Flat-top / distortionless tunable filters based on liquid crystal multi cavities for DWDM applications

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