Design of a microwave photonic filter using FBG-based delay lines and the FIR filtering technique for photonic integrated circuits

A new method, to our knowledge, for designing microwave photonic filters (MWPFs) using fiber Bragg grating (FBG)-based delay lines, employing a zero-pole placement approach, has been proposed and successfully demonstrated. This technique leverages the concept of linear phase finite impulse response (FIR) filters. The focus of this work is on calculating the filter tap coefficients for various delay-line-based MWPF configurations to achieve a specified spectral response. The resulting filter coefficients are real and positive, representing the reflectivities of the cascaded FBGs. Lowpass and multi-bandpass MWPFs have been developed to operate within the 0.1-24.5 GHz microwave frequency range. The performance of these filters has been evaluated in terms of bandwidth, order, and size, with the core component of the filter or the overall FBG-based delay line measuring from 0.5 cm to 30 cm. Both theoretical and experimental simulations of the filter have been conducted, yielding strong agreement between the two. The suggested design method is applicable to infinite impulse response (IIR) filters and all other types of filters. This compact filter can be utilized in photonic integrated circuits.