Flat-Top/Distortionless tunable filters based on liquid crystal multi cavities for DWDM applications

Tunable filters are one of the essential components in the DWDM systems. In this paper two types of tunable filters are discussed. First the multi cavities coupled Fabry-Perot band pass filters using liquid crystal are investigated to achieve tunable flat top filtering performance across the C and L bands with a ripple less than 0.01 dB, and wide overall tuning range of 172 mn. Several designs are shown with comparable performance to the commercial fixed single channel filters. The second one is the tunable liquid crystal optical interleaver filter based on the combined Michelson interferometer (NW and the Gires-Tournois interferometer (GTI). Liquid crystal is used to achieve the center wavelength shift of the interleaver filter with less than 0.1 dB ripples in the pass band.