Advancements in thin film filters for telecommunications applications

Abstract

This presentation will discuss advancements in thin-film filter technology for telecommunications applications in the following key topic areas: Narrow Band Channel Spacing: Several years ago, it was thought by industry analysts that thin-film filter technology would not be practical for channel spacings below 100 GHz due to loss and center wavelength stability requirements. Thin-film solutions for 50 GHz and 25 GHz channel spacings have been demonstrated with state of the art low-loss thin-film fabrication and new packaging strategies. Chromatic dispersion and dispersion power penalty for narrow band filters will also be discussed. Wide band filters with fewer dropped channels and near theoretical performance: Optical Add-Drop Multiplexing (OADM) is a key application for wide-band thin-film filters. Application requirements call for a minimization of the number of dropped channels with very steep filter sidewalls. The reflection notch function must have very deep isolation to minimize coherent cross-talk effects. This class of filter requires advancements in total film thickness, accurate layer thickness control, and center wavelength temperature control. High angle of incidence filters: Filter designs that use fixed angle of incidence in the 8 degree to 15 degree range are enjoying resurgence in popularity especially for CWDM applications. Wavelength tunable optical add/drop filters using angle-tuning methods are also emerging as an important application. Special designs have been created to optimize performance in these applications.