Ultra-wideband microwave photonic circulator based on a thin-film lithium niobate electro-optic modulator

A novel ultra-wideband microwave photonic circulator scheme is proposed and demonstrated. In this scheme, the microwave photonic circulator is composed of a laser diode, a specially-designed thin-film lithium niobate modulator and a photodetector. Benefited from the large modulation index difference between the forward modulation and the counter modulation in the MZM, the microwave photonic circulator is with a high isolation. In the experiment, the isolation of the proposed circulator is larger than 10 dB in the frequency range from 6.3 GHz to 50 GHz, while the maximum isolation of the circulator is 30.1 dB at 8.7 GHz. The measured frequency response curves agree well with those obtained in the simulation. This circulator is employed in a simultaneous transmission and reception experimental system. The low EVM values and crosstalk in the operation frequency range from 8.0 GHz to 9.4 GHz can verify that the proposed microwave photonic circulator has large application potential in the wideband full-duplex wireless communications.