All-mode splice-loss estimation and splice-quality evaluation in few-mode fibers from a fundamental-mode power drop

Splice-loss evaluation in few-mode fibers (FMFs) usually requires mode-by-mode measurement of each guided mode, and the complexity of the measurement system and testing procedure increases with the number of supported modes. Although previous studies have established a unified mapping relationship between the splice losses of all guided modes and the parameter d/ω₀, where d and ω₀ denote the axial offset and fundamental-mode field radius, respectively, enabling the splice losses of all guided modes to be determined once this parameter is known, the practical application of this relationship remains limited because d/ω₀ is difficult to obtain directly. In this work, we propose a method for estimating d/ω₀ from the power drop at the splice point in the fundamental-mode backscattering trace. Using the estimated d/ω₀, the splice losses of all guided modes can be further determined through the unified mapping relationship. Meanwhile, the fundamental-mode power drop can be converted into a decision threshold under a specified higher-order-mode loss requirement, thereby determining whether the splice loss satisfies the corresponding splice-quality requirement. The proposed method requires only a single fundamental-mode backscattering signal to achieve all-mode splice-loss estimation and splice-quality assessment, thereby providing a low-complexity solution for FMF splice-loss measurement.