Independently tunable optical notch filter based on double ring resonator structure

A novel technique of designing optical notch filter is proposed from digital filter perspective for Mach–Zehnder interferometer with double ring resonator coupled structure. It is based on Z-transform method. The key advantage of this structure is that it removes phase shifters, which is usually used in existing notch filter with ring resonator structure. So the proposed notch filter has high stability and good reliability. The proposed design method to obtain the structural parameters of the notch filter is not only effective and simple, but also can be used to implement the optical notch filter with arbitrary notch frequency, 3 dB rejection bandwidth and notch point number. One design example of notch filter with two notch frequencies and different 3 dB rejection bandwidth is presented in the paper in detail. The change of the intensity response of the design example is also investigated for each design parameters deviating from ideal value. The results show that the notch frequency and 3 dB rejection bandwidth of each notch point can be tuned independently.