国产30/600μm掺镱光纤实现4.1kW激光输出

采用化学气相沉积结合气相/液相复合掺杂方式制备30/600 μm掺镱双包层光纤,石英纤芯中的掺杂组分为Yb₂O₃, Al₂O₃,P₂O₅。基于976 nm发光二极管反向抽运方式,构建全光纤化的主控振荡器功率放大器结构对增益光纤进行测试。实验中,种子源功率为189 W,当泵浦总功率为4747 W时,激光输出功率为4120 W,放大级光光效率为85%,3 dB带宽为1.6 nm。激光器连续工作1 h,激光功率稳定在4100 W,未发生明显的功率衰退现象。     

Probing interfacial properties by optical second-harmonic generation

Optical second-harmonic generation from surfaces has recently proven to be a very effective and versatile probe for surface studies. It allows, among other things, direct probing of molecular adsorption on a solid substrate from a liquid. In this paper we review the most important features of this new technique. We discuss the possibility of applying it to the study of adsorption of ionic surfactants at solid–liquid interfaces, commonly used in a great number of scientific and technological fields including industrial applications. Moreover, we describe the preliminary results of an experiment currently in progress.     

Surface-emitting second-harmonic generation in AlGaAs/GaAs waveguides

We investigate the impact of waveguide properties on the performance of surface-emitting second-harmonic generation (SESHG) devices. Using multi-layer AlGaAs/GaAs ridge waveguides that are optimized for SESHG at fundamental wavelengths = 1060 and 1550 nm, we achieve nonlinear cross-sections among the highest reported so far. In these devices, characteristics of the guided fundamental wave strongly determine the SESHG performance: multiple reflections in the longitudinal direction affect the conversion efficiency while higher order lateral waveguide modes modify the SESHG farfield. Both effects are significant for applications of SESHG in integrated photonic circuits.     

Analysis of second-harmonic generation microscopy under refractive index mismatch

On the basis of the vector diffraction theory and Green＇s function method, this paper investigates the effects of refractive index mismatch on second-harmonic generation （SHG） microscopy. The polarization distribution and SHG intensity are calculated as functions of the sample radius and probe depth. The numerical results show that refractive index mismatch can result in peak intensity degradation, increase secondary lobes and extension of second- harmonic polarization distribution. Because of the attenuation of polarization intensity, the detected SHG intensity significantly decreases with increasing probe depth, which can limit the imaging depth of SHG microscopy inside thick samples. Forward SHG intensity decays slowly than backward SHG, due to the combination of extension second-harmonic polarization distribution and strong dependency of forward SHG on sample radius.[第一段]     

Transverse second-harmonic generation from disordered nonlinear crystals

We investigate the transverse second-harmonic generation in as grown strontium barium niobate (SBN) crystals with a random structure of anti-parallel ferroelectric domains. We consider both, single and counter-propagating pulse geometries. We investigate polarization properties of the second harmonic signal and discuss applications of this process for short pulses characterization. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

Optical second-harmonic generation of Janus MoSSe monolayer

The transition metal dichalcogenides (TMD) monolayers have shown strong second-harmonic generation (SHG) owing to their lack of inversion symmetry. These ultrathin layers then serve as the frequency converters that can be intergraded on a chip. Here, taking MoSSe as an example, we report the first detailed experimental study of the SHG of Janus TMD monolayer, in which the transition metal layer is sandwiched by the two distinct chalcogen layers. It is shown that the SHG effectively arises from an in-plane second-harmonic polarization under paraxial focusing and detection. Based on this, the orientation-resolved SHG spectroscopy is realized to readily determine the zigzag and armchair axes of the Janus crystal with an accuracy better than ±0.6°. Moreover, the SHG intensity is wavelength-dependent and can be greatly enhanced (～ 60 times) when the two-photon transition is resonant with the C-exciton state. Our findings uncover the SHG properties of Janus MoSSe monolayer, therefore lay the basis for its integrated frequency-doubling applications.     

光纤放大器的半经典分析

本文采用半经典理论分析稀土掺杂光纤中光与介质的相互作用机理,讨论了增益、饱和、光纤归一化频率、泵功率、信号功率及掺杂粒子数浓度等各参数之间的关系.计算与实验结果相符,可用这个理论设计所需特性的光纤放大器或对光纤放大器作进一步的改进.     

掺镱光纤放大器泵浦脉宽优化

为抑制低重复频率高能脉冲光纤主振荡功率放大(MOPA)系统的放大自发辐射(ASE)效应,达到脉冲泵浦的最佳放大效果,需要对泵浦脉宽进行优化。基于求解速率方程和功率传输方程,理论研究了脉冲泵浦下掺镱光纤放大器上能级粒子数密度、光纤内存储能量、正反向放大自发辐射的瞬态响应。在给定的泵浦功率、光纤长度、纤芯面积和掺杂数密度等参数下,数值计算得到的优化泵浦脉宽为793 s。此外,实验测定了ASE的建立时间; 通过调节泵浦脉宽,测定了脉冲泵浦下掺镱光纤放大器的放大效果,实验中得到的泵浦脉宽的优化值为800 s,证明了数值模拟的正确性。     

Intra-cavity second-harmonic and sum-frequency generation in a diode-pumped broadband Yb-doped fibre laser

Intra-cavity nonlinear frequency mixing in a diode-pumped, broadband Yb-doped fibre laser has been investigated. Second-harmonic generation of the fibre output, second-harmonic generation of the residual pump beam and sum frequency mixing between the two was achieved simultaneously, resulting in three colour operation in the blue-green region. Including the nonlinear crystal inside the cavity is also shown to be effective in reducing fluctuations in the output power.     

A theoretical study of double-pass thulium-doped fiber amplifiers

An efficient fluoride-based thulium-doped fiber amplifier (TDFA) is theoretically demonstrated using a double-pass scheme. A reflector is incorporated in the double-pass TDFA to allow double propagation of the test signal in the gain medium and thus improve the gain of the TDFA. The small signal gain improvement of more than 15 dB is obtained in the 1465 nm region. A gain as high as 42 dB is obtained in this region with 300 mW of 1050 nm pump using 20 m of thulium-doped fiber. However, a noise figure penalty of approximately 1 dB is also obtained in this wavelength region. Differential equations are solved using the Runge-Kutta method in the theoretical analysis. The theoretical result is in agreement with the experimental result.     

Effect of thermal blooming in second-harmonic generation in nonlinear crystals with a regular domain structure

Analytical expressions are obtained for the power of the second harmonic in nonlinear crystals having a regular domain structure with allowance for thermal blooming for a Gaussian beam of basic radiation in the quasi-stationary plane-wave approximation. Calculations were carried out in both the approximation of an assigned field of basic radiation and a substantially nonlinear regime of exhaustion of basic radiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp,. 257–260, March–April, 2000.     

Characteristics of the bandwidth in gain-clamped erbium-doped fiber amplifiers

1.IntYoductionErbium-dopedfiberamplifiers(EDFAs)arepresentlyofgreatinterestinopticalfibercommunicationsystem.Thegainprofiles,thatis,thegainforallwavelengthsofinter-est,areveryimPortantproPertiesofEDFAsinthewavelength-division-multip1exing(WDM)fibersystems['j.Manynumericalandanalyticalmethods(seeforexampleL1jandreferencestherein)canbeusedtoinvestigatethegainprofile8ofEDFAs,buttheyneedcumbersomemeasurementS(forexampIesPectraImeasurementsofEr-dopingabsorWtionandemission,andsoon)andhence…     

三路光纤放大器相干合成技术的实验研究

实验上实现了三路保偏光纤放大器稳定的锁相控制，达到相干合成的输出目的.介绍了实验方案，详细阐述了相位检测与控制的方法并以一路信号光为例给出了相位噪声的测量结果.最后给出了相干合成的远场图样并对其影响因素加以简单分析.实验表明，利用提出的方案增加相干合成的路数是可行的. 关键词： 光纤放大器 相干合成 锁相     

Time-domain analysis of second-harmonic generation of primary Lamb wave propagation in an elastic plate

Within the second-order perturbation approximation,this paper investigates the physical process of generation of the time-domain second harmonic by a primary Lamb wave waveform in an elastic plate.The present work is performed based on the preconditions that the phase velocity matching is satisfied and that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero.It investigates the influences of the difference between the group velocities of the primary Lamb wave and the double frequency Lamb wave,the propagation distance and the duration of the primary Lamb wave waveform on the envelope shape of the time-domain second harmonic.It finds that the maximum magnitude of the envelope of the second-harmonic waveform can grow within some propagation distance even if the condition of group velocity matching is not satisfied.Our analyses also indicate that the maximum magnitude of the envelope of the second-harmonic waveform is kept constant beyond a specific propagation distance.Furthermore,it concludes that the integration amplitude of the time-domain second-harmonic waveform always grows with propagation distance within the second-order perturbation.The present research yields new physical insight not previously available into the effect of generation of the time-domain second harmonic by propagation of a primary Lamb wave waveform.     

Theory of noise in a kilo-Hz cascaded high-energy Yb-doped nanosecond pulsed fiber amplifier

A theoretical analysis of noise in a high-power cascaded fiber amplifier is presented. Unlike the noise theory in low power communication, the noise of a high power system is redefined as the leaked output energy between pulses with coherent beat noise uncounted. This definition is more appropriate for high power usage in which the pulse energy receives more attention than the pulse shape integrity. Then the low power pre-amplifying stages are considered as linear amplification and analyzed by linear theory. In the high-power amplification stages, the inversion is assumed to recover linearly in the time interval between pulses. The time shape of the output pulse is different from that of the input signal because of different gains at the front and back ends of the pulse. Then, a criterion is provided to distinguish the nonlinear and linear amplifications based on the signal-to-noise ratio （SNR） analysis. Then, an experiment that shows that the output SNR actually drops off in nonlinear amplification is performed. The change in the noise factor can be well evaluated by pulse shape distortion.     

Electro-optic modulation on nonlinear phase shift and fundamental transmission in quasi-phase-matched second-harmonic generation

Nonlinear phase shift and transmission experienced by a beam at the fundamental frequency during electro-optic modulated quasi-phase-matched second-harmonic generation are studied. Numerical results indicate that the nonlinear phase shift of fundamental wave shows a difference of π, while fundamental transmission is controllable only by applying a DC electric field along z-axis. The above effect can be implemented on high-contrast optical switching devices such as Mach-Zehnder push-pull device. The relationships between the characteristic (peak and dip) electric fields and the initial pump intensity are also discussed.     

Efficient second, third, fourth, and fifth harmonic generation of a Yb-doped fiber amplifier

We report generation of the second, third, fourth, and fifth harmonics of the output of a Yb-doped fiber amplifier seeded by a passively Q-switched Nd:YAG microchip laser. We obtained high conversion efficiencies using a simple optical arrangement and critically phase-matched nonlinear crystals. Starting with 320 mW of average power at 1064 nm (86 μJ per pulse at a 3.7 kHz repetition rate), we generated 160 mW at 532 nm, 38 mW at 355 nm, 69 mW at 266 nm, and 18 mW at 213 nm. The experimental results are in excellent agreement with calculations.     

W波段二次谐波回旋行波管放大器的模拟与设计

回旋行波管放大器是一种具有高功率、高频率、宽带宽的毫米波放大器，TE₀₂模二次谐波回旋行波管放大器在保持基波回旋行波管放大器的基础上极大地减小了工作磁场,从而具有广阔的应用前景. 利用两段分布式损耗的互作用结构，有效抑制了绝对不稳定性和回旋返波振荡,避免了模式互作用电路引起的模式畸变，提高了输出功率，在一定程度上克服了谐波互作用较弱的缺点，满足了扩展功率容量和放大器长时间稳定工作的要求. 非线性模拟结果和粒子模型(particle in cell)模拟结果均表明，在工作电压为100k 关键词： W波段 二次谐波 回旋行波管放大器     

国产纺锤形增益光纤主振荡功率放大器实现5 kW输出

设计了纤芯直径小—大—小变化的“纺锤形”增益光纤,利用该光纤可均衡模式不稳定和受激拉曼散射抑制的矛盾,提升光纤激光器的输出功率。基于自研的纺锤形增益光纤搭建了主振荡功率放大器（MOPA）,实现了5 kW的功率输出,放大器光光效率为66.6%,拉曼散射抑制比大于45 dB,M²因子约2.0。通过优化光纤的设计,可以提升激光器的光束质量和效率。

     

Optimization of core size in erbium doped holey fiber amplifiers

Holey fibers (HFs) can be used as amplifier in optical communication systems. These new fiber structures have flexibility to change the fiber parameters such as refractive index of guided mode, air filling factor (AFF), V number, group velocity dispersion (GVD) and numerical aperture, only by the change of the hole size and air-hole spacing. In this paper we will use improved fully vectorial effective index method (IFEIM) to analyze the erbium doped holey fiber amplifier (EDHFA) with hexagonal unit cell. The range that core size can change in any air-hole spacing will determine and the growth of core size in the amplifier character such as maximum gain and optimum length will study. By determination of single mode region the effect of pump power and dopant concentration growth, on the amplifier parameter will define.