A new technique for generating negative coefficients in photonic signal processors based on dual-input and dual-output intensity modulator sagnac interferometers

New structures that can realize bias drift-free dual-input and dual-output intensity modulators, and which can generate negative coefficients in photonic signal processors, are presented. They are based on a Sagnac loop comprising a travelling-wave optical phase modulator, together with a routing structure that gives outputs with opposite radio-frequency phases. Results using the dual-input mode of operation demonstrate a new technique for generating negative coefficients in an all-optical microwave photonic filter.