Photonics-enabled simultaneous self-interference cancellation and image-reject mixing

Both self-interference and image interference are key practical impediments to realize in-band full-duplex radio-frequency (RF) systems. The previous photonics-based approaches can realize either self-interference cancellation or image-reject mixing. The only approach to realize both functions relies on electrical operations of phase shift, power weighting, and time delay, leading to limited bandwidth and frequency. This Letter proposes and demonstrates a photonic approach to realize simultaneous self-interference cancellation and image-reject mixing. The key is that by introducing only one polarization-multiplexed 90° optical hybrid, simultaneous 0, π, π/2, and 3π/2 phase shifts can be introduced in the optical domain. In addition, power weighting and time delay of the reference signal for self-interference cancellation can be realized in the optical domain with the help of polarization multiplexing. In this way, all the operations required by both functions are realized using optical methods. Both theoretical and experimental investigations are performed. Simultaneous self-interference cancellation and image-reject mixing are achieved, with a self-interference cancellation depth of 35 dB over 100-MHz bandwidth, 24 dB over 400-MHz bandwidth, and 18 dB over 1-GHz bandwidth in the X and Ku bands, and an image-rejection ratio larger than 53 dB over 1-GHz bandwidth in the X band.