多波长激光主动式相干合成理论初探

本文从相干合成的基本原理出发,建立计算模型,通过对多波长两路相干合成实例的仿真计算,得到了多波长两路相干合成效果的预测公式;在多波长相干合成中光程差至关重要,按照能否进一步通过主动控制,获得好的合成效果,可将光程差划分为可控区和不可控区两类,只有当光程差处于可控区时,才能进一步通过主动控制获得好的合成效果;在光程差任取的情况下,光程差处于可控区,能够通过主动控制获得好的合成效果的概率与光谱结构紧密相关,近似随着波长数目的增多成反比减少. 对于多波长相干合成可采取复合控制的方式,先利用大光程控制器件将光程差 关键词： 光纤激光 多波长相干合成 光程差     

Coherent beam combination of an optical array using adaptive fiber optics collimators

A novel adaptive-fiber-optics-collimator (AFOC) compensating both piston-type and tip/tilt-type phase errors of output beam is introduced, and has been employed in experiments of coherent beam combination (CBC) of a delta distributed fiber array. Feedback control is realized using stochastic parallel gradient descent (SPGD) algorithm. Excellent CBC effect has been achieved when piston and tip/tilt errors among beamlets corrected. The necessity of wavefront tip/tilt control in CBC is verified. Experimental results exhibit great potential applications of this kind of AFOC in fiber amplifier arrays.     

基于随机并行梯度下降算法的多波长激光相干合成

由于受到受激布里渊散射(SBS)等非线性效应的限制,单频激光放大器的功率在百瓦量级,以非单频激光多波长激光作为种子源能够有效地抑制SBS并提高放大器功率.与单频激光相干合成相比,非单频率、多波长激光的相干合成有望将输出激光功率成量级地提高.基于随机并行梯度下降(stochastic parallel gradient descent,SPGD)算法,实现了四波长激光的相干合成.在系统闭环时,四路多波长激光合成后的主瓣能量能够提高3倍,达到理想值的75%.验证了多波长、非单频激光相干合成的可行性,为高功率相干合成的发展提供了新的途径.     

倾斜相差对光纤激光相干合成的影响与模拟校正

选取不同路数和不同填充因子的合成光束模型,模拟并分析了倾斜相差对相干合成的影响.介绍了倾斜校正的关键器件--自适应光纤光源准直器.在主振荡功率放大器结构的光纤激光相干合成系统中,模拟了随机并行梯度下降(SPGD)算法校正七路激光阵列间时变倾斜相差的动态过程,分析了不同倾斜相差幅值和频率对校正能力的影响.实验表明,要提高相干合成的效果,必须校正倾斜相差;而SPGD算法校正倾斜相差的能力随着倾斜相差幅值和频率的增加而降低.文章为在实际大气环境中实现多路高功率光纤激光的相干合成提供了参考. 关键词： 光纤激光 相干合成 倾斜相位差 动态分析     

基于目标在回路的三路光纤传输激光相干合成实验

实验验证了一种利用目标回光在远场实现相干合成的技术——目标在回路技术.建立了目标在回路相干合成的物理模型,利用可同时调整光程和光束倾斜的自适应光纤光源准直器,同时补偿合成光束间的平移和倾斜相差,实现了基于目标在回路的三路光纤传输激光间相干合成,获得了接近理想情况的合成效果.文章为在实际大气环境中实现多路相干组束的长距离传输提供了参考.     

Active coherent beam combining of diode lasers

We have demonstrated active coherent beam combination (CBC) of up to 218 semiconductor amplifiers with 38.5?W cw output using up to eleven one-dimensional 21-element individually addressable diode amplifier arrays operating at 960?nm. The amplifier array elements are slab-coupled-optical-waveguide semiconductor amplifiers (SCOWAs) set up in a master-oscillator-power-amplifier configuration. Diffractive optical elements divide the master-oscillator beam to seed multiple arrays of SCOWAs. A SCOWA was phase actuated by adjusting the drive current to each element and controlled using a stochastic-parallel-gradient-descent (SPGD) algorithm for the active CBC. The SPGD is a hill-climbing algorithm that maximizes on-axis intensity in the far field, providing phase locking without needing a reference beam.     

Experimental study on the polarization extinction ratio degradation in high power hybrid fiber amplifier chains employing PM/non-PM Yb-doped fibers

Hybrid fiber amplifier chains employing polarization-maintaining (PM)/non-polarization-maintaining (non-PM) Yb-doped fibers (YDF) were proposed and the polarization extinction ratio (PER) degradation in the amplifier chains was studied experimentally. It was found that the PER increased if the PM YDF was pumped, while the PER decreased gradually if the non-PM YDF was pumped. In addition, it was shown that the hybrid high power fiber amplifier was also coherently combinable experimentally, and it was found that the contrast of pattern captured while using the PM/non-PM hybrid amplifier chains just decreased by 17% compared with only using PM amplifier, which confirmed the feasibility and potential application of the hybrid fiber amplifier chains in the coherent beam combination (CBC) of fiber lasers.     

双抽运光纤光参变放大的全光多波长变换与码型转换

利用强度调制的数据信号光作为一路抽运光,与另一路直流或者正弦强度调制抽运光组合可以在双抽运光纤光参变放大过程中实现全光多波长变换或者在全光多波长变换的同时实现码型转换.理论上,从信号增益的角度分析了波长转换与码型转换的原理.实验上演示了2.5Gb/s的非归零(NRZ)码信号的全光多波长转换与到归零(RZ)码信号的转换.多波长转换实验表明:双抽运条件下的光参变过程可以实现多波长转换并得到正、反码的输出,还同时对信号有一定的再生作用.码型转换后信号的占空比为30%,消光比也得到提高.     

Multi-wavelength laser source based on enhanced four-wave-mixing effect in a highly nonlinear fiber

We propose a multi-wavelength laser source based on an enhanced four-wave-mixing (FWM) effect which is achieved when a highly nonlinear fiber (HNLF) and an Erbium-doped fiber amplifier (EDFA) are employed in a fiber loop. A multi-wavelength laser source with totally 28 new wavelengths and a wavelength spacing of 0.8 nm is demonstrated. The wavelength spacing of the proposed multi-wavelength laser source can be tuned from 0.1 to 5.0 nm, and output spectrum of the multi-wavelength laser source with the wavelength spacing of 0.4, 0.8, and 1.6 nm are presented.     

Wavelength-spacing continuously tunable multi-wavelength SOA-fiber ring laser based on Mach–Zehnder interferometer

A Mach–Zehnder interferometer (MZI) which is used as a wavelength-spacing tunable comb filter in a fiber ring laser is built by employing an optical variable delay line (OVDL). Stable multi-wavelength semiconductor optical amplifier (SOA)-fiber ring laser based on an SOA and the MZI comb filter is achieved. Wavelength spacing can be continuously tuned by adjusting the OVDL and, as an example, multi-wavelength lasing with the wavelength spacing of 0.4, 0.8, or 1.6 nm is demonstrated. The output of the proposed multi-wavelength SOA-fiber ring laser is quite stable at room temperature and the output spectrum can be adjusted by controlling the bias current of the SOA.     

82-channel multi-wavelength comb generation in a SOA fiber ring laser

We demonstrate a multi-wavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual-pass Mach-Zehnder interferometer (MZI) filter. Two SOAs with different gain spectra provide sufficient gain and a wider gain spectrum to facilitate multi-wavelength lasing. The dual-pass MZI, configured by adding an optical isolator to the two outputs of the conventional MZI, serves as comb filter for multi-wavelength operation, and its extinction ratio can be enhanced to twofold as that of the conventional MZI in the same parameters. To investigate the influences of a dual-pass MZI filter and a conventional MZI filter on multi-wavelength operation, two different cavity configurations are presented and compared, including a single-SOA ring cavity and a double-SOA ring cavity. Stable simultaneous operation at 82 wavelengths, with a wavelength spacing of 40 GHz and a power deviation of 5 dB, and with a minimum optical signal-to-noise ratio (OSNR) of 28 dB, is observed from the double-SOA ring cavity using a dual-pass MZI filter.     

基于功率合束器的多路光纤激光自组织相干合成

提出了基于功率合束器的多路光纤激光自组织被动相干合成结构,研究了多模状态下泵浦功率、合成路数对激光合成效率和光束质量的影响,并对2,3,4路激光合成进行了实验研究,合成效率大于90%。实验结果表明:激光中心主瓣所占能量比随着泵浦功率的增加而增大,随激光合成路数增多而增大;在相同的输出功率下,单路激光的主瓣所占能量比比合成激光主瓣所占能量比要高;降低输出光栅反射率,激光输出能量增强,但合成效率有所降低;增加功率和增加路数可以增加中心亮斑的能量比,但增加幅度变低。     

基于光纤合束器件的高功率全光纤相干合成技术研究进展与展望

介绍了目前研究中相干合成多采用空间结构的研究现状,分析了空间结构的相干合成方案需要复杂的光路调节且长时间工作稳定性欠缺,肯定了基于光纤合束器件的全光纤激光相干合成在相干合成光源中的稳定性与实用性,梳理了近年来基于光纤合束器件的全光纤激光相干合成方案,分别介绍了基于光纤耦合器、光子灯笼、相干信号合束器以及基于自成像效应实现全光纤合束的技术方案及研究现状,分析了不同光纤器件目前的主要限制因素和发展瓶颈,并展望了未来的发展方向。     

基于自适应桶中功率评价函数的光纤放大器相干合成实验研究

光纤激光光束合成技术被公认为是实现高亮度、高光束质量激光束的优秀方法, 而激光阵列间的倾斜像差是影响合成效果的重要因素. 针对当前光束合成中存在的倾斜校正量受限问题, 提出了基于自适应桶中功率(PIB)评价函数的倾斜控制策略. 搭建了两路2 W光纤放大器的相干合成实验平台, 利用自制的压电环光纤相位调制器和自适应光纤准直器分别实现锁相和倾斜像差校正, 验证了基于自适应PIB的倾斜控制策略的可行性, 并实现了相干合成. 关键词： 光纤激光阵列 倾斜控制 自适应桶中功率 相干合成     

增强实验室X激光的亮度

实验室X激光已经取得重大进展,但均属自发辐射放大,缺乏模式限制的措施,故激光功率分散在多横模中,提高激光亮度的措施之一是模式限制.由于X光多层膜一般为高吸收膜,用以形成谐振腔作模式限制看来是困难的.本文建议采用相距足够远的二段激光等离子体作同步延迟行波放大来进行横模限制.分析表明,达到衍射极限的单横模X激光是可能的,这对X光全息术以及高亮度X激光的实现是十分重要的.本文还建议改变一般采用的产生线状等离子体的光学系统设计,使激光功率密度在长线上达到均匀;认为过去的光学系统不良是长焦线时,X激光增益-长度乘积低的一个可能原因.     

基于SOA和级联取样光纤光栅的多波长激光器

研究了基于半导体光放大器(SOA)和双段级联取样光纤光栅构成的新型结构多波长激光器.设 计了取样光纤光栅，计算了其反射谱，模拟了多波长激光器的输出光谱.基于自行制作的SOA 和取样光纤光栅，进行了多波长激光器的实验研究，得到了间隔为0.8nm、输出功率不平坦 度小于1.0dB的11个波长输出.理论和实验两个方面都可以验证：与基于普通取样光栅的多波 长方案相比，基于双段级联取样光栅的方案能改善输出谱平坦度，并可提高可激射波长数. 关键词： 半导体光放大器 取样光纤光栅 多波长激光器     

Coherent beam combining of fiber amplifier based on adaptive polarization and active phase control

Coherent beam combining (CBC) of a polarization-maintaining fiber amplifier and a non-polarization-maintaining fiber amplifier is presented. The experiment is based on adaptive polarization control and active phase control. The stochastic parallel gradient decent (SPGD) algorithm is used for the adaptive polarization control in the non-polarization-maintaining fiber amplifier and the active phase control is realized by single frequency dithering (SFD) algorithm. When the adaptive polarization control system and the phase control system go into closed loop, the fringe contrast of far-field intensity pattern is improved to more than 87.7%. A scalable architecture for CBC of two styles fiber amplifiers is also proposed.     

基于半导体光放大器的可调谐多波长光纤激光器

报道了一种新型环形腔可调谐多波长光纤激光器,腔内以半导体光放大器为增益介质,利用高双折射光纤构成的高双折射环形镜的滤波特性,在室温下,获得了基本符合ITU-T标准100GHz的17个波长以上的稳定多波长输出.各信道峰值功率差小于6 dB,线宽小于0.102 nm,信噪比大于25 dB.通过调节高双折射环形镜内的偏振控制器状态实现了这一组波长整体在50GHz范围内连续可调谐.并利用实验方法,对该光纤激光器应用于掺铒光纤放大器对多信道放大性能测试的可行性进行了初步探讨.     

Simultaneous all-solid-state multi-wavelength lasers --- a promising pump source for generating highly coherent terahertz waves

A diode-end-pumped Nd:YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M² of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino--methyl-stilbazolium tosylate (DAST) crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate (LBO) crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M² of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.     

基于空间滤波的光纤激光被动相位锁定技术研究

基于空间滤波的被动相位锁定,对掺Yb光纤激光阵列的相干组束进行了理论和实验研究.分析了基于空间滤波光反馈相位锁定的原理,研究了远场相干光斑Strehl比与激光波长及光谱带宽的关系.建立了二维四路掺Yb光纤放大器阵列的被动相位锁定实验系统,实现了稳定的相干耦合激光输出,远场光斑Strehl比为0.77.测得输出激光光谱中单个纵模的带宽约为9.1 GHz,与理论计算符合较好. 关键词： 光纤激光 相干合成 环形腔