Reflective Amplified Recirculating Delay Line Bandpass Filter

A new microwave photonic filter structure that can achieve a high $Q$ factor, high stopband rejection, and high skirt selectivity bandpass filter response simultaneously is presented. It is based on reflecting the signal back into a single amplified optical recirculating delay line and comprises coherent summation of the multiple signals that constitute each tap and incoherent summation of the successive taps. This introduces a new class of filter operation and effectively enables the realization of a higher order bandpass filter characteristic in a very simple structure. Experimental results are presented that demonstrate a multiple-tap high-$Q$ bandpass filter response that also displays high stopband rejection level and high skirt selectivity.