2020

• Record 481 of
  
  Title:Optical data transmission at 44Tb/s and 10 bits/s/Hz over the c-band with standard fibre and a single micro-comb source
  
  Author(s):Corcoran, Bill(1); Tan, Mengxi(2); Xu, Xingyuan(2); Boes, Andreas(3); Wu, Jiayang(2); Nguyen, Thach G.(3); Chu, Sai T.(4); Little, Brent E.(5); Morandotti, Roberto(6); Mitchell, Arnan(3); Moss, David J.(2)
  Source: arXiv  Volume:   Issue:   DOI: null  Published: March 1, 2020  
  Abstract:Micro-combs [1-4] - optical frequency combs generated by integrated micro-cavity resonators - offer the full potential of their bulk counterparts [5,6], but in an integrated footprint. The discovery of temporal soliton states (DKS - dissipative Kerr solitons) [4,7-11] as a means of mode-locking microcombs has enabled breakthroughs in many fields including spectroscopy [12,13], microwave photonics [14], frequency synthesis [15], optical ranging [16,17], quantum sources [18,19], metrology [20,21] and more. One of their most promising applications has been optical fibre communications where they have enabled massively parallel ultrahigh capacity multiplexed data transmission [22,23]. Here, by using a new and powerful class of micro-comb called "soliton crystals" [11], we achieve unprecedented data transmission over standard optical fibre using a single integrated chip source. We demonstrate a line rate of 44.2 Terabits per second (Tb/s) using the telecommunications C-band at 1550nm with a spectral efficiency - a critically important performance metric - of 10.4 bits/s/Hz. Soliton crystals exhibit robust and stable generation and operation as well as a high intrinsic efficiency that, together with a low soliton micro-comb spacing of 48.9 GHz enable the use of a very high coherent data modulation format of 64 QAM (quadrature amplitude modulated). We demonstrate error free transmission over 75 km of standard optical fibre in the laboratory as well as in a field trial over an installed metropolitan optical fibre network. These experiments were greatly aided by the ability of the soliton crystals to operate without stabilization or feedback control. This work demonstrates the capability of optical soliton crystal micro-combs to perform in demanding and practical optical communications networks. Copyright © 2020, The Authors. All rights reserved.
  Accession Number: 20200380803
• Record 482 of
  
  Title:Preventing critical collapse of higher-order solitons by tailoring unconventional optical diffraction and nonlinearities
  
  Author(s):Zeng, Liangwei(1,2); Zeng, Jianhua(1,2,3)
  Source: Communications Physics  Volume: 3  Issue: 1  DOI: 10.1038/s42005-020-0291-9  Published: December 1, 2020  
  Abstract:Self-trapped modes suffer critical collapse in two-dimensional cubic systems. To overcome such a collapse, linear periodic potentials or competing nonlinearities between self-focusing cubic and self-defocusing quintic nonlinear terms are often introduced. Here, we combine both schemes in the context of an unconventional and nonlinear fractional Schrödinger equation with attractive-repulsive cubic–quintic nonlinearity and an optical lattice. We report theoretical results for various two-dimensional trapped solitons, including fundamental gap and vortical solitons as well as the gap-type soliton clusters. The latter soliton family resembles the recently-found gap waves. We uncover that, unlike the conventional case, the fractional model exhibiting fractional diffraction order strongly influences the formation of higher band gaps. Hence, a new route for the study of self-trapped modes in these newly emergent higher band gaps is suggested. Regimes of stability and instability of all the soliton families are obtained with the help of linear-stability analysis and direct simulations. © 2020, The Author(s).
  Accession Number: 20201708524014
• Record 483 of
  
  Title:Biomimetic curved compound-eye camera with a high resolution for the detection of distant moving objects
  
  Author(s):Xu, Huangrong(1,2); Zhang, Yuanjie(1,2); Wu, Dengshan(1); Zhang, Geng(1,2); Wang, Ziyuan(1,2); Feng, Xiangpeng(1); Hu, Bingliang(1,2); Yu, Weixing(1,2)
  Source: Optics Letters  Volume: 45  Issue: 24  DOI: 10.1364/OL.411492  Published: December 15, 2020  
  Abstract:In this Letter, we demonstrate the design and fabrication of a biomimetic curved compound-eye camera (BCCEC) with a high resolution for detecting distant moving objects purpose. In contrast to previously reported compound-eye cameras, our BCCEC has two distinct features. One is that the ommatidia of the compound eye are deployed on a curved surface which makes a large field of view (FOV) possible. The other is that each ommatidium has a relatively large optical entrance and long focal length so that a distant object can be imaged. To overcome the mismatch between the curved focal plane formed by the curved compound eye and the planar focal plane of the CMOS image sensor (CIS), an optical relay subsystem is introduced between the compound eye and the CIS. As a result, a BCCEC with 127 ommatidia in the compound eye is designed and fabricated to achieve a large FOV of up to 98◦ × 98◦. The experimental results show that objects with a size of 100 mm can be clearly resolved at a distance of 25 m. The capture of the motion trajectories of a moving object is also demonstrated, which makes it possible to detect and track the moving targets in a huge FOV for security surveillance purposes. © 2020 Optical Society of America
  Accession Number: 20205109634841
• Record 484 of
  
  Title:Atmospheric correction of geostationary satellite ocean color data under high solar zenith angles in open oceans
  
  Author(s):Li, Hao(1,2,3); He, Xianqiang(1,2,3); Bai, Yan(1,2,3); Shanmugam, Palanisamy(4); Park, Young-Je(5); Liu, Jia(6); Zhu, Qiankun(1,2); Gong, Fang(1,2); Wang, Difeng(1,2); Huang, Haiqing(1,2)
  Source: Remote Sensing of Environment  Volume: 249  Issue:   DOI: 10.1016/j.rse.2020.112022  Published: November 2020  
  Abstract:With a revisit time of 1 h, spatial resolution of 500 m, and high radiometric sensitivity, the Geostationary Ocean Color Imager (GOCI) is widely used to monitor diurnal dynamics of oceanic phenomena. However, atmospheric correction (AC) of GOCI data with high solar zenith angle (>70°) is still a challenge for traditional algorithms. Here, we propose a novel neural network (NN) AC algorithm for GOCI data under high solar zenith angles. Unlike traditional NN AC algorithms trained by radiative transfer-simulated dataset, our new AC algorithm was trained by a large number of matchups between GOCI-observed Rayleigh-corrected radiance in the morning and evening and GOCI-retrieved high-quality noontime remote-sensing reflectance (Rrs). When validated using hourly GOCI data, the new NN AC algorithm yielded diurnally stable Rrs in open ocean waters from the morning to evening. Furthermore, when validated by in-situ data from three Aerosol Robotic Network-Ocean Color (AERONET-OC) stations (Socheongcho, Gageocho and Ieodo), the GOCI-retrieved Rrs at visible bands obtained using the new AC algorithm agreed well with the in-situ values, even under high solar zenith angles. Practical application of the new algorithm was further examined using diurnal GOCI observation data acquired in clear open ocean waters. Results showed that the new algorithm successfully retrieved Rrs for the morning and evening GOCI data. Moreover, the amount of Rrs data retrieved by the new algorithm was much higher than that retrieved by the standard AC algorithm in SeaDAS. Our proposed NN AC algorithm can not only be applied to process GOCI data acquired in the morning and evening, but also has the potential to be applied to process polar-orbiting satellite ocean color data at high-latitude ocean that also include satellite observation with high solar zenith angles. © 2020 Elsevier Inc.
  Accession Number: 20203209011122
• Record 485 of
  
  Title:W-shaped common-path interferometer
  
  Author(s):Wei, Ruyi(1,2,3); Di, Lamei(1,2,3); Qiao, Nianzu(4); Chen, Shasha(1,2)
  Source: Applied Optics  Volume: 59  Issue: 34  DOI: 10.1364/AO.411150  Published: December 1, 2020  
  Abstract:We present a novel static W-shaped common-path interferometer. In particular, the W-shaped common-path corner-cube retroreflector interferometer (W-CPRI) is introduced via detailed analysis of its working principles and performance. It comprises two corner-cube retroreflectors (CCRs), a reflecting mirror (RM), and a beam splitter. For each interference output of an ideal W-CPRI, the two beams recombine and have the same output direction, including a tilted CCR. In a deformed W-CPRI structure, an optical path difference can be produced by inserting an optical element that changes the optical path in the interferometer arm of the W-CPRI. The posture deviations of the RM and the CCRs in the W-CPRI are analyzed. In addition, a proof-of-concept experiment is conducted, with the stability analyzed using the fringe similarity method. The average cosine similarity is 0.9953, revealing that this W-CPRI has high stability and strong coherence while avoiding the tilt and displacement of the interferometer arm. © 2020 Optical Society of America
  Accession Number: 20205109635259
• Record 486 of
  
  Title:Optimization of a multi-TW few-cycle 1.7-µm source based on Type-Ⅰ BBO dual-chirped optical parametric amplification
  
  Author(s):Xu, Lu(1); Nishimura, Kotaro(1,2); Fu, Yuxi(1,3); Suda, Akira(2); Midorikawa, Katsumi(1); Takahashi, Eiji J.(1)
  Source: arXiv  Volume:   Issue:   DOI: null  Published: March 2, 2020  
  Abstract:This paper presents the optimization of a dual-chirped optical parametric amplification (DC-OPA) scheme for producing an ultrafast intense infrared (IR) pulse. By employing a total energy of 0.77 J Ti:sapphire pump laser and type-Ⅰ BBO crystals, an IR pulse energy at the center wavelength of 1.7 µm exceeded 0.1 J using the optimized DC-OPA. By adjusting the injected seed spectrum and prism pair compressor with a gross throughput of over 70%, the 1.7-µm pulse was compressed to 31 fs, which resulted in a peak power of up to 2.3 TW. Based on the demonstration of the BBO type-Ⅰ DC-OPA, we propose a novel OPA scheme called the "dual pump DC-OPA" for producing a high-energy IR pulse with a two-cycle duration. Copyright © 2020, The Authors. All rights reserved.
  Accession Number: 20200375407
• Record 487 of
  
  Title:Real-time infrared image detail enhancement based on fast guided image filter and plateau equalization
  
  Author(s):Chen, Yaohong(1,2,3); Kang, Jin U.(3); Zhang, Gaopeng(1); Cao, Jianzhong(1); Xie, Qingsheng(1); Kwan, Chiman(4)
  Source: Applied Optics  Volume: 59  Issue: 21  DOI: 10.1364/AO.396417  Published: July 20, 2020  
  Abstract:Image detail enhancement is critical to the performance of infrared imaging systems because the original images generally suffer from low contrast and a low signal-to-noise ratio. Although conventional decomposition-based methods have advantages in enhancing image details, they also have clear disadvantages, which include intensive computations, over-enhanced noise, and gradient reversal artifacts. In this paper, we propose to accelerate enhancement processing by using a fast guided filter and plateau equalization. Our method consists of image decomposition, base and detail layers processing, and projection of the enhanced image to an 8-bit dynamic range. Experimental results demonstrated that our proposed method achieves a good balance among detail enhancement performance, noise and gradient reversal artifacts suppression, and computational cost, with a frame rate around 30 fps for 640 × 512 infrared images. © 2020 Optical Society of America.
  Accession Number: 20203709150814
• Record 488 of
  
  Title:Design and verification of the HXI collimator on the ASO-S mission
  
  Author(s):Dengyi, Chen(1,2); Zhe, Zhang(1); Yiming, Hu(1,2); Guangzhou, Xu(3); Tao, Ma(1,2); Jianping, Wang(4); Xiankai, Jiang(1,2); Jianhua, Guo(1,2); Yongqiang, Zhang(1); Jin, Chang(1)
  Source: arXiv  Volume:   Issue:   DOI: null  Published: December 2, 2020  
  Abstract:A space borne hard X-ray collimator, consists of 91 pairs of grids, has been developed for the Hard X-ray Imager (HXI). The HXI is one of the three scientific instruments onboard the first Chinese solar mission: the Advanced Space-based Solar Observatory (ASO-S). The HXI collimator (HXI-C) is a spatial modulation X-ray telescope focus on the hard X-rays emitted from energetic electrons in solar flares. In this paper, detailed design of the HXI-C is introduced for the qualification model which will be inherited by the flight model. Series tests on the HXI-C qualification model are reported to verify its capability to survive the launch and to operate normally in on-orbit environments. Further, results of the X-ray beam test for the HXI-C is present to indirectly identify its working performance. Copyright © 2020, The Authors. All rights reserved.
  Accession Number: 20210015979
• Record 489 of
  
  Title:Geant4 simulation for the responses to X-rays and charged particles through the eXTP focusing mirrors
  
  Author(s):Qi, L.Q.(1); Li, G.(1); Xu, Y.P.(1); Zhang, J.(1); Yang, Y.J.(1); Sheng, L.Z.(5); Basso, S.(2); Campana, R.(3); Chen, Y.(1); De Rosa, A.(4); Pareschi, G.(2); Qiang, P.F.(5); Santangelo, A.(6); Sironi, G.(2); Song, L.M.(1); Spiga, D.(2); Tagliaferri, G.(2); Wang, J.(1); Wilms, J.(7); Zhang, Y.(1); Lu, F.J.(1)
  Source: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  Volume: 963  Issue:   DOI: 10.1016/j.nima.2020.163702  Published: 21 May 2020  
  Abstract:A geometrical and physical model of Wolter-I type mirrors has been implemented in Geant4 for the design of the enhanced X-ray Timing and Polarimetry observatory (eXTP). It can simultaneously simulate the mirror responses to X-rays and charged particles. A new geometry class G4Hyperboloid is created and verified, which allows an exact surface profile description of Wolter-I optics. A physics model for the interaction of X-rays and matter is implemented to effectively estimate the focusing performances with reasonable accuracy, including the effective area and the point spread function. Scattering models of charged particles at grazing incidence are discussed. The multiple scattering model provided by the latest Geant4 release can be used instead of the single scattering model with reasonable accuracy and CPU cost when the step size is properly constrained. © 2020 Elsevier B.V.
  Accession Number: 20201008270542
• Record 490 of
  
  Title:Optimization of a multi-TW few-cycle 1.7-µm source based on Type-I BBO dual-chirped optical parametric amplification
  
  Author(s):Xu, Lu(1); Nishimura, Kotaro(1,2); Suda, Akira(2); Midorikawa, Katsumi(1); Fu, Yuxi(1,3); Takahashi, Eiji J.(1)
  Source: Optics Express  Volume: 28  Issue: 10  DOI: 10.1364/OE.392045  Published: May 11, 2020  
  Abstract:This paper presents the optimization of a dual-chirped optical parametric amplification (DC-OPA) scheme for producing an ultrafast intense infrared (IR) pulse. By employing a total energy of 0.77 J Ti:sapphire pump laser and type-I BBO crystals, an IR pulse energy at the center wavelength of 1.7 µm exceeded 0.1 J using the optimized DC-OPA. By adjusting the injected seed spectrum and prism pair compressor with a gross throughput of over 70%, the 1.7-µm pulse was compressed to 31 fs, which resulted in a peak power of up to 2.3 TW. Based on the demonstration of the BBO type-I DC-OPA, we propose a novel OPA scheme called the "dual pump DC-OPA" for producing a high-energy IR pulse with a two-cycle duration. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
  Accession Number: 20202008648633
• Record 491 of
  
  Title:Apparatus for generation of nanojoule-class water-window high-order harmonics
  
  Author(s):Nishimura, Kotaro(1,2); Fu, Yuxi(1,3); Suda, Akira(2); Midorikawa, Katsumi(1); Takahashi, Eiji J.(1)
  Source: arXiv  Volume:   Issue:   DOI: null  Published: December 29, 2020  
  Abstract:In our recent study [Y. Fu et al., Commun. Phys. 3, 92 (2020)], we have developed an approach for energy-scaling of high-order harmonic generation in water-window region under neutral-medium condition. More specifically, we obtained nanojoule-class water-window soft x-ray harmonic beam under phase match condition. It has been achieved by combining a newly developed terawatt-class mid-infrared femtosecond laser and a loose focusing geometry for high-order harmonic generation. The generated beam is more than 100 times intense compared to previously reported results. The experimental setup included two key parts: terawatt mid-infrared femtosecond driving laser [Y. Fu et al., Sci. Rep. 8, 7692 (2018)] and specially designed gas cell. Despite the dramatic drop in the optimal gas pressure due to loose focusing geometry, it still reached 1 bar level for helium. Moreover, faster leaking speed caused by larger pinhole size of the gas cell made the use of a normal gas cell impossible. Thus, we have designed a double-structured pulsed-gas cell with a differential pumping system, which enabled providing sufficiently high gas pressure. Moreover, it allowed reducing gas consumption significantly. Robust energy-scalable apparatus for high-order harmonic generation developed in in this study will enable the generation of over tens nanojoule water-window attosecond pulses in the nearest future. Copyright © 2020, The Authors. All rights reserved.
  Accession Number: 20210050664
• Record 492 of
  
  Title:High-performance concealment of defective pixel clusters in infrared imagers
  
  Author(s):Chen, Yaohong(1,2,3); Kang, Jin U.(3); Zhang, Gaopeng(1); Cao, Jianzhong(1); Xie, Qingsheng(1); Kwan, Chiman(4)
  Source: Applied Optics  Volume: 59  Issue: 13  DOI: 10.1364/AO.391668  Published: May 1, 2020  
  Abstract:Defective pixel concealment is a necessary procedure in infrared image processing and is widely used. However, current approaches are mainly focused on the concealment of isolated pixels and small defective pixel clusters. Consequently, these approaches cannot meet the requirements when applied to infrared detectors with large defective pixel clusters. In this paper, we present a novel and comprehensive approach to processing the image data acquired from infrared imagers with large and small defective pixel clusters. Our approach consists of preprocessing, coarse concealment, high dynamic range enhancement, and fine concealment by generative adversarial networks. Experiments using mid-wave infrared and long-wave infrared images demonstrated that the proposed approach achieves better results than the best conventional approach, known as transforming image completion, with the peak signal-to-noise ratio and structural similarity metrics improved by 2.7063 dB (16.3%) and 0.1951 dB (34.1%), respectively. © 2020 Optical Society of America.
  Accession Number: 20202008648088