Efficient compensation methods for modal dispersion in radio over multimode fiber links

The multimode fiber (MMF) is a proper choice for short range optical fiber connections. Several applications need cost effective solutions. These connections can apply MMFs, however, the transmission parameters are degraded by the fiber modal dispersion. Therefore any efficient method to compensate modal dispersion is very important. In this paper mode filtering technique is introduced for that purpose. Two types of mode filters are proposed and tested by simulations and measurements. By the application of mode filters significant improvement is achieved in the transmission of QPSK and QPSK-OFDM signals. E.g. in case of a 500m long multimode fiber link transmitting signals with 500Mb/s bit rate the error vector magnitude (EVM) is improved from 40% to 5%.