Variable Mode Excitation Ratio Method for Measuring Attenuation Coefficients of LP Mode Groups

We propose a variable mode excitation ratio method for measuring the attenuation coefficients of individual transmission modes in few-mode fiber (FMF). The experimental results we obtained with 2LP mode fiber agree well with those measured by the conventional mode-selective launching method and the optical time domain reflectometer (OTDR) method. We also show that the proposed method can be applied to an FMF with more than two mode groups by measuring the transmitted power property under various mode excitation ratios with a multiple mode group combination. Finally, we reveal that our method can provide an accurate modal attenuation coefficient even if we cannot use a mode multiplexer with a sufficient mode extinction ratio.