多芯光纤激光器中共相位模式功率的提高

 以七芯光纤激光器为例,提出一种提高多芯光纤激光器总输出光功率中共相位模式所占比例的方法,即把多芯光纤激光器作为种子光源,输出信号光再经过多芯光纤放大器进行放大。基于速率方程组对激光器和放大器中的模式竞争进行了数值分析。计算表明：激光器输出端与放大器输入端之间距离存在一个最佳值,以使得放大器输出信号中低阶模式功率占总输出功率的比例最低,可以下降到小于1%。研究表明：级联放大系统可以有效增强共相位模式同时抑制低阶模式,比传统的塔耳博特腔激光器具有更好的光束质量。     

Phase locking and in-phase supermode selection in monolithic multicore fiber lasers

We report a compact multicore fiber laser that utilizes an all-fiber approach for phase locking and in-phase supermode selection. By splicing passive coreless fibers of controlled lengths to both ends of an active 19-core fiber, we demonstrate that the fundamental in-phase supermode can be selectively excited with a completely monolithic fiber device, instead of conventional free-space and bulk optics, to achieve phase-locked operation for a multiemitter laser device.     

Stable single frequency and single polarization DFB fiber lasers operated at 1053 nm

Stable single-frequency and single-polarization distributed-feedback (DFB) fiber laser was realized by giving a pressure on the phase shift region of the fiber grating. The output wavelength of the DFB fiber laser is 1053 nm. When the pump power of 980 nm laser diode is 100 and 254 mW, the output power can reach 8.3 and 37.1 mW and the polarization extinction ratio was 26 and 20 dB, respectively. After chopped by Acousto-optic modulator (0.3 Hz), the pulse peak value variance is 4.65%(peak to peak) and 1.098% (RMS) for 31 min.     

Phase locking and supermode selection in multicore photonic crystal fiber lasers with a large doped area

We report on the laser properties of multicore photonic crystal fiber lasers. A stable phase locking of six- and seven-core structures through evanescent coupling is observed. Effective supermode selection is obtained by using both diffraction losses and the Talbot effect. A pure in-phase supermode is obtained (1.1 times diffraction limited). The laser operating in this mode has a slope efficiency of 70% with up to 44 W of output power. The modal area of the in-phase supermode multicore fiber is 1150 microm2, which makes it, to our knowledge, the single-mode fiber laser with the largest mode field area. In-phase laser action is stable when the fiber is bent.     

Supermode analysis of multicore photonic crystal fibers

We reported on the supermode selection of total-internal-reflection photonic crystal fibers (PCFs) with linearly and circularly distributed multicores. The supermode characteristics were investigated using a full-vector finite-element method (FEM). The near and far-field patterns of supermodes supported by the multicore photonic crystal fiber were presented. A Talbot cavity was employed to select the wanted supermode.     

多芯光子晶体光纤优化掺杂分布实现同相位超模输出

本文基于多横模运转的传输速率方程,建立了多芯光子晶体光纤放大器的数值模型.利用分步傅里叶方法,分析了掺杂浓度分布、耦合强度、抽运功率对于放大器各模式输出功率的影响.通过对多芯光子晶体光纤掺杂浓度的阶梯设计和纤芯间耦合强度的优化,实现了无需插入其他外加元件,利用光纤本身特性就可以实现选定同相位超模的方法,并且数值计算表明高抽运功率也能够提高放大器输出同相位超模的比例,进一步优化了多芯光子晶体光纤放大器输出脉冲的光束质量.     

Photonic crystal fiber for fundamental mode operation of multicore fiber lasers and amplifiers

A mode-selection method based on a single-mode photonic crystal fiber (PCF) in the multicore fiber (MCF) lasers is presented. The designed PCF has a central core region formed by a missing air-hole, and three air-hole rings. With an appropriate choice of the design parameters of the PCF, the power coupling between the fundamental mode (FM) of the PCF and the fundamental MCF mode can be much higher than those between the FM and the other supermodes. As a result, the fundamental MCF mode has the maximum power reflection coefficient on the right-hand side of the MCF laser cavity, and dominates the output laser power. Since the maximum power of the fundamental MCF mode will lead to the desired laser beam profile, higher the fraction of the fundamental MCF mode power contained in the total output power contributes to higher beam quality. The numerical simulations show that the effectiveness of the fundamental MCF mode-selection is higher in the MCF lasers with the PCF as a mode-selection component than in the MCF lasers based on the free-space Talbot cavity method. Additionally, for the MCF amplifiers, an approach is presented to decrease the sensitivity of the amplifier performance to the variation of Gaussian beam waist utilizing the coupling between the Gaussian beam and the FM of the PCF. The numerical results show that this method can effectively increase the design flexibility for a broad range of the Gaussian beam waist.     

单偏振单模聚合物光子晶体光纤设计

 设计了一种聚甲基丙烯酸甲酯(PMMA)基的单偏振单模(SPSM)微结构聚合物光纤(MPOF)。利用全矢量有限元法和光束传播法相结合分析了这种光纤的偏振特性和约束损耗。通过优化光纤结构参数,发现在0.51 μm～0.62 μm的可见光波长范围,由于基模两个正交偏振模的截止波长不同,这种微结构聚合物光纤只能传输基模中的一个偏振模,从而实现单偏振单模运转。该11圈圆空气孔六角排列光纤结构的传导偏振模在0.57 μm波长处约束损耗仅为1.13 dB/m,这种低损耗的单偏振单模微结构聚合物光纤可有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Mechanism of mode coupling in multicore fiber lasers

We present what is believed to be the first experimental demonstration of a new mechanism of mode coupling in multicore fibers (MCFs) based on their indirect interaction inside the fiber via intermediate mode, analogous to the Bragg mode, which is very sensitive to bending of the fiber. Very strong coupling between the core modes regardless of large spacing (approximately 28 microm) between them has been demonstrated in the MCF laser as well as in the probe beam schemes. 70% of power conversion from one core to another with beating length of tens of centimeters in 4-core MCF is measured.     

被动锁模光纤激光器多孤子脉冲形成机理

基于非线性耦合薛定谔方程,在非线性偏振技术锁模的掺铒环形光纤激光器中,理论研究多孤子脉冲的形成和演化规律。研究结果表明：随着小信号增益不断增加,光纤激光器的锁模透过率函数影响多脉冲输出,多脉冲产生受色散波和脉冲分裂形成的峰值功率的限制效应和孤子能量量子化的影响,这是增益竞争和非线性偏振旋转引起的损耗之间动态平衡的最终结果。     

2 kW级光纤激光相干偏振合成

基于主动锁相相干偏振合成系统实现了四路500 W级全光纤窄线宽保偏放大器的共孔径合成输出。当相位控制系统处于闭环状态时, 整个合成系统的输出功率达2164 W, 合成效率为94.5%。实验中, 随着功率的提升, 合成效率未发生明显退化。这是目前相干偏振合成系统的最高输出功率。     

单模光纤系统激光偏振传输特性的研究

本文运用激光偏振性矢量传输理论,分析了在单模光纤传输系统中激光偏振性的传输特性.得出了激光偏振状态与单模光纤的双折射、传输系数和拍长的关系.     

利用全光纤耦合环实现三路光纤激光器的相位锁定

利用三个2×2的光纤耦合器按一定规则联接成一个全光纤耦合环,该耦合环将三个独立的掺铒光纤激光器连成一个锁相阵列. 由于耦合环的引入,锁相阵列的整体损耗减小,且三个单元激光器之间可以进行有效的能量相互注入耦合,进而实现阵列的锁相输出. 实验中观察到的远场干涉图样和锁相前后的输出光谱均表明三路光纤激光器实现了相位锁定,当三路抽运源的功率均为100 mW时,获得了92 mW的稳定相干输出. 关键词： 光纤激光器 相干合成 光纤耦合器 相位锁定     

A theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers

We report on a theoretical and experimental study of an all-normal-dispersion (ANDi) Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation (NPR) is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schrdinger (CNLS) equation, a model simulating the mode-locked process of an allnormal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller (PC) along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9mW at repetition rate 36MHz are obtained.     

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.     

基于外差法的光纤激光器相干合成

采用波长1064 nm,功率为1 W的种子激光实现了两路光纤激光的相干合成,采用了两只保偏光纤准直器接收两路光干涉信号,与利用透镜直接把干涉信号会聚在探测器上相比,这种耦合方式得到的光干涉信号的条纹对比度更高。对相位噪声以及相位噪声的带宽进行了研究,结果表明,相位噪声由电信号串扰以及环境扰动产生。通过人为拨动光纤来增加相位噪声带宽,当相位噪声带宽增加时,相位控制精度下降。提出了提高相位控制精度的方法,实验获得了桶中功率为21.3%、斯特列尔比为79%、相位控制精度为0.008的相干合成效果。     

Core temperature in super-Gaussian pumped air-clad photonic crystal fiber lasers compared with double-clad fiber lasers

In this paper we investigate the core temperature of air-clad photonic crystal fiber (PCF) lasers pumped by a super-Gaussian (SG) source of order four. The results are compared with conventional double-clad fiber (DCF) lasers pumped by the same super-Gaussian and by top-hat pump profiles.      

基于相位调制-解调的光纤激光相位噪声检测方法研究

在主动相位控制相干合成中,常用的光纤激光主动相位控制方法主要有外差法、多抖动法和随机并行梯度下降算法等. 基于多抖动法和外差法的原理,提出了一种新型的基于相位调制-解调的相位检测与控制方法. 该方法利用周期信号对参考光进行相位调制,将调制后的参考光与待检测信号光进行相干检测,通过对相干光强信号和相位调制信号的融合处理,实现相位噪声的检测和控制. 对该方法进行了数值模拟和实验研究. 实验结果表明,对于频率为2 kHz,噪声范围为[0,2π)的正弦噪声,相位检测精度优于λ/50,控制精度可达 关键词： 光纤激光 相干合成 相位噪声检测 调制-解调     

注入噪声对光纤激光器锁模启动的影响

 从掺镱光纤激光器腔内的激光场出发,讨论了掺镱光纤激光器腔内的噪声信号对锁模启动的影响,并针对我们设计的8字腔超短脉冲光纤激光器进行了研究。通过对激光器腔内锁模过程的分析发现：在泵浦功率为214.75 mW时,自行研制的8字形腔掺Yb³⁺光纤激光器在未注入噪声信号时,输出端在30～50 s内获得稳定的锁模脉冲激光输出;在腔内注入脉宽30 ns,频率10 kHz,平均功率0.2 mW的脉冲噪声后,输出端在1~2 s内获得同样稳定的锁模脉冲激光输出。实验结果表明,注入激光器谐振腔内一定的噪声信号,可加速锁模的启动。     

Single-polarization single-mode hollow-core negative curvature fiber with nested U-type cladding elements

Hollow-core negative curvature fibers (HC-NCFs) have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions. In this work, a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed. To achieve the single-polarization single-mode transmission, we use two different silica tubes in thickness, which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes, respectively. Besides, the elliptical elements are introduced to achieve good single-mode performance. By studying the influences of the structure parameters on the propagation characteristics, the optimized structure parameters are obtained. The simulation results show that when the wavelength is fixed at 1550 nm, the single-polarization single-mode transmission is achieved, with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174. Furthermore, the confinement loss is only 0.0015 dB/m.