Broadband Microwave Photonic Mixer With High Spurs Suppression and Image Rejection

A microwave photonic mixer for up- and down-conversion based on dual parallel in-phase and quadrature (I/Q) modulators is proposed. Dual parallel I/Q modulators and 90-degree electrical hybrid couplers are used to obtain carrier-suppressed single-sideband modulation of radio frequency (RF), intermediate frequency (IF), and local oscillator (LO) signals. The optical bandpass filter (OBPF) is employed to select the -1st-order or +1st-order sideband of the LO signal to realize up and down conversion. In the experiments, an IF frequency range of 5-17 GHz can be upconverted to an RF frequency range of 15-37 GHz, and an RF frequency range of 8-40 GHz can be downconverted to an IF frequency range of 2-5 GHz. The spurs suppression ratio exceeds 50 dB for up and down conversion. To the best of our knowledge, this is the highest reported spurs suppression in a broadband microwave photonic mixer. Moreover, the OBPF is also utilized to obtain an image rejection ratio (IRR) of 45.91 dB at an IF frequency of 4 GHz. To obtain a lower frequency of IF signal and a higher IRR, a Brillouin-assisted notch filter is applied to attenuate the image signal. In this way, an IRR of more than 60 dB can be obtained at an IF frequency of 2 GHz.