Generation of frequency-doubling mm-wave signal using a MachZehnder modulator with three arms to overcome fiber chromatic dispersion
We propose a novel method to generate optical frequency-doubling mm-wave signal by using a three-arm MachZehnder modulator (MZM) for radio-over-fiber (RoF) systems. Since the optical carrier and its two 2nd-order sidebands are dominant, the 2nd-order harmonic in the photocurrent gets maximal. When the optical mm-wave signal is transmitted in standard single-mode fiber (SSMF), there is no time shift of code edges because the data signal is only carried by the optical carrier. The 2nd-order harmonic in the photocurrent consists of two beating products, so it experiences a periodical fading effect when the optical mm-wave signal is transmitted in SSMF. However, if a proper direct-current (DC) bias is applied to the data modulation arm in the MZM architecture to adjust the position of the fading nodes, the degradation on the photocurrent can be avoided. A RoF link is built based on the novel scheme by simulation, and the transmission performance of the proposed scheme is presented. The eye diagram still keeps open and clear even after 40km transmission. Simulation results prove our theoretical analysis.
fiber chromatic dispersion machzehnder modulator (mzm) radio-over-fiber (rof) frequency doubling