Microwave photonic phase-tunable mixer.

Traditional microwave photonic systems cannot implement frequency up-conversion with phase tunable capability, which plays an important role for phase array beamforming. Here, a method that can implement both upconversion and downconversion with a broadband full-degree phase-shift capability by constructing an optical path with a Hilbert transform function is presented. Owing to the Hilbert transform path, the dual-drive Mach-Zehnder modulator (DMZM) bias information, which initially influences the amplitudes of the output signals, are transferred to their phases. As a result, the phase-shift capability of the output radio frequencies (RFs) and intermediate frequencies (IFs) can be achieved by simply adjusting the bias voltage of the DMZM without using an optical filter. Experimental results demonstrate that a 360° phase shift can be achieved when the IF signal below 4-GHz and the RF signal between 8 and 16-GHz are converted into each other.