Spurious Noises Analysis of Microwave Photonic Filters Based on Phase Modulation to Intensity Modulation Conversion Using an Optical Notch Filter

The spurious noises of a narrow-bandpass microwave photonic filter (MPF) using phase modulation to intensity modulation (PM-IM) conversion and an optical notch filter are analyzed in theory and demonstrated experimentally. Due to the difference between the nonlinear filtering effect of PM-IM conversion and the linear one of finite impulse response or infinite impulse response, additional spurious noises will be generated in the former filter. Analysis models with two input microwave tones are developed for revealing the spurious noises in the MPF based on PM-IM conversion under small-signal and large-signal modulations, which are then verified by simulations and experiments, respectively. The results show that, besides the target microwave signal to be selected, the inter-modulation noise and the harmonic noises also coexist at the output of the MPF, wherein the 2nd-order inter-modulation noises and the 2nd-order harmonic noise of the target signal are the dominant spurious ones. Therefore, an excellent agreement among the results from analysis models, the simulations, and the experiments is obtained.