Broadband Microwave Photonic Mixer with Flexibly Tunable Phase Shift and Supporting Dispersion-Induced Power-Fading-Free Fiber Transmission

A broadband microwave photonic mixer with tunable phase shift and supporting dispersion-induced power-fading-free fiber transmission is proposed and demonstrated based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). In this scheme, the intermediate-frequency (IF)/radiofrequency (RF) signal and the local oscillation (LO) signal are applied to the four sub-MZMs biased at their minimum transmission points via a power splitter and a 90 degrees hybrid coupler, respectively. Through mutual beating between the IF/RF and the LO modulation sidebands in a high-speed photodetector at the remote site, high-efficiency frequency conversion is achieved. The dispersion-induced power fading over long-distance fiber transmission is eliminated through setting the biased-induced phase difference between the parent-MZMs in the two sub-DPMZMs of the DP-DPMZM to be pi/2. In addition, the phase shift of the frequency-converted signal can be continuously tuned over 360 degrees through synchronously adjusting the bias voltages of the parent-MZMs in the two sub-DPMZMs. The proposed scheme is experimentally demonstrated, where a microwave photonic mixer with a 6-dB operation bandwidth of 40 GHz and supporting dispersion-induced power-fading-free transmission over 20 km SMF is realized. Meanwhile, a continuously tunable phase shift over 360 degrees in the frequency range of 0.1 GHz to 29.9 GHz is achieved, where the power variation during phase tuning is smaller than 4 dB.