GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the con...GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates.As a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.展开更多
We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump sourc...We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser.The chirped pulses from a figure of eight-cavity modelocked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator.The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches,each of which is composed of 13 subpulses.The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers：one-stage is core-pumped and the other is cladding-pumped.A fiberized acousto-optic modulator is inserted to control the pulse repetition rate（PRR） of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area（LMA） PM Yb-doped fiber.The maximum average powers from the final amplifier are 85 W,60 W,and 45 W,respectively,corresponding to the PRR of2.72 MHz,1.36 MHz,and 0.68 MHz.The amplified pulses are directed to pump an MgO：PPLN-based optical parametric oscillator（OPO）.A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW.Detailed performance characteristics are presented.展开更多
In this paper, a newly approved standard G.984 for Gigabit-capable Passive Optical Networks (GPON) is introduced. Technical challenges about high-speed burst-mode data transmission in GPON are discussed and key issues...In this paper, a newly approved standard G.984 for Gigabit-capable Passive Optical Networks (GPON) is introduced. Technical challenges about high-speed burst-mode data transmission in GPON are discussed and key issues such as Forward Error Correction (FEC), timing to uplink performance of burst mode are high- lighted.展开更多
An additional sensitivity penalty of burst mode receivers due to the extinction ratio is analyzed considering the specific transmitter control in Ethernet PON. For an extinction ratio of 6dB, a penalty of 8dB occurs a...An additional sensitivity penalty of burst mode receivers due to the extinction ratio is analyzed considering the specific transmitter control in Ethernet PON. For an extinction ratio of 6dB, a penalty of 8dB occurs additionally.展开更多
在露天矿山向地下延伸开采工程实践中,探究充填体−岩石(Cemented Paste Backfill-Rock,CPB-R)组合体结构的力学特征与变形破坏规律,对保证地下采场稳定性和煤矿岩爆灾害防治具有特殊重要性。采用PFC^(2D)软件的刚性块体弹簧网络方法(Rig...在露天矿山向地下延伸开采工程实践中,探究充填体−岩石(Cemented Paste Backfill-Rock,CPB-R)组合体结构的力学特征与变形破坏规律,对保证地下采场稳定性和煤矿岩爆灾害防治具有特殊重要性。采用PFC^(2D)软件的刚性块体弹簧网络方法(Rigid Body Spring Network,RBSN)对单轴压缩条件下含不同界面倾角的CPB-R组合体结构的破坏行为进行了数值模拟研究,从宏细观角度探究了不同界面倾角对CPB-R组合体的强度特征、破坏模式和声发射特征的影响规律,并开展室内单轴压缩试验对数值模拟结果进行了验证和对比分析。研究结果表明:CPB-R组合体的强度随界面倾角增大呈现出先增大后减小的“U”形变化,且在倾角达到60°左右时具有最小的峰值强度;界面倾角超过30°后,应力应变曲线屈服阶段削弱,脆性特征显著增加,随着界面倾角的增大,CPB-R组合体的破坏模式呈现出“Y”形失效向界面滑移失效转变,再向混合失效转变的演变趋势,极限承载力呈现由充填体控制向界面控制转变,再转变为由岩石控制的演变趋势;随着CPB-R组合体界面倾角的增大,界面破坏程度不断提高,界面破损会阻止界面的进一步滑移(界面倾角<60°)并导致张拉破坏的出现;岩爆指数(K_(E))在充填体与岩石的弹性模量比增大过程中先降低后升高,控制充填体与岩石的弹性模量比在0.4~0.5时可以有效地降低岩爆的风险。展开更多
在详细分析MOSFET输出电容对CLLLC谐振变换器运行原理和工作特性影响的基础上,针对MOSFET输出电容在续流阶段会产生振荡的问题,提出一种优化的参数设计方法,可在保持自然软开关特性的同时减轻振荡;针对由输出电容引起的变换器轻空载工...在详细分析MOSFET输出电容对CLLLC谐振变换器运行原理和工作特性影响的基础上,针对MOSFET输出电容在续流阶段会产生振荡的问题,提出一种优化的参数设计方法,可在保持自然软开关特性的同时减轻振荡;针对由输出电容引起的变换器轻空载工作时输出电压漂高的问题,采取电压滞环间歇模式控制,可有效将输出电压调节至额定值,同时降低变换器轻空载工作时的损耗;最后,搭建了一台1 k W、400 V/48 V的实验样机,实验结果证明了所提优化设计和控制策略的正确性和可行性。展开更多
基金supported by MEXT Quantum Leap Flagship Program(MEXT Q-LEAP)Grant Number JPMXS0118067246.
文摘GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates.As a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.
基金supported by the National Natural Science Foundation of China(Grant No.61078015)the National Basic Research Program of China(Grant No.2011CB311803)
文摘We demonstrate a compact periodically poled MgO-doped lithium niobate（MgO：PPLN）-based optical parametric oscillator（OPO） quasi-synchronously pumped by a fiber laser system with burst-mode operation.The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser.The chirped pulses from a figure of eight-cavity modelocked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator.The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches,each of which is composed of 13 subpulses.The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers：one-stage is core-pumped and the other is cladding-pumped.A fiberized acousto-optic modulator is inserted to control the pulse repetition rate（PRR） of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area（LMA） PM Yb-doped fiber.The maximum average powers from the final amplifier are 85 W,60 W,and 45 W,respectively,corresponding to the PRR of2.72 MHz,1.36 MHz,and 0.68 MHz.The amplified pulses are directed to pump an MgO：PPLN-based optical parametric oscillator（OPO）.A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW.Detailed performance characteristics are presented.
文摘In this paper, a newly approved standard G.984 for Gigabit-capable Passive Optical Networks (GPON) is introduced. Technical challenges about high-speed burst-mode data transmission in GPON are discussed and key issues such as Forward Error Correction (FEC), timing to uplink performance of burst mode are high- lighted.
文摘An additional sensitivity penalty of burst mode receivers due to the extinction ratio is analyzed considering the specific transmitter control in Ethernet PON. For an extinction ratio of 6dB, a penalty of 8dB occurs additionally.
文摘在露天矿山向地下延伸开采工程实践中,探究充填体−岩石(Cemented Paste Backfill-Rock,CPB-R)组合体结构的力学特征与变形破坏规律,对保证地下采场稳定性和煤矿岩爆灾害防治具有特殊重要性。采用PFC^(2D)软件的刚性块体弹簧网络方法(Rigid Body Spring Network,RBSN)对单轴压缩条件下含不同界面倾角的CPB-R组合体结构的破坏行为进行了数值模拟研究,从宏细观角度探究了不同界面倾角对CPB-R组合体的强度特征、破坏模式和声发射特征的影响规律,并开展室内单轴压缩试验对数值模拟结果进行了验证和对比分析。研究结果表明:CPB-R组合体的强度随界面倾角增大呈现出先增大后减小的“U”形变化,且在倾角达到60°左右时具有最小的峰值强度;界面倾角超过30°后,应力应变曲线屈服阶段削弱,脆性特征显著增加,随着界面倾角的增大,CPB-R组合体的破坏模式呈现出“Y”形失效向界面滑移失效转变,再向混合失效转变的演变趋势,极限承载力呈现由充填体控制向界面控制转变,再转变为由岩石控制的演变趋势;随着CPB-R组合体界面倾角的增大,界面破坏程度不断提高,界面破损会阻止界面的进一步滑移(界面倾角<60°)并导致张拉破坏的出现;岩爆指数(K_(E))在充填体与岩石的弹性模量比增大过程中先降低后升高,控制充填体与岩石的弹性模量比在0.4~0.5时可以有效地降低岩爆的风险。
文摘在详细分析MOSFET输出电容对CLLLC谐振变换器运行原理和工作特性影响的基础上,针对MOSFET输出电容在续流阶段会产生振荡的问题,提出一种优化的参数设计方法,可在保持自然软开关特性的同时减轻振荡;针对由输出电容引起的变换器轻空载工作时输出电压漂高的问题,采取电压滞环间歇模式控制,可有效将输出电压调节至额定值,同时降低变换器轻空载工作时的损耗;最后,搭建了一台1 k W、400 V/48 V的实验样机,实验结果证明了所提优化设计和控制策略的正确性和可行性。
