A triple-frequency microwave photonic link is proposed based on a polarization-multiplexing dual-parallel Mach- Zehnder modulator (PM-DPMZM). The lower sub-DPMZM is biased at the maximum transmission point to obtain the 2nd-order RF sidebands. Meanwhile, the RF signal modulates the upper sub-DPMZM through an electrical 90° hybrid coupler. The upper sub-DPMZM works at the carrier-suppressed single-sideband (CS-SSB) modulation to obtain the +1st order RF sideband. An optical band pass filter is used to filter out the +2nd-order RF sideband, and only the +1storder and -2nd-order RF sidebands are output for the frequency beating at a photodetector (PD). The frequency triple signal of 3ωRF is obtained correspondingly. The experimental link is built. The results show that the RF signal from 8 to 12 GHz is tripled, and frequency tripled signal at 24 to 36 GHz is acquired. The minimal spur suppression ratio of triple-frequency signal is 20dB. A relatively low-frequency signal can be used to generate a high-frequency signal with well quality by this triple-frequency link. The proposed method can be applied in various microwave photonic transmitting systems.
A reconfigurable microwave photonic frequency upconverter with local oscillator (LO) doubling or LO quadrupling is proposed based on two cascaded dual-parallel Mach–Zehnder modulators (DPMZMs) and a fiber Bragg grating (FBG) with a wide bandwidth (0.4 nm). The first DPMZM is used to generate the ±1st-order or ±2nd-order sidebands of the LO signal. The FBG is inserted to separate the positive and negative sidebands. Only the transmitted LO sideband is sent to the second DPMZM, and the carrier-suppressed single-sideband (CS-SSB) modulation of the intermediate frequency (IF) signal is realized by using an electrical 90 deg hybrid coupler. The reflected LO sideband via FBG and the −1st-order IF sideband are combined. Then, the upconverted signal with the frequency of 2ωLO + ωIF or 4ωLO + ωIF can be generated by a photodetector. The experimental results show that the spur suppression ratios of the upconverter with LO doubling and quadrupling are 21.3 and 11.3 dB, respectively. The proposed approach greatly reduces the frequency requirement of the LO signal. The purity of electrical spectrum is largely improved in both the LO doubling and LO quadrupling upconversion benefiting from the CS-SSB modulation. Furthermore, these two upconversion modes can be easily switched by tuning the DC biases of the first DPMZM.