Distortion equalization in multi-mode fiber links carrying radio frequency OFDM signals

Abstract

Multimode fiber (MMF) links are currently attracting much interest as a medium for the transmission of radio signals over optical links called Radio over Fiber (RoF) link. However, the application is restricted, because the capacity of MMF transmission is limited by intermodal dispersion which is caused by the different propagation speeds of the fiber modes. The free space propagation of radio waves has a similar effect caused by multipath wave propagation. However, to overcome that effect a promising candidate is the orthogonal frequency division multiplexing (OFDM) method which has been rapidly and widely adopted in wireless, wire-line and broadcast systems for efficiently dealing with linear signal distortions encountered when transmitting over fading channels. Therefore, OFDM has recently gained significant attention in access networks. In this paper OFDM signals will be applied to investigate a Radio over MMF link. By using OFDM equalization the dispersion of the transmission system can be well estimated and mitigated, hence the distortion of the multimode dispersion can be compensated. The compensation method will be demonstrated for graded index (GI) and step index (SI) fibers as well. Performance of the transmission will be analyzed; it is investigated for different fiber lengths, fiber types, optical source types; and the optimal OFDM parameters will be determined.