Coherence-Free High-Resolution RF/Microwave Photonic Bandpass Filter With High Skirt Selectivity and High Stopband Attenuation

A new coherence-free high-resolution RF/microwave photonic bandpass filter with high skirt selectivity and high stopband attenuation is presented. It is based on a frequency shifting amplified recirculating delay line loop with a wavelength dependent element at the output. The amplitudes of the delayed optical signals at the output of the frequency shifting loop are windowed by a wavelength dependent element to improve the signal processor frequency response performance. The frequency shifting amplified recirculating delay line enables a large number of taps to be generated using a simple structure for high-resolution signal processing. It has no coherent interference and phase-induced intensity noise limitations, and can be inserted into conventional fibre optic links. Experimental results demonstrate a high-resolution bandpass filter having a high performance with a shape factor of only 3.1 and an extremely high stopband attenuation of over 70 dB.