Optical source coherence controller for fibre optic delay line RF/microwave signal processors

A technique for optical source coherence control that can suppress the important coherent interference effects in photonic delay line RF/microwave signal processors is presented. The concept is based on phase modulation of the optical carrier to transform the laser coherence to meet the requirements of the photonic signal processor that suppresses coherent interference. It enables conventional narrow-linewidth, high quality DFB lasers to be used for high frequency photonic signal processors, and tailors their coherence length to meet the processor design requirements. Experimental results show that the optical source coherence controller can realise photonic RF/microwave filters with robust response using narrow-linewidth sources, demonstrating the effectiveness of this technique for coherent interference suppression in photonic signal processors.