Dexing Yang

Northwestern Polytechnical University, Xi’an, Liaoning, China

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Publications (35)59.95 Total impact

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    ABSTRACT: Molybdenum disulfide (MoS2 ) and tungsten disulfide (WS2 ), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS2 and WS2 , molybdenum ditelluride (MoTe2 ) and tungsten ditelluride (WTe2 ) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near-infrared wavelength regime. Here, few-layer MoTe2 /WTe2 nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe2 /WTe2 nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode-locking operations are realized separately in erbium-doped fiber lasers utilizing two types of MoTe2 /WTe2 -based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe2 /WTe2 nanosheets, such as visible/near-infrared pulsed laser, materials processing, optical sensors, and modulators.
    No preview · Article · Jan 2016 · Small
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    ABSTRACT: To meet the requirements of riser safety monitoring in offshore oil fields, a new Fiber Bragg Grating (FBG)-based bundle-structure riser stress monitoring sensor has been developed. In cooperation with many departments, a 49-day marine test in water depths of 1365 m and 1252 m was completed on the "HYSY-981" ocean oil drilling platform. No welding and pasting were used when the sensor was installed on risers. Therefore, the installation is convenient, reliable and harmless to risers. The continuous, reasonable, time-consistent data obtained indicates that the sensor worked normally under water. In all detailed working conditions, the test results show that the sensor can do well in reflecting stresses and bending moments both in and in magnitude. The measured maximum stress is 132.7 MPa, which is below the allowable stress. In drilling and testing conditions, the average riser stress was 86.6 MPa, which is within the range of the China National Offshore Oil Corporation (CNOOC) mechanical simulation results.
    Preview · Article · Nov 2015 · Sensors
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    ABSTRACT: An all-fiber optical heterodyne detection configuration was proposed based on an all-fiber acousto-optic structure, which acted as both frequency shifter and coupler at the same time. The vibration waveform within a frequency range between 1 Hz to 200 kHz of a piezoelectric mirror was measured using this optical heterodyne detection system. The minimal measurable vibration amplitude and resolution are around 6 pm and 1 pm in the region of tens to hundreds of kilohertz, respectively. The configuration has advantages of compact size, high accuracy and non-contact measurement. Moreover, it is of a dynamically adjustable signal-to-noise ratio to adapt different surface with different reflections in the measurement, which will improve the usage efficiency of the light power.
    Full-text · Article · Jun 2015 · Optics Express
  • Chuan Qin · Dexing Yang
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    ABSTRACT: A numerical model of a ring cavity wavelength-swept laser based on semiconductor optical amplifier (SOA) is described. In this model, the SOA is restricted by a carrier density rate equation and set of traveling wave equations, which describe the amplified signal and spontaneous emission photon rates. In addition, fiber Fabry–Perot tunable filter, which is used to select the transmission wavelength, is modeled by a multibeam interference transmission function. Thereafter, a coupler, which outputs and feedbacks the laser is simply described by its splitting ratio. Finally, an isolator is idealized to ensure unidirectional lasing. By numerically solving the model, the spectra evolution, carrier density, signal, and amplified spontaneous emission forward and backward distributions along the transmission direction, the output power versus filtering center wavelength, injection current, and coupling ratio were studied, respectively. The results are used for deeply understanding the kinetic process of such swept laser and predicting the sweep range, the bandwidth, the output power, and the threshold current of the laser.
    No preview · Article · Oct 2014 · IEEE Journal of Quantum Electronics
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    ABSTRACT: A magnetic field sensor based on a tilted fiber Bragg grating (TFBG) coated with magnetic fluid is proposed and demonstrated experimentally. The sensing element is made by injecting the magnetic fluid into a capillary tube which contains a TFBG. The resonant wavelengths of the cladding modes of TFBG shift by varying the magnetic field which is perpendicular to the axis of TFBG. The results indicate that the resonant wavelength shifts of the cladding modes show a nonlinear dependence on the magnetic field. As the magnetic field increases to 32 mT, the largest resonant wavelength shift reaches to 106 pm. Moreover, this sensor shows good repeatability when it is used for magnetic field sensing.
    No preview · Article · Feb 2014 · Applied Physics Letters
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    Yuning Guo · Dexing Yang · Ying Chang · Wei Gao
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    ABSTRACT: The effect of asymmetry caused by oblique line-shaped laser ablation on the generation of ultrasonic waves in metal, especially the effect of transverse component of the ablation force source on the ultrasonic waves is analyzed. Due to the oblique force source, the displacements of shear wave increase obviously by the enhanced shear force, the energy concentration area of longitudinal wave deflects to the small range centered on the incident direction while that of shear wave is approximately perpendicular to incident direction. In addition, surface wave enhances in the direction of transverse power flow. Furthermore, some ultrasonic characteristics under vortex laser ablation condition are inferred.
    Full-text · Article · Jan 2014 · Optics Express
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    ABSTRACT: Wavelength-swept laser technique is an active demodulation method which integrates laser source and detecting circuit together to achieve compact size. The method also has the advantages such as large demodulation range, high accuracy, and comparatively high speed. In this paper, we present a FBG interrogation method based on wavelength-swept Laser, in which an erbium-doped fiber is used as gain medium and connected by a WDM to form a ring cavity, a fiber FP tunable filter is inserted in the loop for choosing the laser frequency and a gas absorption cell is adopted as a frequency reference. The laser wavelength is swept by driving the FP filter. If the laser wavelength matches with that of FBG sensors, there will be some strong reflection peak signals. Detecting such signals with the transmittance signal after the gas absorption cell synchronously and analyzing them, the center wavelengths of the FBG sensors are calculated out at last. Here, we discuss the data processing method based on the frequency reference, and experimentally study the swept laser characteristics. Finally, we adopt this interrogator to demodulate FBG stress sensors. The results show that, the demodulation range almost covers C+L band, the resolution and accuracy can reach about 1pm or less and 5pm respectively. So it is very suitable for most FBG measurements.
    No preview · Conference Paper · Jun 2013
  • Yuning Guo · Dexing Yang · Wen Feng · Ying Chang
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    ABSTRACT: Numerical models are established to investigate the influence of transparent coating hardness on the laser-generated thermoelastic force source and ultrasonic waves in coating-substrate systems by using finite element method. With the increase of coating hardness, the characteristic of longitudinal wave in substrate is more obvious due to the gradual increase of reactive force produced by coating constraint; the directivity patterns of longitudinal wave show that the energy concentration area transfers from bilateral area to the axial direction area gradually. Therefore, the directivity pattern can be regulated to obtain the better ultrasonic signals by coating different hardness materials. It is significant for further development of the experiment in composite evaluation and in extreme condition.
    No preview · Article · Jan 2013 · Journal of Applied Physics
  • Chuan Qin · Jianlin Zhao · Biqiang Jiang · Dexing Yang
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    ABSTRACT: The spectrum of Gauss apodized fiber Bragg grating (FBG) is analyzed by using transfer matrix method, and the basic principles of sub-pixel curve fitting algorithms including mass center, Gauss and full-width-at-half-maximum (FWHM) are discussed. Based on this, simulation and experimental results are given to compare the three curve fitting algorithms. The results reveal that in simulation, mass center fitting method with an accuracy of 13pm while in experiment, FWHM fitting method with an accuracy of 23pm provides a better match to the actual curve. The research achievements have been applied on the prototype of linear-array detector grating spectrometer and have potential market in portable FBG interrogation field.
    No preview · Conference Paper · Nov 2012
  • Yuning Guo · Dexing Yang · Wen Feng · Xiangchao Zhu · Ying Chang
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    ABSTRACT: Sound velocity is important to study the elastic behaviors of materials in high pressure physics and the accuracy acquisition of travel time for velocity calculation is very essential. Thermoelastic finite element models of ultrasonic displacement field induced by a subnanosecond pulsed laser in metal films with a diamond anvil cell are established and the processes of laser ultrasonic generation are analyzed in detail. By confirming the initial time, we improved the accuracy of calculating the longitudinal wave velocity in the aluminum and copper thin films. The formulas of delay time are obtained by a set of simulations, and the overall errors of modified longitudinal velocity are reduced by 10-60 times of the unmodified ones.
    No preview · Article · Nov 2012 · Ultrasonics
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    Wen Feng · Dexing Yang · Yuning Guo · Ying Chang
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    ABSTRACT: Thermoelastic finite element models are established to study the bulk ultrasonic waves of an aluminum film generated by ring-shaped laser illumination in a diamond anvil cell. By analyzing the amplitudes of bulk ultrasonic waves arrived at the rear surface of film in detail, it shows that there exists strong enhancement effects on the central axis of the ring due to the constructive interference among the waves created by different parts of the ring source. The displacement distributions along the central axis indicate that the focal depth of shear wave is mainly determined by its directivity induced by a point-like laser source in a DAC system while it is more complicated to determine the focal depth of longitudinal wave. In particular, through changing the ring radius, we quantitatively demonstrate that the signal amplitudes generated by a ring source are far greater than those generated by a point-like source.
    Full-text · Article · Mar 2012 · Optics Express
  • Lingchen Kong · Enpu Li · Dexing Yang · Hui Xing
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    ABSTRACT: The general response of a 1-D position-sensitive detector (PSD) is derived by solving the Lucovsky equation in a fully general way. A general light source is divided into many sections in space domain and pulse elements in time domain. Each section is regarded as a plane-wave element and each pulse as a square-wave pulse. By virtue of the linear superposition of the Green function, the general response is regarded as the summation of respective responses to those elements. The response indicates that a PSD is a decaying photocurrent accumulator, both in space and time domains. Results discussed in this paper are quite in agreement with the facts and the conclusions from the previous papers. In addition, analysis on the alternating current (ac) response characteristics by virtue of the general response shows that there is a hysteretic oscillation in accord with the light intensity variation and that the response is insensitive to high-frequency ac light signals.
    No preview · Article · Mar 2012 · IEEE Transactions on Electron Devices
  • Wen Feng · Dexing Yang · Xiangchao Zhu · Yuning Guo · Wei Liao
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    ABSTRACT: Based on the thermoelastic theory, a numerical model of ultrasonic displacement field induced by a vertical incident pulsed laser in an aluminum film in a diamond anvil cell (DAC) is established by using the finite element method (FEM). After precisely calculating the transient temperature field distributions, the bulk ultrasonic waveforms on the rear surface of the film and the characteristics of ultrasonic displacement field with time are obtained. Then directivity patterns of laser-generated longitudinal and shear ultrasonic waves are analyzed in details. The numerical results indicate that the thermoelastic force source and the characteristics of ultrasonic directivity are strongly affected by the diamond window. The energy of longitudinal wave is concentrated near the laser incident direction, and the one of shear wave is concentrated between 30° and 60° that deflected from the laser incident direction to the excited source. These characteristics in DAC system are different from the results of free surface in thermoelastic effect, while are similar to the results of free surface in ablation effect.
    No preview · Article · Jan 2012 · Journal of Applied Physics
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    ABSTRACT: It is very important to monitor the lateral and axial strains of drilling riser for evaluation its health in deepwater. An optical fiber strain sensing system based on optical fiber Bragg gratings (FBGs) used for monitoring the strain of drilling riser is presented. The optical fiber strain sensors are made by embedding FBGs into thin columned fiber reinforced polymer which protect FBGs from seawater corrosion. Four optical fiber strain sensors are installed parallel to the riser axis and arranged at 90° angles around the riser by a home-made metal belt, at the same time, twelve resistance strain gauges are pasted near the sensors around the drilling riser at 30° angles as reference sensors. A scaled drilling riser about 1 meter long and 0.245m diameter is pressed in the lateral and axial direction in the range of 0-400KN, the experimental results show that the relative error between optical fiber strain sensors and resistance strain gauges is less than 6%.
    No preview · Article · Nov 2011 · Proceedings of SPIE - The International Society for Optical Engineering
  • Dexing Yang · Jinhu Zhao · Teng Zhao · Lingchen Kong
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    ABSTRACT: A kind of optical beam with controllable rotating intensity blades is generated by coaxially superposing two optical vortex beams with frequency difference (Δω), different topological charges (m1 and m2) and equal amplitude. It is shown theoretically that the number of the blades is determined by the subtraction of topological charges (m1−m2) and the angular velocity of the rotating pattern is equal to Δω/(m1−m2). In our experiment, the rotating beams were generated by two optical vortex beams with opposite topological charges, where the frequency difference is acquired by a rotating plate glass. The results are quite in accordance with the simulations.
    No preview · Article · Jul 2011 · Optics Communications
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    ABSTRACT: A kind of bare fiber Bragg grating (FBG) gas pressure sensor based on fiber loop ring-down is presented, in which there are no sensitizing means or assistant structure on the bare FBG. The pressure sensitivity is analyzed theoretically via discussing the relationship between the ring-down time and the gas pressure. By detecting the ring-down time at different gas pressure levels, the gas pressure characteristics of the bare FBG are investigated in the time domain. The experimental results demonstrate that there exists a linear dependence of the pressure applied to the bare FBG on the ring-down time. A high sensitivity of −0.384μs/MPa (being equivalent to −240pm/MPa) could be achieved, which is 79 times larger than that of the optical spectral analyzer interrogated. This kind of pressure sensor could be used for gas or liquid pressure measurement.
    No preview · Article · Dec 2010 · Optics and Lasers in Engineering
  • Wei Liao · Dexing Yang · Wen Feng
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    ABSTRACT: Process of laser ultrasonic generation was simulated in detail for confirming the exact time and location ultrasonic produced. The particular generating information in thin-film could help to accurately analyze the ultrasonic characteristics, especially in high pressure physics. Numerical models based on the two-dimensional axis-symmetry was built in cylinder coordinate system and calculated by finite element method (FEM). The duration and penetration-depth of pulse laser were considered instead of point approximation. In addition, parameters of material were set as functions related with temperature. According to the results, strain energy accumulated below the incidence point, so that the maximum amplitude of ultrasonic wave appeared few distances inside of the sample. Non-negligible errors were caused by that distances in velocity calculation. Without amendment, the errors increased with the broadening of pulse width and decreased with the growth of propagation distance. Therefore, the time ultrasonic generated should be fixed a head of the time that laser peak arrived. Furthermore, wave shape were easy to distinguish but inaccurately while the sample were covered with a transparent window.
    No preview · Article · Nov 2010 · Proceedings of SPIE - The International Society for Optical Engineering
  • Yajun Jiang · Jianlin Zhao · Dexing Yang · Daqing Tang
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    ABSTRACT: A transverse pressure sensor with high-sensitivity based on a mechanically induced long-period fiber grating (MLPFG) and fiber loop ring-down technique is presented. When a MLPFG is spliced into a fiber loop, an extra loss is introduced, which leads to a decrease of the ring-down time. The results demonstrate that the difference between the reciprocals of the ring-down time with and without pressure increases exponentially with increasing the pressure in the range of 0–23.4MPa. This sensor shows good repeatability, and the least detectable pressure is only 0.0068MPa which is about 18 times less than detecting the output light intensity directly.
    No preview · Article · Oct 2010 · Optics Communications
  • Yajun Jiang · Dexing Yang · Daqing Tang · Jianlin Zhao
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    ABSTRACT: We present a theoretical and experimental study on sensitivity enhancement of a fiber-loop cavity ring-down pressure sensor. The cladding of the sensing fiber is etched in hydrofluoric acid solution to enhance its sensitivity. The experimental results demonstrate that the pressure applied on the sensing fiber is linearly proportional to the difference between the reciprocals of the ring-down time with and without pressure, and the relative sensitivity exponentially increases with decreasing the cladding diameter. When the sensing fiber is etched to 41.15 microm, its sensitivity is about 36 times that of nonetched fiber in the range of 0 to 32.5 MPa. The measured relative standard deviation of the ring-down time is about 0.15% and, correspondingly, the least detectable loss is about 0.00069 dB.
    No preview · Article · Nov 2009 · Applied Optics
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    ABSTRACT: In digital speckle interferometry, subtracted fringe patterns are always influenced by inhomogeneous light that is reflected from the tested object and received by the CCD. In this paper, by analyzing speckle's statistic property, we propose a numerical processing method to correct this nonuniform light intensity distribution within adaptive windows. This method includes estimating light intensity distribution of the tested object, constructing an adaptive window for every pixel, and correcting the intensity in the adaptive windows. By applying this method to our experiment, we find it is valid for intensity correction without changing necessary phase information.
    No preview · Article · Nov 2009 · Applied Optics