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    Vol. 12 Issue 8 2023

      News & Views

    • Ting-Hui Xiao,Yuqi Zhou,Keisuke Goda
      Vol. 12, Issue 8, Pages: 1439-1440(2023) DOI: 10.1038/s41377-023-01199-y
      Abstract:In-silico clearing enables deep optical imaging of biological samples by correcting image blur caused by scattering and aberration. This breakthrough method offers researchers unprecedented insights into three-dimensional biological systems, with enormous potential for advancing biology and medicine to better understand living organisms and human health.  
        
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    • Tian Yang
      Vol. 12, Issue 8, Pages: 1441-1443(2023) DOI: 10.1038/s41377-023-01203-5
      Abstract:Fabrication of optical fiber tapers is realized with a combination of plasmonic microheaters and specially designed structural bending of optical fibers, which provide the necessary elements of “heat and pull”. The resultant compactness and flame-free condition enable monitoring of the tapering process inside a scanning electron microscope.  
        
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    • Kuen Yao Lau,Jianrong Qiu
      Vol. 12, Issue 8, Pages: 1444-1445(2023) DOI: 10.1038/s41377-023-01210-6
      Abstract:Sensors based on graphene materials have promising applications in the fields of biology, medicine and environment etc. A laser-scribed graphene provides a versatile, low-cost, and environmental friendly method for stress, bio, gas, temperature, humidity and multifunctional integrated sensors.  
        
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    • Zhihui Yan,Xiaojun Jia
      Vol. 12, Issue 8, Pages: 1446-1448(2023) DOI: 10.1038/s41377-023-01216-0
      Abstract:Quantum teleportation has been developed to simultaneously realize the Hertz rate and the 64-km distance through fiber channels, which is essential to real-world application of quantum network.  
        
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    • Peixia Zheng,Xuan Zhang,Hong-Chao Liu
      Vol. 12, Issue 8, Pages: 1449-1451(2023) DOI: 10.1038/s41377-023-01217-z
      Abstract:A multi-foci metalens and a leaky-mode microtaper provide innovative platforms to achieve high-resolution, wideband light spectra in millimeter-sized devices, thereby paving new ways for the commercialization of on-fingertip spectrometers.  
        
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    • Changyuan Yu,Zhi Cheng,Jiaqi Qu
      Vol. 12, Issue 8, Pages: 1452-1453(2023) DOI: 10.1038/s41377-023-01222-2
      Abstract:The remarkable capacity of metasurfaces to exert precise control over the propagation of light has ushered in a realm of unprecedented possibilities for “Lab-on-fiber”, and in this work, showcased real-time full-color imaging in a meta-optical fiber endoscope.  
        
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    • Jiawen Liu,Laurent Coolen
      Vol. 12, Issue 8, Pages: 1454-1456(2023) DOI: 10.1038/s41377-023-01227-x
      Abstract:An extensive analysis of biexciton luminescence in high-quality, large perovskite CsPbBr3 nanocrystals shows how the biexciton Auger decay rate deviates from the “universal” volume scaling as the exciton confinement becomes weaker.  
        
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    • Xiao Lin,Hongsheng Chen
      Vol. 12, Issue 8, Pages: 1457-1458(2023) DOI: 10.1038/s41377-023-01221-3
      Abstract:The van der Waals heterostructures with aperiodic stackings have been exploited to shape the spatiotemporal wavefront of free-electron X-ray radiation.  
        
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      Light People

    • Yating Wan,Chenzi Guo
      Vol. 12, Issue 8, Pages: 1459-1466(2023) DOI: 10.1038/s41377-023-01192-5
      Abstract:As part of our Light People series, we are delighted to have invited Prof. Evelyn Hu, a highly accomplished scientist from Harvard University, to share with us her personal journey. Prof. Hu's remarkable contributions in both academia and industry have taken her from industry giants to academia's most prestigious institutions, traversing various research frontiers that have played a critical role in the ongoing digital revolution. Through this interview, we aim to offer the Light community valuable insights into nanophotonics, quantum engineering, and Prof. Hu's research methodology and life philosophy, while also celebrating her outstanding achievements as a female role model. Ultimately, our goal is to inspire more women to pursue careers in this important and rapidly expanding field, which has a profound impact on all sectors of society. The following is a summary of an interview with Professor Evelyn Hu, available in the Supplementary Information.  
        
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      Reviews

    • Younghwan Yang,Junhwa Seong,Minseok Choi,Junkyeong Park,Gyeongtae Kim,Hongyoon Kim,Junhyeon Jeong,Chunghwan Jung,Joohoon Kim,Gyoseon Jeon,Kyung-il Lee,Dong Hyun Yoon,Junsuk Rho
      Vol. 12, Issue 8, Pages: 1467-1493(2023) DOI: 10.1038/s41377-023-01169-4
      Abstract:Metasurfaces have been continuously garnering attention in both scientific and industrial fields, owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. To date, research has mainly focused on the full control of electromagnetic characteristics, including polarization, phase, amplitude, and even frequencies. Consequently, versatile possibilities of electromagnetic wave control have been achieved, yielding practical optical components such as metalenses, beam-steerers, metaholograms, and sensors. Current research is now focused on integrating the aforementioned metasurfaces with other standard optical components (e.g., light-emitting diodes, charged-coupled devices, micro-electro-mechanical systems, liquid crystals, heaters, refractive optical elements, planar waveguides, optical fibers, etc.) for commercialization with miniaturization trends of optical devices. Herein, this review describes and classifies metasurface-integrated optical components, and subsequently discusses their promising applications with metasurface-integrated optical platforms including those of augmented/virtual reality, light detection and ranging, and sensors. In conclusion, this review presents several challenges and prospects that are prevalent in the field in order to accelerate the commercialization of metasurfacesintegrated optical platforms.  
        
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    • Wenye Ji,Jin Chang,He-Xiu Xu,Jian Rong Gao,Simon Gröblacher,H. Paul Urbach,Aurèle J. L. Adam
      Vol. 12, Issue 8, Pages: 1494-1509(2023) DOI: 10.1038/s41377-023-01218-y
      Abstract:As a two-dimensional planar material with low depth profile, a metasurface can generate non-classical phase distributions for the transmitted and reflected electromagnetic waves at its interface. Thus, it offers more flexibility to control the wave front. A traditional metasurface design process mainly adopts the forward prediction algorithm, such as Finite Difference Time Domain, combined with manual parameter optimization. However, such methods are time-consuming, and it is difficult to keep the practical meta-atom spectrum being consistent with the ideal one. In addition, since the periodic boundary condition is used in the meta-atom design process, while the aperiodic condition is used in the array simulation, the coupling between neighboring meta-atoms leads to inevitable inaccuracy. In this review, representative intelligent methods for metasurface design are introduced and discussed, including machine learning, physics-information neural network, and topology optimization method. We elaborate on the principle of each approach, analyze their advantages and limitations, and discuss their potential applications. We also summarize recent advances in enabled metasurfaces for quantum optics applications. In short, this paper highlights a promising direction for intelligent metasurface designs and applications for future quantum optics research and serves as an up-to-date reference for researchers in the metasurface and metamaterial fields.  
        
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    • Xin Chen,Suyi Zhong,Yiwei Hou,Ruijie Cao,Wenyi Wang,Dong Li,Qionghai Dai,Donghyun Kim,Peng Xi
      Vol. 12, Issue 8, Pages: 1510-1543(2023) DOI: 10.1038/s41377-023-01204-4
      Abstract:Structured illumination microscopy (SIM) has become the standard for next-generation wide-field microscopy, offering ultrahigh imaging speed, superresolution, a large field-of-view, and long-term imaging. Over the past decade, SIM hardware and software have flourished, leading to successful applications in various biological questions. However, unlocking the full potential of SIM system hardware requires the development of advanced reconstruction algorithms. Here, we introduce the basic theory of two SIM algorithms, namely, optical sectioning SIM (OS-SIM) and superresolution SIM (SR-SIM), and summarize their implementation modalities. We then provide a brief overview of existing OS-SIM processing algorithms and review the development of SR-SIM reconstruction algorithms, focusing primarily on 2D-SIM, 3D-SIM, and blind-SIM. To showcase the state-of-the-art development of SIM systems and assist users in selecting a commercial SIM system for a specific application, we compare the features of representative off-the-shelf SIM systems. Finally, we provide perspectives on the potential future developments of SIM.  
        
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    • Wei Luo,Lin Cao,Yuzhi Shi,Lingxiao Wan,Hui Zhang,Shuyi Li,Guanyu Chen,Yuan Li,Sijin Li,Yunxiang Wang,Shihai Sun,Muhammad Faeyz Karim,Hong Cai,Leong Chuan Kwek,Ai Qun Liu
      Vol. 12, Issue 8, Pages: 1544-1565(2023) DOI: 10.1038/s41377-023-01173-8
      Abstract:Recent years have witnessed significant progress in quantum communication and quantum internet with the emerging quantum photonic chips, whose characteristics of scalability, stability, and low cost, flourish and open up new possibilities in miniaturized footprints. Here, we provide an overview of the advances in quantum photonic chips for quantum communication, beginning with a summary of the prevalent photonic integrated fabrication platforms and key components for integrated quantum communication systems. We then discuss a range of quantum communication applications, such as quantum key distribution and quantum teleportation. Finally, the review culminates with a perspective on challenges towards high-performance chip-based quantum communication, as well as a glimpse into future opportunities for integrated quantum networks.  
        
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    • Xiaoyu Yang,Li Ma,Maotao Yu,Hao-Hsin Chen,Yongqiang Ji,An Hu,Qixuan Zhong,Xiaohan Jia,Yanju Wang,Yuzhuo Zhang,Rui Zhu,Xinqiang Wang,Changjun Lu
      Vol. 12, Issue 8, Pages: 1566-1582(2023) DOI: 10.1038/s41377-023-01206-2
      Abstract:Blue perovskite light-emitting diodes (PeLEDs) are essential in pixels of perovskite displays, while their progress lags far behind their red and green counterparts. Here, we focus on recent advances of blue PeLEDs and systematically review the noteworthy strategies, which are categorized into compositional engineering, dimensional control, and size confinement, on optimizing microstructures, energy landscapes, and charge behaviors of wide-bandgap perovskite emitters (bandgap > 2.5 eV). Moreover, the stability of perovskite blue emitters and related devices is discussed. In the end, we propose a technical roadmap for the fabrication of state-of-the-art blue PeLEDs to chase and achieve comparable performance with the other two primary-color devices.  
        
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      Original Articles

    • Dayanand Kumar,Lana Joharji,Hanrui Li,Ayman Rezk,Ammar Nayfeh,Nazek El-Atab
      Vol. 12, Issue 8, Pages: 1583-1594(2023) DOI: 10.1038/s41377-023-01166-7
      Abstract:Optoelectronic devices are advantageous in in-memory light sensing for visual information processing, recognition, and storage in an energy-efficient manner. Recently, in-memory light sensors have been proposed to improve the energy, area, and time efficiencies of neuromorphic computing systems. This study is primarily focused on the development of a single sensing-storage-processing node based on a two-terminal solution-processable MoS2 metal–oxide–semiconductor (MOS) charge-trapping memory structure—the basic structure for charge-coupled devices (CCD)—and showing its suitability for in-memory light sensing and artificial visual perception. The memory window of the device increased from 2.8 V to more than 6 V when the device was irradiated with optical lights of different wavelengths during the program operation. Furthermore, the charge retention capability of the device at a high temperature (100 ℃) was enhanced from 36 to 64% when exposed to a light wavelength of 400 nm. The larger shift in the threshold voltage with an increasing operating voltage confirmed that more charges were trapped at the Al2O3/MoS2 interface and in the MoS2 layer. A small convolutional neural network was proposed to measure the optical sensing and electrical programming abilities of the device. The array simulation received optical images transmitted using a blue light wavelength and performed inference computation to process and recognize the images with 91% accuracy. This study is a significant step toward the development of optoelectronic MOS memory devices for neuromorphic visual perception, adaptive parallel processing networks for in-memory light sensing, and smart CCD cameras with artificial visual perception capabilities.  
        
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    • Yanze Wang,Wenjing Zhao,Yuanyuan Guo,Wenbo Hu,Chenxi Peng,Lei Li,Yuan Wei,Zhongbin Wu,Weidong Xu,Xiyan Li,Yung Doug Suh,Xiaowang Liu,Wei Huang
      Vol. 12, Issue 8, Pages: 1595-1603(2023) DOI: 10.1038/s41377-023-01208-0
      Abstract:The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity, robust stability, low toxicity, and a uniform size distribution. Despite significant progress in this field, the discovery of a material that satisfies all of these criteria remains a challenge. In this study, we report the synthesis of monodisperse copper(Ⅰ)-iodide cluster microcubes as a new class of X-ray scintillators. The as-prepared microcubes exhibit remarkable sensitivity to X-rays and exceptional stability under moisture and X-ray exposure. The uniform size distribution and high scintillation performance of the copper(Ⅰ)-iodide cluster microcubes make them suitable for the fabrication of large-area, flexible scintillating films for X-ray imaging applications in both static and dynamic settings.  
        
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    • Jiaqun Li,Jianfeng Yan,Lan Jiang,Jiachen Yu,Heng Guo,Liangti Qu
      Vol. 12, Issue 8, Pages: 1604-1615(2023) DOI: 10.1038/s41377-023-01178-3
      Abstract:Photonic crystals are utilized in many noteworthy applications like optical communications, light flow control, and quantum optics. Photonic crystal with nanoscale structure is important for the manipulation of light propagation in visible and near-infrared range. Herein, we propose a novel multi beam lithography method to fabricate photonic crystal with nanoscale structure without cracking. Using multi-beam ultrafast laser processing and etching, parallel channels with subwavelength gap are obtained in yttrium aluminum garnet crystal. Combining optical simulation based on Debye diffraction, we experimentally show the gap width of parallel channels can be controlled at nanoscale by changing phase holograms. With the superimposed phase hologram designing, functional structures of complicated channel arrays distribution can be created in crystal. Optical gratings of different periods are fabricated, which can diffract incident light in particular ways. This approach can efficiently manufacture nanostructures with controllable gap, and offer an alternative to the fabrication of complex photonic crystal for integrated photonics applications.  
        
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    • Hongwei Jia,Mudi Wang,Shaojie Ma,Ruo-Yang Zhang,Jing Hu,Dongyang Wang,Che Ting Chan
      Vol. 12, Issue 8, Pages: 1616-1622(2023) DOI: 10.1038/s41377-023-01209-z
      Abstract:Chiral zeroth Landau levels are topologically protected bulk states. In particle physics and condensed matter physics, the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise to the chiral anomaly. Previous experimental works on such chiral Landau levels are mainly based on three-dimensional Weyl degeneracies coupled with axial magnetic fields. Their realizations using two-dimensional Dirac point systems, being more promising for future applications, were never experimentally realized before. Here we propose an experimental scheme for realizing chiral Landau levels in a two-dimensional photonic system. By introducing an inhomogeneous effective mass through breaking local parity-inversion symmetries, a synthetic in-plane magnetic field is generated and coupled with the Dirac quasi-particles. Consequently, the zeroth-order chiral Landau levels can be induced, and the one-way propagation characteristics are experimentally observed. In addition, the robust transport of the chiral zeroth mode against defects in the system is also experimentally tested. Our system provides a new pathway for the realization of chiral Landau levels in two-dimensional Dirac cone systems, and may potentially be applied in device designs utilizing the chiral response and transport robustness.  
        
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    • Peiyu Fang,Peihao Huo,Liding Wang,Zifeng Zhao,Gang Yu,Yanyi Huang,Zuqiang Bian,Zhiwei Liu
      Vol. 12, Issue 8, Pages: 1623-1632(2023) DOI: 10.1038/s41377-023-01211-5
      Abstract:White organic light-emitting diodes (WOLEDs) is a new generation of lighting technology and has stimulated wide-ranging studies. Despite the advantage of simple device structure, single-emitting-layer WOLEDs (SEL-WOLEDs) still face the challenges of difficult material screening and fine energy level regulation. Herein, we report efficient SEL-WOLEDs with a sky-blue emitting cerium(Ⅲ) complex Ce-TBO2Et and an orange-red emitting europium(Ⅱ) complex Eu(Tp2Et)2 as the emitters, showing a maximum external quantum efficiency of 15.9% and Commission Internationale de l'Eclairage coordinates of (0.33, 0.39) at various luminances. Most importantly, the electroluminescence mechanism of direct hole capture and hindered energy transfer between the two emitters facilitate a manageable weight doping concentration of 5% for Eu(Tp2Et)2, avoiding the low concentration (< 1%) of the low-energy emitter in typical SEL-WOLEDs. Our results indicate that d-f transition emitters may circumvent fine energy level regulation and provide development potential for SEL-WOLEDs.  
        
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    • Giuseppe Ortolano,Alberto Paniate,Pauline Boucher,Carmine Napoli,Sarika Soman,Silvania F. Pereira,Ivano Ruo-Berchera,Marco Genovese
      Vol. 12, Issue 8, Pages: 1633-1643(2023) DOI: 10.1038/s41377-023-01215-1
      Abstract:Quantum entanglement and squeezing have significantly improved phase estimation and imaging in interferometric settings beyond the classical limits. However, for a wide class of non-interferometric phase imaging/retrieval methods vastly used in the classical domain, e.g., ptychography and diffractive imaging, a demonstration of quantum advantage is still missing. Here, we fill this gap by exploiting entanglement to enhance imaging of a pure phase object in a non-interferometric setting, only measuring the phase effect on the free-propagating field. This method, based on the so-called "transport of intensity equation", is quantitative since it provides the absolute value of the phase without prior knowledge of the object and operates in wide-field mode, so it does not need time-consuming raster scanning. Moreover, it does not require spatial and temporal coherence of the incident light. Besides a general improvement of the image quality at a fixed number of photons irradiated through the object, resulting in better discrimination of small details, we demonstrate a clear reduction of the uncertainty in the quantitative phase estimation. Although we provide an experimental demonstration of a specific scheme in the visible spectrum, this research also paves the way for applications at different wavelengths, e.g., X-ray imaging, where reducing the photon dose is of utmost importance.  
        
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    • Garima Gupta,Kenji Watanabe,Takashi Taniguchi,Kausik Majumdar
      Vol. 12, Issue 8, Pages: 1644-1650(2023) DOI: 10.1038/s41377-023-01220-4
      Abstract:In monolayer transition metal dichalcogenide semiconductors, valley coherence degrades rapidly due to a combination of fast scattering and inter-valley exchange interaction. This leads to a sub-picosecond valley coherence time, making coherent manipulation of exciton a highly challenging task. Using monolayer MoS2 sandwiched between top and bottom graphene, here we demonstrate fully valley-coherent excitons by observing ~100% degree of linear polarization in steady state photoluminescence. This is achieved in this unique design through a combined effect of (a) suppression in exchange interaction due to enhanced dielectric screening, (b) reduction in exciton lifetime due to a fast inter-layer transfer to graphene, and (c) operating in the motional narrowing regime. We disentangle the role of the key parameters affecting valley coherence by using a combination of calculation (solutions of Bethe-Salpeter and Maialle-Silva-Sham equations) and a careful choice of design of experiments using four different stacks with systematic variation of screening and exciton lifetime. To the best of our knowledge, this is the first report in which the excitons are found to be valley coherent in the entire lifetime in monolayer semiconductors, allowing optical readout of valley coherence possible.  
        
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    • Yonghao Bu,Xiansong Ren,Jing Zhou,Zhenhan Zhang,Jie Deng,Hangyu Xu,Runzhang Xie,Tianxin Li,Weida Hu,Xia Guo,Wei Lu,Xiaoshuang Chen
      Vol. 12, Issue 8, Pages: 1651-1660(2023) DOI: 10.1038/s41377-023-01193-4
      Abstract:Filterless light-ellipticity-sensitive optoelectronic response generally has low discrimination, thus severely hindering the development of monolithic polarization detectors. Here, we achieve a breakthrough based on a configurable circular-polarization-dependent optoelectronic silent state created by the superposition of two photoresponses with enantiomerically opposite ellipticity dependences. The zero photocurrent and the significantly suppressed noise of the optoelectronic silent state singularly enhance the circular polarization extinction ratio (CPER) and the sensitivity to light ellipticity perturbation. The CPER of our device approaches infinity by the traditional definition. The newly established CPER taking noise into account is 3–4 orders of magnitude higher than those of ordinary integrated circular polarization detectors, and it remains high in an expanded wavelength range. The noise equivalent light ellipticity difference goes below 0.009° Hz−1/2 at modulation frequencies above 1000 Hz by a light power of 281 μW. This scheme brings a leap in developing monolithic ultracompact circular polarization detectors.  
        
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    • Genki Ishigane,Keiichiro Toda,Miu Tamamitsu,Hiroyuki Shimada,Venkata Ramaiah Badarla,Takuro Ideguchi
      Vol. 12, Issue 8, Pages: 1661-1674(2023) DOI: 10.1038/s41377-023-01214-2
      Abstract:Advancement in mid-infrared (MIR) technology has led to promising biomedical applications of MIR spectroscopy, such as liquid biopsy or breath diagnosis. On the contrary, MIR microscopy has been rarely used for live biological samples in an aqueous environment due to the lack of spatial resolution and the large water absorption background. Recently, mid-infrared photothermal (MIP) imaging has proven to be applicable to 2D and 3D single-cell imaging with high spatial resolution inherited from visible light. However, the maximum measurement rate has been limited to several frames s−1, limiting its range of use. Here, we develop a significantly improved wide-field MIP quantitative phase microscope with two orders-of-magnitude higher signal-to-noise ratio than previous MIP imaging techniques and demonstrate live-cell imaging beyond video rate. We first derive optimal system design by numerically simulating thermal conduction following the photothermal effect. Then, we develop the designed system with a homemade nanosecond MIR optical parametric oscillator and a high full-well-capacity image sensor. Our high-speed and high-spatial-resolution MIR microscope has great potential to become a new tool for life science, in particular for live-cell analysis.  
        
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    • Weizhen Liu,Xuhui Yang,Zhongqiang Wang,Yuanzheng Li,Jixiu Li,Qiushi Feng,Xiuhua Xie,Wei Xin,Haiyang Xu,Yichun Liu
      Vol. 12, Issue 8, Pages: 1675-1685(2023) DOI: 10.1038/s41377-023-01223-1
      Abstract:Visual adaptation that can autonomously adjust the response to light stimuli is a basic function of artificial visual systems for intelligent bionic robots. To improve efficiency and reduce complexity, artificial visual systems with integrated visual adaptation functions based on a single device should be developed to replace traditional approaches that require complex circuitry and algorithms. Here, we have developed a single two-terminal opto-sensor based on multilayer γ-InSe flakes, which successfully emulated the visual adaptation behaviors with a new working mechanism combining the photo-pyroelectric and photo-thermoelectric effect. The device can operate in self-powered mode and exhibit good human-eye-like adaptation behaviors, which include broadband light-sensing image adaptation (from ultraviolet to near-infrared), near-complete photosensitivity recovery (99.6%), and synergetic visual adaptation, encouraging the advancement of intelligent opto-sensors and machine vision systems.  
        
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    • Shengqiang Liu,Jingxuan Du,Zhen Song,Chonggeng Ma,Quanlin Liu
      Vol. 12, Issue 8, Pages: 1686-1695(2023) DOI: 10.1038/s41377-023-01219-x
      Abstract:The increasing demand for high-contrast biological imaging, non-destructive testing, and infrared night vision can be addressed by the development of high-performance NIR light-emitting materials. Unlike lanthanide (Ln3+) with sharp-line multiplets and isolated Cr3+ with NIR-Ⅰ emission, this study reports the first-ever NIR-Ⅱ broadband luminescence based on the intervalence charge transfer (IVCT) of Cr3+-Cr3+ aggregation in gallate magentoplumbite. In particular, LaMgGa11O19:0.7Cr3+ exhibits dual-emission (NIR-Ⅰ, 890 nm and NIR-Ⅱ, 1200 nm) with a full width at half maximum (FWHM) of 626 nm under 450 nm blue LED excitation. Moreover, this dual-emission exhibits anti-thermal quenching behavior (432% @ 290 K), attributed to the energy transfer among multiple Cr3+ centers. Cryogen absorption spectra, lifetimes decay (2.3 ms), and electron paramagnetic experiments reveal the NIR-Ⅱ luminescence of the Cr3+-Cr3+ → Cr2+-Cr4+ IVCT transition. The application of LaMgGa11O19:0.7Cr3+ in NIR-Ⅱ biological imaging as an optical contrast agent, non-destructive testing, and night vision is demonstrated. This work provides new insights into broadband NIR-Ⅱ luminescence under UV-NIR excitation based on the IVCT of Cr3+-Cr3+ aggregation.  
        
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    • Bozhang Dong,Mario Dumont,Osama Terra,Heming Wang,Andrew Netherton,John E. Bowers
      Vol. 12, Issue 8, Pages: 1696-1707(2023) DOI: 10.1038/s41377-023-01225-z
      Abstract:Frequency-modulated (FM) laser combs, which offer a quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion, Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of –5 dB allows the QD laser to generate FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs).  
        
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      Published:2024-07-25
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