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 andmillimeter-wave receivers to eliminate the interference from the image frequency. The keys to realizing a wideband IRM are the precise 90 degrees 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 degrees 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 similar to 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.