Dual-Wavelength-Modulation mm-Wave and THz Systems: Analysis and Experimental Demonstration At 60 GHz With a Gain-Switched Laser

Dual-wavelength-modulation (dual-
$\lambda$
-mod) photonic mm-wave/THz transmitters are an attractive alternative to conventional heterodyne systems for their simplicity. In this article, dual-
$\lambda$
-mod systems are analysed, paying special attention to the impact of fiber dispersion and signal-signal beat interference. In contrast to what has been reported in the literature, it is concluded here that dual-
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-mod systems based on optical double sideband (DSB) modulation are subjected to power fading, rendering them useless for high-speed mm-wave/THz communications. To solve this, the use of optical single sideband (SSB) modulation – which is immune to power fading – is proposed here. Using a gain-switched (GS) laser, a 60-GHz SSB dual-
$\lambda$
-mod system transmitting 2.5-GBd 16-QAM signals is demonstrated experimentally. A penalty of around 2.8 dB is measured with respect to the conventional dual-path heterodyne transmitter over optical B2B and 10-km transmission. The reduction in complexity enabled by the demonstrated system aids in the deployment of cost-effective mm-wave/THz networks.