Optical couplers in multimode MIMO transmission systems measurement results and performance analysis

The concept of MIMO (multiple input multiple output) transmission over multimode fibers has attracted increasing interest within the last years. Theoretically, the performance of the optical MIMO multimode channel is well predictable. However, the realization of the optical MIMO channel requires substantial further research. In this work the efficiency of optical couplers in MIMO systems is studied in a 1,4 km multimode testbed. Optical couplers have long been used as passive optical components able to combine or split SISO (single-input single-output) data transmission from optical fibers. Our results show by the obtained measured impulse responses together with the simulated BER performance that optical couplers are well suited for the optical MIMO transmission despite their insertion losses and asymmetries. Comparing the different couplers those which maintain the different optical mode groups support the MIMO transmission more efficiently.