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 Select Semi-Ellipsoid Nanoarray for Angle-Independent Plasmonic Color Printing Jiancai Xue , Limin Lin , Zhang-Kai Zhou, and Xue-Hua Wang  Chin. Phys. Lett.    2020, 37 (11): 114201 .   DOI: 10.1088/0256-307X/37/11/114201 Abstract   HTML   PDF (1590KB) Employing a silver nano semi-ellipsoid nanoarray with high symmetry into applications in plasmonic color printing, we fulfill printing images with colors independent of observing angles. Also, by decreasing the period of a nano semi-ellipsoid array into deep-subwavelength scales, we obtain high reflectivity over 50%, promising high efficiency for imaging generations. A facile technique based on the transfer of anodized aluminum oxide template is developed to fabricate the silver nano semi-ellipsoid nanoarray, realizing plasmonic color printing with features of low cost, scalable, full color and high flexibility. Our approach provides a feasible way to address the angle-dependent issue in the previous practice of plasmonic color printing, and boosts this field on its way to real-world commercial applications.
 Select Generation of Intense Sub-10 fs Pulses at 385 nm Fan Xiao , Xiaohui Fan , Li Wang , Dongwen Zhang , Jianhua Wu , Xiaowei Wang, and Zengxiu Zhao Chin. Phys. Lett.    2020, 37 (11): 114202 .   DOI: 10.1088/0256-307X/37/11/114202 Abstract   HTML   PDF (1225KB) We demonstrated the generation and characterization of 9.7 fs, 180 μJ pulses centered at 385 nm via the frequency doubling of few-cycle near-infrared pulses. Both moderate conversion efficiency (9.5%) and broad phase matching bandwidth (20 nm) were achieved by shaping the spectra of the fundamental pulses. The strong intensity dependence of second-order harmonic generation and well controlled material dispersion ensured the inexistence of satellite pulses, which was confirmed by the self-diffraction frequency resolved optical gating measurement.
 Select Rapid Measurement and Control of Nitrogen-Vacancy Center-Axial Orientation in Diamond Particles Guobin Chen, Yang Hui, Junci Sun, Wenhao He, and Guanxiang Du Chin. Phys. Lett.    2020, 37 (11): 114203 .   DOI: 10.1088/0256-307X/37/11/114203 Abstract   HTML   PDF (905KB) Determination and control of nitrogen-vacancy (NV) centers play an important role in sensing the vector field by using their quantum information. To measure orientation of NV centers in a diamond particle attached to a tapered fiber rapidly, we propose a new method to establish the direction cosine matrix between the lab frame and the NV body frame. In this method, only four groups of the ODMR spectrum peaks shift data need to be collected, and the magnetic field along $\pm Z$ and $\pm Y$ in the lab frame is applied in the meantime. We can also control any NV axis to rotate to the $X$, $Y$, $Z$ axes in the lab frame according to the elements of this matrix. The demonstration of the DC and microwave magnetic field vector sensing is presented. Finally, the proposed method can help us to perform vector magnetic field sensing more conveniently and rapidly.
 Select Tunable Optical Bandpass Filter via a Microtip-Touched Tapered Optical Fiber Peng-Fei Zhang, Li-Jun Song, Chang-Lin Zou, Xin Wang, Chen-Xi Wang, Gang Li, and Tian-Cai Zhang Chin. Phys. Lett.    2020, 37 (10): 104201 .   DOI: 10.1088/0256-307X/37/10/104201 Abstract   HTML   PDF (1465KB) We demonstrate a tunable bandpass optical filter based on a tapered optical fiber (TOF) touched by a hemispherical microfiber tip (MFT). Other than the interference and selective material absorption effects, the filter relies on the controllable and wavelength-dependent mode–mode interactions in TOF. Experimentally, a large range of tunability is realized by controlling the position of the MFT in contact with the TOF for various TOF radii, and two distinct bandpass filter mechanisms are demonstrated. The center wavelength of the bandpass filter can be tuned from 890 nm to 1000 nm, while the FWHM bandwidth can be tuned from 110 nm to 240 nm when the MFT touches the TOF in the radius range from 160 nm to 390 nm. The distinction ratio can reach $28 \pm 3$ dB experimentally. The combined TOF-MFT is an in-line tunable bandpass optical filter that has great application potential in optical networks and spectroscopy, and the principle could also be generalized to other integrated photonic devices.
 Select A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids Qing Xi, Jinxin Zhong, Jixiong He, Xiangfan Xu, Tsuneyoshi Nakayama, Yuanyuan Wang, Jun Liu, Jun Zhou, and Baowen Li Chin. Phys. Lett.    2020, 37 (10): 104401 .   DOI: 10.1088/0256-307X/37/10/104401 Abstract   HTML   PDF (1069KB) The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time. There have been several approaches to explain the thermal conductivities in these systems, for example, Bridgman's formula for simple liquids, the concept of the minimum thermal conductivity for amorphous solids, and the thermal resistance network model for amorphous polymers. Here, we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way, and compare it with previous ones. The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data. Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems, but also resolves the discrepancies between existing formulae and experimental data.
 Select Novel Polarization Control Approach to Long-Term Fiber-Optic Frequency Transfer Dong-Jie Wang, Xiang Zhang, Jie Liu, Dong-Dong Jiao, Xue Deng, Jing Gao, Qi Zang, Dan Wang, Tao Liu, Rui-Fang Dong, and Shou-Gang Zhang Chin. Phys. Lett.    2020, 37 (9): 094201 .   DOI: 10.1088/0256-307X/37/9/094201 Abstract   HTML   PDF (913KB) We demonstrate a novel polarization control system based on a gradient descent algorithm, applied to a 450-km optical frequency transfer link. The power of the out-loop beat note is retrieved by controlling the polarization state of the transferred signal, with a recovery time of 24 ms, thereby ensuring the long-term evaluation of the fiber link. As a result, data utilization is enhanced from 70% to 99% over a continuous measurement period of $\sim$12 h. A fractional transfer instability of $7.2 \times 10^{-20}$ is achieved at an integration time of 10000 s. This work lays the foundation for the comparison of a remote optical clock system via a long-haul optical fiber link.
 Select Extended Nernst–Planck Equation Incorporating Partial Dehydration Effect Zhong Wang, Zhiyang Yuan, and Feng Liu Chin. Phys. Lett.    2020, 37 (9): 094701 .   DOI: 10.1088/0256-307X/37/9/094701 Abstract   HTML   PDF (880KB) Novel ionic transporting phenomena emerge as nanostructures approach the molecular scale. At the sub-2 nm scale, widely used continuum equations, such as the Nernst–Planck equation, break down. Here, we extend the Nernst–Planck equation by adding a partial dehydration effect. Our model agrees with the reported ion fluxes through graphene oxide laminates with sub-2 nm interlayer spacing, outperforming previous models. We also predict that the selectivity sequences of alkali metal ions depend on the geometries of the nanostructures. Our model opens a new avenue for the investigation of the underlying mechanisms in nanofluidics at the sub-2 nm scale.
 Select Electro-Optically Switchable Optical True Delay Lines of Meter-Scale Lengths Fabricated on Lithium Niobate on Insulator Using Photolithography Assisted Chemo-Mechanical Etching Jun-xia Zhou, Ren-hong Gao, Jintian Lin, Min Wang, Wei Chu, Wen-bo Li, Di-feng Yin, Li Deng, Zhi-wei Fang, Jian-hao Zhang, Rong-bo Wuand Ya Cheng Chin. Phys. Lett.    2020, 37 (8): 084201 .   DOI: 10.1088/0256-307X/37/8/084201 Abstract   HTML   PDF (1221KB) Optical true delay lines (OTDLs) of low propagation losses, small footprints and high tuning speeds and efficiencies are of critical importance for various photonic applications. Here, we report fabrication of electro-optically switchable OTDLs on lithium niobate on insulator using photolithography assisted chemo-mechanical etching. Our device consists of several low-loss optical waveguides of different lengths which are consecutively connected by electro-optical switches to generate different amounts of time delay. The fabricated OTLDs show an ultra-low propagation loss of $\sim 0.03$ dB/cm for waveguide lengths well above 100 cm.
 Select Multi-Core Conformal Lenses Xinghong Zhu, Pengfei Zhao, and Huanyang Chen Chin. Phys. Lett.    2020, 37 (8): 084202 .   DOI: 10.1088/0256-307X/37/8/084202 Abstract   HTML   PDF (1320KB) We propose multi-core conformal lenses by combining conformal transformation optics with absolute instruments. Depending on the cores and incident angles, the conformal lenses have tunable functionalities like focusing, reflection, and transparency, thereby providing a feasible general method for designing multi-functional devices.
 Select Photon Coalescence in a Lossy Non-Hermitian Beam Splitter Zhiqiang Ren , Rong Wen , and J. F. Chen Chin. Phys. Lett.    2020, 37 (8): 084203 .   DOI: 10.1088/0256-307X/37/8/084203 Abstract   HTML   PDF (530KB) We investigate photon coalescence in a lossy non-Hermitian system and study a dynamic device modeled by a beam splitter with an extra intrinsic phase term added in the transformation matrix, with which the device is a lossy non-Hermitian linear system. The two-photon interference behavior is altered accordingly since this extra intrinsic phase affects the unitary of transformation and the coalescence of the incoming photons. We calculate the coincidence between two single-photon pulses, considering the interferometric phase between two pulses and the extra intrinsic phase as the tunable parameters. The extra phase turns the famous Hong–Ou–Mandel dip into a bump, with the visibility dependent on both the interferometric phase and the extra phase.
 Select Direct Spatially Resolved Snapshot Interferometric Phase and Stokes Vector Extraction by Using an Imaging PolarCam Dahi Ibrahim and Daesuk Kim Chin. Phys. Lett.    2020, 37 (7): 074201 .   DOI: 10.1088/0256-307X/37/7/074201 Abstract   HTML   PDF (977KB) We extract the 3D phase $\varDelta$ and the Stokes parameter $S_{3}$ of a transmissive anisotropic object spatially using an interferometric PolarCam. Four parallel interferograms with a phase shift of $\pi$/2 between the images are captured in a single snapshot and then reconstructed by the four-bucket algorithm to extract the 3D phase of the object. The $S_{3}$ is then calculated directly from the obtained 3D phase $\varDelta$. The extracted results of $\varDelta$ and $S_{3}$ were compared with those extracted from the non-interferometric PolarCam and the Thorlabs polarimeter, and the results match quite well. The merit of using the interferometric PolarCam is that no mechanical movement mechanisms are included, and hence the $\varDelta$ and $S_{3}$ of the object can be extracted, with high accuracy and within a part of a second (three times faster than non-interferometric PolarCam and Thorlabs polarimeter methods). Moreover, this method can be applied in the field of the dynamic spectro–interferometric PolarCam and can be implemented using swept-wavelength approaches.
 Select An Experimental Approach for Detection of the Acoustic Radiation Induced Static Component in Solids Ming-Xi Deng Chin. Phys. Lett.    2020, 37 (7): 074301 .   DOI: 10.1088/0256-307X/37/7/074301 Abstract   HTML   PDF (1452KB) We propose an experimental approach to directly detect the acoustic radiation induced static component (SC) of primary longitudinal (L) wave propagation in solids using an ultrasonic pitch-catch technique, where a low-frequency ultrasonic transducer is used to detect the SC generated by the co-propagating primary L-wave tone burst that is excited by a high-frequency ultrasonic transducer. Essentially, the experimental approach proposed uses a dynamic method to detect the SC generated. The basic requirement is that the central frequency of the low-frequency ultrasonic transducer needs to be near the center of the main lobe frequency range of the time-domain envelope of the primary L-wave tone burst. Under this condition, the main lobe of the frequency spectrum of the SC pulse generated adequately overlaps with that of the low-frequency ultrasonic transducer. This will enable the generated SC pulse to be directly detected by the low-frequency ultrasonic transducer. The performed experimental examination validates the feasibility and effectiveness of the proposed approach for direct detection of the acoustic radiation induced SC generated by L-wave propagation in solids.
 Select Higher-Order Topological Spin Hall Effect of Sound Zhi-Kang Lin, Shi-Qiao Wu, Hai-Xiao Wang, and Jian-Hua Jiang Chin. Phys. Lett.    2020, 37 (7): 074302 .   DOI: 10.1088/0256-307X/37/7/074302 Abstract   HTML   PDF (4768KB) We theoretically propose a reconfigurable two-dimensional (2D) hexagonal sonic crystal with higher-order topology protected by the six-fold, $C_{6}$, rotation symmetry. The acoustic band gap and band topology can be controlled by rotating the triangular scatterers in each unit cell. In the nontrivial phase, the sonic crystal realizes the topological spin Hall effect in a higher-order fashion: (i) the edge states emerging in the bulk band gap exhibit partial spin-momentum correlation and are gapped due to the reduced spatial symmetry at the edges. (ii) The gapped edge states, on the other hand, stabilize the topological corner states emerging in the edge band gap. The partial spin-momentum correlation is manifested as pseudo-spin-polarization of edge states away from the time-reversal invariant momenta, where the pseudospin is emulated by the acoustic orbital angular momentum. We reveal the underlying topological mechanism using a corner topological index based on the symmetry representation of the acoustic Bloch bands.
 Select Head-on Collision of Solitary Waves Described by the Toda Lattice Model in Granular Chain Qianqian Wu, Xingyi Liu, Tengfei Jiao, Surajit Sen, and Decai Huang Chin. Phys. Lett.    2020, 37 (7): 074501 .   DOI: 10.1088/0256-307X/37/7/074501 Abstract   HTML   PDF (580KB) We study the head-on collision of two solitary waves in a precompressed granular chain using the discrete element method. Our study takes the Toda chain solution as the initial condition for the simulations. The simulation covers the dynamical evolution of the collision process from the start of the incident wave to the end of the collision. The interaction has a central collision region of about five-grain width in which two solitary waves merge completely and share only one peak. Four stages, i.e., the pre-in-phase traveling stage, lag-phase collision state, lead-phase collision state, and post-in-phase traveling stage, are identified to describe the complex collision processes. Our results may be helpful for explaining the existence of long-lived solitary waves seen in the simulations by Takato and Sen [Europhys. Lett. 100 (2012) 24003].
 Select Evolution of Energy in Submerged Granular Column Collapse Wen-Tao Zhang, Yi An, Qing-Quan Liu, Xiao-Liang Wang, and Yun-Hui Sun Chin. Phys. Lett.    2020, 37 (7): 074502 .   DOI: 10.1088/0256-307X/37/7/074502 Abstract   HTML   PDF (634KB) The evolution of energy in subaerial and subaqueous granular column collapses is studied. Employing the refractive index matching method and planar laser-induced fluorescence technique, we obtain granular and liquid images simultaneously in a single experiment of subaqueous flow. Particle image velocimetry and particle tracking velocimetry are used to process the data for the fluid and granular phase. We find stepwise decreases in the total kinetic energy of the granular material. The stage of rapidly falling energy corresponds to large transverse changes in the direction of the massive granular particles. Moreover, in this stage, a major fraction of the granular kinetic energy transferred from the granular potential energy is lost or transferred. Interestingly, compared with dry granular flow, the existence of an ambient liquid seems to reduce the total dissipated energy, which may be the reason why previous studies observed similar granular runout distances in subaqueous and dry granular collapses.
 Select Transverse Propagation Characteristics and Coherent Effect of Gaussian Beams Fei Xiang, Lin Zhang, Tao Chen, Yuan-Hong Zhong, Jin Li Chin. Phys. Lett.    2020, 37 (6): 064101 .   DOI: 10.1088/0256-307X/37/6/064101