Tunable photonic microwave bandpass filter using phase modulation and a chirped fiber grating in a Sagnac loop

We propose a novel all-optical microwave bandpass filter configuration, which uses phase modulation and a linearly chirped fiber grating in a Sagnac loop. The free spectral range (FSR) of the filter can be tuned continuously by tuning the grating. We also derive an expression for the filter transfer function. Calculated and measured results, which agree well, are presented to show a large notch rejection and an easily tunable FSR.