Tunable optical filters for dense WDM networks

TLDR

Wavelength‑division multiplexing (WDM) dominates point‑to‑point optical links, requiring dynamic devices such as tunable optical filters that combine low loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning, simple control, small size, and cost‑effectiveness. The paper provides an extensive overview of technologies for tunable optical filters. The review discusses fiber Bragg gratings and fiber Fabry‑Perot filters as commercially available but slow devices, micro‑machined and acousto‑optic filters for microsecond tuning, and microresonator, electro‑optic, and active DBR filters for nanosecond tuning.

Abstract

WDM is currently taking over as the leading technology in point-to-point transmission links. For optical implementation of WDM networks, logical functionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, the development of dynamic optical devices is required. One key device is a tunable optical filter. Important features of such a filter include low insertion loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning speed, a simple control mechanism, small size, and cost effectiveness. Here, an extensive overview of the different technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Perot are the most commercialized, yet inherently limited in their dynamic speeds. For high demanding dynamics, micro-machined and acousto-optic filters can offer a good solution for microsecond tuning speeds. Faster tunable devices, in nanosecond tuning speeds, might emerge out of microresonators, electrooptic filters, and active DBR filters.