A 980-nm semiconductor saturable absorber mirror（SESAM） mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introdu...A 980-nm semiconductor saturable absorber mirror（SESAM） mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission（ASE） nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.展开更多
The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-ampl...The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-amplifier model, the signal induced by magnetic nanoparticles (MNPs) in a receiving coil was multiplied with a reference signal, and was then fed through a low-pass filter to extract the DC component of the signal (output signal). The MPI signal was defined as the mean of the absolute value of the output signal. The magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively, and the strength of the selection magnetic field (SMF) in MPI was assumed to be given by the product of the gradient strength of the SMF and the distance from the field-free region (x). In addition, Gaussian noise was added to the signal induced by MNPs using normally-distributed random numbers. The relationships between the MPI signal and x were calculated for the odd- and even-numbered harmonics and were investigated for various time constants of the low-pass filter used in the lock-in amplifier and particle sizes and their distributions of MNPs. We found that the behavior of the MPI signal largely depended on the time constant of the low-pass filter and the particle size of MNPs. This lock-in-amplifier model will be useful for better understanding, optimizing, and developing MPI, and for designing MNPs appropriate for MPI.展开更多
Efficient light generation and amplification has long been missing on the silicon platform due to its well-known indirect bandgap nature.Driven by the size,weight,power and cost(SWaP-C)requirements,the desire to fully...Efficient light generation and amplification has long been missing on the silicon platform due to its well-known indirect bandgap nature.Driven by the size,weight,power and cost(SWaP-C)requirements,the desire to fully realize integrated silicon electronic and photonic integrated circuits has greatly pushed the effort of realizing high performance on-chip lasers and amplifiers moving forward.Several approaches have been proposed and demonstrated to address this issue.In this paper,a brief overview of recent progress of the high-performance lasers and amplifiers on Si based on different technology is presented.Representative device demonstrations,including ultra-narrow linewidthⅢ-Ⅴ/Si lasers,fully integratedⅢ-Ⅴ/Si/Si3N4 lasers,high-channel count mode locked quantum dot(QD)lasers,and high gain QD amplifiers will be covered.展开更多
A diode dual-end-pumped Nd：YVO4 regenerative amplifier is reported. The influence of the cavity stability on the performance of the regenerative amplifier is studied. The experimental results match well with the anal...A diode dual-end-pumped Nd：YVO4 regenerative amplifier is reported. The influence of the cavity stability on the performance of the regenerative amplifier is studied. The experimental results match well with the analysis at high pump power. The mode locking seed pulses with 15 ps pulse width and 10 nJ single pulse energy at 86 MHz are amplified up to 4.7 mJ at 1 kHz, corresponding to the maximum amplification about 0.5 x 106, by our regenerative amplifier. And an average power of 4.7 W is obtained at the repetition rate from 1 kHz to 10 kHz.展开更多
A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standar...A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.展开更多
相关检测技术是从噪声中提取有用信号的实用技术。缺陷特征与信号特征密切相关,且呈现对应关系,但在无损检测过程中由于多种因素影响造成信号被噪声强干扰,使信号提取有一定的困难。以正交矢量型数字锁相放大器为核心,通过理论与仿真验...相关检测技术是从噪声中提取有用信号的实用技术。缺陷特征与信号特征密切相关,且呈现对应关系,但在无损检测过程中由于多种因素影响造成信号被噪声强干扰,使信号提取有一定的困难。以正交矢量型数字锁相放大器为核心,通过理论与仿真验证对低信噪比信号相关检测方法进行了研究。首先,基于相关检测的锁相放大技术,并依据相关性原理,进一步研究了正交矢量型数字锁相放大器的检测方案;其次,在该方案的前提下,应用坐标旋转数字计算方法(Coordinate Rotation Digital Computer,CORDIC)来简化复杂的运算,并推导出了反正切值和平方根的计算公式,用于计算低信噪比信号的幅度和相位;最后,通过MATLAB/Simulink进行了建模仿真和误差分析。结果表明,CORDIC旋转算法的计算误差低于1%,该方案的检测误差低于0.3%,检测精度高于99%。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.61205047)
文摘A 980-nm semiconductor saturable absorber mirror（SESAM） mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission（ASE） nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.
文摘The purpose of this study was to present a lock-in-amplifier model for analyzing the behavior of signal harmonics in magnetic particle imaging (MPI) and some simulation results based on this model. In the lock-in-amplifier model, the signal induced by magnetic nanoparticles (MNPs) in a receiving coil was multiplied with a reference signal, and was then fed through a low-pass filter to extract the DC component of the signal (output signal). The MPI signal was defined as the mean of the absolute value of the output signal. The magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively, and the strength of the selection magnetic field (SMF) in MPI was assumed to be given by the product of the gradient strength of the SMF and the distance from the field-free region (x). In addition, Gaussian noise was added to the signal induced by MNPs using normally-distributed random numbers. The relationships between the MPI signal and x were calculated for the odd- and even-numbered harmonics and were investigated for various time constants of the low-pass filter used in the lock-in amplifier and particle sizes and their distributions of MNPs. We found that the behavior of the MPI signal largely depended on the time constant of the low-pass filter and the particle size of MNPs. This lock-in-amplifier model will be useful for better understanding, optimizing, and developing MPI, and for designing MNPs appropriate for MPI.
文摘Efficient light generation and amplification has long been missing on the silicon platform due to its well-known indirect bandgap nature.Driven by the size,weight,power and cost(SWaP-C)requirements,the desire to fully realize integrated silicon electronic and photonic integrated circuits has greatly pushed the effort of realizing high performance on-chip lasers and amplifiers moving forward.Several approaches have been proposed and demonstrated to address this issue.In this paper,a brief overview of recent progress of the high-performance lasers and amplifiers on Si based on different technology is presented.Representative device demonstrations,including ultra-narrow linewidthⅢ-Ⅴ/Si lasers,fully integratedⅢ-Ⅴ/Si/Si3N4 lasers,high-channel count mode locked quantum dot(QD)lasers,and high gain QD amplifiers will be covered.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50721004 and 60978032)
文摘A diode dual-end-pumped Nd：YVO4 regenerative amplifier is reported. The influence of the cavity stability on the performance of the regenerative amplifier is studied. The experimental results match well with the analysis at high pump power. The mode locking seed pulses with 15 ps pulse width and 10 nJ single pulse energy at 86 MHz are amplified up to 4.7 mJ at 1 kHz, corresponding to the maximum amplification about 0.5 x 106, by our regenerative amplifier. And an average power of 4.7 W is obtained at the repetition rate from 1 kHz to 10 kHz.
基金Project supported by the Initiative Research Program of State Key Laboratory of Precision Measurement Technology and Instruments,Chinathe National Natural Science Foundation of China(Grant No.51527901)
文摘A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.
文摘相关检测技术是从噪声中提取有用信号的实用技术。缺陷特征与信号特征密切相关,且呈现对应关系,但在无损检测过程中由于多种因素影响造成信号被噪声强干扰,使信号提取有一定的困难。以正交矢量型数字锁相放大器为核心,通过理论与仿真验证对低信噪比信号相关检测方法进行了研究。首先,基于相关检测的锁相放大技术,并依据相关性原理,进一步研究了正交矢量型数字锁相放大器的检测方案;其次,在该方案的前提下,应用坐标旋转数字计算方法(Coordinate Rotation Digital Computer,CORDIC)来简化复杂的运算,并推导出了反正切值和平方根的计算公式,用于计算低信噪比信号的幅度和相位;最后,通过MATLAB/Simulink进行了建模仿真和误差分析。结果表明,CORDIC旋转算法的计算误差低于1%,该方案的检测误差低于0.3%,检测精度高于99%。
