Investigation of microwave photonic filter based on multiple longitudinal modes fiber laser source

• We study the FIR-MPF by considering the effect of fiber laser longitudinal modes.
• The response of longitudinal mode taps will be convolved with other response terms.
• The effect of longitudinal mode envelope and mode spacing are both investigated.
• The longitudinal mode structure can be managed to engineer the response of the MPF.

We theoretically study the transfer function of a finite impulse response microwave photonic filter (FIR-MPF) system using a multi-wavelength fiber laser source by considering multiple longitudinal modes in each wavelength. The full response function with the response from longitudinal mode taps is obtained. We also discussed the influence of the longitudinal mode envelope and mode spacing on the performance of FIR-MPF. The response function of the longitudinal mode taps is fully discussed and the contribution is compared with the response of the carrier suppression factor for double sideband (DSB) modulation. The multiple longitudinal modes structure in the wavelength taps can be utilized to engineer the response of the FIR-MPF such that desirable features such as high side lode suppression ratio can be realized. The analysis provides a guideline for designing incoherent FIR-MPF systems.