Impulse Response Measurement of Spooled and Twisted Few-Mode Multi-Core Fiber for Short-Range Optical Links

The impact of bending and twisting on the impulse response matrix is investigated using optical vector network analysis. The heterogeneous 36-core 3-mode fiber under test is spooled at bending radii of 8 cm to 50 cm and additionally up to 4 twists per meter along the longitudinal direction are applied. The by-design large differential mode group delay of the fiber enables comprehensive measurement of the inter-mode-group cross-talk of the fiber impulse response matrix, which is directly measured with an optical vector network analyzer. A maximal inter-mode-group cross-talk of -28.1 dB is observed over all 36 cores. Furthermore, no significant changes related to the bending radii or additional strain by twisting the fiber were detected. These results demonstrate that the transmission characteristics of few-mode fibers with large differential mode group delay are fairly unaffected by bend- and twist-related perturbations which may prove beneficial for short-range mode-group multiplexed transmission systems using partial multiple-input multiple-output equalization in conjunction with mode-selective multiplexers.