Comparison of QPSK and 8-QAM in a Three Spatial Modes Transmission

We present a transmission experiment employing three spatial modes through a few-mode fiber coupled to the surrounding single mode equipment by a packaged mode multiplexer and demultiplexer. We evaluate and compare the impact of the residual crosstalk in our system on QPSK and 8QAM modulation schemes after 20- and 40-km transmission. We also give an estimation of the crosstalk induced by splices and by the few-mode fiber in our system.