Piston measurement by quadriwave lateral shearing interferometry

We present what is to our knowledge a new method for measuring the relative piston between two independent beams separated by a physical gap, typical of petawatt facilities. The feasibility of this measurement, based on quadriwave lateral shearing interferometry, has been demonstrated experimentally: piston has been measured with accuracy and sensitivity better than 50 nm.     

光纤激光相干合成高速高精度相位控制器

基于随机并行梯度下降算法（SPGD）和现场可编程逻辑阵列（FPGA）设计制作了相干合成（CBC）相位控制器。理论分析表明,该控制器单次迭代速率大于1.125 MHz,对于2路和16路相干合成,其平均控制带宽的理论值分别大于70 kHz和9 kHz,与现有的SPGD算法相位控制器相比有了量级上的提高。利用该控制器进行了验证性实验,表明该控制器能够实现高速高精度相位控制。当利用相位控制器对两路激光的相位进行锁定时,目标圆孔内能量提高了1.51倍,远场光斑对比度提高了5.29倍。     

All-fiber coherent beam combining of fiber lasers

One half of a 2x2 fused taper single-mode fiber coupler is used for the all-fiber spatial and spectral beam combining of two fiber lasers.     

两光纤激光器相干合成的实验研究

利用迈氏腔技术,进行了光子晶体光纤(PCF)激光器相干合成的实验研究,实现了两光子晶体光纤激光器的相位锁定,获得了功率为47W的相干输出.解释了在迈氏腔的两个输出光路上分别实现相干相长和相干相消的物理机理.实验结果表明,合成激光光谱较单台PCF激光器的激光光谱有显著的改善,波长带宽小于5nm. 关键词： 光子晶体光纤 相位锁定 迈氏腔 光纤激光器     

Step-selective measurement by grating-based lateral shearing interferometry for segmented telescopes

We present an original step-selective mode which allows to measure only the steps and not the slowly varying aberrations of a wave front. This mode can be implemented when measuring segmented wave front by a diffraction-grating-based lateral shearing interferometer. This set-up rests on the different chromatic response of these interferometers depending on the rate of change of the impinging wave front: for smooth defects, the response is classically achromatic whereas it is chromatic for a step variation, which was to our knowledge overlooked. The interest of this mode for astronomical measurements is highlighted. First we present theoretical considerations to show how this mode of measure is possible; then a numerical simulation illustrates them.     

多芯双包层光纤激光器相干合束纤芯最优化排布

 基于衍射理论推导出多芯双包层光纤激光器的远场相干光光强理论模型,并在此基础之上,系统地分析比较了纤芯不同排布方式的合束效果,重点研究了纤芯的单层圆环排布、多层圆环排布、方形排布、正六边形堆积排布4种方案的合束效果,及在一定纤芯排布下纤芯直径、纤芯轴间距、出射平面与衍射平面间距离、波长对合束效果的影响。研究发现：在纤芯数目一定的情况下,单层圆环排布的合束效果最优,其次是方阵排布;纤芯数目越多,截面利用率越高,可获得更大合束最大光强;方阵排布方式及正六边形堆积排布方式可有效提高截面利用率;增大纤芯直径,减小纤芯轴间距、减小出射平面与衍射平面间的距离、减小波长可以获得更好的合束效果。     

多芯双包层光纤激光器相干合束纤芯最优化排布

基于衍射理论推导出多芯双包层光纤激光器的远场相干光光强理论模型,并在此基础之上,系统地分析比较了纤芯不同排布方式的合束效果,重点研究了纤芯的单层圆环排布、多层圆环排布、方形排布、正六边形堆积排布4种方案的合束效果,及在一定纤芯排布下纤芯直径、纤芯轴间距、出射平面与衍射平面间距离、波长对合束效果的影响。研究发现：在纤芯数目一定的情况下,单层圆环排布的合束效果最优,其次是方阵排布;纤芯数目越多,截面利用率越高,可获得更大合束最大光强;方阵排布方式及正六边形堆积排布方式可有效提高截面利用率;增大纤芯直径,减小纤芯轴间距、减小出射平面与衍射平面间的距离、减小波长可以获得更好的合束效果。     

A strip extracting algorithm for phase noise measurement and coherent beam combining of fiber amplifiers

We present a strip extracting algorithm (SEA) for detecting and locking the phase noise of fiber amplifiers. Based on the algorithm, the phase noise of a 10 W Yb fiber amplifier is obtained and locked with an active segment mirror (ASM) and a high-speed CCD camera. Experimental results indicate that within the first 3 seconds after turn-on transients occur the amplitude of phase noise exceeds 20 waves, whereas in thermal steady-state operation it amounts to only several waves for the same time span. After phase locking, the Peak-to-Valley (PV) value of phase noise is close to ～1/10λ (λ=1064 nm), and the control bandwidth of the system is ～25 Hz.     

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.     

Flat-top laser beam generated by coherent beam combining of Gaussian lasers

We present a fiat-top laser beam generation scheme using coherent beam combining of hexagonally arranged Gaussian lasers. To produce a beam with a flat-top profile, we optimize the amplitude and phase of each unit laser using the least-square method. Simulation results show that with 13 unit lasers, a beam with the flatness of less than 1% in the optimizing region can be achieved. The main lobe contains over 95% of the total power. The scheme requires no external beam shaping element and has the potential to be designed for high-power applications.     

光纤激光相控阵相干合成技术研究进展

主要介绍了近年来光纤激光相控阵相干合成技术的发展现状,总结了中国科学院光电技术研究所在这方面的最新研究成果,包括基于振幅调制的光纤激光相控阵相干合成能力优化、光纤激光相控阵实现收发一体相干合成、光纤激光相控阵的目标在回路相干合成、光纤激光相控阵在大气湍流下实现耦合接收光束的共相合束、基于多孔径波前探测的相干合成方法、基于自适应光纤准直器和微透镜阵列的光束大角度高精度连续寻址扫描等。以上研究工作将促进光纤激光相控阵技术朝向更多单元、更高功率、更远距离等方向演进,并推动其与激光大气传输、空间激光通信、自适应光学等理论和应用的结合与发展。     

Mutual injection locking and coherent beam combining of two thulium doped fiber lasers

We demonstrate which we believe the first investigation on mutual injection-locking and coherent combining of two thulium-doped fiber lasers. Mutual coherence between the two fiber lasers is established by means of mutual coupling through two 3 dB couplers. High combining efficiency of 99% for two fiber laser has been obtained, and the fringe contrast of the intensity pattern at the receiving plane is as high as 93%. The solution to scale to high power coherent beam combining is briefly discussed.     

Coherent beam combining of pulsed fiber lasers with hybrid phase control

We demonstrate a scalable architecture for coherent combining of all-fiber pulsed lasers with hybrid phase control involving passive phasing and active phasing for the first time. Synchronized and passive phased pulsed laser array is built by intra-activity phase modulation. Active phase control on the passive phased pulsed laser array using stochastic parallel gradient descent algorithm provides stable in-phase coherent beam combining pattern in a turbulent atmosphere. The fringe visibility is increased from 0 two 0.43 and the power encircled in the main-lobe is 1.616 times increased when the system evolves from passive phasing to hybrid phasing. The architecture can be easily scaled up to high power by increasing power of each individual laser, number of laser elements and introduction of power amplifiers, which will lead a promising way for scaleable high power coherent beam combining of pulsed lasers.     

All-fiber phase actuator based on an erbium-doped fiber amplifier for coherent beam combining at 1064 nm

Active phase control in fiber amplifiers is of considerable interest for low-noise single-frequency amplifiers and for coherent beam combining. We demonstrate phase control at 1064 nm by use of an erbium-doped fiber. We investigated the phase shift by guiding the beam through an erbium-doped fiber amplifier in a Mach-Zehnder configuration and applied the results to stabilize the relative phase of two ytterbium-doped fiber amplifiers. To the best of our knowledge, this is the first demonstration of an all-fiber coherent beam combining at 1064 nm employing an erbium-doped fiber as a phase actuator.     

Tolerance on tilt error for coherent combining of fiber lasers

Limited by the precision of optical machining and assembling, the optical axes of lasers in an array cannot be strictly parallel to each other, which will result in the beam quality degradation of the combined beam. The tolerance on tilt error for coherent combining of fiber lasers is studied in detail. The complex amplitude distribution in the far field for the Gaussian beam with tilt angle is obtained by a novel coordinate transform method. Effect of tilt error on coherent combining is modelled analytically. Beam propagation factor is used to evaluate the effect of coherent combining. Numerical results show that for ring-distributed fiber laser array with central wavelength A and geometry size D, if the root-mean-square （RMS） value of the tilt error is smaller than 0.72A/D, the energy encircled in the diffraction-limited bucket can be ensured to be more than 50% of the value when there is no tilt error. The results are helpful to the designing and manufacturing of fiber array for coherent combining.     

Wavelength beam combining of ytterbium fiber lasers

Wavelength beam combining of five ytterbium fiber lasers is demonstrated in a master-oscillator power-amplifier configuration at combined powers up to 6 W. The combined beam profile has an M2 value of 1.14, which is equal to that of an individual fiber. Beam steering in one dimension over 140 resolvable spots is also demonstrated.     

Phase locking and coherent combining of high-order-mode fiber lasers

Efficient free-space configurations for phase locking and coherent addition of two fiber lasers, each operating with a high-order mode, are presented. Experimental results reveal that when the two fiber lasers are coupled, the polarization and modal distribution of one are imposed on the other. Coherent addition with a combining efficiency larger than 90% was achieved.     

Synchronization and coherent combining of two pulsed fiber lasers

We demonstrate a scalable architecture for coherent combining of pulsed fiber lasers.A new method for generating synchronous pulsed fiber lasers by direct phase modulation is proposed and investigated.It is shown that phase modulated mutually coupled laser array can be a steady synchronous pulsed fiber laser source.The synchronous pulsed fiber lasers are coherently combined with an invariable phase difference of π in adjacent lasers.Neither active phase control nor polarization control is taken in our experiment.     

光纤激光器阵列相干合成中的位相探测与校正方法研究

介绍一高速的位相检测与控制方法，可以对高功率光纤激光器阵列中每一路信号光波的位相进行实时探测与控制，从而使整个系统达到锁相输出的目的.以一路信号光为例，给出该方法的实验研究结果，从中可以看出，闭环控制的结果，可以将该信号光的位相稳定在一设定的静态工作点上. 关键词： 光纤激光器阵列 锁相 外差探测     

两路光纤激光器自组织相干合成实验研究

 建立了两路光纤激光器自组织相干合成的理论模型,并进行实验验证。结果表明,通过能量的相互注入,可以实现光纤激光器的自组织相干合成,合成效率达到92%。当外界基本没有干扰时,远场光斑为稳定、高对比度的干涉条纹,激光器阵列输出模式为异相模,与理论分析的结果一致;当外界环境存在轻微干扰时,实验出现条纹移动现象,输出模式也不再是恒定的异相模。对外界干扰对自组织相干合成的影响进行了数值分析,结果表明：外界干扰的幅度与频率越大,两束激光的相位差的变化幅度与频率也就越大;当外界干扰超过一定程度,两束激光之间的相位差将不能被锁定,始终处于变化状态。