Inline Microring Resonator Based Microwave Photonic Phase Shifter With Self-Mitigation of RF Power Variations

We present a new technique to self-mitigate the RF power variations in microwave photonic phase shifters (MPPS) based on microring resonators by exploiting the root problem of varying optical intensities at different optical phase shifts to harness a varying and opposing optical equalization gain. Whilst optical gain mediums are commonly present in microwave photonic systems to overcome optical loss, choosing an appropriate equalization gain point to strike a balance between the optical gain transformation of weak and preservation of strong signals allows the proposed system to effectively achieve minimal radio frequency (RF) power variation across all signals without interfering with the RF phase shifting operation. Simulation results show an inline MPPS based on the phase and amplitude of conventional resonant structures with a capability to successfully minimize the RF power variations by 80% for up to 25 dB of phase-dependent power variations throughout the full 360° phase tuning range. Experimental results verify the MPPS operation based on a single microring resonator by significantly reducing the large RF power variations from 9 dB to less than ±1.25 dB, while maintaining the same RF phase shifting operation. We then verify the use of the proposed inline MPPS to adaptively minimize the self-interference by optimizing the phase compensation in a self-interference cancellation system. We demonstrate a cancellation bandwidth of 100 MHz with peak in-band cancellation of up to 40 dB while exhibiting the capability to recover weak signals of interest at operating center frequencies ranging from 5 - 20 GHz.