Quasi-Color-Free LD-Based Long-Reach 28-GHz MMWoF With 512-QAM OFDM

By using a 512-quadrature amplitude modulating-orthogonal frequency division multiplexing (512-QAM OFDM) data stream with universal filtered multicarrier (UFMC) process to directly encode a quasi-color-free laser diode (QCFLD) with dual-mode carrier, a long-reach 28-GHz millimeter-wave over fiber (MMWoF) link over 50-km single-mode fiber (SMF) is demonstrated for future fiber network with 5G wireless link. At the fiber-wired optical transmission stage, the dual-mode QCFLD can support raw data rates up to 54, 42, and 24 Gbit/s after 0, 25, and 50-km SMF transmissions. The data-rate degradation results from chromatic dispersion induced power fading effect. The 28-GHz MMW carrier optically heterodyned at remote node with a carrier-to-noise ratio of 53.5 dB is generated after 25-km SMF propagation, which achieves 6-m free-space transmission at 16 Gbit/s. Lengthening the SMF to 50 km still allows the MMWoF for wireless transmission at 16-Gbit/s over 5 m and 14-Gbit/s over 10 m. To favor the 5G wireless access with high data capacity, the UFMC processed QAM-OFDM was further adopted for noise suppression via sidelobe filtering operation. By lengthening the cyclic prefix and the filter window for the OFDM, the tradeoff between data quality and net-data-rate ratio without and with UFMC process is discussed. With UFMC, the MMWoF transmission capacity can deliver 3-GHz wide 32-QAM UFMC processed OFDM data at 15 Gbit/s over 50 km in SMF and 10 m in free space. Even within a limited subcarrier bandwidth as narrow as 140 MHz for practical 5G users, the 512-QAM UFMC data can be allocated to provide a raw data rate of 1.26 Gbit/s.