Comparative analysis between FSO and bidirectional fiber transmission links for Sub-THz transceiver design compatible for future 6G networks

A photonic sub-THz transceiver design for use in the remote radio head (RRH) for future high capacity 6G networks that employ THz frequencies is demonstrated. The work studies the backscattering effects when a single fiber is used for fronthauling to and from the RRH. The work also demonstrates replacing the fiber link with free space optical (FSO) channel and draws a comparative analysis between the two optical channels in term of nonlinear effects. Bit error rate (BER) performance for 10Gb/s NRZ signals is measured by varying the received optical power at the uplink photodiode (for a fixed optical launch power) and also by varying the launched optical power at the transmitter side (for a fixed received optical power at the uplink photodiode) for 25 km bidirectional fibre transmission and 25 km of FSO transmission respectively. At +5 dBm optical launch power (received optical power at photodiode being 0.080 dBm), BER is found to be 10^-5 while using a single fibre and 10^-7 while using FSO link. This is due to the presence of backscattering effects in single mode fibre when used for bi-directional transmission, which signifies that FSO may be more suitable than optical fiber for sub-THz transceiver designs.