Based on the theory of one-dimensional photonic crystal,an asymmetrical interleaver filter composed of thin-film glass cavities is designed.Three thin-film glass cavities are cascaded in the structure.Each cavity is formed by evaporating several layers of reflecting films on two surfaces of the glass medium.Compared with other proposed structures,this interleaver filter is very simple and easy to realize,and it has flat passband and stopband.A design example of a 50 GHz interleaver filter with the duty cycle of 1:5 is presented.The influence of the structural parameters of each reflecting film(including the glass cavity) on the spectral performance is discussed.And the design results with duty cycles of 1:3 and 1:4 are also shown and analyzed.
Based on digital signal processing theory,a novel method of designing optical notch filter is proposed for Mach-Zehnder interferometer with cascaded optical fiber rings coupled structure.The method is simple and effective,and it can be used to implement the designing of the optical notch filter which has arbitrary number of notch points in one free spectrum range(FSR).A design example of notch filter based on cascaded single-fiber-rings is given.On this basis,an improved cascaded double-fiber-rings structure is presented to eliminate the effect of phase shift caused by the single-fiber-ring structure.This new structure can improve the stability and applicability of system.The change of output intensity spectrum is finally investigated for each design parameter and the tuning characteristics of the notch filter are also discussed.
