Relationship Between Mode Coupling and Fiber Characteristics in Few-Mode Fibers Analyzed Using Impulse Response Measurements Technique

When few-mode fibers are employed in mode-division multiplexing (MDM), mode coupling between the propagation modes must be suppressed. In this study, the impulse response for a two-mode fiber (TMF) is theoretically described to estimate the mode coupling in the fiber and at a splice point. We then propose a technique for measuring the mode-coupling coefficient in a TMF based on the impulse response technique. The mode-coupling behavior in a fiber and at splice points is measured experimentally using the proposed technique for several fabricated TMFs. We clarify the relationship between the effective-index difference <inline-formula><tex-math notation="LaTeX">$\Delta n_{{\rm{eff}}}$ </tex-math></inline-formula> between <inline-formula><tex-math notation="LaTeX">${\text{LP}}_{{01}}$</tex-math> </inline-formula> and <inline-formula><tex-math notation="LaTeX">${\text{LP}}_{{11}}$</tex-math></inline-formula> modes and the mode-coupling coefficient <italic>h</italic> for our fabricated TMFs.