• Chinese Journal of Lasers
  • Vol. 50, Issue 14, 1405002 (2023)
Qingqing Yan1, Zheqiang Zhong1, Bin Zhang1、*, Zhen Wu2, and Wei Cai2
Author Affiliations
  • 1College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, Sichuan, China
  • 2School of Science, Xihua University, Chengdu 610039, Sichuan, China
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    DOI: 10.3788/CJL221145 Cite this Article Set citation alerts
    Qingqing Yan, Zheqiang Zhong, Bin Zhang, Zhen Wu, Wei Cai. Crosstalk of Spectral Combining System and Its Influence on Beam Combining Characteristics[J]. Chinese Journal of Lasers, 2023, 50(14): 1405002 Copy Citation Text show less

    Abstract

    Objective

    In diode laser array (DLA) grating-external cavity spectral beam combining (SBC) systems, the combining efficiency and beam quality are very important indicators. However, the beam crosstalk caused by imperfect factors including the divergence angle and deflection angle of DLA emitters results in the degradation of the output beam quality and combining efficiency. Therefore, to understand the physical mechanism of crosstalk in the round-trip propagation of the beams in a DLA grating-external cavity SBC system and further analyze its influence on the performance of the SBC system, the relationship between the crosstalk and the combining efficiency or beam quality is established. In addition, the influences of key factors, including the DLA spacing, focal length of the lens, and line density of the grating, on the performance of the SBC system are analyzed.

    Methods

    To study the behavior of beam crosstalk and its influence on the performance of an SBC system, a round-trip propagation model of a DLA is established. On this basis, by taking the semiconductor laser rate equation involving beam crosstalk injection into consideration, a physical model of combining efficiency of the SBC system is also developed. Furthermore, the influence of the divergence angle and deflection angle on the beam combining performance is studied using numerical calculations and statistical analysis.

    Results and Discussions

    With only the divergence angle considered, there is no obvious crosstalk (Fig. 4). This is because the beam emitted by each emitter can be fed back to itself after being reflected by the external cavity. Even when the divergence angle increases to 12 mrad, the beam quality factor M2, beam combining efficiency η, and feedback intensity κ are not strongly affected by the divergence angle. With only the deflection angle considered, the feedback beam from the external cavity exhibits different degrees of deviation (Fig. 5). With an increase in the deflection angle, the feedback beam reflected to its own emitter decreases in intensity, whereas the feedback intensity from the other emitters increases, resulting in crosstalk. When the effects of the divergence and deflection angles are considered comprehensively, the feedback beam to the emitters deviates significantly, resulting in an obvious degradation of the output beam quality and combining efficiency (Fig. 6). For a given maximum divergence angle, the combining efficiency remains almost unchanged as the maximum deflection angle increases and then decreases sharply beyond a certain angle. The output beam quality exhibits the same trend. For a given maximum deflection angle, the beam combining efficiency remains almost unchanged up to a divergence angle of 12 mrad, whereas the beam quality decreases significantly. In addition, the DLA spacing, focal length of the lens, and line density of the grating have almost no influence on the combining efficiency with an increase in the maximum deflection angle up to a certain angle, after which the efficiency decreases dramatically (Fig. 7).

    Conclusions

    We established a round-trip propagation model of a DLA that can reveal the behavior of beam crosstalk and its influence on the performance of the SBC system. By taking the semiconductor laser rate equation involving beam crosstalk injection into consideration, we established a physical model for the combining efficiency of an SBC system. Based on numerical calculations and statistical analysis, we found that the influence of the deflection angle on the beam combining performance is greater than that of the divergence angle. In addition, we found that the focal length of the lens and the DLA spacing have obvious effects on the critical maximum deflection angle, whereas the line density of the grating has little effect on the critical maximum deflection angle. In conclusion, it is necessary to appropriately reduce the focal length of the lens and increase the DLA spacing in practical applications.

    Qingqing Yan, Zheqiang Zhong, Bin Zhang, Zhen Wu, Wei Cai. Crosstalk of Spectral Combining System and Its Influence on Beam Combining Characteristics[J]. Chinese Journal of Lasers, 2023, 50(14): 1405002
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