Flat-top ultra-wideband photonic filters based on mutual coherence function synthesis

A novel all-incoherent optical circuit that allows for band-pass microwave-photonic filter design is presented and verified through numerical simulation. In contrast to conventional spectrum-sliced optical architectures that operate on the basis of a finite number of discrete taps, our proposal is based on arbitrary shaping of the spectrum of the broadband optical source in a conventional frequency encoder. This fact dramatically increases the free spectral range of the filter with respect to the conventional discrete-time optical processing. The filter transfer function is given by the mutual coherence function of the filtered source which allows, through an inverse problem, sculpting the RF filter response. The effect of higher-order dispersion terms is also included by means of the optical coherence theory. Finally, some strategies are provided in order to alleviate the baseband resonance constraint. Numerical results are also included.