We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd：CaGdAI04 （Nd：CGA） as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser ...We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd：CaGdAI04 （Nd：CGA） as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd：CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.展开更多
Random gain medium based on organic Rhodamine 590 (R590) laser-dye and Titanium dioxide (TiO2) suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Spray-coated homogeneous film sam...Random gain medium based on organic Rhodamine 590 (R590) laser-dye and Titanium dioxide (TiO2) suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Spray-coated homogeneous film samples of 22.4 μm thickness. Optimum concentrations have been determined depending on the normal fluorescence spectra which give evidence that the laser dye provides amplification and TiO2 nanoparticles act as scatter center. At the optimum concentrations, results of the random gain medium under second harmonic Nd: YAG laser excitation shows that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 11 nm and 10 mJ respectively.展开更多
Inducing a significant optical torque remains a challenging task,since the law of angular momentum conservation implies that one has to harvest a lot of light.Such a problem was partially resolved by using optical twi...Inducing a significant optical torque remains a challenging task,since the law of angular momentum conservation implies that one has to harvest a lot of light.Such a problem was partially resolved by using optical twist via strong internal multiple scattering to recycle the photons,and one can induce a large torque per unit of radiation cross section.By using the Maxwell stress tensor and the generalized Lorentz-Mie scattering theory for multi-spheres,we investigate the influence of gain materials in further amplifying optical torque in the optical twist settings.It is found that,when combined with a gain layer,the optical torque of lossy(both in PT-and non-PT-symmetric structures)or lossless(low dielectric materials)clusters at resonance could be one order of magnitude larger than those of a single layer and previous studied plasmonic double layer structures.Moreover,the gain-enhanced large opposite rotations(i.e.,optical twist)of the two layers arise at resonances in these structures.In contrast,in the gain-gain double-layer cluster,optical torques on both layers have no significant increase and the two layers rotate in the same direction at resonances.This work provides an elaborate investigation on the gain media-induced optical twist,which offers more choices for optical micromanipulation.展开更多
Er^(3+)-Tm^(3+)-Pr^(3+)triply-doped graphene-glass-graphene(GGG) nanosheet waveguide amplifier, which is a promising candidate for integrated photonic devices, is modelled and numerically analyzed. The designed wavegu...Er^(3+)-Tm^(3+)-Pr^(3+)triply-doped graphene-glass-graphene(GGG) nanosheet waveguide amplifier, which is a promising candidate for integrated photonic devices, is modelled and numerically analyzed. The designed waveguide is composed of a triply-doped tellurite glass core. The core is sandwiched between two graphene layers.The rate and power propagation equations of a heterogeneous multi-level laser medium are set up and solved numerically to study the effects of waveguide length and active ion concentrations on amplifier performance at five different input signal wavelengths(1.310, 1.470, 1.530, 1.600 and 1.650 μm). The analytical results show that rareearth ion dopant concentrations at an order of 10^(26) ion/m^3, waveguide length at 0.1 m and pump power at 100 m W can amplify 1.530 and 1.600 μm input signals with 1 μW power up to approximately 20.0 and 24.0 dB respectively.Finite-difference time-domain(FDTD) simulation results show that mode field radius of GGG waveguide is smaller than that of silicon waveguide. Consequently, GGG waveguide with the same pump and signal power and the same gain-medium length can produce higher gain than silicon waveguide.展开更多
Energy efficiency has become one of the most important issues in wireless body area network(WBAN).In this paper,an energy-efficient medium access control(MAC)protocol for WBAN is proposed based on human body posture u...Energy efficiency has become one of the most important issues in wireless body area network(WBAN).In this paper,an energy-efficient medium access control(MAC)protocol for WBAN is proposed based on human body posture under walking scenery.Due to person's movements,WBAN is a dynamic network,which means that traditional static protocols are no more suitable for it.For solving this problem,firstly,the feature of human walking at a constant speed is analyzed and we divide a spell of movements into a sequence of key frames just like a video constituted by numbers of continuous frames.As a result,the dynamic walking process is translated into several static postures,which the static MAC protocol could be used for.Secondly,concerning the performance of network lifetime,we design a posture-aware approach for lifetime maximization(PA-DPLM).With analytical and simulation results provided,we demonstrate that PA-DPLM protocol is energy-efficient and can be used under constant speed walking scenery.展开更多
为实现长距离传输及亚波长尺度的模式限制,在传统介质加载型表面等离子结构的基础上,设计了一种微孔介质加载混合表面等离子体波导,采用时域有限差分法(FDTD)对该波导模式场分布及传输特性进行了相应的研究。研究表明所设计的波导结构...为实现长距离传输及亚波长尺度的模式限制,在传统介质加载型表面等离子结构的基础上,设计了一种微孔介质加载混合表面等离子体波导,采用时域有限差分法(FDTD)对该波导模式场分布及传输特性进行了相应的研究。研究表明所设计的波导结构具有较强的局域场限制,通过在孔内填充增益介质,使混合等离子体波导的传输损耗得到了补偿,输出端的表面等离子激元实现了增益放大。结果表明,通过调整波导的几何参数和电磁参数,可以显著提高波导的场限制,降低波导本身的损耗,其中当孔与金属之间距离为44 nm时,波导的损耗达最小约为-13 d B/μm。这一设计可以为光子器件集成提供一定的理论和实验借鉴价值。展开更多
基金Supported by the National Key Basic Research Program of China under Grant No 2013CB922402the International Joint Research Program,and the National Natural Science Foundation of China under Grant Nos 61210017 and 11434016
文摘We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd：CaGdAI04 （Nd：CGA） as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd：CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.
文摘Random gain medium based on organic Rhodamine 590 (R590) laser-dye and Titanium dioxide (TiO2) suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Spray-coated homogeneous film samples of 22.4 μm thickness. Optimum concentrations have been determined depending on the normal fluorescence spectra which give evidence that the laser dye provides amplification and TiO2 nanoparticles act as scatter center. At the optimum concentrations, results of the random gain medium under second harmonic Nd: YAG laser excitation shows that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 11 nm and 10 mJ respectively.
基金the National Natural Science Foundation of China(Grant Nos.11674204 and 11704232)the Fund from HK RGC,China(Grant Nos.AoE/P-02/12 and C6013-18GF).
文摘Inducing a significant optical torque remains a challenging task,since the law of angular momentum conservation implies that one has to harvest a lot of light.Such a problem was partially resolved by using optical twist via strong internal multiple scattering to recycle the photons,and one can induce a large torque per unit of radiation cross section.By using the Maxwell stress tensor and the generalized Lorentz-Mie scattering theory for multi-spheres,we investigate the influence of gain materials in further amplifying optical torque in the optical twist settings.It is found that,when combined with a gain layer,the optical torque of lossy(both in PT-and non-PT-symmetric structures)or lossless(low dielectric materials)clusters at resonance could be one order of magnitude larger than those of a single layer and previous studied plasmonic double layer structures.Moreover,the gain-enhanced large opposite rotations(i.e.,optical twist)of the two layers arise at resonances in these structures.In contrast,in the gain-gain double-layer cluster,optical torques on both layers have no significant increase and the two layers rotate in the same direction at resonances.This work provides an elaborate investigation on the gain media-induced optical twist,which offers more choices for optical micromanipulation.
基金the National Natural Science Foundation of China(Nos.60377023 and 60672017)the Program for New Century Excellent Talents in Universities(NCET)the Shanghai Optical Science and Technology Project(No.05DZ22009)
文摘Er^(3+)-Tm^(3+)-Pr^(3+)triply-doped graphene-glass-graphene(GGG) nanosheet waveguide amplifier, which is a promising candidate for integrated photonic devices, is modelled and numerically analyzed. The designed waveguide is composed of a triply-doped tellurite glass core. The core is sandwiched between two graphene layers.The rate and power propagation equations of a heterogeneous multi-level laser medium are set up and solved numerically to study the effects of waveguide length and active ion concentrations on amplifier performance at five different input signal wavelengths(1.310, 1.470, 1.530, 1.600 and 1.650 μm). The analytical results show that rareearth ion dopant concentrations at an order of 10^(26) ion/m^3, waveguide length at 0.1 m and pump power at 100 m W can amplify 1.530 and 1.600 μm input signals with 1 μW power up to approximately 20.0 and 24.0 dB respectively.Finite-difference time-domain(FDTD) simulation results show that mode field radius of GGG waveguide is smaller than that of silicon waveguide. Consequently, GGG waveguide with the same pump and signal power and the same gain-medium length can produce higher gain than silicon waveguide.
基金supported by the National Natural Science Foundation of China(No.61074165 and No.61273064)Jilin Provincial Science & Technology Department Key Scientific and Technological Project(No.20140204034GX)Jilin Province Development and Reform Commission Project(No.2015Y043)
文摘Energy efficiency has become one of the most important issues in wireless body area network(WBAN).In this paper,an energy-efficient medium access control(MAC)protocol for WBAN is proposed based on human body posture under walking scenery.Due to person's movements,WBAN is a dynamic network,which means that traditional static protocols are no more suitable for it.For solving this problem,firstly,the feature of human walking at a constant speed is analyzed and we divide a spell of movements into a sequence of key frames just like a video constituted by numbers of continuous frames.As a result,the dynamic walking process is translated into several static postures,which the static MAC protocol could be used for.Secondly,concerning the performance of network lifetime,we design a posture-aware approach for lifetime maximization(PA-DPLM).With analytical and simulation results provided,we demonstrate that PA-DPLM protocol is energy-efficient and can be used under constant speed walking scenery.
文摘为实现长距离传输及亚波长尺度的模式限制,在传统介质加载型表面等离子结构的基础上,设计了一种微孔介质加载混合表面等离子体波导,采用时域有限差分法(FDTD)对该波导模式场分布及传输特性进行了相应的研究。研究表明所设计的波导结构具有较强的局域场限制,通过在孔内填充增益介质,使混合等离子体波导的传输损耗得到了补偿,输出端的表面等离子激元实现了增益放大。结果表明,通过调整波导的几何参数和电磁参数,可以显著提高波导的场限制,降低波导本身的损耗,其中当孔与金属之间距离为44 nm时,波导的损耗达最小约为-13 d B/μm。这一设计可以为光子器件集成提供一定的理论和实验借鉴价值。
