In this paper, a novel technique to realize frequency quadrupling and upconversion in a radio over fiber (RoF) link is proposed and experimentally demonstrated. The frequency quadrupling is achieved by using two cascaded Mach–Zehnder modulators (MZMs) that are biased at the minimum transmission point, with a tunable optical delay line placed between the MZMs. By properly adjusting the time delay between the two MZMs, a pair of optical wavelengths with a wavelength spacing corresponding to four times the frequency of the microwave drive signal is generated. The two wavelengths are then sent to a third MZM to which an intermediate-frequency (IF) signal is applied. At the output of the third MZM, a frequency-upconverted signal at the millimeter-wave (mm-wave) band is obtained. The advantages of the technique are that a relatively low-frequency local oscillator (LO) signal is used to generate a high-frequency LO signal and the upconverted signal is more tolerant to the dispersion-induced power fading compared with a conventional RoF link based on double-sideband (DSB) modulation. Experiments are performed to verify the technique.
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