm are obtained with 2 W pump power and the crystal temperature is controlled at 30.8 ℃. The experimental results will provide an important case for compact dual wavelength collinear laser which pumped by a single laser.

Growth and Spectral Properties of Sm³⁺-Doped YAG and Y₃ScAl₄O₁₂ Single Crystal Fibers

XU Jie, SONG Qingsong, LIU Jian, DING Yuchong, LI Dongzhen, XU Xiaodong, XU Jun

2021, 50(7): 1391-1396.

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Sm³⁺-doped YAG and Y₃ScAl₄O₁₂ single crystal fibers were successfully grown by the micro-pulling-down (μ-PD) technique. X-ray diffraction test shows that the crystals are cubic phase structure, the lattice constants of Sm∶YAG and Sm∶Y₃ScAl₄O₁₂ single crystal fibers are calculated to be a=1.199 3 nm and a=1.200 0 nm, respectively. The Raman spectra, absorption spectra, fluorescence spectra and fluorescence lifetimes of the crystal fibers were measured at room temperature. The strong absorption band centered at 405 nm matches well the InGaN/GaN laser diode pumping. Under 404 nm excitation, the emission transition of ⁴G_5/2→⁶H_7/2 peaked at 618 nm appears to be strongest, and the fluorescence lifetime of the ⁴G_5/2 level of Sm³⁺-doped YAG and Y₃ScAl₄O₁₂ single crystal fibers are determined to be 1.86 ms and 1.83 ms, respectively. The experimental data shows that Sm∶YAG and Sm∶Y₃ScAl₄O₁₂ single crystal fibers are potential laser media in the red-orange wavelength range.

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