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Photonic techniques for microwave frequency synthesis

Optical synthesis of microwave signals is attractive for three main reasons. First, it offers the possibility of compact and efficient sources at frequencies where conventional electrical sources are bulky and very inefficient, such as in the THz region. Second, it enables rapid frequency stepping across many octave bandwidths within the microwave spectrum, which is difficult to achieve with electrical sources. Finally, it enables frequency generation to be remoted through optical fibre to a convenient location, with little performance penalty. The object of this paper is to review techniques for the optical synthesis of microwave signals and suggest some possibilities for the creation of new sub-systems of enhanced capability.