COMPARISON OF OPTICAL-PROCESSING TECHNIQUES FOR OPTICAL-MICROWAVE SIGNAL GENERATION

Recently, there have been several proposals on using the higher RF har monics of detected pulses from mode-locked semiconductor lasers as a s ource of microwave and millimeter waves, This paper compares the perfo rmance of three optical techniques of signal processing that have been proposed to select a higher harmonic of a mode-locked loser, by using extensive numerical simulations, We show that techniques using delays and splitters are insensitive to the coherence properties of the sour ce, hut can introduce amplitude patterning if pulses overlap when reco mbined, We see that techniques relying on optical filtering to select optical modes require extremely high-Q filters and, thus, are extremel y sensitive to tuning, A Fabry-Perot interferometer (FPI) is the optim um filter method in terms of power efficiency for low harmonics, but u sing two Separate bandpass filters can give comparable efficiency when selecting higher harmonics, We also show that gain-switched lasers ar e unsuitable as sources when used with narrow-band optical filtering t echniques because of their low pulse-to-pulse optical coherence.