A Microwave Photonic Mixer Using a Frequency-Doubled Local Oscillator

Abstract

A microwave photonic mixer based on a frequency-doubled local oscillator (LO) is proposed. The carrier-suppressed single-sideband (CS-SSB) modulation of the –first-order radio frequency (RF) and +second-order LO sidebands can be generated by using a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM), an electrical 90° hybrid coupler, and an optical bandpass filter. The upconverted intermediate frequency (IF) signal with the frequency of ${\omega _{\boldsymbol{RF}}} + 2{\omega _{\boldsymbol{LO}}}$ is output by frequency beat at a photodetector. Meanwhile, the –first-order RF sideband can be easily changed to +first-order RF sideband by adjusting one dc bias voltage of the DP-DPMZM. The downconverted IF signal with the frequency of ${\omega _{\boldsymbol{RF}}} - 2{\omega _{\boldsymbol{LO}}}$ is obtained correspondingly. The experimental results show that the spur suppression ratios of upconverted and downconverted IF signal are 19.0 dB and 25.5 dB, respectively. The spurious-free dynamic range of the proposed mixer is 96.5 dB·Hz2/3. The output electrical spectrums are pure owing to the optimal design of the CS-SSB modulation. The proposed mixer reduces the frequency requirement of LO signal since the second-order LO single sideband is used, and the upconversion and downconversion can be switched to each other by a simple electrical operation.