Tunability of the multiple-bandpass response of cascaded single-source and continuous-sample microwave photonic filters

We report a theoretical and experimental investigation on the structure and tuning capabilities of cascaded associations of microwave photonic filters composed of a single-source incoherent filter and a continuous-sample filter based on periodically-sliced broadband sources that undergo dispersion after being modulated. We derive the condition that guarantees both incoherent operation and cascading of the radio-frequency responses. This condition implies a lower bound for the ratio between resonance bandwidth (Δf) of the continuous-sample filter and the free spectral range (FSR) of the single-source filter, thus showing the possibility of cascading filters in two complementary regimes, Δf/FSR < 1 and >1. The tunability of the cascaded responses is also explored in a series of proof-of-concept experiments, where a static response of a single-tap, incoherent loop filter is reconfigured by use of a Solc filter. In particular, it is demonstrated a reconfigurable single and dual-bandpass cascaded response, which can be further modified by changes in dispersion, spectral period of the slicing filter, central wavelength or spectral width of the broadband source, and apodization of the resonance. The results are compared with the predictions of the Gaussian model for the degradation of resonances in continuous-sample filters due to second-order dispersion.