All-optical WDM multi-tap microwave filter with flat bandpass

An incoherent photonic microwave filter implementing multiple positive and negative coefficients based on two sets of optical carriers and dispersive media is proposed and demonstrated. Positive and negative coefficients are obtained thanks to the pi phase inversion in a single electro-optic Mach-Zehnder modulator as well as the modulator Vpi dependence with wavelength. To show the feasibility of this technique to implement practical filter transfer functions, the Parks-McClellan algorithm has been used to design a 5-tap flat bandpass filter. Experimental results show an excellent agreement with theory.