  A photonic approach for radio-frequency (RF) self-interference cancellation
(SIC) incorporated in an in-band full-duplex radio-over-fiber system is
proposed. A dual-polarization binary phase-shift keying modulator is used for
dual-polarization multiplexing at the central office (CO). A local oscillator
signal and an intermediate-frequency signal carrying the downlink data are
single-sideband modulated on the two polarization directions of the modulator,
respectively. The optical signal is then transmitted to the remote unit, where
the optical signals in the two polarization directions are split into two
parts. One part is detected to generate the up-converted downlink RF signal,
and the other part is re-modulated by the uplink RF signal and the
self-interference, which is then transmitted back to the CO for the signal
down-conversion and SIC via the optical domain signal adjustment and balanced
detection. The functions of SIC, frequency up-conversion, down-conversion, and
fiber transmission with dispersion immunity are all incorporated in the system.
An experiment is performed. Cancellation depths of more than 39 dB for the
single-tone signal and more than 20 dB for the 20-MBaud 16 quadrature amplitude
modulation signal are achieved in the back-to-back case. The performance of the
system does not have a significant decline when a section of 4.1-km optical
fiber is incorporated.
