Open Access Published by De Gruyter

Volume 10 Issue 3

February 2021

Issue of Nanophotonics

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Contents
Journal Overview

Reviews

Open Access November 24, 2020

Recent progress of dynamic mode manipulation via acousto-optic interactions in few-mode fiber lasers: mechanism, device and applications

Jiafeng Lu, Fan Shi, Jiangtao Xu, Linghao Meng, Longkun Zhang, Peikang Cheng, Xuan Zhou, Fufei Pang, Xianglong Zeng

Page range: 983-1010

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Abstract

The burgeoning advances of spatial mode conversion in few-mode fibers emerge as the investigative hotspot in novel structured light manipulation, in that, high-order modes possess a novel fundamental signature of various intensity profiles and unique polarization distributions, especially orbital angular momentum modes carrying with phase singularity and spiral wave front. Thus, control of spatial mode generation becomes a crucial technique especially in fiber optics, which has been exploited to high capacity space division multiplexing. The acousto-optic interactions in few-mode fibers provide a potential solution to tackle the bottleneck of traditional spatial mode conversion devices. Acousto-optic mode conversion controlled by microwave signals brings tremendous new opportunities in spatial mode generation with fast mode tuning and dynamic switching capabilities. Besides, dynamic mode switching induced by acousto-optic effects contributes an energy modulation inside a laser cavity through nonlinear effects of multi-mode interaction, competition, which endows the fiber laser with new functions and leads to the exploration of new physical mechanism. In this review, we present the recent advances of controlling mode switch and generation employing acousto-optic interactions in few-mode fibers, which includes acousto-optic mechanisms, optical field manipulating devices and novel applications of spatial mode control especially in high-order mode fiber lasers.

Open Access December 18, 2020

Digital nanophotonics: the highway to the integration of subwavelength-scale photonics

Ultra-compact, multi-function nanophotonic design based on computational inverse design

Jie Huang, Hansi Ma, Dingbo Chen, Huan Yuan, Jinping Zhang, Zikang Li, Jingmin Han, Jiagui Wu, Junbo Yang

Page range: 1011-1030

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Abstract

Nanophotonic devices with high densities are extremely attractive because they can potentially merge photonics and electronics at the nanoscale. However, traditional integrated photonic circuits are designed primarily by manually selecting parameters or employing semi-analytical models. Limited by the small parameter search space, the designed nanophotonic devices generally have a single function, and the footprints reach hundreds of microns. Recently, novel ultra-compact nanophotonic devices with digital structures were proposed. By applying inverse design algorithms, which can search the full parameter space, the proposed devices show extremely compact footprints of a few microns. The results from many groups imply that digital nanophotonics can achieve not only ultra-compact single-function devices but also miniaturized multi-function devices and complex functions such as artificial intelligence operations at the nanoscale. Furthermore, to balance the performance and fabrication tolerances of such devices, researchers have developed various solutions, such as adding regularization constraints to digital structures. We believe that with the rapid development of inverse design algorithms and continuous improvements to the nanofabrication process, digital nanophotonics will play a key role in promoting the performance of nanophotonic integration. In this review, we uncover the exciting developments and challenges in this field, analyse and explore potential solutions to these challenges and provide comments on future directions in this field.

Open Access November 19, 2020

Engineering photonic environments for two-dimensional materials

Xuezhi Ma, Nathan Youngblood, Xiaoze Liu, Yan Cheng, Preston Cunha, Kaushik Kudtarkar, Xiaomu Wang, Shoufeng Lan

Page range: 1031-1058

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Abstract

A fascinating photonic platform with a small device scale, fast operating speed, as well as low energy consumption is two-dimensional (2D) materials, thanks to their in-plane crystalline structures and out-of-plane quantum confinement. The key to further advancement in this research field is the ability to modify the optical properties of the 2D materials. The modifications typically come from the materials themselves, for example, altering their chemical compositions. This article reviews a comparably less explored but promising means, through engineering the photonic surroundings. Rather than modifying materials themselves, this means manipulates the dielectric and metallic environments, both uniform and nanostructured, that directly interact with the materials. For 2D materials that are only one or a few atoms thick, the interaction with the environment can be remarkably efficient. This review summarizes the three degrees of freedom of this interaction: weak coupling, strong coupling, and multifunctionality. In addition, it reviews a relatively timing concept of engineering that directly applied to the 2D materials by patterning. Benefiting from the burgeoning development of nanophotonics, the engineering of photonic environments provides a versatile and creative methodology of reshaping light–matter interaction in 2D materials.

Open Access December 8, 2020

Silicon–germanium receivers for short-wave-infrared optoelectronics and communications

High-speed silicon–germanium receivers (invited review)

Daniel Benedikovic, Léopold Virot, Guy Aubin, Jean-Michel Hartmann, Farah Amar, Xavier Le Roux, Carlos Alonso-Ramos, Éric Cassan, Delphine Marris-Morini, Jean-Marc Fédéli, Frédéric Boeuf, Bertrand Szelag, Laurent Vivien

Page range: 1059-1079

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Abstract

Integrated silicon nanophotonics has rapidly established itself as intriguing research field, whose outlets impact numerous facets of daily life. Indeed, nanophotonics has propelled many advances in optoelectronics, information and communication technologies, sensing and energy, to name a few. Silicon nanophotonics aims to deliver compact and high-performance components based on semiconductor chips leveraging mature fabrication routines already developed within the modern microelectronics. However, the silicon indirect bandgap, the centrosymmetric nature of its lattice and its wide transparency window across optical telecommunication wavebands hamper the realization of essential functionalities, including efficient light generation/amplification, fast electro-optical modulation, and reliable photodetection. Germanium, a well-established complement material in silicon chip industry, has a quasi-direct energy band structure in this wavelength domain. Germanium and its alloys are thus the most suitable candidates for active functions, i.e. bringing them to close to the silicon family of nanophotonic devices. Along with recent advances in silicon–germanium-based lasers and modulators, short-wave-infrared receivers are also key photonic chip elements to tackle cost, speed and energy consumption challenges of exponentially growing data traffics within next-generation systems and networks. Herein, we provide a detailed overview on the latest development in nanophotonic receivers based on silicon and germanium, including material processing, integration and diversity of device designs and arrangements. Our Review also emphasizes surging applications in optoelectronics and communications and concludes with challenges and perspectives potentially encountered in the foreseeable future.

Research Articles

Open Access December 17, 2020

High-efficiency and high-speed germanium photodetector enabled by multiresonant photonic crystal

Jinwen Song, Shuai Yuan, Chengcong Cui, Yuxi Wang, Zhiyong Li, Alan X. Wang, Cheng Zeng, Jinsong Xia

Page range: 1081-1087

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Abstract

High-efficiency and high-speed photodetectors with broadband responses are playing pivotal roles for wavelength-division multiplexing optical communications. Germanium photodetectors on silicon platforms exhibit potential cost advantage due to the compatibility for monolithic integration with silicon-based electronic circuits for signal amplification and processing. In this article, we report a normal incidence, germanium photodetector enabled by guided-mode resonances in photonic crystal, which successfully resolved the compromise between quantum efficiency, wavelength coverage and bandwidth requirement, a drawback usually faced by conventional photodetectors operating at normal incidence. The resonant photonic crystal structure is designed to support multiple resonances in the target wavelength range. With an intrinsic absorption layer thickness of 350 nm, the device achieved a high external quantum efficiency of 50% at 1550 nm, along with an enhancement around 300% for the entire C-band. Using a mesa diameter of 14 μm, the fabricated device exhibited a 3-dB bandwidth of 33 GHz and obtained clear eye diagrams at bit rate up to 56 Gbps. This work provides a promising method to design high-efficiency, high-speed, normal incidence germanium photodetectors for optical interconnect systems.

Open Access December 17, 2020

Nanoscale confinement of energy deposition in glass by double ultrafast Bessel pulses

Jesus del Hoyo, Remi Meyer, Luca Furfaro, Francois Courvoisier

Page range: 1089-1097

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Abstract

Ultrafast laser pulses spatially shaped as Bessel beams in dielectrics create high aspect ratio plasma channels whose relaxation can lead to the formation of nanochannels. We report a strong enhancement of the nanochannel drilling efficiency with illumination by double pulses separated by a delay between 10 and 500 ps. This enables the formation of nanochannels with diameters down to 100 nm. Experimental absorption measurements demonstrate that the increase of drilling efficiency is due to an increase of the confinement of the energy deposition. Nanochannel formation corresponds to a drastic change in absorption of the second pulse, demonstrating the occurrence of a phase change produced by the first pulse. This creates a highly absorbing, long-living state. Our measurements show that it is compatible with the semi-metallization of warm dense glass which takes place within a timescale of <10 ps after the first laser pulse illumination.

Open Access December 18, 2020

Far-field optical imaging of surface plasmons with a subdiffraction limited separation

Yifeng Xiang, Junxue Chen, Xi Tang, Ruxue Wang, Qiwen Zhan, Joseph R. Lakowicz, Douguo Zhang

Page range: 1099-1106

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Abstract

When an ultrathin silver nanowire with a diameter less than 100 nm is placed on a photonic band gap structure, surface plasmons can be excited and propagate along two side-walls of the silver nanowire. Although the diameter of the silver nanowire is far below the diffraction limit, two bright lines can be clearly observed at the image plane by a standard wide-field optical microscope. Simulations suggest that the two bright lines in the far-field are caused by the unique phase distribution of plasmons on the two side-walls of the silver nanowire. Combining with the sensing ability of surface plasmons to its environment, the configuration reported in this work is capable of functioning as a sensing platform to monitor environmental changes in the near-field region of this ultrathin nanowire.

Open Access December 14, 2020

Double moiré localized plasmon structured illumination microscopy

Ruslan Röhrich, A. Femius Koenderink

Page range: 1107-1121

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Abstract

Structured illumination microscopy (SIM) is a well-established fluorescence imaging technique, which can increase spatial resolution by up to a factor of two. This article reports on a new way to extend the capabilities of structured illumination microscopy, by combining ideas from the fields of illumination engineering and nanophotonics. In this technique, plasmonic arrays of hexagonal symmetry are illuminated by two obliquely incident beams originating from a single laser. The resulting interference between the light grating and plasmonic grating creates a wide range of spatial frequencies above the microscope passband, while still preserving the spatial frequencies of regular SIM. To systematically investigate this technique and to contrast it with regular SIM and localized plasmon SIM, we implement a rigorous simulation procedure, which simulates the near-field illumination of the plasmonic grating and uses it in the subsequent forward imaging model. The inverse problem, of obtaining a super-resolution (SR) image from multiple low-resolution images, is solved using a numerical reconstruction algorithm while the obtained resolution is quantitatively assessed. The results point at the possibility of resolution enhancements beyond regular SIM, which rapidly vanishes with the height above the grating. In an initial experimental realization, the existence of the expected spatial frequencies is shown and the performance of compatible reconstruction approaches is compared. Finally, we discuss the obstacles of experimental implementations that would need to be overcome for artifact-free SR imaging.

Open Access December 14, 2020

Achromatic terahertz Airy beam generation with dielectric metasurfaces

Qingqing Cheng, Juncheng Wang, Ling Ma, Zhixiong Shen, Jing Zhang, Xiaoying Zheng, Tao Chen, Ye Yu, Dong Yu, Qiong He, Wei Hu, Tao Li, Songlin Zhuang, Lei Zhou

Page range: 1123-1131

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Abstract

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

Open Access January 5, 2021

Multiplexed supercell metasurface design and optimization with tandem residual networks

Christopher Yeung, Ju-Ming Tsai, Brian King, Benjamin Pham, David Ho, Julia Liang, Mark W. Knight, Aaswath P. Raman

Page range: 1133-1143

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Abstract

Complex nanophotonic structures hold the potential to deliver exquisitely tailored optical responses for a range of applications. Metal–insulator–metal (MIM) metasurfaces arranged in supercells, for instance, can be tailored by geometry and material choice to exhibit a variety of absorption properties and resonant wavelengths. With this flexibility, however, comes a vast space of design possibilities that classical design paradigms struggle to effectively navigate. To overcome this challenge, here, we demonstrate a tandem residual network approach to efficiently generate multiplexed supercells through inverse design. By using a training dataset with several thousand full-wave electromagnetic simulations in a design space of over three trillion possible designs, the deep learning model can accurately generate a wide range of complex supercell designs given a spectral target. Beyond inverse design, the presented approach can also be used to explore the structure–property relationships of broadband absorption and emission in such supercell configurations. Thus, this study demonstrates the feasibility of high-dimensional supercell inverse design with deep neural networks, which is applicable to complex nanophotonic structures composed of multiple subunit elements that exhibit coupling.

Open Access December 14, 2020

Directional launching of surface plasmon polaritons by electrically driven aperiodic groove array reflectors

Yuanhai Lin, Thanh Xuan Hoang, Hong-Son Chu, Christian A. Nijhuis

Page range: 1145-1154

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Abstract

Access to surface plasmon polaritons (SPPs) with directional control excited by electrical means is important for applications in (on-chip) nano-optoelectronic devices and to circumvent limitations inherent to approaches where SPPs are excited by optical means (e.g., diffraction limit). This paper describes directional excitation of surface plasmon polaritons propagating along a plasmonic strip waveguide integrated with an aperiodic groove array electrically driven by an Al–Al 2 O 3 –Au tunnel junction. The aperiodic groove array consists of six grooves and is optimized to specifically reflect the SPPs by 180° in the desired direction (+ x or − x ) along the plasmonic strip waveguide. We used constrained nonlinear optimization of the groove array based on the sequential quadratic programming algorithms coupled with finite-difference time-domain (FDTD) simulations to achieve the optimal structures. Leakage radiation microscopy (Fourier and real plane imaging) shows that the propagation direction of selectively only one SPP mode (propagating along the metal–substrate interface) is controlled. In our experiments, we achieved a directionality (i.e., + x /− x ratio) of close to 8, and all of our experimental findings are supported by detailed theoretical simulations.

Open Access December 18, 2020

Expedited circular dichroism prediction and engineering in two-dimensional diffractive chiral metamaterials leveraging a powerful model-agnostic data enhancement algorithm

Shiyin Du, Jie You, Jun Zhang, Zilong Tao, Hao Hao, Yuhua Tang, Xin Zheng, Tian Jiang

Page range: 1155-1168

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Abstract

A model-agnostic data enhancement (MADE) algorithm is proposed to comprehensively investigate the circular dichroism (CD) properties in the higher-order diffracted patterns of two-dimensional (2D) chiral metamaterials possessing different parameters. A remarkable feature of MADE algorithm is that it leverages substantially less data from a target problem and some training data from another already solved topic to generate a domain adaptation dataset, which is then used for model training at no expense of abundant computational resources. Specifically, nine differently shaped 2D chiral metamaterials with different unit period and one special sample containing multiple chiral parameters are both studied utilizing the MADE algorithm where three machine learning models (i.e, artificial neural network, random forest regression, support vector regression) are applied. The conventional rigorous coupled wave analysis approach is adopted to capture CD responses of these metamaterials and then assist the training of MADE, while the additional training data are obtained from our previous work. Significant evaluations regarding optical chirality in 2D metamaterials possessing various shape, unit period, width, bridge length, and separation length are performed in a fast, accurate, and data-friendly manner. The MADE framework introduced in this work is extremely important for the large-scale, efficient design of 2D diffractive metamaterials and more advanced photonic devices.

Open Access December 4, 2020

Interface-induced field-like optical spin torque in a ferromagnet/heavy metal heterostructure

Satoshi Iihama, Kazuaki Ishibashi, Shigemi Mizukami

Page range: 1169-1176

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Abstract

The manipulation of magnetization in a metallic ferromagnet by using optical helicity has been much attracted attention for future opto-spintronic devices. The optical helicity–induced torques on the magnetization, optical spin torque , have been observed in ferromagnetic thin films recently. However, the interfacial effect of the optical spin torque in ferromagnet/nonmagnetic heavy metal heterostructures have not been addressed so far, which are widely utilized to efficiently control magnetization via electrical means. Here, we studied optical spin torque vectors in the ferromagnet/nonmagnetic heavy metal heterostructures and observed that in-plane field-like optical spin torque was significantly increased with decreasing ferromagnetic layer thicknesses. The interfacial field-like optical spin torque was explained by the optical Rashba–Edelstein effect caused by the structural inversion symmetry breaking. This work will aid in the efficient optical manipulation of thin film nanomagnets using optical helicity.

Open Access December 23, 2020

End-to-end nanophotonic inverse design for imaging and polarimetry

Zin Lin, Charles Roques-Carmes, Raphaël Pestourie, Marin Soljačić, Arka Majumdar, Steven G. Johnson

Page range: 1177-1187

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Abstract

By codesigning a metaoptical front end in conjunction with an image-processing back end, we demonstrate noise sensitivity and compactness substantially superior to either an optics-only or a computation-only approach, illustrated by two examples: subwavelength imaging and reconstruction of the full polarization coherence matrices of multiple light sources. Our end-to-end inverse designs couple the solution of the full Maxwell equations—exploiting all aspects of wave physics arising in subwavelength scatterers—with inverse-scattering algorithms in a single large-scale optimization involving ≳104$\gtrsim {10}^{4}$ degrees of freedom. The resulting structures scatter light in a way that is radically different from either a conventional lens or a random microstructure, and suppress the noise sensitivity of the inverse-scattering computation by several orders of magnitude. Incorporating the full wave physics is especially crucial for detecting spectral and polarization information that is discarded by geometric optics and scalar diffraction theory.

Open Access December 4, 2020

Significantly enhanced second-harmonic generations with all-dielectric antenna array working in the quasi-bound states in the continuum and excited by linearly polarized plane waves

Zhanghua Han, Fei Ding, Yangjian Cai, Uriel Levy

Page range: 1189-1196

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Abstract

The recently emerging all-dielectric optical nanoantennas based on high-index semiconductors have proven to be an effective and low-loss alternative to metal-based plasmonic structures for light control and manipulations of light–matter interactions. Nonlinear optical effects have been widely investigated to employ the enhanced interactions between incident light and the dielectrics at the Mie-type resonances, and in particular magnetic dipole resonances, which are supported by the semiconductor. In this paper, we explore the novel phenomenon of bound states in the continuum supported by high-index semiconductor nanostructures. By carefully designing an array of nanodisk structures with an inner air slot as the defect, we show that a novel high quality-factor resonance achieved based on the concept of bound state in the continuum can be easily excited by the simplest linearly polarized plane wave at normal incidence. This resonance further enhances the interactions between light and semiconductors and boosts the nonlinear effects. Using AlGaAs as the nonlinear material, we demonstrate a significant increase in the second-harmonic generation efficiency, up to six orders of magnitude higher than that achieved by magnetic dipole resonances. In particular, a second-harmonic generation efficiency around 10% can be numerically achieved at a moderate incident pump intensity of 5 MW/cm 2 .

About this journal

Nanophotonics covers recent international research results, specific developments in the field and novel applications and is published in partnership with Sciencewise. It belongs to the top journals in the field. Nanophotonics focuses on the interaction of photons with nano-structures, such as carbon nano-tubes, nano metal particles, nano crystals, semiconductor nano dots, photonic crystals, tissue and DNA. The journal covers the latest developments for physicists, engineers and material scientists, working in fields related to:

Plasmonics: metallic nanostructures and their optical properties
Meta materials, fundamentals and applications
Nanophotonic concepts and devices for solar energy harvesting and conversion
Near-field optical microscopy
Nanowaveguides and devices
Nano Lasers
Nanostructures, nanoparticles, nanotubes, nanowires, nanofibers
Photonic crystals
Integrated silicon photonics
Semiconductor quantum dots
Quantum optics & Quantum information
Ultrafast and nonlinear pulse propagation in nano materials and structures
Light-matter interaction, optical manipulation techniques
Nano-biophotonics
Optofluidics
Optomechanics
System applications based on nanophotonic devices
Nanofabrication techniques, thin film processing, self-assembly

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Publication Metrics

Average time from submission to initial Editorial Manager assessment: 5 days
Average time from submission to final decision (all article types): 57 days
Average time from acceptance to publication: 13 days

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Early Career Award 2023

The Early Career Award for 2023 is now open and welcoming nominations!

Do you know someone who has made an outstanding contribution to the field of nanophotonics? Nominate them for the Nanophotonics Early Career Award! This prestigious award recognizes four early career scientists annually for their accomplishments. Help them gain the recognition they deserve by submitting a nomination.

The award winners are awarded a prize of 1000 EUR and a waiver for publishing in Nanophotonics without charge.
Visit the award webpage for more information on the award, the criteria, and how to submit your nomination.
This award is fully sponsored by the Nanophotonics journal.

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Celebrating Young Scientists at Conferences

Nanophotonics supports young scientists through the sponsorship of poster awards at global conferences, recognizing the work of over 50 researchers every year. Please visit the winners' gallery to view their accomplishments.

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Special/Topical Issues

Published in 2023:

Quantum Nanophotonics (Guest Editors: Jaehyuck Jang, Minsu Jeong, and Junsuk Rho)
Neural network learning with photonics and for photonic circuit design (Guest Editors: Daniel Brunner, Miguel C. Soriano, and Shanhui Fan)
Nanofabrication (Guest Editors: Maria Farsari, Sang-Hyun Oh, and Joel Yang) 　
Metamaterials and Plasmonics in Asia (Guest Editors: Lei Zhou, JeongWeon Wu, Q-Han Park, Namkyoo Park and Teruya Ishihara)
Nanophotonics in support of Ukrainian Scientists (Guest Editors: Nader Engheta and Nikolay Zheludev; Publishing Editor: Dennis Couwenberg)

Published in 2022:

Photonic Angular Momentum (Guest Editors: Andrew Forbes, Qiwen Zhan and Siddharth Ramachandran)
New Trends in Nanophotonics and Advanced Photonic Materials (Guest Editor: Junsuk Rho)
Metamaterials and Plasmonics in Asia (Guest Editors: Lei Zhou, Tiejun Cui, JeongWeon Wu and Teruya Ishihara)
Tunable Nanophotonics (Guest Editors: Juejun Hu, Arseniy I. Kuznetsov, Volker J. Sorger, and Isabelle Staude)
Novel Two-Dimensional Materials Based Bio-Nanophotonic (Guest Editors: Hans Ågren, Jong Seung Kim and Han Zhang)

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Highly cited articles:

Polariton panorama
by D. N. Basov, Ana Asenjo-Garcia, P. James Schuck, Xiaoyang Zhu, Angel Rubio

Ultrasensitive terahertz sensing with high-Q toroidal dipole resonance governed by bound states in the continuum in all-dielectric metasurface
by Yulin Wang, Zhanghua Han, Yong Du, Jianyuan Qin

Non-Hermitian and topological photonics: optics at an exceptional point
by Midya Parto, Yuzhou G. N. Liu, Babak Bahari, Mercedeh Khajavikhan, Demetrios N. Christodoulides

Metasurfaces for biomedical applications: imaging and sensing from a nanophotonics perspective
by Shuyan Zhang, Chi Lok Wong, Shuwen Zeng, Renzhe Bi, Kolvyn Tai, Kishan Dholakia, Malini Olivo

THz spintronic emitters: a review on achievements and future challenges
by Evangelos Th. Papaioannou and René Beigang

Machine learning–assisted global optimization of photonic devices
by Zhaxylyk A. Kudyshev, Alexander V. Kildishev, Vladimir M. Shalaev, Alexandra Boltasseva

Topological photonics: Where do we go from here?
by Mordechai Segev, Miguel A. Bandres

Highly ordered arrays of hat-shaped hierarchical nanostructures with different curvatures for sensitive SERS and plasmon-driven catalysis
by Chao Zhang, Zhaoxiang Li, Si Qiu, Weixi Lu, Mingrui Shao, Chang Ji, Guangcan Wang, Xiaofei Zhao, Jing Yu and Zhen Li

Review on fractional vortex beam
by Hao Zhang, Jun Zeng, Xingyuan Lu, Zhuoyi Wang, Chengliang Zhao and Yangjian Cai

Orbital angular momentum and beyond in free-space optical communications
by Jian Wang, Jun Liu, Shuhui Li, Yifan Zhao, Jing Du and Long Zhu