2019

• Record 589 of
  
  Title:Polarization de-multiplexing using a modified Kalman filter in CO-OFDM transmissions
  
  Author(s):Jiang, Yang(1); Yi, Xingwen(1,2); Hu, Shaohua(1); Huang, Xiatao(1); Tang, Wei(1); Zhou, Wenjing(1); Huang, Xinning(3); Zhang, Jing(1); Qiu, Kun(1)
  Source: Chinese Optics Letters  Volume: 17  Issue: 3  DOI: 10.3788/COL201917.030603  Published: March 10, 2019  
  Abstract:We propose the modified Kalman filter (MKF) using the received signal for observation and constructing an inverse process of the conventional Kalman filter (CKF) for polarization de-multiplexing in coherent optical (CO) orthogonal frequency-division multiplexing (OFDM) transmissions. The MKF can avoid the convergence error problem in CKF without matrix inverse operation and has a faster converging speed and a much larger tolerance to the process and measurement noise covariance, about two orders of magnitude more than those of CKF. We experimentally demonstrate the 12 Gbaud OFDM signal transmission over 480 km standard singlemode fiber. The performance of MKF and CKF outperforms pilot-aided polarization de-multiplexing with better accuracy and nonlinearity tolerance. © 2019 Chinese Optics Letters.
  Accession Number: 20192106955856
• Record 590 of
  
  Title:Enhanced four-wave mixing in hybrid integrated waveguides with graphene oxide
  
  Author(s):Wu, Jiayang(1); Yang, Yunyi(1); Xu, Xingyuan(1); Jia, Linnan(1); Liang, Yao(1); Chu, Sai T.(2); Little, Brent E.(3); Morandotti, Roberto(4,5,6); Jia, Baohua(1); Moss, David(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10920  Issue:   DOI: 10.1117/12.2508120  Published: 2019  
  Abstract:Owing to the ease of preparation as well as the tunability of its material properties, graphene oxide (GO) has become a rising star of the graphene family. In our previous work, we found that GO has an ultra-high Kerr nonlinear optical response - several orders of magnitude higher than that of silica and even silicon. Moreover, as compared with graphene, GO has much lower linear loss as well as nonlinear loss (two photon absorption (TPA)), arising from its large bandgap (2.4∼3.1 eV) being more than double the photon energy in the telecommunications band. Here, we experimentally demonstrate enhanced four-wave mixing (FWM) in hybrid integrated waveguides coated with GO films. Owing to strong mode overlap between the integrated waveguides and the high Kerr nonlinearity GO films as well as low linear and nonlinear loss, we demonstrate significant enhancement in the FWM efficiency. We achieve up to ∼9.5-dB enhancement in the conversion efficiency for a 1.5-cm-long waveguide with 2 layers of GO. We perform FWM measurements at different pump powers, wavelength detuning, GO film lengths and numbers of layers. The experimental results verify the effectiveness of introducing GO films into integrated photonic devices in order to enhance the performance of nonlinear optical processes. © 2019 SPIE.
  Accession Number: 20192106948766
• Record 591 of
  
  Title:Enantioselective optical trapping of chiral nanoparticles by tightly focused vector beams
  
  Author(s):Li, Manman(1); Yan, Shaohui(1); Zhang, Yanan(1,2); Zhang, Peng(1); Yao, Baoli(1)
  Source: Journal of the Optical Society of America B: Optical Physics  Volume: 36  Issue: 8  DOI: 10.1364/JOSAB.36.002099  Published: 2019  
  Abstract:Two enantiomers (mirror images) can show drastically different behaviors, resulting in the enantiomers’ identification and separation being in high demand in biomedical research and industry. Here, we introduce an optical approach in which, by using a tightly focused vector beam with radially varied polarizations, we realize the selective trapping of both enantiomeric forms. Numerical results show that such a focused field exhibits bifocal spot intensity distribution and can simultaneously stably trap one enantiomer in one focal spot and the other enantiomer in the other spot in three dimensions, achieving an effective separation of the chiral entities. The trapping distance and position of the enantiomeric pairs can be changed by separately varying the magnitude and sign of the polarization topological charge of the vector beam. And the difference in trapping potentials of the particles with different chirality provides a further identification of the chirality. Our theory indicates that the enantiomers’ identification and separation can be mediated by the same incident beam, providing a possible route to detect, separate, and manipulate chiral objects at nanometer scales. © 2019 Optical Society of America.
  Accession Number: 20193507376977
• Record 592 of
  
  Title:Photon-counting underwater optical wireless communication for reliable video transmission using joint source-channel coding based on distributed compressive sensing
  
  Author(s):Hong, Zhu(1); Yan, Qiurong(1,2); Li, Zihang(1); Zhan, Ting(1); Wang, Yuhao(1)
  Source: Sensors (Switzerland)  Volume: 19  Issue: 5  DOI: 10.3390/s19051042  Published: March 2019  
  Abstract:To achieve long-distance underwater optical wireless communication, a single photon detector with single photon limit sensitivity is used to detect the optical signal at the receiver. The communication signal is extracted from the discrete single photon pulses output from the detector. Due to fluctuation of photon flux and quantum efficiency of photon detection, long-distance underwater optical wireless communication has the characteristics that the link is easily interrupted, the bit error rate is high, and the burst error is large. To achieve reliable video transmission, a joint source-channel coding scheme based on residual distributed compressive video sensing is proposed for the underwater photon counting communication system. Signal extraction from single photon pulses, data frame and data verification are specifically designed. This scheme greatly reduces the amount of data at the transmitter, transfers the computational complexity to the decoder in receiver, and enhances anti-channel error ability. The experimental results show that, when the baud rate was 100 kbps and the average number of photon pulses per bit was 20, the bit error rate (BER) was 0.0421 and video frame could still be restored clearly. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
  Accession Number: 20191306711113
• Record 593 of
  
  Title:Optical properties and applications of molybdenum disulfide/SiO2 saturable absorber fabricated by sol-gel technique
  
  Author(s):Lv, Ruidong(1); Chen, Zhendong(1); Liu, Sicong(1); Wang, Jiang(1); Li, Yongfang(1); Wang, Yonggang(1,2); Wang, Yishan(2)
  Source: Optics Express  Volume: 27  Issue: 5  DOI: 10.1364/OE.27.006348  Published: 2019  
  Abstract:We investigate a new type of molybdenum disulfide (MoS2)-doped sol-gel glass saturable absorber (SA) fabricated by sol-gel technique. The reagents used for the sol-gel glass contain Tetraethyl orthosilicate (TEOS), ethanol, water, and hydrochloric acid. Different from the traditional ways of fabricating SAs, the MoS2 in our method is encapsulated by inorganic sol-gel glass instead of polymer compound with low laser damage resistance, which greatly increases the optical damage threshold of MoS2 SA. The MoS2-doped sol-gel glass as an SA is experimentally demonstrated in a passively mode-locked ytterbium-doped fiber laser (YDFL). Stable mode-locked pulse trains are successfully generated in the normal dispersion regime with a pulse width of 13.8 ps and the average output power of 34.6 mW. The fluctuation of the central wavelength and spectral bandwidth is as low as 0.9% in one week, which indicates that the mode-locking state has good environmental stability. To the best of our knowledge, it is the first example of sol-gel glass SA for ultrafast pulses generated in YDFL, which potentially gives a new approach to improve optical damage threshold and long-term working stability for broadband absorbers. © 2019 Optical Society of America.
  Accession Number: 20191106643742
• Record 594 of
  
  Title:Hybrid phase-amplitude superoscillation element for nonscanning optical superresolution imaging
  
  Author(s):Xie, Qingkun(1,2); Jiang, Yanru(1,2); Liang, Jian(1); Qu, Enshi(1); Ren, Liyong(1)
  Source: Journal of the Optical Society of America A: Optics and Image Science, and Vision  Volume: 36  Issue: 2  DOI: 10.1364/JOSAA.36.000196  Published: February 2019  
  Abstract:In this paper, we report a nonscanning optical superresolution imaging method based on a hybrid phase-amplitude superoscillation element. Using the Chebyshev polynomials as a basis set on the superoscillation waveform, the optimal combination of these, representing the optimal focal -spot in the local field of view, is found by genetic algorithm. Our numerical calculations demonstrate that a subwavelength focal spot with a full width at half-maximum as small as 253 nm is realized, which has more than 30 times improvement in sidelobe suppression ratio, and crucially, a greatly extended needle with continuously shrunken focal spot is yielded, which allows a large imaging tolerance in the axial displacement of the object. We then present our simulated results of the superresolution imaging on sparse point objects and continuous objects, where the practicality and effectiveness of this method are analyzed and discussed in detail. © 2019 Optical Society of America
  Accession Number: 20190606469790
• Record 595 of
  
  Title:Local and global feature learning for subtle facial expression recognition from attention perspective
  
  Author(s):Wang, Shaocong(1,2); Yuan, Yuan(3); Feng, Yachuang(1)
  Source: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)  Volume: 11858 LNCS  Issue:   DOI: 10.1007/978-3-030-31723-2_57  Published: 2019  
  Abstract:Subtle facial expression recognition is important for emotion analysis. In the field of subtle facial expression recognition, there are two intrinsic characters. Firstly, subtle facial expression usually exhibits very small variations in different facial areas. Secondly, those small variations are closely correlated, and they together form an expression. Inspired by these two characteristics of facial expression, a model focus on local variations and their correlations is proposed in this paper. We utilize several attention maps to automatically attend to distinct local regions and extract local features. And then, a self-attention operation is ensembled to extract global correlation feature over the whole image. The global and local features are further fused in an efficient way to classify the facial expression. Extensive experiments have been carried out on LSEMSW and CK+ datasets. © Springer Nature Switzerland AG 2019.
  Accession Number: 20195207942081
• Record 596 of
  
  Title:Generation of a double-ring perfect optical vortex by the Fourier transform of azimuthally polarized Bessel beams
  
  Author(s):Liang, Yansheng(1); Yan, Shaohui(1); He, Minru(1,2); Li, Manman(1); Cai, Yanan(1,2); Wang, Zhaojun(1,2); Lei, Ming(1); Yao, Baoli(1)
  Source: Optics Letters  Volume: 44  Issue: 6  DOI: 10.1364/OL.44.001504  Published: 2019  
  Abstract:The perfect optical vortex (POV), the ring size being independent of its topological charge, has found potential applications in optical tweezers and optical communications. In this Letter, we report a new kind of POV, termed as double-ring POV (DR-POV), whose diameters of the two rings are independent of topological charge. We theoretically demonstrate that such a vortex is the Fourier transform of an azimuthally polarized Bessel beam. Experimental results agree well with theoretical prediction. We further investigate the vortex nature of the DR-POV through an interferometric method, showing that the two rings of the vortex have the same topological charge value (magnitude and sign). The specular properties of the DR-POV may find application in optical tweezers, such as trapping and rotating of low-refractive-index particles in the dark region between the two rings. © 2019 Optical Society of America.
  Accession Number: 20191206671571
• Record 597 of
  
  Title:Gaussian-like and flat-top solitons of atoms with spatially modulated repulsive interactions
  
  Author(s):Zeng, Liangwei(1,2); Zeng, Jianhua(1,2)
  Source: Journal of the Optical Society of America B: Optical Physics  Volume: 36  Issue: 8  DOI: 10.1364/JOSAB.36.002278  Published: 2019  
  Abstract:Solitons, nonlinear particle-like excitations with inalterable properties (amplitude, shape, and velocity) as they propagate, are omnipresent in many branches of science—and in physics in particular. Flat-top solitons are a novel type of bright solitons that have not been well explored in pure nonlinear media. Here, a model of nonlinear Kerr (cubic) media of ultracold atoms with spatially modulated repulsive interactions is proposed and shown to support a vast variety of stable flat-top matter-wave solitons, including one-dimensional flat-top fundamental and multipole solitons, and two-dimensional flat-top fundamental and vortex solitons. We demonstrate that by varying the relevant physical parameters (nonlinearity coefficient and chemical potential), the ordinary bright (Gaussian) solitons can transform into the novel flat-top solitons. The (in)stability domains of the flat-top soliton families are checked by means of linear stability analysis and reconfirmed by direct numerical simulations. This model is generic in the contexts of nonlinear optics and Bose–Einstein condensates, which provides direct experimental access to observe the predicted solutions. © 2019 Optical Society of America.
  Accession Number: 20193507376980
• Record 598 of
  
  Title:Measurement matrix construction for large-area single photon compressive imaging
  
  Author(s):Wang, Hui(1); Yan, Qiurong(1,2); Li, Bing(1); Yuan, Chenglong(1); Wang, Yuhao(1)
  Source: Sensors (Switzerland)  Volume: 19  Issue: 3  DOI: 10.3390/s19030474  Published: February 1, 2019  
  Abstract:We have developed a single photon compressive imaging system based on single photon counting technology and compressed sensing theory, using a photomultiplier tube (PMT) photon counting head as the bucket detector. This system can realize ultra-weak light imaging with the imaging area up to the entire digital micromirror device (DMD) working region. The measurement matrix in this system is required to be binary due to the two working states of the micromirror corresponding to two controlled elements. And it has a great impact on the performance of the imaging system, because it involves modulation of the optical signal and image reconstruction. Three kinds of binary matrix including sparse binary random matrix, m sequence matrix and true random number matrix are constructed. The properties of these matrices are analyzed theoretically with the uncertainty principle. The parameters of measurement matrix including sparsity ratio, compressive sampling ratio and reconstruction time are verified in the experimental system. The experimental results show that, the increase of sparsity ratio and compressive sampling ratio can improve the reconstruction quality. However, when the increase is up to a certain value, the reconstruction quality tends to be saturated. Compared to the other two types of measurement matrices, the m sequence matrix has better performance in image reconstruction. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
  Accession Number: 20190706490483
• Record 599 of
  
  Title:Non-local restoration of sparse 3D single-photon data
  
  Author(s):Chen, Songmao(1,2,3); Halimi, Abderrahim(3); Ren, Ximing(3); McCarthy, Aongus(3); Su, Xiuqin(1,2); Buller, Gerald S.(3); McLaughlin, Steve(3)
  Source: European Signal Processing Conference  Volume: 2019-September  Issue:   DOI: 10.23919/EUSIPCO.2019.8902525  Published: September 2019  
  Abstract:This paper presents a new algorithm for the non-local restoration of single-photon 3-Dimensional Lidar images acquired in the photon starved regime or with a reduced number of scanned spatial points (pixels). The algorithm alternates between two steps: evaluation of the spatial correlations between pixels using a graph, then restore the depth and reflectivity images by their spatial correlations. To reduce the computational cost associated with the graph, we adopt a non-uniform sampling approach, where bigger patches are assigned to homogeneous regions and smaller ones to heterogeneous regions. The restoration of 3D images is achieved by minimizing a cost function accounting for the data Poisson statistics and the non-local spatial correlations between patches. This minimization problem is efficiently solved using the alternating direction method of multipliers (ADMM) that presents fast convergence properties. Results on real Lidar data show the benefits of the proposed algorithm in improving the quality of the estimated depth images, especially in photon starved cases, which can contain a reduced number of photons. © 2019 IEEE
  Accession Number: 20194807762643
• Record 600 of
  
  Title:A moving target extraction algorithm based on the fusion of infrared and visible images
  
  Author(s):Qiu, Shi(1); Luo, Junsong(2); Yang, Song(3); Zhang, Meiyang(4); Zhang, Wei(1)
  Source: Infrared Physics and Technology  Volume: 98  Issue:   DOI: 10.1016/j.infrared.2019.03.022  Published: May 2019  
  Abstract:According to the principle of thermal imaging, moving targets can be better located in infrared images, but their boundary is blurred, and the details of objects cannot be displayed. The details of objects in natural images can be better shown, but for the condition of shelter, shadow and etc., miss-tracking and false-tracking may easily occur. Thus, we construct a framework for moving target extraction and tracking in infrared and natural images. For infrared images: according to the rough fuzzy set theory, we propose the rough entropy model based on the traditional frame difference method. The model is fused with the infrared imaging characteristics to locate moving target regions. For natural images: a time-space fusion LBP model is proposed for target coding. The model is integrated into the GMM model to obtain moving target information. The moving regions in infrared images and natural images are fused to form a priori model, and the C-V model is improved to extract targets accurately. © 2019
  Accession Number: 20191406722938