10-MSymbols/s QAM-16 externally-modulated optical link for radio-over-fiber applications

In baseband optical communications, information is encoded in the modulated intensity of light propagating over singlemode optical fiber. In radio communications, information is encoded in the phase and amplitude modulation of a signal oscillating at the carrier frequency. This type of modulation can also be employed in optics by creating an intensity modulated beam oscillating a carrier frequency and then modulating the amplitude and phase of this carrier. This paper discusses a preliminary investigation this technology with aim to ultimately apply it to incoherent-light communications by investigating the linearity of a Mach-Zendher optical modulator and an optical link involving QAM-16 modulation over 20-km of singlemode fiber. The conclusion of this work is that without linearization and higher optical power, the system is limited to less than 35 dBc in ACLR and bit-error rate at <; 10 ^-3 .