Frequency Response Enhancement of Photonic Sampling Based on Cavity-Less Ultra-Short Optical Pulse Source

The influence of the residual pulse chirp and the spectrum shape from a cavity-less optical pulse source on the sampling performance is theoretically analyzed. According to the theoretical analysis, an optimization method for enlarging the operation bandwidth of a photonic sampling system based on a cavity-less ultra-short pulse source is proposed and experimentally demonstrated. Through biasing the Mach-Zehnder modulator in the cavity-less optical pulse source below its quadrature point, the output spectrum flatness can be greatly improved, which is beneficial for optimizing the photonic sampling frequency response introduced by the ultrashort optical pulse train. In the experiment, the 3-dB bandwidth of the photonic sampling frequency response is increased from less than 10 GHz to more than 35 GHz by using the proposed method without sacrificing the output signal-to-noise ratio.