Tunable Photonic Microwave Notch Filter With Negative Coefficient Based on Polarization Modulation

A novel tunable photonic microwave notch filter with negative and positive coefficients is proposed and experimentally demonstrated. The coefficients can be achieved by polarization modulation along with an electrical signal. The two polarization-modulated signals, which have a relative time delay, are combined, and detected by a photodetector. The transfer response of the filter shows a very stable operation irrespective of the coherence length of the source used. Moreover, the free spectral range of the filter, which shows a sharp notch, can be changed by using a tunable differential group delay generator over the range of 3.16-4.31 GHz