Tunable microwave photonic duplexer for full-duplex radio-over-fiber access

A tunable microwave photonic duplexer (MPD) for full-duplex radio-over-fiber access is proposed and experimentally demonstrated. The proposed MPD is implemented by two single-bandpass microwave photonic filters (MPFs) to separate the transmit (Tx) and receive (Rx) channels. More specifically, a broadband optical source (BOS) is spectrally sliced by a differential-group-delay interferometer (DGDI) and a Mach-Zehnder interferometer (MZI) to form two tunable single-bandpass MPFs with different central frequencies. The two MPFs are used for the Tx and Rx channels, respectively. By adjusting the free spectral ranges (FSRs) of the DGDI and MZI, the central frequencies of the Tx and Rx channels can be tuned independently in a wide frequency range. In the experiments, tunable ranges from 0 to 6.1 GHz for the Tx channel and from 0 to 17 GHz for the Rx channel are achieved. Meanwhile, a high isolation up to 44 dB between the Tx and Rx channels is also obtained. Based on the proposed MPD, the duplex transmission of a 10-MBaud 16-quadrature-amplitude-modulation (QAM) signal at 2.45 GHz and 2.82 GHz is demonstrated.