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1.
Ecotoxicology ; 2021 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-33432458

RESUMO

Long-term frequent tillage would cause black soil degradation and serious soil erosion as soil microbial communities and soil structure are extremely sensitive to tillage process. However, there is no unified conclusion on the relationship between the distribution of soil water-stable aggregates (WSAs), and microbial community construction and diversity under long-term tillage in black soil during different seasons. In this study, we used wet-sieving method to evaluate the composition and stability of soil WSAs and employed Illumina MiSeq high-throughput sequencing technology to study the diversity, taxonomic composition and co-occurrence network properties of microbial community, comparing outcomes between uncultivated soil and long-term cultivated soil for 60 years in Keshan farm of Heilongjiang Province. The results showed that after long-term tillage, the proportion of larger than 1 mm WSAs reduced by 34.17-51.37%, and the stability of WSAs, soil pH, organic matter (OM), total nitrogen (TN) contents decreased significantly in all seasons (P < 0.05), while soil available phosphorus (AP) and available potassium (AK) contents increased remarkably (P < 0.05). The diversity of bacteria increased, while that of fungi decreased. Soil fungal communities were more susceptible to long-term tillage than bacterial and archaeal communities. Actinobacteria mainly exist in large WSAs (˃1 mm), and when their relative abundance is high, it is beneficial to improve the water-stability of black soil; while Proteobacteria and Gemmatimonadetes may exist in small WSAs (˂1 mm), whose high relative abundance will weaken the water-stability of black soil. The experimental results provide a scientific theoretical basis for sustainable utilization of black soil.

2.
Opt Lett ; 45(19): 5381-5384, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-33001899

RESUMO

A photonic scanning receiver with optical frequency scanning and electrical intermediate frequency envelope detection is proposed to implement wide-range microwave frequency measurement. This system applies photonic in-phase and quadrature frequency mixing to distinguish and measure the signals in two frequency bands that mirror each other. Combined with the photonic frequency octupling technique, the proposed system has a frequency measurement range that is 16 times that of the sweeping range of the electrical signal source. Besides, optical frequency sweeping with up and down chirps is used to relax the requirement for precise synchronization between the sweeping source and the analog-to-digital converter. In the experiment, using an electrical sweeping local oscillator having a bandwidth of 1.75 GHz, the system achieves a frequency measurement range as large as 28 GHz. The measurement errors are kept within 24 MHz with an average error of 9.31 MHz.

3.
Opt Lett ; 45(11): 3038-3041, 2020 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-32479453

RESUMO

A microwave instantaneous frequency measurement system with a photonic scanning receiver is proposed in which deep neural network (DNN)-assisted frequency estimation is used to deal with the system defects and improve the accuracy. The system performs frequency-to-time mapping by optical-domain frequency scanning and electrical-domain intermediate frequency envelop detection. Thanks to the optical frequency multiplication, the system can measure high frequency signals in a large spectral range. The DNN establishes an accurate mapping between the digital samples and real frequencies, based on which high-accuracy measurement is achieved. The measurement of signals from 43 to 52 GHz is experimentally demonstrated. Compared with the direct measurements, the DNN-assisted method achieves obviously reduced average errors of about 3.2 MHz.

4.
Opt Express ; 27(9): 13194-13203, 2019 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-31052848

RESUMO

A photonics-based broadband phased array radar is demonstrated to realize high-resolution imaging based on digital beamforming. This photonics-based phased array radar can achieve a high range resolution enabled by a large operation bandwidth, and can realize squint-free beam steering by digital true time delay (TTD) compensation. In addition, the photonic dechirp processing applied in the receiver can alleviate the hardware requirements for data sampling and storage, and hence remarkably enhance the real-time signal processing capability. In a proof-of-concept experiment, target imaging by a photonics-based 1 × 4 phased array radar that has a bandwidth of 4 GHz (22-26 GHz) is demonstrated, of which the range and azimuth resolution is measured to be 3.85 cm and 2.68°, respectively. The proposed scheme provides good solution to overcoming the bandwidth limitation and implementing high-resolution imaging in a phased array radar.

5.
Opt Lett ; 44(8): 1948-1951, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30985782

RESUMO

A photonics-based dual-functional system is proposed that can simultaneously implement high-resolution radar imaging and fast frequency measurement. In this system, the radar is realized based on photonic frequency doubling and de-chirp receiving, and the frequency measurement is achieved by a novel frequency-to-time mapping method. In the experimental demonstration, the radar works in Ku band with a bandwidth of 6 GHz (12-18 GHz), through which inverse synthetic aperture radar imaging with a resolution as high as ∼2.6 cm×∼2.8 cm is achieved. The frequency measurement module operates in Ka band, which can achieve a measurement frequency range from 28 GHz to 37 GHz, with a measurement resolution of 40 MHz and a refresh rate of 100 kHz.

6.
Cytometry A ; 95(5): 549-554, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-31006981

RESUMO

By virtue of the combined merits of optical microscopy and flow cytometry, imaging flow cytometry is a powerful tool for rapid, high-content analysis of single cells in large heterogeneous populations. However, its efficiency (defined by the ratio of the number of clearly imaged cells to the total cell population) is not high (typically 50-80%), due to out-of-focus image blurring caused by imperfect fluidic focusing of cells, a common drawback that not only reduces the number of cell images useable for high-content analysis but also increases the probability of false events and missed rare cells. To address this challenge and expand the efficacy of imaging flow cytometry, here, we propose and demonstrate intelligent deblurring of out-of-focus cell images in imaging flow cytometry. Specifically, by using our machine learning algorithms, we show an 11% increase in variance and a 95% increase in first-order gradient summation of cell images taken with an optofluidic time-stretch microscope. Without strict hardware requirements, our intelligent de-blurring method provides a promising solution to the out-of-focus blurring problem of imaging flow cytometers and holds promise for significantly improving their performance. © 2019 International Society for Advancement of Cytometry.


Assuntos
Citometria por Imagem/métodos , Processamento de Imagem Assistida por Computador , Algoritmos , Humanos , Células K562 , Aprendizado de Máquina , Microfluídica
7.
Opt Lett ; 43(21): 5439-5442, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30383027

RESUMO

An approach to enhancing the performance of an optically-injected-semiconductor-laser-based optoelectronic oscillator (OEO) is proposed by subharmonic microwave modulation. A free-running OEO is first established based on period-one dynamics of an optically injected semiconductor laser. The oscillation frequency can be tuned in the range of 8.87 to 18.41 GHz by controlling the injection strength, but the output signal suffers from strong side modes and poor frequency stability. To address these problems, subharmonic microwave modulation is applied to the injected semiconductor laser. In the experiment, microwave modulation with 1/2, 1/4, and 1/6 subharmonics is demonstrated. The side-mode suppression ratio is improved by over 40 dB, while the phase noise at a 1 kHz offset is reduced by about 18 dB. Furthermore, the frequency drift over a period of 20 min, which characterizes the long-term stability, is reduced from 8.7 kHz to less than 1 Hz, indicating a significant reduction of over three orders.

8.
Opt Lett ; 43(20): 5029-5032, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30320810

RESUMO

Phase noise analyzers (PNAs) are indispensable for evaluating the short-term stability of microwave signals. In this Letter, a high-sensitivity PNA with self-calibration capability is proposed based on an optical frequency comb generator and an optical-hybrid-based I/Q detector. The negative factors that result in inaccurate measurement, including the direct component interference, amplitude noises of the microwave signal under test and the laser, and phase noise of the laser, are all eliminated through digital signal processing. A proof-of-concept experiment is performed. The established PNA can achieve accurate phase noise measurement with a high sensitivity of -146.1 dBc/Hz at 10 kHz, and the self-calibrating property of the PNA is also verified.

9.
Opt Express ; 26(14): 18457-18469, 2018 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-30114025

RESUMO

A fiber-distributed ultra-wideband (UWB) radar network based on wavelength-reusing transceivers is proposed and demonstrated. In the proposed system, wavelength-division multiplexing technology is applied to connect a central unit (CU) and several spatially separated transceivers. The optically generated UWB pulses in different transceivers are designed to have different polarities or shapes, so the CU can easily identify which transceiver the echo UWB pulse is emitted from. By applying the wavelength reusing, the wavelength of the uplink UWB pulse can also be used by the CU to identify which transceiver it is received by. Therefore, with very simple cooperative signal processing in the CU, the information of the target in the radar detection area can be extracted. In addition, because the fiber lengths in the network are known, clock synchronization in the transceivers is not required, which simplifies further the entire system. In an experiment, 2-D localization with localization accuracy of about one centimeter is achieved using the proposed radar network with two distributed transceivers.

10.
Appl Opt ; 57(18): 4977-4984, 2018 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-30117954

RESUMO

A multi-circular optical phased array (OPA) is proposed and investigated through simulation to realize fast and wide-range optical beam steering with ultralow side lobes. The proposed multi-circular OPA has a circularly symmetrical distribution, and its radical element spacings are optimized by a modified genetic algorithm to achieve the best side lobe suppression. Specifically, the peak side lobe level (PSLL) of the far-field pattern in 0° beam direction reaches as low as 0.0715 for a 73-element optimized multi-circular OPA, which is much better than a multi-circular OPA with uniform radical element spacing (the PSLL is 0.3686). The prominent feature of the proposed OPA is that, once the OPA is optimized towards a specific elevation direction by the modified genetic algorithm, a wide-angle optical beam steering with nearly the same side lobe suppression can be achieved without updating the OPA distribution, which makes it possible for fast optical beam steering over a wide scanning range. In the simulation, ultralow side lobe beam steering with an elevation angle from 0° to 30° and an azimuth angle from 0° to 360° is achieved with the PSLL variation less than 0.001. The relationship between the optimized PSLL and the elevation angle used for OPA optimization is also investigated, which is helpful in achieving the best side lobe suppression for different scanning ranges. The proposed OPA is expected to find applications such as laser radar, high-resolution display, and free space optical communications.

11.
Opt Express ; 26(13): 17529-17540, 2018 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-30119564

RESUMO

A photonics-based multiple-input-multiple-output (MIMO) radar is proposed and demonstrated based on wavelength-division-multiplexed broadband microwave photonic signal generation and processing. The proposed radar has a large operation bandwidth, which helps to achieve an ultra-high range resolution. Compared with a monostatic radar, improved radar performance and extended radar applications originated from the MIMO architecture can be achieved. In addition, low-speed electronics with real-time signal processing capability is feasible. A photonics-based 2 × 2 MIMO radar is established with a 4-GHz bandwidth in each transmitter and a sampling rate of 100 MSa/s in the receiver. Performance of the photonics-based multi-channel signal generation and processing is evaluated, and an experiment for direction of arrival (DOA) estimation and target positioning is demonstrated, through which the feasibility of the proposed radar system can be verified.

12.
Opt Express ; 25(19): 22760-22768, 2017 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-29041582

RESUMO

A wideband microwave phase noise measurement system is proposed based on quadrature phase demodulation of the mixing components of a signal under test (SUT) and its delayed replica. The time delay is introduced by a low-loss optical fiber, which can be sufficiently large to achieve a high phase noise measurement sensitivity, and the quadrature phase demodulation is achieved by photonic-assisted in-phase and quadrate (I/Q) mixing together with digital signal processing. Thanks to the optoelectronic hybrid quadrature phase demodulation, the use of feedback loops, which are usually required in conventional photonic-delay-line-based phase noise measurement systems, is avoided, and the measurable frequency range is expanded. An experiment is implemented. Accurate phase noise measurement of SUTs in a frequency range of 5-35 GHz is demonstrated. With a 2-km single-mode fiber serving as the photonic delay line, the phase noise floor is as low as -131 dBc/Hz at the offset frequency of 10 kHz. The proposed scheme can be applied for evaluating the performance of microwave systems using low-phase-noise and wideband tunable microwave sources.

13.
Sci Rep ; 7(1): 13848, 2017 10 23.
Artigo em Inglês | MEDLINE | ID: mdl-29062093

RESUMO

Real-time and high-resolution target detection is highly desirable in modern radar applications. Electronic techniques have encountered grave difficulties in the development of such radars, which strictly rely on a large instantaneous bandwidth. In this article, a photonics-based real-time high-range-resolution radar is proposed with optical generation and processing of broadband linear frequency modulation (LFM) signals. A broadband LFM signal is generated in the transmitter by photonic frequency quadrupling, and the received echo is de-chirped to a low frequency signal by photonic frequency mixing. The system can operate at a high frequency and a large bandwidth while enabling real-time processing by low-speed analog-to-digital conversion and digital signal processing. A conceptual radar is established. Real-time processing of an 8-GHz LFM signal is achieved with a sampling rate of 500 MSa/s. Accurate distance measurement is implemented with a maximum error of 4 mm within a range of ~3.5 meters. Detection of two targets is demonstrated with a range-resolution as high as 1.875 cm. We believe the proposed radar architecture is a reliable solution to overcome the limitations of current radar on operation bandwidth and processing speed, and it is hopefully to be used in future radars for real-time and high-resolution target detection and imaging.

14.
Opt Express ; 25(14): 16274-16281, 2017 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-28789134

RESUMO

A photonics-based radar with generation and de-chirp processing of broadband linear frequency modulated continuous-wave (LFMCW) signal in optical domain is proposed for high-resolution and real-time inverse synthetic aperture radar (ISAR) imaging. In the proposed system, a broadband LFMCW signal is generated by a photonic frequency quadrupler based on a single integrated electro-optical modulator, and the echoes reflected from the targets are de-chirped to a low frequency signal by a microwave photonic frequency mixer. The proposed radar can operate at a high frequency with a large bandwidth, and thus achieve an ultra-high range resolution for ISAR imaging. Thanks to the wideband photonic de-chirp technique, the radar receiver could apply low-speed analog-to-digital conversion and mature digital signal processing, which makes real-time ISAR imaging possible. A K-band photonics-based radar with an instantaneous bandwidth of 8 GHz (18-26 GHz) is established and its performance for ISAR imaging is experimentally investigated. Results show that a recorded two-dimensional imaging resolution of ~2 cm × ~2 cm is achieved with a sampling rate of 100 MSa/s in the receiver. Besides, fast ISAR imaging with 100 frames per second is verified. The proposed radar is an effective solution to overcome the limitations on operation bandwidth and processing speed of current radar imaging technologies, which may enable applications where high-resolution and real-time radar imaging is required.

15.
Opt Lett ; 41(17): 3956-9, 2016 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-27607946

RESUMO

A hardware-compressive optical true time delay architecture for 2D beam steering in a planar phased array antenna is proposed using fiber-Bragg-grating-based tunable dispersive elements (TDEs). For an M×N array, the proposed system utilizes N TDEs and M wavelength-fixed optical carriers to control the time delays. Both azimuth and elevation beam steering are realized by programming the settings of the TDEs. An experiment is carried out to demonstrate the delay controlling in a 2×2 array, which is fed by a wideband pulsed signal. Radiation patterns calculated from the experimentally measured waveforms at the four antennas match well with the theoretical results.

16.
Opt Express ; 24(16): 18460-7, 2016 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-27505809

RESUMO

A scheme for photonic generation of linearly chirped microwave waveforms (LCMWs) with a large time-bandwidth product (TBWP) is proposed and demonstrated based on an optically injected semiconductor laser. In the proposed system, the optically injected semiconductor laser is operated in period-one (P1) oscillation state. After optical-to-electrical conversion, a microwave signal can be generated with its frequency determined by the injection strength. By properly controlling the injection strength, an LCMW with a large TBWP can be generated. The proposed system has a simple and compact structure. Besides, the center frequency, bandwidth, as well as the temporal duration of the generated LCMWs can be easily adjusted. An experiment is carried out. LCMWs with TBWPs as large as 1.2x105 (bandwidth 12 GHz; temporal duration 10 µs) are successfully generated. The flexibility for tuning the center frequency, bandwidth and temporal duration is also demonstrated.

17.
Opt Express ; 23(20): 25539-52, 2015 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-26480071

RESUMO

In this paper, a novel microwave photonic filter (MPF) with multiple independently tunable passbands is proposed. A broadband optical source (BOS) is employed and split by a 1:N coupler into several branches. One branch is directed to a phase modulator which is modulated by a radio frequency signal and the other branches are delayed by optical delay lines (ODLs), respectively. All of these branches are combined by another 1:N coupler and sent to a dispersion compensation fiber which is used to introduce group delay dispersion to the optical signal. At a photodetector, each time-delayed broadband lightwave beating with the sidebands produced by the phase modulator forms a passband of the MPF. By tuning the delay of each broadband lightwave, the center frequency of the passband can be independently tuned. An MPF with two independently tunable passbands is experimentally demonstrated. The two passbands can be tuned from DC to 30 GHz with a 3-dB bandwidth of about 250 MHz. The stability and dynamic range of the MPF are also evaluated. By employing more branches delayed by ODLs, more passbands can be generated.

18.
Opt Express ; 23(17): 21867-74, 2015 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-26368162

RESUMO

A novel scheme for photonic generation of a phase-coded microwave signal is proposed and its application in one-dimension distance measurement is demonstrated. The proposed signal generator has a simple and compact structure based on a single dual-polarization modulator. Besides, the generated phase-coded signal is stable and free from the DC and low-frequency backgrounds. An experiment is carried out. A 2 Gb/s phase-coded signal at 20 GHz is successfully generated, and the recovered phase information agrees well with the input 13-bit Barker code. To further investigate the performance of the proposed signal generator, its application in one-dimension distance measurement is demonstrated. The measurement accuracy is less than 1.7 centimeters within a measurement range of ~2 meters. The experimental results can verify the feasibility of the proposed phase-coded microwave signal generator and also provide strong evidence to support its practical applications.

19.
Opt Express ; 23(8): 10002-8, 2015 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-25969041

RESUMO

An optical true time delay (TTD) unit capable of adding independent time delays to multiple RF signals is proposed, which can be used for multi-beamforming in both transmit and receive modes. In the proposed unit, N RF signals with different center frequencies are modulated on an optical frequency comb (OFC). After transmission through a dispersive element, the RF-modulated OFC is split into N paths. In each path, a comb line is selected by a tunable optical filter. Thanks to the chromatic dispersion of the dispersive element, independently-controllable TTDs can be obtained in all paths. Then, a microwave photonic filter (MPF) is incorporated in each path, allowing a designated RF signal to undergo the TTD in that path. A proof-of-concept experiment is carried out. A two-path unit with a low-pass MPF in one path and a high-pass MPF in the other path is built. Controllable TTDs up to ~1.4 ns with a step of ~69 ps are demonstrated based on a 25-GHz-spacing OFC. In addition, a wideband multi-beam phased-array antenna system that can work in both transmit and receive modes is designed using the proposed TTD unit.

20.
Opt Lett ; 40(7): 1326-9, 2015 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-25831324

RESUMO

An approach for phase noise measurement of microwave signal sources based on a microwave photonic frequency down-converter is proposed. Using the same optical carrier, the microwave signal under test is applied to generate two +1st-order optical sidebands by two stages of electro-optical modulations. A time delay is introduced between the two sidebands through a span of fiber. By beating the two +1st-order sidebands at a photodetector, frequency down-conversion is implemented, and phase noise of the signal under test can be calculated thereafter. The system has a very large operation bandwidth thanks to the frequency conversion in the optical domain, and good phase noise measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. An experiment is carried out. The phase noise measured by the proposed system agrees well with that measured by a commercial spectrum analyzer or provided by the datasheet. A large operation bandwidth of 5-40 GHz is demonstrated using the proposed system. Moreover, good phase noise floor is achieved (-123 dBc/Hz at 1 kHz and -137 dBc/Hz at 10 kHz at 10 GHz), which is nearly constant over the full measurement range.

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