Structure design of interleaver based on birefringent-crystals

We put forward an improved structure with three cascaded birefringent plates. This interleaver consists of four parts which are input spectral displacer, wavelength filter, birefringence crystal combination and spectral coupler. We carry on the preliminary design of structures of the four parts and the simulation of three-level crystal filter. Analyze the relationship between the filtering performance and the parameters of crystal plates. From the result of simulation, this kind of interleaver can meet the requirement of de-multiplexing of 25GHz grid and the isolation is significantly improved by increasing the crystal cascade grades, as well as 0.5-dB bandwidth. Finally we can get a relatively flattopped spectra. Besides the isolation can reach to 40-dB and the 0.5-dB bandwidth is 17GHz.