Optical Generation of a Modulated Microwave Carrier for SDR Applications

The ideal software-defined radio (SDR) application requires a highly versatile mm-wave signal generator which, combined with software-implemented waveforms, emulates a large set of communication protocols in a single, stand-alone product. Optical carrier generation is a prime candidate for the development of such transmitters, allowing the generation of microwave carriers with frequencies ranging from hundreds of MHz up to terahertz. These signals can then be optically transported in virtually loss-less waveguides to feed multiple Tx/Rx sites. In this paper, we extend a previously reported generation method to include the addition of data to the carrier. The method uses a single laser and an optical intensity modulator to generate the carrier, and the data is directly superimposed without additional components. The generated channel includes a main carrier, optional sub-carriers and other spectral components related to frequency modulation of the baseband data. The properties of this communication channel, created using the non-linear response of the optical intensity modulator, are analyzed in detail both analytically and experimentally.