Numerical Modeling of in-Band Pumped Ho-Doped Silica Fiber Lasers

Wang, Jiachen,Yeom, Dong-il,Simakov, Nikita,Hemming, Alexander,Carter, Adrian,Lee, Sang Bae,Lee, Kwanil IEEE 2018 Journal of Lightwave Technology Vol.36 No.24

<P>A theoretical model to describe in-band pumped holmium doped silica fiber lasers is presented. The model is established based upon theory and parameters obtained from published research works. Both core-pumped system and cladding-pumped system are simulated with the model. The simulation results agree well with most experimental results, and for the cases in which the simulation results show discrepancy with the experimental results the disagreement can be reasonably explained. Through numerical analysis it is found that besides common negative factors such as non-radiative decay, fiber loss, and non-optimized resonator configuration, energy transfer upconversion plays a deleterious role in the performance of in-band pumped holmium doped silica fiber lasers. In particular, inhomogeneous upconversion associated with ion clustering is found to cause significant degradation of slope efficiencies of lasers, a fact that is useful to understand the unsolved problem regarding the lower-than-expected slope efficiencies observed in previous studies of in-band pumped holmium doped fiber lasers.</P>

Study on the Development and Trade Effect of China-South Korea Free Trade Area

Wang Jiachen 한중경제문화학회 2022 한중경제문화연구 Vol.18 No.-

Design of broadband multilayer dichroic coating for a high-efficiency solar energy harvesting system

Jiachen, Wang,Lee, Sang Bae,Lee, Kwanil The Optical Society 2015 Applied Optics Vol.54 No.15

<P>We report on the design and performance of a broadband dichroic coating for a solar energy conversion system. As a spectral beam splitter, the coating facilitates a hybrid system that combines a photovoltaic cell with a thermal collector. When positioned at a 45° angle with respect to incident light, the coating provides high reflectance in the 40-1100??nm and high transmission in the 1200-2000??nm ranges for a photovoltaic cell and a thermal collector, respectively. Numerical simulations show that our design leads to a sharp transition between the reflection and transmission bands, low ripples in both bands, and slight polarization dependence.</P>

28 W CW linearly polarized single mode all-fiber thulium-doped fiber laser operating at 1.95 μ m

Wang, Jiachen,Yeom, Dong-il,Lee, Sang Bae,Lee, Kwanil SPIE - International Society for Optical Engineeri 2017 Optical Engineering Vol. No.

Compact Non-Cascaded All-Fiber Raman Laser Operating at 1174 nm

Jiachen Wang,Sang-Bae Lee,Kwanil Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.1

We investigate a non-cascaded, all-fiber, single-mode Raman fiber laser (RFL) operating at 1174 nm with an optical slope efficiency of 68%. An 1-km commercial single-mode fiber is used as the Raman gain medium. The RFL cavity is formed between a high reflectivity fiber Bragg grating (FBG) and a perpendicularly-cleaved fiber facet. The laser is pumped by using a homemade ytterbium-doped fiber laser (YDFL) and can be frequency doubled to generate yellow light. Under the optimum condition, A 6.9-W 1174-nm laser is obtained at maximum available power (24 W) of a laser diode pump. The optical conversion efficiency and the net slope efficiency of the RFL were respectively, 29% and 38%, with respect to launched diode laser power. We also demonstrate yellow-light generation by frequency doubling of the RFL.

Proposal for the Development of Digital Trade Rules in China

Wang Jiachen 한중경제문화학회 2023 한중경제문화연구 Vol.22 No.-

Role of Preoperative Albumin Quotient in Surgical Planning for Posttraumatic Syringomyelia: A Comparative Cohort Study

Pingchuan Xia,Houyuan Lv,Chenghua Yuan,Wanru Duan,Jiachen Wang,Jian Guan,Yueqi Du,Can Zhang,Zhenlei Liu,Kai Wang,Zuowei Wang,Xingwen Wang,Hao Wu,Zan Chen,Fengzeng Jian 대한척추신경외과학회 2024 Neurospine Vol.21 No.1

Objective: Surgical procedures for patients with posttraumatic syringomyelia (PTS) remain controversial. Until now, there have been no effective quantitative evaluation methods to assist in selecting appropriate surgical plans before surgery. Methods: We consecutively enrolled PTS patients (arachnoid lysis group, n = 42; shunting group, n = 14) from 2003 to 2023. Additionally, 19 intrathecal anesthesia patients were included in the control group. All patients with PTS underwent physical and neurological examinations and spinal magnetic resonance imaging preoperatively, 3–12 months postoperatively and during the last follow-up. Preoperative lumbar puncture was performed and blood-spinal cord barrier disruption was detected by quotient of albumin (Qalb, cerebrospinal fluid/serum). Results: The ages (p = 0.324) and sex (p = 0.065) of the PTS and control groups did not differ significantly. There were also no significant differences in age (p = 0.216), routine blood data and prognosis (p = 0.399) between the arachnoid lysis and shunting groups. But the QAlb level of PTS patients was significantly higher than that of the control group (p < 0.001), and the shunting group had a significantly higher QAlb (p < 0.001) than the arachnoid lysis group. A high preoperative QAlb (odds ratio, 1.091; 95% confidence interval, 1.004–1.187; p = 0.041) was identified as the predictive factor for the shunting procedure, with the receiver operating characteristic curve showing 100% specificity and 80.95% sensitivity for patients with a QAlb > 12.67. Conclusion: Preoperative QAlb is a significant predictive factor for the types of surgery. For PTS patients with a QAlb > 12.67, shunting represents the final recourse, necessitating the exploration and development of novel treatments for these patients.

Experimental Study on Spray Characteristics of The Internal Impinging Nozzle

( Jiachen Zhai ),( Zongjie Hu ),( Wei Xie ),( Huizhi Chen ),( Cong Xue ),( Yufeng Wang ),( Zhijun Wu ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-

The internal impinging nozzle with a bluff body set inside can form a periodic oscillating spray, which is a novel approach of atomization. In this paper, the flow distribution characteristics of the spray are studied with low-pressure water as the medium. Meanwhile, the characteristics of spray cone angle, oscillating frequency, spatial distribution of droplet velocity and particle size are also studied with high-speed Schllieren technique and Malwen particle size analyzer. The results demonstrate that with the increase of the injection pressure, the spray cone angle is almost constant, while the spray oscillating frequency increases gradually, which is tantamount to the variation trend of axial velocity and radial velocity of the droplet. When the injection pressure is elevated from 0.16MPa to 0.18MPa, at the same position, the increase of droplet axial velocity distinctly reaches a maximum. Furthermore, with the development of the spray, the particle size decreases accordingly, and the velocity of the well atomized area near the spray symmetrical center axis is also gradually reduced. The farther away from the nozzle outlet, the more pronounced the symmetry of the spatial distribution of the axial velocity and radial velocity becomes. Moreover, when the injection pressure reaches 0.16MPa, at the position 250mm away from the outlet, the particle size achieves a minimum, and the spray obtains a stable distribution, which is rarefied and uniform in the middle area, while generous on both sides. With the injection pressure increasing to 0.18MPa, the flow of the well atomized area near the spray symmetrical center axis reaches its maximum, and that of the area farthest away from the symmetry center is also raised by degrees as the injection pressure increases.

Novel asymmetric duty modulation for DAB converters to improve light load efficiency

Feng Wang,Xinyu Cui,Fang Zhuo,Jiachen Tian,Zhi Zheng,Ruixin Xu 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.4

In a DC distribution network, the solid-state transformer (SST) and energy storage systems require an isolated bidirectionalDC–DC converter (IBDC). Among the many IBDCs, the dual active bridge (DAB) converter has been widely studied dueto its advantages in terms of high power density and high efficiency. The traditional control strategy for DAB is phase shiftcontrol. However, when the primary and secondary side voltages do not match, the soft-switching characteristic and increasingcurrent in the phase shift control affect the application of DAB in scenarios involving input and output voltage changes. To improve the above-mentioned defects, a novel asymmetric duty modulation (ADM) control is proposed in this paper. Among the various multi-variable ADM controls, the two-variable ADM control is simple, but its current is higher under light loads. To improve this defect, this paper introduces trapezoidal modulation (TZM) control proposed for phase shift control into ADM to form a similar TZM (STZM) control corresponding to TZM control. This paper first expounds the basic principle of STZM control. On this basis, its basic characteristics are researched. With current stress as the optimization goal, an optimal STZM (OSTZM) control scheme with minimum current stress is proposed, and the effectiveness of the theoretical analysis is verified on the experimental bench. The result shows that STZM control can improve efficiency under light loads by reducing the current and ensuring full ZVS.

Fluid Mud Dynamics and Its Correlation to Hydrodynamics in Jiaojiang River Estuary, China

Li Li,Wang Jiachen,Zheng Yiqun,Yao Yanming,Guan Weibing 한국해양과학기술원 2023 Ocean science journal Vol.58 No.1

The Jiaojiang Estuary is a macro-tidal estuary with high turbidity and funnel-shaped geomorphology. Estuarine geomorphology and shipping are highly afected by sediments and heavy coastal engineering. Based on observed data and numerical simulation results, we studied the characteristics of the suspended sediments and fuid mud in the estuary. By considering two-way coupling of water–sediment density and the process of fne sediment focculation, a three-dimensional sediment model of the Jiaojiang Estuary was established and efectively calibrated using the measured data on tides, currents, and suspended sediment concentration (SSC). Field data analysis indicated that SSC and sediment transport rate in both the main tidal channel and shoals were positively correlated with the fow velocity in the low-frequency part during both the spring and neap tides. The model results revealed that the net sediment fux is controlled by advection and moves landward upstream of the main tidal channel. Fluid mud is formed near Haimen station, with tides infuencing the spatial and temporal variations in its thickness and speed. Sediment is actively exchanged among fuid mud-water-seabed, with sink and source processes dominating near the bay mouth and the Haimen station, respectively. Sediments weaken the seaward residual currents slightly by changing their viscosity and the von Karman constant, and the stratifcation process is afected by changes in water density. The fndings of this study provide a foundation for the study of material transportation in an estuarine ecosystem.