Abstract
We propose and experimentally demonstrate a polarization-tracking-free polarization division multiplexing (PDM) intermediate frequency over fiber (IFoF) based on multiband direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) with adaptive modulation (AM) technique downstream, as well as polarization insensitive on-off-keying upstream. The polarization tracking mechanism is eliminated, hence the complicated cell sites are simplified and letting more cost-effective and power-efficient for every radio access unit (RAU). Moreover, under the C-RAN architecture the mobile fronthual is thus establish with high spectra flexibility and complexity centralized which will be a promising selection for next generation mobile communication. In the downstream system, only a simple optical filter at each receiver can passively demultiplex the corresponding signal band in both PDM scheme and multiband scheme. An adaptively modulated multiband OFDM signals with 3.5-GHz bandwidth, 50-Gb/s transmission 25-km single mode fiber is experimentally demonstrated. A spectral efficiency is doubled with applied PDM technique and data capacity is 8-Gb/s increased compare with employing AM or not. Furthermore, it provides 4 dB power margins, where may support wireless transmissions[1]. In the upstream generation, the polarization insensitive is implemented for using MZM by directly reuse the two orthogonal carriers without additional filtering or polarization controlling. The results show a 1.8dB power penalty with respect to those with traditional best polarization aligned mechanism, which can be negligible. The polarization tracking mechanisms are out of consideration and establish a true polarization tracking free mobile fronthaul system.