Fiber and free-space hybrid optical networking for new generation mobile radio access network

This paper proposes fiber and free-space hybrid optical (FFHO) networking for radio access networks (RANs) in the new generation mobile communication systems. FFHO networking applies technologies that cause fiber transmitted optical signals to be emitted directly into free-space and make free-space transmitted optical signals focus directly onto fibers by using beam size converters such as a lens. This networking provides flexibility to the optical network structure and expands the application areas of the existing optical fiber infrastructure such as dark fiber. Optical signals with 1.55-μm band transmission characteristics such as BER and atmosphere attenuation caused by weather conditions through free-space transmission are presented as the basis of the transmission evaluation. The evaluation results show that FFHO transmission incurs a penalty of about 1.5 dB in received power compared to fiber transmission and that FFHO has atmosphere attenuation characteristics comparable to conventional optical free-space transmission systems using the 800-nm wavelength band.