Analysis of the physical mechanism of beam crosstalk in a semiconductor laser array spectral-beam-combined system

In spectral beam combining systems based on a grating-external cavity, due to factors such as the "smile" effect of the semiconductor laser array, the error of the optical components in the external cavity, the beam from one emitter transmits in the external cavity, and can return to other emitters, forming beam crosstalk between the two emitters. In this paper, in order to investigate the beam crosstalk physical mechanism and its influence on beam properties such as locked spectra and beam combining efficiency, based on the optical feedback semiconductor rate equation, the beam modes that can stably oscillate in the coupling cavity are derived, and the coupling cavity oscillating model is built. On the consideration of the mode competition mechanism in the coupling cavity, the effects of different crosstalk (happened between two emitters with different intervals) on the locked spectra are analyzed in detail. The results show that crosstalk leads locked spectra have peak shift, sub-peak, et al. The crosstalk that happened between two closer emitters has a more serious impact on the beam spectrum, combined beam spot, and combining efficiency. The combining efficiencies influenced the 1st, 2nd and 3rd crosstalk are 45.5%, 50.2%, and 63.8%, respectively (When there is no crosstalk, the efficiency is 80.1%). Finally, the results of the theoretical analysis were experimentally verified, and the experimentally observed spectra under the influence of crosstalk show phenomena such as peak degradation, peak shift, edge burrs, and side lobes in spectra, which are consistent with the theoretical predictions. Moreover, according to the results obtained by simulation analysis and experimental verification, it is found that crosstalk can be suppressed to a certain extent by increasing the spacing of emitters, and the Galileo telescope system is suggested to suppress crosstalk and optimize the spectral structure and beam combining efficiency. Compared with the Kepler telescope structure, the Galileo telescope does not have a real focal point, which can prevent the local power from being too high, thereby damaging the optical components.