Integrated Microwave Photonic Circuit for Self-Interference Cancellation

We present the first experimental demonstration of an integrated microwave photonic circuit for active, analog self-interference cancellation. The circuit is unique in its ability to operate in any radio frequency (RF) band from 400 MHz up to 6 GHz while not requiring any optical inputs or outputs. We focus on two topics related to the functional performance of the circuit. First, we investigate the amount of interference cancellation that can be achieved over a wide range of operating frequencies. We show that the circuit can achieve nearly -30 dB of interference cancellation across all existing frequency-division duplexed local thermal equilibrium and WiFi bands. Second, we investigate the control aspects of the integrated circuit and determine how much amplitude and phase tunability can be generated to perform active cancellation. Using dispersive techniques, the integrated circuit achieves 10 dB and 52° of independent amplitude and phase tunability, respectively, at 1.25 GHz. The range decreases with increasing frequency. We find that the sensitivity of the circuit's cancellation performance to the control biases are 2 and 0.5 mA at cancellation depths of -40 and -50 dB, respectively. Finally, we use the integrated circuit to demonstrate adaptive interference cancellation. Our results show that an integrated solution is able to achieve a cancellation performance comparable to a discrete fiber-optic system. Additionally, it is one of the first demonstrations of an integrated microwave photonic circuit that only possesses RF inputs and outputs.