Reconfigurable microwave photonic filter with negative coefficient based on an optoelectronic oscillator

We report a reconfigurable multi-tap microwave photonic filter with negative coefficient based on an optoelectronic oscillator (OEO). The key novelty of this work is that a single polarization modulator (PolM) is used to build the OEO as well as to generate a multi-wavelength optical source. Thus, an external microwave source which is usually involved in the generation of multi-wavelength optical source by externally modulating a single tone optical beam is saved. In addition, the spectrum of the multi-wavelength optical source is reconfigurable in terms of the number of the optical components and the frequency interval between the adjacent components. The negative coefficient of the microwave photonic filter is achieved using a phase modulator (PM) and a dispersive element. The proposed approach is theoretically analyzed and experimentally verified. The generated fundamental microwave signal has a frequency of 9.95 GHz and a phase noise of −118 dBc/Hz at 10 kHz offset. By adjusting the optical power inside the OEO loop and the polarization controller (PC) outside the OEO loop, the tap number of the microwave photonic filter can be adjusted from 2 to 5, leading to a reconfigurable microwave photonic filter. The measured frequency responses of the microwave photonic filters agree well with the simulated ones.