在少模光纤的模分复用(MDM)系统中,少模光纤之间的熔接不可避免。精确测量少模光纤熔接点处的模式耦合,可以为评估熔接质量和定位系统故障提供可靠依据。基于背向瑞利散射原理,分析了少模光纤熔接点处模式耦合特性,基于光子灯笼结构和光纤环形器建立了少模光纤熔接点耦合测量系统,成功测试了两段3模光纤(长度分别为0.9 km和9.8 km)熔接点处的模式耦合。实验结果表明:当偏移量为1.5 μm和2.0 μm时,熔接点处模式耦合分别为-14.9 dB和-13.9 dB。

In mode division multiplexing systems based on few-mode fibers, it is inevitable to carry out the fusion splice between the few-mode fibers. Precise measurement of mode coupling at each splice point can provide reliable bases for evaluating welding-quality and positioning faults of the system. We analyze the mode coupling characteristics at a splice point between few mode fibers based on Rayleigh backscattering theory, then build a measurement system of mode coupling at a splice point based on the structure of a photonic lantern and an optical circulator, and successfully measure the mode coupling at a splice ponit between two pieces of three modes fibers(the lengths are 0.9 km and 9.8 km, respectively). The experimental results show that the mode couplings at the splice point are respectively -14.9 dB and -13.9 dB with the offset distances of 1.5 μm and 2 μm.