Tunable all-optical microwave filter using Cross-Phase Modulation in Semiconductor Optical Amplifier Mach-Zehnder interferometer

We have implemented for the first time to our knowledge a tunable photonic filter with negative coefficients based on exploiting the cross-phase modulation (XPM) effect in a SOA Mach-Zehnder interferometer. The positive coefficient is also modulated by the SOA Mach-Zehnder interferometer in order to equalize the frequency responses of both taps. The tuning of the filter FSR is achieved by elemental fibre delay lines or by dispersive optical fibre. Carrier suppression effect has to be considered as a limitation of the operation range of the filter. Cross-phase modulation exhibits less chirp and allows higher operation bandwidth that the filter where the negative coefficients are obtained via cross-gain modulation