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
针对水轮机调节系统簇发振荡的抑制问题,提出一种基于浸入与不变(immersion and invariance, I&I)原理的自适应反步滑模控制策略。首先,建立两时间尺度下的水轮机调节系统动力学模型,并分析系统的簇发振荡行为;其次,结合反步理论和...针对水轮机调节系统簇发振荡的抑制问题,提出一种基于浸入与不变(immersion and invariance, I&I)原理的自适应反步滑模控制策略。首先,建立两时间尺度下的水轮机调节系统动力学模型,并分析系统的簇发振荡行为;其次,结合反步理论和基于趋近律的滑模原理设计控制器,同时,对水轮机调节系统在运行过程受到的外部扰动,引入I&I理论对扰动估计误差建立流形,通过自适应律的选取保持其吸引与不变,并采用Lyapunov稳定性理论对所提控制方法进行收敛性证明;最后,对上述控制策略进行仿真验证。结果表明,该方法能有效抑制系统的簇发振荡现象,且具有较好的扰动跟踪精度。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.
文摘针对水轮机调节系统簇发振荡的抑制问题,提出一种基于浸入与不变(immersion and invariance, I&I)原理的自适应反步滑模控制策略。首先,建立两时间尺度下的水轮机调节系统动力学模型,并分析系统的簇发振荡行为;其次,结合反步理论和基于趋近律的滑模原理设计控制器,同时,对水轮机调节系统在运行过程受到的外部扰动,引入I&I理论对扰动估计误差建立流形,通过自适应律的选取保持其吸引与不变,并采用Lyapunov稳定性理论对所提控制方法进行收敛性证明;最后,对上述控制策略进行仿真验证。结果表明,该方法能有效抑制系统的簇发振荡现象,且具有较好的扰动跟踪精度。
