多波长激光主动式相干合成理论初探

Preliminary theoretical analysis of multi-wavelength laser active coherent beam combination

本文从相干合成的基本原理出发,建立计算模型,通过对多波长两路相干合成实例的仿真计算,得到了多波长两路相干合成效果的预测公式;在多波长相干合成中光程差至关重要,按照能否进一步通过主动控制,获得好的合成效果,可将光程差划分为可控区和不可控区两类,只有当光程差处于可控区时,才能进一步通过主动控制获得好的合成效果;在光程差任取的情况下,光程差处于可控区,能够通过主动控制获得好的合成效果的概率与光谱结构紧密相关,近似随着波长数目的增多成反比减少.对于多波长相干合成可采取复合控制的方式,先利用大光程控制器件将光程差控制在可控区,然后进一步采用光程精控器件实现锁相.

In active coherent beam combination （CBC） , a single-frequency seed laser is often considered to be indispensable for improving the spatial coherence property and obtaining high brightness in the far field. Nevertheless, the single-frequency radiation restricts the output power of coherently combined fiber amplifiers, owing to low stimulated Brillouin scattering （SBS） threshold. The seed laser oscillating at different frequencies proves to have the potential in mitigating SBS effects in fiber amplifiers, and therefore it is able to increase the emission power of CBC greatly. In this study, the basic mathematical model is founded on the basis of the fundamentals of CBC, and the muhi-wavelength two-channel CBC estimation formula is proposed on the calculation of some two-channel examples. The optical path difference is the key factor in multi-wavelength CBC. We propose the concepts of ＂controllable area＂ and ＂uncontrollable area＂ for the optical path difference. If and only if the optical path difference fails into the controllable area, desirable combination effects can be obtained by the active control. In the case of getting the value of optical path difference randomly, excellent combination effects can still be gained and the probability has a close correlation with the spectrum profile, which is inversely proportional to the number of wavelengths approximatively. The multiple control method is competent for the muhi-wavelength CBC. In this method, the optical path difference is adjusted into the controllable area by large optical path controllers and then the phase of each channel is locked by precise optical path controllers.