Filter-free photonic microwave upconverter with frequency quadrupling.

A novel method, to the best of our knowledge, of frequency upconversion with frequency quadrupling is presented and experimentally demonstrated. The scheme is based on an integrated polarization-division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) and an intensity modulator (IM). Polarization-multiplexed second-order sidebands are obtained by properly adjusting the bias voltage of the PDM-DPMZM. By adjusting the polarization controller, the +2-order sideband is aligned with the IM's slow axis to be modulated by the intermediate frequency (IF) signal, and the -2-order sideband is aligned with the IM's fast axis with a much lower modulation efficiency. An upconverted signal with frequency quadrupling is generated at the photodetector. The experiment result shows that the working bandwidth range is 6-40 GHz, the spur suppression ratio of the upconverted signals is 37.5 dB, and the conversion efficiency is -32 dB. 100 MSym/s quadrature phase shift keying (QPSK) or a 16QAM signal at 26 GHz is generated using a 6 GHz local oscillator signal and transmitted through 25 km SMF.