Photonic-Assisted Reconfigurable LO Harmonic Downconverter With RF Self-Interference Cancellation and Image-Rejection

A photonic-assisted reconfigurable LO harmonic downconverter with simultaneous image-rejection and RF self-interference cancellation (SIC) for in-band full-duplex communication is proposed and experimentally investigated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The received signal from the antenna, which includes the radio frequency (RF) signal, image signal (IM) and self-interference (SI) signal, is input into one sub-MZM of the X-DPMZM. The self-reference (SR) signal is input into the other. The Y-DPMZM is used to load the LO signal and is properly biased to obtain the high-order sideband of the LO signal, which was then set as the LO signal of the reconfigurable harmonic frequency downconverter. By matching the power and delay of the SR signal and changing the main bias of the X-DPMZM, the SI signal can be eliminated directly in optical domain. With power splitting after the output of the DP-DPMZM, the quadrature IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Then, photonics image-rejection down-conversion based on phase cancellation is realized after a low-frequency electrical 90° hybrid coupler (HC) combines the quadrature IF signals. Both theoretical and experimental investigations are performed. The results show that the SIC has a cancellation depth more than 32 dB for the 10-MHz bandwidth and greater than 19 dB for the 500-MHz bandwidth, the image-rejection has an image-rejection ratio larger than 31 dB for 10-MHz bandwidth and larger than 22 dB for the 100-MHz bandwidth, both in 2
^nd
- and 3
^rd
-order harmonic down-conversion mode. Experiments are also carried out on the reconfigurable LO harmonic downconverter with simultaneous SIC and image-rejection. A 16-quadrature amplitude modulation (16-QAM) -modulated RF signal is successfully down-converted to a 1-GHz intermediate frequency (IF) signal with self-interference and image frequency cancelled. It is verified that the RF signal can be well recovered from SI and IM signals by the proposed system.