Phase-tunable microwave photonic mixer based on lithium-niobate-on-insulator chip

We propose and experimentally demonstrate a phase-tunable microwave photonic mixer. The mixer consists of an optically generated local oscillator (LO) and a wavelength-division modulation chip. The chip, which is fabricated on a lithium niobate on insulator (LNOI) substrate, consists of two micro-ring filters, two phase modulators, and two optical couplers. In the experiment, a frequency-doubled optically generated LO at 33.7 GHz is generated by double-sideband suppressed-carrier modulation. The two sidebands are coupled into the chip, and two micro-ring filters select and separate them into two phase modulators (PMs) to achieve wavelength-division modulation. A radio frequency (RF) signal and a direct current bias voltage signal are applied to the two PMs respectively. As a result, a 12 GHz RF signal is successfully converted to a signal with a frequency of 21.7 GHz, and the phase of the converted signal can be tuned from 0° to 360°.