Polarization-Tracking-Free IFoF Mobile Fronthaul With Adaptively Modulated PDM Multiband DDO-OFDM

This letter proposes a polarization-tracking-free polarization division multiplexing (PDM) in an intermediate frequency over fiber mobile fronthaul system based on multiband direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) with adaptive modulation. The use of two orthogonally polarized optical carriers with a simple optical filter at each radio access unit is sufficient to perform passive demultiplexing of the corresponding multiband signals in PDM schemes without transmission efficiency loss in training signal, which is commonly found in conventional PDM demultiplexing schemes. We experimentally achieved a multiband OFDM signal with adaptive modulation, which maximizes signal capacity, in a PDM scheme with the data rate of 49.64 Gb/s, which doubles that of corresponding single polarization schemes, over a 25-km single mode fiber. We also achieved a 6-dB power margin which is sufficient for the wireless transmission part.