Photonics-Based Wideband Microwave Phase Shifter

A wideband microwave photonic phase shifter implemented based on a special dual-parallel Mach-Zehnder modulator (DP-MZM) consisting of two sub-MZMs and a polarization rotator is proposed and demonstrated. A microwave signal to be phase shifted is applied to the two sub-MZMs, via a 90° hybrid coupler, to generate two orthogonally polarized intensity-modulated optical signals, which are combined at a polarization beam combiner. A phase-shifted microwave signal is obtained by detecting the combined signal at a photodetector. The tuning of the phase shift is realized by tuning the DC bias voltages applied to the sub-MZMs. Since the phase shift tuning has been done electrically, high speed phase tuning can be implemented. The proposed phase shifter is experimentally demonstrated. A continuous phase tuning from 0° to 360° with small magnitude variations of less than ±1 dB and phase ripple standard deviation of less than 2.7° in a decade bandwidth from 2.5 to 25 GHz is realized. The system insertion loss is measured to be 10.8 dB. Investigation on the cause of magnitude and phase deviations is also performed by simulations, which are confirmed by experimental measurements.