空间光到单模多芯光纤耦合效率分析及影响因素研究

为了降低空间激光通信系统中空间光到单模光纤的对准难度，采用单模多芯光纤对信号光进行接收。以单模七芯光纤为例，建立了空间光耦合到单模多芯光纤的数学模型，分析了数值孔径对不同纤芯排列的七芯光纤耦合效率影响，结果表明：随着数值孔径的增加，七芯光纤的耦合效率先增加、后减小；纤芯呈正六边形排列较纤芯呈直线形排列的耦合效率高。比较了存在倾斜、离焦、随机角抖动情况下空间光到单模七芯和单模单芯光纤的耦合效率，结果发现：光纤发生横向偏移时,七芯光纤耦合效率呈周期性变化，当横向偏移量分别取值10 μm，15 μm和17 μm时，多芯光纤平均耦合效率比相同纤芯面积的单芯光纤分别高出14.4%，39.6%，36.9%；当光纤轴向偏移0.1 mm时，七芯光纤的耦合效率比相同纤芯面积的单芯光纤耦合效率高约12.9%；当光纤随机抖动的幅度标准差为6 μm时，七芯光纤的耦合效率比相同纤芯面积的单芯光纤耦合效率高约7%. 由此可知，单模多芯光纤对倾斜、离焦和随机角抖动都有很好的抑制作用。

Study of the Coupling Efficiency of Spatial Light into Single-mode Multi-core Fiber

In space laser communication, the coupling efficiency of spatial light into single-mode fiber is a key parameter of studying the performance of the system receiver. In order to reduce the difficulty of spatial light coupling into single-mode fiber, a single-mode multi-core fiber is used to receive signal light, a coupling efficiency model is established by taking seven-core fiber for example, and the effect of numerical aperture on the coupling efficiency of seven-core fibers with different fiber core arrangements is analyzed. The coupling efficiency of seven-core fiber increases first and then decreases with the increase in numerical aperture; the coupling efficiency of fiber which fiber cores are arranged in regular hexagon is higher than that which fiber cores are arranged in line. The coupling efficiencies in the presence of tilt, defocus and random angular jitter are studied. In the presence of lateral offset, the coupling efficiency of seven-core fiber has a periodic change. When the lateral offsets are 10 μm, 15 μm and 17 μm, the coupling efficiencies of seven-core fiber are about 14.4%, 39.6% and 36.9% higher than those of single-core fiber with the same core area, respectively. When the axial offset is 0.1 mm, the coupling efficiency of seven-core fiber is about 12.9% higher than that of single-core fiber with the same core area. When the standard deviation of random jitter amplitude is 6μm, the coupling efficiency of seven-core fiber is about 7% higher than that of single-core fiber with the same core area. Accordingly, the multi-core fiber inhibits tilt, defocus and random angular jitter.