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 ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RF</sub> + 2ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LO</sub> 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 ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RF</sub> 2ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LO</sub> 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·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> . 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.