Cascaded microwave photonic filters with multiple infinite impulse responses based on wavelength conversion

A new cascaded microwave photonic filter consisting of two or more infinite impulse response (IIR) filters based on active loops. is presented. Owing to wavelength conversion, the interference between the modulated optical signals of different taps from different active loops can be avoided and the stable transmission characteristic of the cascaded filter can then be achieved. The cascaded filter can increase the free spectral range (FSR) and the Q value significantly by designing the FSR differences of the IIR filters. The cascaded filter with two IIR filters is demonstrated, and the measured results of a high Q of 3338 and rejection ratio of about 40 dB are obtained. The tunability can also be realized.