The Experts below are selected from a list of 6705 Experts worldwide ranked by ideXlab platform
Zhichao Luo - One of the best experts on this subject based on the ideXlab platform.
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flexible generation of coherent Rectangular Pulse from an ultrafast fiber laser based on dispersive fourier transformation technique
Optics Express, 2015Co-Authors: Fuzao Wang, Hao Liu, Meng Liu, Aiping Luo, Yuqi Huang, Zhichao LuoAbstract:We propose a new solution to flexibly generate the coherent Rectangular Pulse from an ultrafast fiber laser based on the dispersive Fourier transformation (DFT) technique. The Rectangular dissipative soliton (DS) spectra emitted from a net-normal dispersion mode-locked fiber laser is mapped into a time-domain coherent Rectangular waveform through the DFT technique. The Rectangular Pulse can be broadened flexibly with the adjustments of the pump power. The coherence and shot-to-shot fluctuations of the achieved Rectangular Pulses are further verified by the Mach-Zehnder interference experiment and the recorded single-shot Pulse train, respectively. The results demonstrate that the combination of DS mode-locked laser and DFT technique might be indeed an effective and flexible way to achieve highly coherent Rectangular Pulses.
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dual wavelength Rectangular Pulse yb doped fiber laser using a microfiber based graphene saturable absorber
Optics Express, 2014Co-Authors: Nian Zhao, Xuwu Zheng, Hao Liu, Qiuyi Ning, Meng Liu, Aiping Luo, Zhichao LuoAbstract:We reported on the generation of dual-wavelength Rectangular Pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength Rectangular Pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the Rectangular Pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength Rectangular Pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.
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high energy noiselike Rectangular Pulse in a passively mode locked figure eight fiber laser
Applied Physics Express, 2014Co-Authors: Xuwu Zheng, Zhichao Luo, Hao Liu, Nian Zhao, Qiuyi Ning, Meng Liu, Xinhuan Feng, Xiaobo Xing, Aiping LuoAbstract:We report on the generation of a high-energy noiselike Rectangular Pulse in a mode-locked figure-eight fiber laser. The noiselike Pulse appeared to have a Rectangular shape on the oscilloscope. The Pulse duration increased with increasing pump power, while the peak amplitude remained constant, which is very similar to the Pulse evolution of dissipative soliton resonance. However, the Pulse type is confirmed as a noiselike Pulse using an autocorrelator. With the maximum pump power of 350 mW, the 135 nJ noiselike Rectangular Pulse with 76 ns duration was achieved. The results provide a new guideline for clarifying an alternative formation mechanism of the high-energy Rectangular Pulses in fiber lasers.
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wave breaking free Pulse in an all fiber normal dispersion yb doped fiber laser under dissipative soliton resonance condition
Optics Express, 2013Co-Authors: Lan Liu, Zhichao Luo, Qiuyi Ning, Aiping Luo, Junhong Liao, Zhongmin YangAbstract:We reported on the dissipative soliton resonance (DSR) phenomenon in a mode-locked Yb-doped fiber laser by using the nonlinear polarization rotation technique. It was found that the multi-Pulse oscillation under high pump power could be circumvented by properly adjusting the polarization controllers, namely, the wave-breaking-free Rectangular Pulse in DSR region was achieved. As the DSR signature, the Pulse duration varied from 8.8 ps to 22.92 ns with the increasing pump power. Correspondingly, the maximum Pulse energy was 3.24 nJ. The results demonstrated that the DSR phenomenon could exist in Yb-doped fiber lasers, which could be used to achieve wave-breaking-free, ultrahigh-energy Pulse.
Aiping Luo - One of the best experts on this subject based on the ideXlab platform.
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flexible generation of coherent Rectangular Pulse from an ultrafast fiber laser based on dispersive fourier transformation technique
Optics Express, 2015Co-Authors: Fuzao Wang, Hao Liu, Meng Liu, Aiping Luo, Yuqi Huang, Zhichao LuoAbstract:We propose a new solution to flexibly generate the coherent Rectangular Pulse from an ultrafast fiber laser based on the dispersive Fourier transformation (DFT) technique. The Rectangular dissipative soliton (DS) spectra emitted from a net-normal dispersion mode-locked fiber laser is mapped into a time-domain coherent Rectangular waveform through the DFT technique. The Rectangular Pulse can be broadened flexibly with the adjustments of the pump power. The coherence and shot-to-shot fluctuations of the achieved Rectangular Pulses are further verified by the Mach-Zehnder interference experiment and the recorded single-shot Pulse train, respectively. The results demonstrate that the combination of DS mode-locked laser and DFT technique might be indeed an effective and flexible way to achieve highly coherent Rectangular Pulses.
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dual wavelength Rectangular Pulse yb doped fiber laser using a microfiber based graphene saturable absorber
Optics Express, 2014Co-Authors: Nian Zhao, Xuwu Zheng, Hao Liu, Qiuyi Ning, Meng Liu, Aiping Luo, Zhichao LuoAbstract:We reported on the generation of dual-wavelength Rectangular Pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength Rectangular Pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the Rectangular Pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength Rectangular Pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.
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high energy noiselike Rectangular Pulse in a passively mode locked figure eight fiber laser
Applied Physics Express, 2014Co-Authors: Xuwu Zheng, Zhichao Luo, Hao Liu, Nian Zhao, Qiuyi Ning, Meng Liu, Xinhuan Feng, Xiaobo Xing, Aiping LuoAbstract:We report on the generation of a high-energy noiselike Rectangular Pulse in a mode-locked figure-eight fiber laser. The noiselike Pulse appeared to have a Rectangular shape on the oscilloscope. The Pulse duration increased with increasing pump power, while the peak amplitude remained constant, which is very similar to the Pulse evolution of dissipative soliton resonance. However, the Pulse type is confirmed as a noiselike Pulse using an autocorrelator. With the maximum pump power of 350 mW, the 135 nJ noiselike Rectangular Pulse with 76 ns duration was achieved. The results provide a new guideline for clarifying an alternative formation mechanism of the high-energy Rectangular Pulses in fiber lasers.
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wave breaking free Pulse in an all fiber normal dispersion yb doped fiber laser under dissipative soliton resonance condition
Optics Express, 2013Co-Authors: Lan Liu, Zhichao Luo, Qiuyi Ning, Aiping Luo, Junhong Liao, Zhongmin YangAbstract:We reported on the dissipative soliton resonance (DSR) phenomenon in a mode-locked Yb-doped fiber laser by using the nonlinear polarization rotation technique. It was found that the multi-Pulse oscillation under high pump power could be circumvented by properly adjusting the polarization controllers, namely, the wave-breaking-free Rectangular Pulse in DSR region was achieved. As the DSR signature, the Pulse duration varied from 8.8 ps to 22.92 ns with the increasing pump power. Correspondingly, the maximum Pulse energy was 3.24 nJ. The results demonstrated that the DSR phenomenon could exist in Yb-doped fiber lasers, which could be used to achieve wave-breaking-free, ultrahigh-energy Pulse.
Dongkyun Kim - One of the best experts on this subject based on the ideXlab platform.
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a simple scheme to adjust poisson cluster Rectangular Pulse rainfall models for improved performance at sub hourly timescales
Journal of Hydrology, 2021Co-Authors: Jeongha Park, David Cross, Christian Onof, Yuting Chen, Dongkyun KimAbstract:Abstract Although sub-hourly rainfall temporal characteristics play an important role in occurrences and magnitudes of urban flash floods, most stochastic rainfall models struggle to reproduce them when rainfall information is not available at sub-hourly timescales. This study suggests a simple approach to modifying Poisson cluster Rectangular Pulse rainfall models to resolve this issue. In this model, the original rectangles representing a rain cell are replaced by a bell shape that is mathematically represented as y = sin2(x). Such an alteration no longer makes it possible to obtain closed form expressions for the various rainfall statistics for model parameter calibration. Based on an assumption that this alteration would hardly alter the hourly and supra-hourly statistics, we calibrated the parameters of a Rectangular Pulse model with these statistics (from 1 to 32 h) and transplanted the same parameters to the sine-squared Pulse model to generate 500 years of 5-minute rainfall. Importantly, this parameter transplant procedure does not require any sub-hourly information so that it amounts to a downscaling algorithm for the generation of sub-hourly rainfall. Our results show that both models reproduced well the rainfall mean, variance, autocovariance, proportion of dry periods, and extreme values at hourly to 72-hour timescales. However, the sine-squared Pulse model performed significantly better at sub-hourly time scales. The same 500 years of synthetic rainfall data and 69 years of observed rainfall data were then used as input of a dual-drainage urban watershed model developed for a frequently flooded urban area of Seoul. While the traditional Rectangular Pulse model significantly underestimated the flooded area, the new sine-squared Pulse model successfully reproduced the flooded area caused by the observed rainfall.
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a hierarchical bayesian approach to the modified bartlett lewis Rectangular Pulse model for a joint estimation of model parameters across stations
Journal of Hydrology, 2017Co-Authors: Janggyeong Kim, Hyunhan Kwon, Dongkyun KimAbstract:Abstract Poisson cluster stochastic rainfall generators (e.g., modified Bartlett-Lewis Rectangular Pulse, MBLRP) have been widely applied to generate synthetic sub-daily rainfall sequences. The MBLRP model reproduces the underlying distribution of the rainfall generating process. The existing optimization techniques are typically based on individual parameter estimates that treat each parameter as independent. However, parameter estimates sometimes compensate for the estimates of other parameters, which can cause high variability in the results if the covariance structure is not formally considered. Moreover, uncertainty associated with model parameters in the MBLRP rainfall generator is not usually addressed properly. Here, we develop a hierarchical Bayesian model (HBM)-based MBLRP model to jointly estimate parameters across weather stations and explicitly consider the covariance and uncertainty through a Bayesian framework. The model is tested using weather stations in South Korea. The HBM-based MBLRP model improves the identification of parameters with better reproduction of rainfall statistics at various temporal scales. Additionally, the spatial variability of the parameters across weather stations is substantially reduced compared to that of other methods.
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regionalization of the modified bartlett lewis Rectangular Pulse stochastic rainfall model across the korean peninsula
Journal of Hydro-environment Research, 2016Co-Authors: Dongkyun Kim, Hyunhan Kwon, Seung Oh Lee, Sooyoung KimAbstract:Abstract The six parameters of the Modified Bartlett–Lewis Rectangular Pulse (MBLRP) model were regionalized across the Korean Peninsula for all 12 calendar months. The parameters of the MBLRP model were estimated at each of the 59 rain gauges and they were spatially interpolated using the Ordinary Kriging method in order to produce maps. The parameter search space used in the parameter estimation process was repetitively narrowed through cross-validation in order to remove the impact of the multi-modality of the MBLRP model. The synthetic rainfall time series generated based on the parameter maps successfully reproduced the various statistical properties of the observed rainfall, such as mean, variance, lag-1 autocorrelation, and probability of zero rainfall at a wide range of time accumulation levels (e.g. hourly through daily). The maps representing the general rainfall characteristics, such as the average rainfall depth per rain storm, the average rain storm duration, the average number of rain cells per rain storm, and the average rain cell duration were also produced based on the estimated parameters. Lastly, some helpful tips in regionalizing the parameters of the Poisson cluster rainfall models are discussed.
Qiuyi Ning - One of the best experts on this subject based on the ideXlab platform.
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dual wavelength Rectangular Pulse yb doped fiber laser using a microfiber based graphene saturable absorber
Optics Express, 2014Co-Authors: Nian Zhao, Xuwu Zheng, Hao Liu, Qiuyi Ning, Meng Liu, Aiping Luo, Zhichao LuoAbstract:We reported on the generation of dual-wavelength Rectangular Pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength Rectangular Pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the Rectangular Pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength Rectangular Pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.
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high energy noiselike Rectangular Pulse in a passively mode locked figure eight fiber laser
Applied Physics Express, 2014Co-Authors: Xuwu Zheng, Zhichao Luo, Hao Liu, Nian Zhao, Qiuyi Ning, Meng Liu, Xinhuan Feng, Xiaobo Xing, Aiping LuoAbstract:We report on the generation of a high-energy noiselike Rectangular Pulse in a mode-locked figure-eight fiber laser. The noiselike Pulse appeared to have a Rectangular shape on the oscilloscope. The Pulse duration increased with increasing pump power, while the peak amplitude remained constant, which is very similar to the Pulse evolution of dissipative soliton resonance. However, the Pulse type is confirmed as a noiselike Pulse using an autocorrelator. With the maximum pump power of 350 mW, the 135 nJ noiselike Rectangular Pulse with 76 ns duration was achieved. The results provide a new guideline for clarifying an alternative formation mechanism of the high-energy Rectangular Pulses in fiber lasers.
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wave breaking free Pulse in an all fiber normal dispersion yb doped fiber laser under dissipative soliton resonance condition
Optics Express, 2013Co-Authors: Lan Liu, Zhichao Luo, Qiuyi Ning, Aiping Luo, Junhong Liao, Zhongmin YangAbstract:We reported on the dissipative soliton resonance (DSR) phenomenon in a mode-locked Yb-doped fiber laser by using the nonlinear polarization rotation technique. It was found that the multi-Pulse oscillation under high pump power could be circumvented by properly adjusting the polarization controllers, namely, the wave-breaking-free Rectangular Pulse in DSR region was achieved. As the DSR signature, the Pulse duration varied from 8.8 ps to 22.92 ns with the increasing pump power. Correspondingly, the maximum Pulse energy was 3.24 nJ. The results demonstrated that the DSR phenomenon could exist in Yb-doped fiber lasers, which could be used to achieve wave-breaking-free, ultrahigh-energy Pulse.
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dissipative soliton resonance in a passively mode locked figure eight fiber laser
Optics Express, 2013Co-Authors: Shike Wang, Qiuyi Ning, Wencheng XuAbstract:The generation of mode-locked Rectangular Pulses operating in dissipative soliton resonance (DSR) region is demonstrated in an erbium-doped figure-eight fiber laser with net anomalous dispersion. The duration of the wave-breaking-free Rectangular Pulse broadens with the increase of pump power. At a maximum pump power of 341mW, the Pulse energy can be up to 3.25 nJ with a repetition rate of 3.54 MHz. Particularly, the spectrum of Rectangular Pulse operating in DSR exhibits conventional soliton sidebands. The observed results show that the formation of Pulse operating in DSR region is independent of mode-locking techniques, which may be helpful for further understanding the DSR phenomenon.
H S Wheater - One of the best experts on this subject based on the ideXlab platform.
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improvements to the modelling of british rainfall using a modified random parameter bartlett lewis Rectangular Pulse model
Journal of Hydrology, 1994Co-Authors: Christian Onof, H S WheaterAbstract:Abstract The Random Parameter Bartlett-Lewis Rectangular Pulse Model (RPBLRPM) was shown in a previous paper to provide generally good results when applied to a 38.5 year record of hourly rainfall from the Elmdon raingauge, Birmingham, UK: second-order properties of the depth and the interevent time distributions and the proportion of dry periods for different time-scales were on the whole well reproduced by the optimized parameters. However, two main problems arose, namely an overestimation of the autocorrelations for daily data in particular, and relatively poor performance in reproducing the extreme values of the depth distribution. The first of these problems is here addressed by superposition of a jitter process on the Rectangular Pulse, thus providing a more realistic representation of the continuous time process. Applying the jitter to each rainfall cell appears more effective than applying it to the instantaneous rainfall depth and enables a more satisfactory reproduction of the autocorrelations. The use of a gamma variable to replace the exponential distribution of the cell intensity provides a good reproduction of the extreme rainfall depths at different time-scales. Moreover, the values of the parameters providing an optimal reproduction of the extreme values of the depth distribution are in most cases close to those obtained by optimizing on the interevent time features, which provides a method for estimation and ensures that the two objectives do not conflict.
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modelling of british rainfall using a random parameter bartlett lewis Rectangular Pulse model
Journal of Hydrology, 1993Co-Authors: Christian Onof, H S WheaterAbstract:Abstract The performance of a stochastic model, in which Poisson cluster processes represent the arrival of rain cells within a rainstorm, is assessed for hourly point rainfall data from Birmingham, UK. The Bartlett-Lewis Rectangular Pulse Model is extended to include random cell duration, and its performance is compared with that of the basic model analysed previously. Both models perform well in reproducing statistics of the rainfall depth distribution at different time-scales for individual months, but the randomised model also enables a good reproduction of the proportions of dry periods of different durations. Performance is improved by an optimisation method which addresses issues of parameter identification. However, some deficiencies remain with respect to extreme values. Finally, the seasonal variability of parameters is represented on a daily, rather than monthly basis, with comparable results.