Modified steady tracking strategy for composite axes system in free-space laser communication

Dual-detector and single-detector strategies are the main tracking methods used in pointing, acquiring, and tracking (PAT) system. The coarse pointing subsystem (CPS) and the fine pointing subsystem (FPS) have different detectors in dual-detector tracking method (DTM). In contrast, they use one common detector in single-detector tracking method (STM). These two methods have their own advantages and defects in terms of cost, volume, weight, and performance. Based on the analysis of these two methods, two modified STMs (MSTMs) are proposed to promote the tracking performance for the PAT system. In the first MSTM, the information of the tracking error of the FPS is introduced to construct a virtual detector for the CPS. This makes the proposed method have a tracking performance close to that of the DTM. Furthermore, the second MSTM is presented to balance the bandwidth difference between the CPS and the FPS. Compared with the first MSTM, the second one includes the first one as a special case and it provides more design degree of freedom for the PAT system. Experimental results have shown the effectiveness of the presented methods.