Publications by authors named "Deming Liu"

212 Publications

Geometric shaping optimization of 64-APSK constellation in discrete nonlinear frequency division multiplexing systems.

Opt Lett 2021 Jul;46(14):3368-3371

We experimentally demonstrated a geometric shaped (GS) 64-ary amplitude phase shift keying (64-APSK) eigenvalue transmission. The signal is modulated on the scatter coefficient of a single eigenvalue and linear minimum mean square error (LMMSE) estimator is used to reduce the noise. The channel response is estimated by transmitting a normally distributed 64-APSK constellation through a communication link. Based on the polar coordinates distribution of the received constellation, the diameter distributions for each circle can be obtained so that circles with larger noise can obtain larger judgment width. After optimization, the experimental results show that the Q-factor gain is 1.13 dB under 22 dB received optical signal to noise ratio (OSNR) configuration and 0.88 dB after 900 km transmission compared with normally distributed APSK configuration.
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http://dx.doi.org/10.1364/OL.430391DOI Listing
July 2021

Reconfigurable generation of double-ring perfect vortex beam.

Opt Express 2021 May;29(11):17353-17364

Perfect vortex beam (PVB), whose ring radius is independent of its topological charge, play an important role in optical trapping and optical communication. Here, we experimentally demonstrate the reconfigurable double-ring PVB (DR-PVB) generation with independent manipulations of the amplitude, the radius, the width, and the topological charge for each ring. Based on complex amplitude modulation (CAM) with a phase-only spatial light modulator (SLM), we successfully verify the proposed DR-PVB generation scheme via the computer-generated hologram. Furthermore, we carry out a quantitative characterization for the generated DR-PVB, in terms of both the generation quality and the generation efficiency. The correlation coefficients of various reconfigurable DR-PVBs are above 0.8, together with the highest generation efficiency of 44%. We believe that, the proposed generation scheme of reconfigurable DR-PVB is desired for applications in both optical tweezers and orbital angular momentum (OAM) multiplexing.
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http://dx.doi.org/10.1364/OE.424664DOI Listing
May 2021

Simple and precise characterization of differential modal group delay arising in few-mode fiber.

Opt Lett 2021 Jun;46(12):2856-2859

In this Letter, we propose a simple and high-precision differential modal group delay (DMGD) characterization method for few-mode fibers (FMF) by using the frequency-modulated continuous wave. Since the detected signals are located at the low-frequency range, our DMGD characterization method waives the use of expensive equipment, such as vector network or optical spectrum analyzers. Due to the high linearity of the used Mach-Zehnder modulator, our DMGD measurement is free from the complex auxiliary interferometer, leading to an improvement of characterization precision. Meanwhile, we propose a novel spectrum recovery algorithm to overcome the shortcoming that the traditional fast Fourier transform (FFT) method is incapable to deal with spectrum features arising in a periodic signal. Therefore, the characterization precision is no longer limited by the FFT length. When a commercial 23299.8 m two-mode fiber is used in the experiment, the DMGD measurement of mode relative to mode has a high precision of ±0.007/ over the C-band. Our proposed method shows the potential for characterizing the wavelength-dependent DMGD of FMF with more than two LP modes.
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http://dx.doi.org/10.1364/OL.423950DOI Listing
June 2021

All-optical polarization split of the signal and LO for a bi-directional self-homodyne coherent system.

Opt Lett 2021 Jun;46(12):2819-2822

In this Letter, we propose a cost-efficient bi-directional (BiDi) polarization-multiplexed self-homodyne coherent detection (SHCD) system, in which only one fiber link and one adaptive polarization controller (APC) are required. By employing the correlation of the state of polarization (SOP) between the upstream and downstream light, one APC is capable of stabilizing SOPs of the counterpropagating waves at the same time. The signal and local oscillator (LO) can be optically split by a polarization beam splitter (PBS), relaxing pressure of the digital signal processing (DSP) and simplifying the coherent receiver. The impact induced by polarization cross talk and delay mismatch is collectively investigated by theoretical analysis and simulation. Finally, the proposed scheme is experimentally verified through 120 Gbit/s 16-quadrature amplitude modulation (16-QAM) transmission, achieving a satisfying laser-linewidth tolerance of 10 MHz and a polarization rotation tolerance of up to 45 rad/s.
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http://dx.doi.org/10.1364/OL.427789DOI Listing
June 2021

Low-Temperature-Induced Controllable Transversal Shell Growth of NaLnF Nanocrystals.

Nanomaterials (Basel) 2021 Mar 8;11(3). Epub 2021 Mar 8.

State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics Fine Mechanics and Physics Chinese Academy of Sciences, Changchun 130033, China.

Highly controllable anisotropic shell growth is essential for further engineering the function and properties of lanthanide-doped luminescence nanocrystals, especially in some of the advanced applications such as multi-mode bioimaging, security coding and three-dimensional (3D) display. However, the understanding of the transversal shell growth mechanism is still limited today, because the shell growth direction is impacted by multiple complex factors, such as the anisotropy of surface ligand-binding energy, anisotropic core-shell lattice mismatch, the size of cores and varied shell crystalline stability. Herein, we report a highly controlled transversal shell growth method for hexagonal sodium rare-earth tetrafluoride (β-NaLnF) nanocrystals. Exploiting the relationship between reaction temperature and shell growth direction, we found that the shell growth direction could be tuned from longitudinal to transversal by decreasing the reaction temperature from 310 °C to 280 °C. In addition to the reaction temperature, we also discussed the roles of other factors in the transversal shell growth of nanocrystals. A suitable core size and a relative lower shell precursor concentration could promote transversal shell growth, although different shell hosts played a minor role in changing the shell growth direction.
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http://dx.doi.org/10.3390/nano11030654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7999601PMC
March 2021

Analog-digital hybrid chaos-based long-haul coherent optical secure communication.

Opt Lett 2021 Apr;46(7):1506-1509

We propose and numerically investigate a chaotic optical coherent secure communication scheme, which supports long-haul secure transmission for signals in advanced modulation formats. A hybrid optical chaos system is designed with coordination of digital and analog signals. The hybrid entropy source provides a broadband analog optical chaos signal, which could serve as the carrier to load quadrature amplitude modulation (QAM) data. Simultaneously, a digital binary signal generated from the entropy source is transmitted to establish long-haul chaotic synchronization. Coherent detection is utilized at the receiver, and a digital signal processing (DSP) algorithm is adopted to reduce transmission distortion. A 5 Gbaud 16QAM signal is encrypted by a phase chaos carrier with the effective bandwidth of 5.8 GHz. A bit error rate (BER) below forward error correction (FEC) can be achieved after transmitting over 1600 km based on digital-signal-induced chaos synchronization technology. Optimal launch power is investigated to minimize nonlinear effects of transmission links. System security is guaranteed by the high dynamical complexity of the chaotic source and the sensitive time delay as the secret key.
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http://dx.doi.org/10.1364/OL.421770DOI Listing
April 2021

Dietary daidzein inhibits hepatitis C virus replication by decreasing microRNA-122 levels.

Virus Res 2021 Jun 26;298:198404. Epub 2021 Mar 26.

Department of Dermatology, Chongqing Traditional Chinese Medicine Hospital, Chongqing, 400011, PR China. Electronic address:

MicroRNAs are emerging as critical endogenous regulators of gene function. Aberrant regulation of microRNAs is associated with various human diseases, most importantly cancer. MicroRNA-122 (miR-122), a liver-specific microRNA, has been implicated in the control of hepatitis C virus (HCV) RNA replication and its response to interferon (IFN) in human hepatoma cells. Here, we report that daidzein, a naturally occurring plant isoflavone, inhibits HCV replication and enhances the antiviral effect of IFN-α on HCV therapy by decreasing microRNA-122 levels in vitro without significantly affecting cell growth. Moreover, daidzein was found to inhibit the expression of miR-122 and miR-21 by down-regulating the expression of TRBP, indicating that daidzein is possibly a general inhibitor of the miRNA pathway. Thus, daidzein provides new insights for drug discovery and HCV prevention.
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http://dx.doi.org/10.1016/j.virusres.2021.198404DOI Listing
June 2021

Improved receiver of ICI compensation for a spectral efficient frequency division multiplexing IM/DD system.

Opt Express 2021 Feb;29(3):3067-3080

Spectral efficient frequency division multiplexing (SEFDM) can greatly increase the spectral efficiency for intensity modulation/direct detection (IM/DD) optical communication systems. The sphere detection algorithm (SD) is the most efficient way to get the maximum likelihood (ML) solution to solve the inter-carrier interference (ICI) induced by the bandwidth compression of SEFDM system. However, SD algorithm is restricted by the numbers of subcarriers for SEFDM system, especially for larger numbers. Therefore, a sorted Gram-Schmidt (SGS) orthogonal decomposition algorithm, which can be applied to any subcarrier numbers, is proposed to overcome this restriction. To the best of our knowledge, the searched paths of FSD are researched for the first time to balance performance and complexity. Based on the analysis, a soft-tree-width sphere detection algorithm (SSD) is proposed and demonstrated by simulation and experiment. The results show that the proposed algorithm can greatly reduce the computational complexity (at least 40%) with the same system performance. The proposed algorithms are a promising candidate for flexible and efficient SEFDM systems. The SEFDM with the proposed detector is significant for the IM/DD optical systems.
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http://dx.doi.org/10.1364/OE.413161DOI Listing
February 2021

Experimental demonstration of secure 100 Gb/s IMDD transmission over a 50 km SSMF using a quantum noise stream cipher and optical coarse-to-fine modulation.

Opt Express 2021 Feb;29(4):5475-5486

In this paper, we experimentally demonstrate a secure 100 Gb/s 2-level intensity modulation and direct detection transmission over a 50 km standard single-mode fiber (SSMF) using a quantum noise stream cipher (QNSC) technique and 8-bit digital to analog converters. Optical coarse-to-fine modulation (CTFM) has been proposed to simultaneously enhance the security and overcome the weakness of low modulation depth in the traditional CTFM scheme. The optical power instead of the radio-frequency signal power is adjusted to satisfy the required peak-to-peak relation for CTFM, and thus the coarse and fine modulation has the same modulation depth. Two optical CTFM schemes based on an optical coupler and a polarizing beam combiner (PBC) are proposed and their pros and cons are analyzed and compared. Considering the trade-off of transmission performance and security performance, the optical CTFM scheme based on PBC is preferred in our experiment. 2-level pulse amplitude modulation (PAM) is achieved using two dual-drive Mach-Zehnder modulators (DD-MZM). Simultaneously, each DD-MZM is also used to achieve single-sideband (SSB) modulation to eliminate the power fading induced by fiber dispersion. By these means, 100 Gb/s 2-level PAM-QNSC signal transmission over 50 km SSMF with the bit error rate below the 7% overhead hard-decision forward error correction threshold of 3.8×10 is achieved. The results validate that the proposed scheme is effective to realize low-cost, high-speed, and highly secure optical transmission in the data center.
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http://dx.doi.org/10.1364/OE.418589DOI Listing
February 2021

Joint Fiber Nonlinear Noise Estimation, OSNR Estimation and Modulation Format Identification Based on Asynchronous Complex Histograms and Deep Learning for Digital Coherent Receivers.

Sensors (Basel) 2021 Jan 7;21(2). Epub 2021 Jan 7.

The School of Optics and Electronics Information, Huazhong University of Science and Technology, Wuhan 430074, China.

In this paper, asynchronous complex histogram (ACH)-based multi-task artificial neural networks (MT-ANNs), are proposed to realize modulation format identification (MFI), optical signal-to-noise ratio (OSNR) estimation and fiber nonlinear (NL) noise power estimation simultaneously for coherent optical communication. Optical performance monitoring (OPM) is demonstrated with polarization mode multiplexing (PDM), 16 quadrature amplitude modulation (QAM), PDM-32QAM, as well as PDM-star 16QAM (S-16QAM) for the first time. The range of launched power is -3 to -2 dBm with a fiber link of 160-1600 km. Then, the accuracy of MFI reaches 100%. The average root mean square error (RMSE) of OSNR estimation can reach 0.37 dB. The average RMSE of NL noise power estimation can reach 0.25 dB. The results show that the monitoring scheme is robust to the increase of fiber length, and the solution can monitor more optical network parameters with better performance and fewer training data, simultaneously. The proposed ACH MT-ANN has certain reference significance for the future long-haul coherent OPM system.
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http://dx.doi.org/10.3390/s21020380DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7827563PMC
January 2021

Starch and mineral element accumulation during root tuber expansion period of Pueraria thomsonii Benth.

Food Chem 2021 May 22;343:128445. Epub 2020 Oct 22.

Hunan Provincial Key Laboratory of Crop Germplasm Innovation and Utilization, Hunan Agricultural University, Changsha 410128, People's Republic of China. Electronic address:

Pueraria is a medicine plant with rich starch, and thus can be a potential agricultural and industrial resource. In this study, we evaluated the root tuber yield of a cultivar of starch kudzu (Pueraria thomsonii) and the starch accumulation during expansion period of root tuber. Additionally, mineral elements were quantified in root tuber and starch. The results indicated that the starch kudzu cultivar owned high yield of root tuber (greater than42 tons/hm), high starch content (greater than17% FW) in root tuber, and rich accumulation of beneficial mineral elements. Interestingly, the root tuber of P. thomsonii contained a high concentration of selenium (70 mg/kg FW) and strontium (40 mg/kg FW), and thus it can be utilized as a Se and Sr rich food. Furthermore, Se and Sr can be well preserved in starch through the optimized starch extraction method.
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http://dx.doi.org/10.1016/j.foodchem.2020.128445DOI Listing
May 2021

Sensitivity Characterization of Cascaded Long-Period Gratings Operating near the Phase-Matching Turning Point.

Sensors (Basel) 2020 Oct 22;20(21). Epub 2020 Oct 22.

School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China.

We characterized a cascaded long-period gratings (LPGs)-based sensor that was operating at the phase-matching turning point (PMTP). The cascaded LPGs constructed an in-fiber Mach-Zehnder interferometer (MZI), which exhibited a series of high-quality-factor () narrow-bandwidth resonance peaks. As the LPG operated at the PMTP, the proposed sensor showed an ultrahigh refractive index (RI) and temperature sensitivity, and high measurement precision. In this study, we took an in-depth look at the effects of grating separation on Q-factor and sensitivity. The results showed that the sensitivity to the surrounding refractive index (SRI) reached 4741.5 nm/RIU at 1.4255 and 2138 nm/RIU, over the range of 1.335-1.373. In addition, the temperature sensitivity was around 4.84 nm/°C. With a 0.02 nm wavelength resolution, the RI and temperature sensing limits were 9.3 × 10 RIU and 5.5 × 10 °C.
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http://dx.doi.org/10.3390/s20215978DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7659956PMC
October 2020

Inverse design of a single-step-etched ultracompact silicon polarization rotator.

Opt Express 2020 Sep;28(19):28343-28351

We propose and experimentally demonstrate a novel ultracompact silicon polarization rotator based on equivalent asymmetric waveguide cross section in only single-step etching procedure for densely integrated on-chip mode-division multiplexing system. In the conventional mode hybridization scheme, the asymmetric waveguide cross section is employed to excite the hybridized modes to realize high performance polarization rotator with compact footprint and high polarization extinction ratio. However, the fabrication complexity severely restricts the potential application of asymmetric waveguide cross section. We use inverse-designed photonic-crystal-like subwavelength structure to realize an equivalent asymmetric waveguide cross section, which can be fabricated in only single-step etching process. Besides, a theory-assisted inverse design method based on a manually-set initial pattern is employed to optimize the device to improve design efficiency and device perform. The fabricated device exhibited high performance with a compact footprint of only 1.2 × 7.2 µm, high extinction ratio (> 19 dB) and low insertion loss (< 0.7 dB) from 1530 to 1590 nm.
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http://dx.doi.org/10.1364/OE.399052DOI Listing
September 2020

Glyoxalase system: A systematic review of its biological activity, related-diseases, screening methods and small molecule regulators.

Biomed Pharmacother 2020 Nov 25;131:110663. Epub 2020 Aug 25.

Department of Dermatology, Chongqing Traditional Chinese Medicine Hospital, Chongqing, 400011, PR China. Electronic address:

The glyoxalase system is a ubiquitous enzymatic network which plays important roles in biological life. It consists of glyoxalase 1 (GLO1), glyoxalase 2 (GLO2), and reduced glutathione (GSH), which perform an essential metabolic function in cells by detoxifying methylglyoxal (MG) and other endogenous harmful metabolites into non-toxic d-lactate. MG and MG-derived advanced glycation endproducts (AGEs) are associated with various diseases, such as diabetes, cardiovascular disease, neurodegenerative disorders and cancer, and GLO1 is a key rate-limiting enzyme in the anti-glycation defense. The abnormal activity and expression of GLO1 in various diseases make this enzyme a promising target for drug design and development. This review focuses on the regulatory mechanism of GLO1 in diverse pathogenic conditions with a thorough discussion of GLO1 regulators since their discovery, including GLO1 activators and inhibitors. The different classes, chemical structure and structure-activity relationship are embraced. Moreover, assays for the discovery of small molecule regulators of the glyoxalase system are also introduced in this article. Compared with spectrophotometer-based assay, microplate-based assay is a more simple, rapid and quantitative high-throughput method. This review will be useful to design novel and potent GLO1 regulators and hopefully provide a convenient reference for researchers.
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http://dx.doi.org/10.1016/j.biopha.2020.110663DOI Listing
November 2020

Femtosecond laser micro-machining enabled all-fiber mode selective converter.

Opt Lett 2019 Dec;44(24):5941-5944

We demonstrate a compact all-fiber mode selective converter enabled by femtosecond laser micro-machining on the few-mode fiber (FMF) facet. By introducing a micro-structure into the FMF core, we can achieve a spatial phase difference to the fundamental mode of light to be converted. Theoretical optimization reveals that various high-order modes, including , , and modes, can be selectively converted by various micro-structures on the FMF facet, with a mode extinction ratio of more than 25 dB and mode coupling efficiency of better than 45% over the C-band. Finally, a proof-of-concept experiment is conducted by inscribing a micro-slot on the two-mode fiber facet for the to mode conversion. A micro-slot with a width of 6.7 µm and a depth of 5.4 µm is fabricated under the optimal femtosecond laser parameters. A to mode conversion with an average insertion loss of 2.7 dB is realized over the C-band, together with a mode intensity profile correlation efficient of more than 65%. Efficient higher-order mode conversion is feasible with a precise femtosecond laser micro-machining.
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http://dx.doi.org/10.1364/OL.44.005941DOI Listing
December 2019

Robust chaotic-shift-keying scheme based on electro-optical hybrid feedback system.

Opt Express 2020 Apr;28(8):10847-10858

A chaotic-shift-keying (CSK) scheme is designed based on a chaos system with electro-optical hybrid time delayed feedback structure. By switching the time delay parameter as a message feeding method, the generated chaotic signal is no longer suffered from return map attack, which is an innate vulnerability of traditional CSK. When the coupling of the seed electrical chaotic system and the nonlinear optical time delay feedback loop is carefully weighed, this CSK scheme shows a good robustness in terms of handling noise for transmitting digital signals. By demodulating the digital signals with the chaotic coherent detection method, a bit error rate of 6×10 is achieved at the signal-to-noise ratio of 10dB in the simulation. The proposed method has a promising application prospect in some harsh environments.
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http://dx.doi.org/10.1364/OE.389251DOI Listing
April 2020

Unveil the time delay signature of optical chaos systems with a convolutional neural network.

Opt Express 2020 May;28(10):15221-15231

We propose a time delay signature extraction method for optical chaos systems based on a convolutional neural network. Through transforming the time delay signature of a one-dimensional time series into two-dimensional image features, the excellent ability of convolutional neural networks for image feature recognition is fully utilized. The effectiveness of the method is verified on chaos systems with opto-electronic feedback and all optical feedback. The recognition accuracy of the method is 100% under normal conditions. For the system with extremely strong nonlinearity, the accuracy can be 93.25%, and the amount of data required is less than traditional methods. Moreover, it is verified that the proposed method possesses a strong ability to withstand the effects of noise.
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http://dx.doi.org/10.1364/OE.388182DOI Listing
May 2020

Low-complexity equalization scheme for suppressing FFE-enhanced in-band noise and ISI in 100 Gbps PAM4 optical IMDD system.

Opt Lett 2020 May;45(9):2555-2558

The commonly used feed-forward equalizer (FFE) in an intensity modulation and direct-detection (IMDD) system is seriously restrained by the enhanced in-band noise in the high-frequency region. In this Letter, a low-complexity equalization scheme including FFE, post-filter (PF), and a newly designed interference cancellation (IC) algorithm is proposed to cope with the FFE-enhanced noise and serious inter-symbol interference (ISI) simultaneously. In our experiment, the achieved bit error rate value of 100 Gb/s optical double-sideband (ODSB) four-level pulse amplitude modulation (PAM4) signal transmission over 10 km standard single-mode fiber (SSMF) can go below the 20% overhead soft-decision forward error correction threshold of ${2.7} \times {{10}^{ - 2}}$2.7×10 when the FFE is replaced by the proposed equalizer. Even a 100 Gb/s optical single-sideband (OSSB) PAM4 signal can be successfully transmitted over 80 km SSMF. The results show that the proposed ${\rm FFE}+{\rm PF}+{\rm IC}$FFE+PF+IC algorithm can effectively suppress the FFE-enhanced noise and ISI with a quite low increase in complexity. Moreover, compared to the joint FFE, PF, and maximum likelihood sequence detection (MLSD) algorithm, the proposed ${\rm FFE}+{\rm PF}+{\rm IC}$FFE+PF+IC algorithm has 1.2 dB and 0.4 dB power penalties after 10 km SSMF in ODSB and 80 km SSMF in OSSB cases, respectively. However, the complexity of this IC algorithm is approximately 3% that of the MLSD.
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http://dx.doi.org/10.1364/OL.392344DOI Listing
May 2020

Multiple High-Affinity K Transporters and ABC Transporters Involved in K Uptake/Transport in the Potassium-Hyperaccumulator Plant Roxb.

Plants (Basel) 2020 Apr 8;9(4). Epub 2020 Apr 8.

Hunan Provincial Key Laboratory of Phytohormones and Growth Development, Hunan Agricultural University, Changsha 410128, China.

Potassium is an important essential element for plant growth and development. Long-term potassium deprivation can lead to a severe deficiency phenotype in plants. Interestingly, is a plant with an unusually high potassium content and can grow well and complete its lifecycle even in severely potassium deficient soil. In this study, we found that its stems and leaves were the main tissues for high potassium accumulation, and showed a strong ability of K absorption in roots and a large capability of potassium accumulation in shoots. Analysis of plant growth and physiological characteristics indicated that had an adaptability in a wide range of external potassium levels. To reveal the mechanism of K uptake and transport in the potassium-hyperaccumulator plant , K uptake-/transport-related genes were screened by transcriptome sequencing, and their expression profiles were compared between K starved plants and normal cultured plants. Eighteen members of HAK/KT/KUPs, ten members of AKTs, and one member of HKT were identified in . Among them, six , and two and showed significantly different expression. These transporters might be coordinatively involved in K uptake/transport in and lead to high potassium accumulation in plant tissues. In addition, significantly changed expression of some ABC transporters indicated that ABC transporters might be important for K uptake and transport in under low K concentrations.
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http://dx.doi.org/10.3390/plants9040470DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7238005PMC
April 2020

Transfer learning simplified multi-task deep neural network for PDM-64QAM optical performance monitoring.

Opt Express 2020 Mar;28(5):7607-7617

We experimentally demonstrate a transfer learning (TL) simplified multi-task deep neural network (MT-DNN) for joint optical signal-to-noise ratio (OSNR) monitoring and modulation format identification (MFI) from directly detected PDM-64QAM signals. First, we investigate the quality of amplitude histogram (AH) generation on the performance of OSNR monitoring and experimentally clarify the importance of higher electronic sampling rate in order to realize precise OSNR monitoring for high-order QAM format. Next, by implementing TL from simulation to experiment, when both 10Gbaud PDM-16QAM and PDM-64QAM signals are considered, the accuracy of MFI reaches 100% and the root-mean-square error (RMSE) of OSNR monitoring is 1.09dB over a range of 14-24dB and 23-34dB for PDM-16QAM and PDM-64QAM, respectively. Meanwhile, the used training samples and epochs can be substantially reduced by 24.5% and 44.4%, respectively. Since single photodetector (PD) and one TL simplified MT-DNN are used, the proposed optical performance monitoring (OPM) scheme with high cost performance can be applied for advanced modulation formats.
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http://dx.doi.org/10.1364/OE.388491DOI Listing
March 2020

Laser linewidth tolerance for nonlinear frequency division multiplexing transmission with discrete spectrum modulation.

Opt Express 2020 Mar;28(7):9642-9652

Although fruitful investigations of carrier phase estimation (CPE) have been conducted for a traditional coherent fiber optical transmission, there are few studies on the CPE for a nonlinear Fourier transform (NFT) based transmission. A laser linewidth induced phase noise leads to a phase rotation of the nonlinear spectra and the scattering data, which is similar to its effect on the linear spectra. Here, we first identify that both feed forward the M-th power, and the blind phase search (BPS)-based CPE can function well in the nonlinear frequency division multiplexing (NFDM) transmission with discrete spectrum modulation. Then, a performance comparison between two CPE schemes is presented for various modulation formats under the scenario of a single eigenvalue NFDM transmission. Our simulation results indicate that the laser linewidth tolerances of 2 GBaud quadrature phase shift keying (QPSK), 8-phase shift keying (8-PSK), and 16-amplitude phase shift keying (16-APSK) are 2.3 MHz, 1.05 MHz, and 250 KHz, respectively, given a 1-dB optical signal to noise ratio (OSNR) penalty at BER = 10. Finally, the BPS algorithm is experimentally verified under the same scenario of a 2 GBaud back-to-back transmission, due to the use of a semiconductor laser with a 100 KHz linewidth.
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http://dx.doi.org/10.1364/OE.387560DOI Listing
March 2020

Ultra-narrow-linewidth measurement utilizing dual-parameter acquisition through a partially coherent light interference.

Opt Express 2020 Mar;28(6):8484-8493

Laser linewidths of the order of 100 Hz are challenging to measure with existing technology. We propose a simple, efficient method to measure ultra-narrow linewidths using dual-parameter acquisition based on partially coherent light interference. The linewidth is obtained using two parameters that are easily extracted from the power spectrum. This method reduces the influence of 1/f noise by utilizing a kilometer-order-length delay fiber and is independent of the fiber-length error for a general situation. Simulation results show that, for a length error less than 10%, the total linewidth measurement error is less than 0.3%. Experimental results confirm the feasibility and superior performance of this method.
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http://dx.doi.org/10.1364/OE.387398DOI Listing
March 2020

Polarization and direction-controlled asymmetric multifunctional metadevice for focusing, vortex and Bessel beam generation.

Opt Express 2020 Feb;28(3):3732-3744

Integrating multiple independent functionalities into one single photonic device has been an important part in optoelectronic system. In this paper, we here propose a kind of asymmetric multifunctional metadevice operating at 1550 nm (in optical communication band), which can manipulate the light with four different functions, depending on the polarization and illumination direction of incident light. As a proof of our concept, we design this metadevice composed of the upper metasurface layer, middle grating layer and lower metasurface layer. For x-polarized incident light, the metadevice under forward illumination works as transmissive focusing lens and vortex beam generator of y-polarized light, while under backward illumination it acts as a reflective vortex beam generator. In contrast, for y-polarized incident light, the metadevice under forward illumination behaves as a reflective Bessel beam generator, while a combination of transmissive vortex beam generator and focusing lens of x-polarized light under backward illumination. Our findings may motivate the realization of high-performance multifunctional metadevices and extend the application in complex integrated optical system.
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http://dx.doi.org/10.1364/OE.382580DOI Listing
February 2020

Parallel Fabry-Perot interferometers fabricated on multicore-fiber for temperature and strain discriminative sensing.

Opt Express 2020 Feb;28(3):3190-3199

We experimentally demonstrate parallel Fabry-Perot interferometers (FPIs) fabrication in multicore-fiber with individually variable cavity length, for the purpose of discriminative sensing of temperature and strain. First, we theoretically find that, in order to obtain a small condition number of sensitivity matrix, it is necessary to fabricate parallel FPIs with large cavity difference in single multicore fiber. Then, parallel FPIs are inscribed by femtosecond laser selective micro-holes drilling on the seven-core fiber facet, together with fiber fusion splicing process. By the use of image processing algorithm, individual core position is precisely locked, and then parallel FPIs can be obtained on arbitrary two cores of seven-core fiber. With the location of parallel micro-holes and duration time of fiber fusion splicing adjusted, parallel FPIs with different cavity length of 26µm and 61µm can be simultaneously obtained at the central core and surrounding core, respectively. Consequently, each FPI possesses different sensitivity towards environmental temperature and strain. Finally, a proof-of-concept experiment verifies that relative measurement errors of both temperature and strain discriminative sensing are less than 0.5% and 2.5%, respectively.
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http://dx.doi.org/10.1364/OE.384922DOI Listing
February 2020

Single-axis soliton molecule and multiple solitons generation from a vector fiber laser.

Opt Express 2020 Feb;28(4):5212-5220

We investigate various patterns of vector solitons arising in a passively mode-locked fiber laser based on semiconductor saturable absorber mirror (SESAM). By properly adjusting the cavity parameters including the pump power and intra-cavity birefringence, the fundamental vector solitons, vector soliton molecules, and macroscopic vector solitons can be separately observed. In particular, both vector soliton molecule and macroscopic vector solitons exhibit multi-pulse structure along one polarization axis while there occurs single pulse profile at its orthogonal polarization component. Thus, they can be treated as "1 + 2" and "1+n" vector solitons. Moreover, the size of the macroscopic solitons can be manipulated from half of the cavity to even the whole cavity. The generation mechanisms of these vector soliton patterns are also investigated.
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http://dx.doi.org/10.1364/OE.385217DOI Listing
February 2020

Peak-power-clamping in an all-polarization-maintaining Q-switched mode-locking fiber laser.

Opt Express 2019 Dec;27(26):37614-37621

We report the peak-power-clamping (PPC) effect in a polarization-maintaining (PM) Q-switched mode locking fiber laser. The laser cavity with a compact and stable all-PM fiber configuration can clearly demonstrate three different output states including normal Q-switching, PPC Q-switching, and PPC Q-switched mode-locking (QML) with the increasing pump power. To the best of our knowledge, it is the first time that PPC effect is successfully obtained and analyzed from the Q-switching to QML. This research extends the theory of PPC in pulsed lasers and reveals the potential to achieve ultra-high pulse energy.
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http://dx.doi.org/10.1364/OE.27.037614DOI Listing
December 2019

Optimized self-interference cancellation based on optical dual-parallel MZM for co-frequency and co-time full duplex wireless communication under nonlinear distortion and emulated multipath effect.

Opt Express 2019 Dec;27(26):37286-37297

Co-frequency and co-time full duplex (CCFD) technique has the potential to further improve the capacity of the fifth-generation (5G) system. However, in a CCFD-based transceiver, the self-interference-cancellation (SIC) module is essential because the transmitted signal is also captured by the receiving antenna. In this paper, an optimized SIC technique is proposed based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In addition to the multipath effect between the transmitting and receiving antennas, the nonlinear distortion induced by the used optical and electrical components is considered and analyzed for the first time. In this scheme, one of the children MZMs is biased at 90°. The bias points of the other child MZM and the parent MZM are swept for SIC optimization. Compared to the traditional SIC scheme using DP-MZM, the power of the received signal is increased by 6 dB and the robustness to the bias point drift is improved. In our experiment, over 35 dB cancellation ratio is achieved for 200 MHz filtered orthogonal frequency division multiplexing (F-OFDM) interference signal with carrier frequency from 2.5 GHz to 6 GHz. To mitigate the influence of multipath effect and nonlinear distortion, the recursive least squared (RLS) linear equalizer and the RLS Volterra equalizer are designed and compared. Finally, 42 dB cancellation ratio is achieved for 200 MHz F-OFDM signal with carrier frequency of 4.5 GHz in the presence of nonlinear distortion and emulated multipath effect.
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http://dx.doi.org/10.1364/OE.27.037286DOI Listing
December 2019

Single-step digital backpropagation for subcarrier-multiplexing transmissions.

Opt Express 2019 Dec;27(25):36680-36690

We propose and demonstrate a single-step digital back propagation (DBP) algorithm for metro and regional transmissions with high order modulation formats. Based on subcarrier-multiplexing (SCM)-DBP, two modifications are made to improve performance and reduce complexity for the targeted link scenarios. First, an infinite impulse response (IIR) filter is adopted in self-subcarrier nonlinear compensation. Second, the second stage chromatic dispersion (CD) compensation is incorporated into an existing adaptive filter. Through experiment, we demonstrate the performance of the proposed scheme, denoted as M-SCM-DBP, for single channel 34.94-GBd SCM PDM-32QAM transmission. With 86.3% complexity reduction compared with the low-pass filter assisted DBP, the proposed M-SCM-DBP achieves 0.6-dB Q improvement for SCM-PDM-32QAM transmission over 960-km standard single mode fiber (SSMF). The reach extension of 36% to 1220-km is achieved with only 30.5 complex multiplications per sample, in comparison with the linear compensation scheme. Since the adaptive filter is used to simultaneously compensate 50% CD and other linear impairments, we also investigate the required number of filter taps and its polarization tracking ability.
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http://dx.doi.org/10.1364/OE.27.036680DOI Listing
December 2019

Design of elliptical-core five-mode group selective photonic lantern over the C-band.

Opt Express 2019 Sep;27(20):27979-27990

We report the design of an elliptical-core five-mode group selective photonic lantern (EC-F-MGS-PL) supporting ten spatial modes over the C-band, whose output fiber is an elliptical-core few mode fiber (EC-FMF). Initially, we fix the cladding diameters of all input fibers to form an elliptical structure. With the help of beam propagation methods (BPM), we carry out comprehensive geometrical optimization of various input fiber bundle, and identify the optimal setting of input fiber bundle in order to achieve the maximum mode selectivity, low insertion loss (IL), and high mode conversion efficiency (MCE) for all five mode groups. Next, we optimize each fiber core diameter and propose a two-step tapering process, for the ease of performance enhancement for the EC-F-MGS-PL. Finally, the mode field evolution and the wavelength dependent operation of the proposed EC-F-MGS-PL is numerically investigated. A mode selectivity of 9∼17 dB and IL of 0.1∼0.38 dB for all five mode groups can be achieved over the C-band, while MCE keeps between 83.3%-95.8%. By taking into account of the fabrication process, we believe that both the design strategy and optimization procedure of the EC-F-MGS-PL are helpful for the implementation of multi-input-multi-output (MIMO)-less mode division multiplexing (MDM) transmission.
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http://dx.doi.org/10.1364/OE.27.027979DOI Listing
September 2019

Microwave photonic RF front-end for co-frequency co-time full duplex 5G communication with integrated RF signal self-interference cancellation, optoelectronic oscillator and frequency down-conversion.

Opt Express 2019 Oct;27(22):32147-32157

A novel RF front-end, which could simultaneously realize wideband RF signal self-interference cancellation (SIC), local oscillator (LO) generator based on optoelectronic oscillator (OEO) and frequency down-conversion has been proposed and experimentally demonstrated. In our microwave photonic RF front-end, only one single-polarization optical in-phase and quadrature-phase (IQ) modulator are required. The upper Mach-Zehnder modulator (MZM) of this optical IQ modulator works as a mixer; the lower MZM works as a reference arm; the parent Mach-Zehnder interferometer (MZI) is used to combine two output optical signals of these two child MZMs. In this way, not only self-interference signal is cancelled in optical domain but also frequency down-conversion is realized at the same time. On the other hand, the upper MZM is also shared to form an OEO by using a self-polarization-stabilization technique. By this means, no external LO signal for frequency down-conversion and electrical attenuator for SIC are needed in our scheme, contributing to compact structure and cost reduction. In our proof-of-concept experiment, a LO signal with central frequency of 10 GHz and phase noise of -108.66 dBc/[email protected] is generated. By optimizing the bias points of the used optical IQ modulator, a 5×20MHz 64-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (64QAM-OFDM) LTE-A signal with central frequency of 12.6 GHz is down-converted to 2.6 GHz, and about 28 dB cancellation ratio is achieved. The proposed scheme is suitable for wideband, integrated co-frequency co-time full duplex 5G communication.
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http://dx.doi.org/10.1364/OE.27.032147DOI Listing
October 2019
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