A high performance tunable optical filter based on cascaded polarization interference filter

A new kind of tunable optical filter is proposed for DWDM optical communication application. It isbased on cascaded polarization interference filter (PIF). The period and bandpass width of each PIF are decided by its optical path difference between o-ray and e-ray (OPDOE). When their OPDOEs areproportionately designed, the tuning range and bandpass width depend on OPDOE in the first and thelast PIF, respectively. The tuning range, bandpass width and crosstalk are independent each other. Thecrosstalk is related to the OPDOE ratios among PIFs and can be suppressed by designing the PIF's OPDOE. A set of OPDOE is suggested that are l1, 2*l1, 2^2*l1, 2^3*l1, 2^4*l1,……, 2^N^-^4*/1,15 x 2^N^-^7 x l1, 10 x 2^N^-^6 x l1 and 2^N^-^2 x l1 from the first to the last. This suggested OPDOEs can yield-50-dB crosstalk for any tuning range and bandpass width. The insert loss is less than 1 dB. As its loosealignment requirement, there is no limitation on cascaded PIF number. When 11 PIFs are cascaded, itcan achieve 170-nm tuning range, -50-dB crosstalk, bandpass width applicable to 25-GHz channel spacingand 1 dB insert loss.