Simultaneous measurement of mode dependent loss and mode coupling in few mode fibers by analyzing the Rayleigh backscattering amplitudes.

In this paper, we propose and experimentally demonstrate a nondestructive method for simultaneously measuring the mode-dependent loss (MDL) and mode coupling (MC) in few-mode fibers (FMFs). The method is based on analyzing the Rayleigh backscattering amplitudes obtained with an optical time domain reflectometer (OTDR). The experimental results show that, in about 4 km six-mode FMF, the MDL and MC values are 0.132 dB and -23.13  dB/km between LP and LP, 0.176 dB and -23.73  dB/km between LP and LP, 0.272 dB and -26.17  dB/km between LP and LP, 0.284 dB and -26.70  dB/km between LP and LP, and 0.380 dB and -20.21  dB/km between LP and LP. And it also demonstrated that the proposed scheme can be scalable to measure MDL and MC between higher-order modes. The values of the MC and MDL obtained by the proposed method agree well with that by the conventional transmission method. However, the proposed method has the merits of simultaneous and single-end measurement of MDL and MC in the FMF and could be a good solution to the characterization of FMFs used in large-capacity mode-division-multiplexing transmission systems.