Image-Reject Mixer With Large Suppression of Mixing Spurs Based on a Photonic Microwave Phase Shifter

Image-reject mixers (IRMs) play an important role in microwave and millimeter-wave receivers to eliminate the interference from the image frequency. The keys to realizing a wideband IRM are the precise 90° phase shifting and parallel frequency mixing within a large operational frequency range. In this paper, we propose and demonstrate a novel photonic scheme that can perform simultaneously wideband 90° phase shifting and parallel frequency mixing based on a dual-polarization dual-drive Mach-Zehnder modulator and an optical filter. An IRM is thus implemented. A proof-of-concept experiment is carried out. The experimental results show that the image rejection ratio of the proposed IRM reaches ~60 dB, when the RF and LO frequencies are tuned in a frequency range of 10-40 GHz. In addition, since the optical filter is employed to select only the two +first-order RF and LO sidebands, the unwanted mixing spurs are all suppressed below the noise floor.