RF Characterization of an Integrated Microwave Photonic Circuit for Self-Interference Cancellation

Abstract

We perform a full radio frequency (RF) characterization of the first integrated microwave photonic interference canceller. The photonic integrated circuit is one of the first to possess only RF inputs and outputs, with monolithically integrated optical sources and detectors. The characterization is important to developing an in-depth understanding of the integrated circuit’s effect on RF receivers. We characterize the circuit’s gain, noise figure, input intercept point, 1-dB compression point, and spurious-free dynamic range as functions of on -chip device bias points and frequency up to 6 GHz. We find that the circuit’s RF properties are almost exclusively determined by the directly modulated laser. Link gain is primarily driven by the laser slope efficiency. The noise figure is dominated by signal attenuation and laser relative intensity noise. The circuit nonlinearity is the third-order intermodulation product limited. With the exception of link gain, all properties improved with increasing laser bias, saturating at 30 mA. Meanwhile, all properties degraded with increasing frequency. External optical feedback from the reflections off of waveguide transitions in the monolithic circuit created operating points of high noise figure and low gain, and should be avoided during operation. The circuit can be improved by implementing a balanced link architecture to suppress the laser relative intensity noise and using external modulators to improve the link linearity and bandwidth.