A Selectable Multiband Bandpass Microwave Photonic Filter

A multiband bandpass microwave photonic filter (MPF) whose passband number and position can be selected is theoretically analyzed and experimentally demonstrated. The proposed MPF is based on a wide-band optical source (WBOS) and a two-order high-birefringence fiber loop mirror (HB-FLM), which serves as a slicing filter. Two segments of high-birefringence fiber (HBF) with the lengths of 3 m and 6 m are used in the HB-FLM, and three typical spectral periods or their combinations can be independently achieved by simply adjusting the polarization controllers (PCs) in the HB-FLM. Subsequently, the light source is sliced with uniform or mixing wavelength spacing. A coil of single-mode fiber (SMF) is then used to act as a dispersive medium to introduce time delay between taps. Thus, a single or multiband bandpass response is obtained at the output of a high-speed photodetector (PD). In addition, the passband centered at dc frequency is removed due to the use of phase modulation. All of the radio frequency (RF) characteristics of the proposed MPF show good agreement with the theoretical prediction. It has the merits of good flexibility, high spectrum efficiency, and great potential of extension.