Synchronization and coherent addition of three pulsed fiber lasers by mutual injection and phase modulation

The coherent beam addition of pulsed fiber lasers is an effective way to improve the average power and the peak pulse power. We demonstrate a new architecture based on mutual injection and phase modulation to generate synchronous pulsed fiber lasers. Firstly, we realize the synchronization of the pulses of three fiber lasers using this technique. Secondly, coherent addition of three synchronous pulsed fiber lasers is obtained. Experimental results show that the three fiber lasers are phase locked and have good temporal and spatial coherence under mutual injection locking. This method can be extended to combine more beams.     

Semiconductor lasers and fiber lasers for fiber-optic telecommunications

Be performance characteristics of semiconductor lasers for fiber telecommunication systems will be reviewed. Modulation speed, intensity noise, singlefrequency line width, and tunability are addressed. In addition, recent results concerning the same characteristics in single-frequency, tunable, fiber lasers are reviewed and compared with the semiconductor laser.     

两路关联光纤激光器互注入锁相实验

基于角锥互注入锁相相干合成方案,利用光纤Bragg光栅（R=85％@1064nm）作为两路光纤激光器的共用腔镜,实现了两路光纤激光器相关联,进一步提高了激光的互注入能量。采用外腔结构,较容易实现了两路光纤激光器的能量互注入锁相。在实验上观察到了远场清晰稳定的干涉条纹（可见度超过0．8）,获得了功率合成效率约为80％的线偏振相干激光输出。     

Coherent addition of two dimensional array of fiber lasers

Configurations for efficient free space coherent addition of four separate fiber lasers arranged in two dimensional array are presented. They include compact and robust interferometric combiners that can be inserted either inside or outside the cavity of the combined lasers system. The results reveal that over 85% combining efficiency can be obtained.     

1018 nm短波长掺镱光纤激光高功率自组织相干合成

搭建了两台高功率、低量子损耗的1018 nm短波长掺镱光纤激光器,进行了全光纤结构下两路光纤激光器的相干合成实验。获得了功率为55 W、合成效率为90.2%的相干输出,这是当前严格单模1018 nm光纤激光器的最高功率水平。同时,验证了Michelson腔自组织相干合成技术能够实现光纤激光器的高功率单模输出。     

Simulataneous coherent and spectral addition of fiber lasers

A new approach for the simultaneous coherent and spectral addition of a two-dimensional array of fiber lasers is presented. A combining efficiency of over 80% and a combined beam profile with M(2)=1.15 were experimentally obtained with an array of four fiber lasers. This approach can lead to significant upscaling in fiber laser additions.     

Coherent combining of tunable erbium-doped fiber lasers by a single-mode fiber feedback loop

We experimentally demonstrate the coherent combining of two tunable erbium-doped fiber lasers by using a single-mode fiber feedback loop configuration. A single-mode fiber is arranged in the feedback loop to filter the far-field pattern, and the energy of desired in-phase mode is collected and injected into the resonators of two component fiber lasers. The coherently combined laser is tunable over a wide spectrum ranging from 1536 to 1569 nm, which means that the combining scheme is compatible with wavelength tuning. The effects and necessity of whether adopting polarization controlling measures or not in component lasers are investigated in detail. The results indicate that adding polarization controlling can improve the array＇s coherence, whereas it will decrease the output power and efficiency simultaneously.     

两个光纤激光器的互相注入锁定

光纤激光器的相干合成技术是实现高功率、高亮度光纤激光系统的重要技术途径.利用分束器分光使两个光纤激光器的能量互相注入，从而使两个光纤激光器达到锁相锁模实现相干输出. 实验研究表明：在独立运行的情况下，两个光纤激光器的远场光斑只是两个激光器光强的简单叠加；在互相注入锁定的情况下，两个光纤激光器的远场光斑是具有高对比度的干涉条纹，并得到两个激光器的输出模式总为异相模.这与理论分析的结果相一致. 关键词： 光纤激光器 相干合成 锁相     

Theoretical analysis of feedback high birefringence fiber loop mirror for application in single-frequency fiber lasers

A feedback high birefringence fiber loop mirror with a piece of erbium-doped fiber and a polarization controller is newly proposed. When the erbium-doped fiber is properly pumped to offset the loss of the feedback ring in the loop mirror, narrowband transmission peaks with large effective free spectral range can be achieved by the intrinsic vernier effect between orthogonally polarized lights respectively traveling along the two primary axes of the high birefringence fiber. In addition, the side transmission suppression ratio can reach about 6 dB. These special properties are independent of the polarization state of the input signal, which makes it feasible for the proposed feedback high birefringence fiber loop mirror to be employed as a narrowband filter in single-frequency fiber lasers.     

谱线和耦合系数对光纤激光器相互注入锁定的影响

相互注入锁定是相干合成技术中最具发展前景的方案之一. 在两个光纤激光器相互注入锁定的基础上,利用可调节光纤光栅改变其中一个激光器的中心谱线和利用不同的分束器改变两个激光器间的耦合系数,同时监测两个激光器的远场光斑和谱线,判断激光器谱线和耦合系数对相互注入锁定的影响. 通过理论和实验得到：提高耦合系数可以提高锁定的频率差;两个激光器的谱线越接近锁定的效果越好,当激光器的谱线超过一定范围时,两个激光器将不能被锁定. 关键词： 光纤激光器 相干合成 相位锁定     

分布反馈光纤激光器阵列中外腔反馈特性研究

以半导体激光器中的复合腔模型和实测的分布反馈光纤激光器的外腔端面反射率为基础,对不同反射率条件下分布反馈光纤激光器的输出功率进行了仿真,同时搭建了二基元分布反馈光纤激光器阵列实验平台,对仿真结果进行了验证.仿真与实验结果表明:外腔反馈光重新注入分布反馈光纤激光器会增加激光器的输出功率,降低了阵列的输出功率平坦性.并且外腔端面反射率越大,这种平坦性降低的效果越明显.在构建分布反馈光纤激光器阵列时,应考虑外腔反馈对阵列输出功率平坦性造成的影响,尽量选择外腔端面反射率较小的激光器进行组阵.     

Theoretical and experimental study on rare-eath element-doped silicon single-mode fiber laser with two different structures of resonators

Abstract: Laser resonator is very important in the study and fabrication of lasers. The work conditions and work parameters of rare-earth element-doped optical fiber lasers with two different structures of laser resonators, i. e., the fiber ring resonator and Fabry-Perot resonator are studied. The fineness, laser resonant conditions, laser oscillation conditions and threshold inversion of these two different cavity are deduced. A series of experiments are also given. The result is very valuable to evaluate the output of optical fiber laser and can be a foundation of device fabrication. The Nd~(3 )-doped silica single-mode fiber laser pumped by Ar~ laser with a low threshold of 1.02 mW and a maximum output of more than 1 mW are presented in this paper.     

大模面积双包层光纤激光频谱组束的实验效果

基于透射体布拉格光栅频谱组束的设计方案,采用半导体激光器作为泵浦源,以大模面积双包层Er3+/Yb3+共掺光纤为增益介质,报道了两束光纤激光频谱组束的实验结果。在两束光纤激光输出功率分别为0.39和0.53 W、光栅实际衍射效率不到60%的情况下,实现了组束功率为0.64 W、绝对组束效率高达69.6%的组束激光输出,并分析了实验过程中影响组束效率的因素。     

单模光纤激光极限功率的数值研究

对光纤激光极限功率的探索和其受限因素的分析, 有利于为大功率光纤激光器的发展提供理论依据和实验指导. 本文考虑热效应、光效应、非线性效应和抽运亮度等因素对光纤激光极限功率的影响, 分析了掺镱和掺铥光纤的极限功率和受限因素. 在此基础上, 结合激光在光纤中单模传输的条件, 计算了单模掺镱和掺铥光纤激光的极限功率. 计算结果表明, 在现有技术条件下, 使用常规的976 nm和793 nm激光二极管抽运, 单模掺镱和掺铥光纤激光的极限功率分别为4.2 kW和7.8 kW, 其中单模掺铥光纤激光的功率水平还远低于它的极限功率的原因是受抽运亮度的限制. 最后分析指出减小纤芯的数值孔径和改进少模光束的光束质量是提升单模光纤激光极限功率的重要途径.     

Optical properties of ytterbium-doped tandem-pumped fiber oscillator

With the rapid development of ytterbium-doped fiber lasers, some obtrusive limitations on power scaling appeared. In order to avoid these problems, a scheme called tandem pumping is introduced into the fiber laser field. In this paper, the optical properties of an ytterbium-doped tandem-pumped fiber oscillator are presented. According to the oscillator profile, the proper gain fiber type and pump wavelength range are picked out, under the comprehensive consideration of laser conversion efficiency and beam quality. In addition, the photodarkening performances of tandem pumping lasers and conventional ones are compared based on practical application, with all possible impact parameters taken into account. Moreover, an all-fibered tandem-pumped oscillator centered at 1079.5 nm is built, in the way of clad pumping by a 1030-nm fiber laser. The laser power of the oscillator reaches 7 W, with an opto-optic efficiency of 82.4%.     

Polarization-resolved analysis of the characteristics of a Raman laser made with a polarization maintaining fiber

We derive a simple model describing steady characteristics of Raman fiber lasers made with polarization maintaining fibers. We show both theoretically and experimentally that this kind of laser simply consists of two independent Raman lasers linearly polarized along the fiber birefringence axes. The output power characteristics of the laser are shown not to be influenced by optical Kerr effect. Finally, we use our model to propose answers to questions recently raised about efficiency of Raman lasers made with polarization maintaining fibers.     

Mutual injection locking and coherent combining of three individual fiber lasers

Mutual injection locking and coherent combining of three individual erbium-doped fiber lasers are reported. Theoretical model of the three fiber lasers under mutual injection is also analyzed. Under free running state, the far field beam profile is a simple intensity superposition as three incoherent beams. Under mutual injection locking, interference lobes with high contrast ratio are obtained in the far field of three fiber lasers, which shows that the three fiber lasers have good interference characteristic under mutual injection. The experimental results are in good agreement with the theoretical results. According to this method, we can also realize coherent beam combining in more fiber lasers.     

Broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror

A broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror (HiBi-FLM) and a polarization controller is demonstrated experimentally. The measured transmission spectrum of HiBi-FLM covers a wide range from 1525 to 1575 nm. The wavelength of proposed laser can be flexibly tunable during this range of ∼50 nm by adjusting the polarization controller. In addition, the spacing of two wavelengths is adjustable by changing the length of HiBi fiber. The dual-wavelength lasers with the HiBi fiber length of 1 and 2 m are experimentally demonstrated and compared. The experimental results show that the proposed laser can stably operate on two wavelengths simultaneously at room temperature, and the output peak power variation is about 0.5 dB during 40 min.     

高功率光纤激光受激拉曼散射效应研究新进展北大核心CSCD

由于具有高品质、高效率、高鲁棒性、结构紧凑等优点,光纤激光系统在近20年飞速发展,并得到广泛应用。然而发展至今,依旧存在着一些因素(如非线性效应、热效应、模式不稳定性等)限制着光纤激光系统功率的进一步提升。作为其中的一种主要限制因素,受激拉曼散射效应不仅降低了光纤激光器的输出效率,后向斯托克斯光还会提高系统的损毁风险。最近的研究结果表明,少模光纤中受激拉曼散射在引起模式不稳定性的同时,还会导致准静态的模式退化。因此,需要发展有效的拉曼抑制手段来突破现有瓶颈,促进高功率高光束质量光纤激光发展。在介绍高功率少模光纤激光中受激拉曼散射效应新表征的同时,从高功率光纤激光系统整体优化角度出发,总结整理了相关抑制技术研究新进展,并展望未来可能的研究方向。     

Efficiency improvement of multimode Tm3+ doped double cladding silica fiber laser by in-line biconical tapers

Efficiencies improvement of LD (laser diode) pumped multimode large mode area (LMA) Tm³⁺ doped double cladding silica fiber lasers with different in-line biconial tapers were reported. Two types of multimode Tm³⁺ doped fiber were used in this experiment. Each type of fiber was made into three fiber lasers, a uniform geometry fiber laser and two tapered fiber lasers with different taper parameters. Biconical tapers located several centimeters from the output end of the multimode fiber lasers were made by heating and stretching method. Although the threshold of the best tapered fiber laser was added 200 mW, the slope efficiency (25.3%) and the maximum output power (1.31 W) of the fiber laser increased by 10.3% and 350 mW respectively, in comparison with the un-tapered one. Pre and post output laser power ratio was 6.3–15.6. Simultaneously, the laser spectrum moved to shorter wavelengths. The same trends of these characteristics were also observed in the other three tapered fiber lasers.