Optical Synthesis of Microwave Signals

Microwave signals can be generated by the photo-detection of multiple optical signals. This approach has potential for the generation of signals having characteristics not readily obtainable by other means, such as fast tuning over multi-octave ranges, low dispersion and non-linearity penalties in millimetre-wave over fibre transmission and compact millimetre-wave local oscillator generation. Obtaining the spectral purity required for practical applications is however a significant challenge. This paper describes techniques for the optical synthesis of microwave signals, focusing on optical heterodyne generation techniques and including recent results for a high spectral purity optical injection phase lock loop.