Advanced VCSEL photonics: Multi-level PAM for spectral efficient 5G wireless transport network

摘要

Transitions to 5G are accompanied by rapid increase in data traffics, creating exciting opportunities for competitive edges in 5G spectral efficiency (SE) solutions. We present the first reported vertical cavity surface emitting laser (VCSEL)-based heterodyne technique in context of four-level pulse amplitude modulation (PAM-4) over 15 km SMF fibre and 12 m radio frequency (RF) wireless link. Two low-cost temperature stabilized VCSELs with an extinction ratio (ER) of 4.6 dB and aggregated bit rate of 7 Gbps OOK data to meet the high data demands in wireless connectivity are heterodyned to dynamically generate low phase noise 37.9 GHz RF for 30 m wireless transmission link. PAM-4 modulation technique is adopted to maximize the RF carrier SE in transmission of 14 Gbps data over 12 m wireless link, doubling the network bit rate. It is the first time a VCSEL-based photonically generated RF carrier system is reported with a doubled network bitrate upgrade functionality in the contest of PAM-4. A receiver sensitivity of -23.19 dBm is attained on the 7 Gbps OOK data with a transmission penalty of 2.62 dB over a 30 m link. However, a 14 Gbps PAM-4 modulation incurred a 6.17 dB penalty over the 12 m wireless transmission link. Heterodyned VCSEL technology offer dynamic RF carrier flexibility while PAM-4 upgrades the RF carrier SE without replacing the network optics.