Link Optimization of a Microwave Photonic Phase Shifter Using Brillouin-Induced Low Biasing

In this paper, we demonstrate a microwave photonic phase shifter using stimulated Brillouin scattering with Brillouin-induced low biasing of the carrier to improve the dynamic range of operation and the noise performance. Mathematical expressions for the analog photonic link's performance metrics are derived and experimentally optimized for the first time for a Brillouin-based microwave photonic phase shifter. Gain and loss responses are imparted on the carrier to induce a phase shift, and low-biasing of the carrier is achieved by using unbalanced loss and gain pumps, which results in a stronger Brillouin loss response compared to the gain response being imparted on the carrier, thereby improving the performance. The results indicate a 3 dB increase in link gain, a >2 dB improvement in noise figure, and >2 dB and >4 dB enhancements in compression dynamic range (CDR) and spurious free dynamic range (SFDR), respectively, when compared to the without low biasing while maintaining the same photocurrent. We also demonstrate the real-life application of the Brillouin RF phase shifter by transmitting 16- and 64-QAM signals using different Brillouin pump powers and have analysed its effect on the error vector magnitude, with minimal distortions being observed in the performance. Furthermore, a phase shift operation is performed on a linear frequency-modulated signal to demonstrate a potential application in RADAR systems.