Fiber Laser Beam Combination Research Articles

Common aperture spectral beam combination of fiber lasers with 5 kW power high-efficiency and high-quality output

Common Aperture Spectral Beam Combination (SBC) of multiple high power fiber lasers output into a composite beam via a multi-layer dielectric (MLD) gratingis a promising approach for the fiber laser system to scale the output power further while maintaining high efficiency and excellent beam quality simultaneously. A common aperture SBC system with dual-grating dispersion compensation configuration based on five kW-level narrow-linewidth fiber amplifier chains in all-fiber format is set up. A common aperture combing beam is achieved with high efficiency and excellent beam quality in the system by using China-made MLD gratings. The maximum average output power of 5.07 kW of the combined beam and the combination efficiency of 91.2% are obtained. The beam quality factor M2 at a power level of 5 kW is less than 3. The preliminary experimental results have shown that MLD grating, which can maintain high diffraction efficiency in a wide spectrum range under high power level operation, is a perfect element for SBC of high power fiber laser. The results also demonstrate that the beam quality and the linewidth of the individual fiber laser are the key factors affecting the beam quality of the spectral combining beam. Presently, the output power is limited by the amount of the narrow-linewidth fiber amplifier chains and the output power of the individual narrow-linewidth fiber amplifier. So it can be expected that the common aperture SBC system output power can be further scaled.

光纤激光共孔径光谱合成实现5 kW高效优质输出

光纤激光共孔径光谱合成实现5 kW高效优质输出

Coherent beam combination of fiber lasers with a strongly confined tapered self-imaging waveguide: theoretical modeling and simulation

Coherent beam combination (CBC) of fiber lasers based on self-imaging properties of a strongly confined tapered waveguide (SCTW) is studied systematically. Analytical formulas are derived for the positions, amplitudes, and phases of the N self-images at the output of a SCTW, which are important for quantitative analysis of waveguide-based CBC. The formulas are verified with numerical examples by a finite difference beam propagation method (FDBPM) and the errors of the analytical expressions are studied. This study shows that the analytical formulas agree well with the FDBPM simulation results when the taper angle is less than 1.4° and the phase distortion is less than λ/10. The relative errors increase as the taper angle increases. Based on the theoretical model and the FDBPM, we simulated the CBC of fiber laser array and compared the CBC based on the tapered waveguide with that based on the nontapered one. The effects of input beam number, aperture fill factor, and taper angle on the combination performance have been studied. The study reveals that a beam which has near-diffraction limited beam quality (M2≤1.41) and a single beam without side lobe in the far field can be achieved with tapered-waveguide-based CBC. It is shown that beam quality depends on input beam number, aperture fill factor, and taper angle. There exists a best fill factor which will increase as input beam number increases. The tolerance of the system on the fill factor and the taper angle is studied, which is 0.45<t<0.67 and θ<0.8°, respectively. The results may be useful for practical, high-power fiber laser systems.

Coherent beam combination of fiber lasers with a strongly confined waveguide: numerical model

Self-imaging properties of fiber lasers in a strongly confined waveguide (SCW) and their application in coherent beam combination (CBC) are studied theoretically. Analytical formulas are derived for the positions, amplitudes, and phases of the N images at the end of an SCW, which is important for quantitative analysis of waveguide CBC. The formulas are verified with experimental results and numerical simulation of a finite difference beam propagation method (BPM). The error of our analytical formulas is less than 6%, which can be reduced to less than 1.5% with Goos-Hahnchen penetration depth considered. Based on the theoretical model and BPM, we studied the combination of two laser beams based on an SCW. The effects of the waveguide refractive index and Gaussian beam waist are studied. We also simulated the CBC of nine and 16 fiber lasers, and a single beam without side lobes was achieved.

Influence of temporal error with different pulse shapes on coherent beam combination system

Coherent beam combination of fiber laser array is an important technology for high-power output fiber laser systems. However, the coherent beam combination is influenced by temporal error, which always exists in the laser array. The coherent beam combination of pulse fiber lasers in the presence of temporal error is investigated in theory in this paper. The effects of pulse shape and temporal error on the coherently combined beam are studied. The characteristics of combined beam, i.e. pulse shape, peak power, far-field pattern and power in barrel (PIB) are calculated and analyzed when the pulse shapes (including square, triangle and sine) and temporal errors are different. It is revealed that for coherently combining square pulse lasers, the pulse shape of the combined beam changes acutely because of temporal error, and the far-field pattern and PIB change proportionally with temporal error increasing; for coherently combining triangle pulse lasers, the pulse shape and the peak power of the combined beam are acutely influenced by temporal error, and the far-field pattern and the PIB change acutely when temporal error is large. It is revealed that coherently combined beam of sinusoidal pulse lasers has good characteristics when two pulse laser with sinusoidal pulse shapes are coherently combined and the time delay between the two pulses is less than 10% of pulse duration.

抖动法激光阵列相干合成技术中的性能评价函数研究

抖动法激光阵列相干合成技术中的性能评价函数研究

基于量子系统的超高亮度光纤激光合成体系概念与构想

基于量子系统的超高亮度光纤激光合成体系概念与构想

High-power fiber laser combination technology

Research on fiber laser combination is discussed briefly in this paper. High-power double clad-fiber laser beam combination technology is introduced and different kinds of fiber laser beam combination and coherent combination technologies are evaluated. Tapered fused bundle (TFB) couplers are used in laser combine for higher power. In this paper, the theory and progress in TFB coupling are introduced. The experiment on our self-fabricated TFB is presented. The efficiency of the fiber coupler exceeded 70% and increased as the input power went up. A maximum total output power of 689W was obtained, with an efficiency of 74%. The fiber coupler displayed stability during the course of the experiment, without any cooling provided.

基于级联体光栅的光纤激光阵列谱组束

基于级联体光栅的光纤激光阵列谱组束

A method of beam combination of high- power incoherent fiber laser

Diffraction efficiency of grating plays an important role in output power of incoherent fiber laser beam combination. Through theoretic analysis and numerical simulations it has been proved that the diffraction efficiency would increase with the decrease of grating frequency and wavelength bandwidth. On the condition that the width of a fiber array is fixed at W=10 cm, an optimum grating frequency were numerically simulated as f=230 mm−1. Also an unequal interval method was proposed to improve the system efficiency of diffraction into 0.4293, which is higher than 0.3824 under the equal interval condition.