Passive optical devices for photonic networks

This paper reviews the recent progress made by those working on optical filters and switches for photonic networks based on dense wavelength division multiplexing (WDM). While various kinds of optical devices have been developed for flexible and large-capacity networks, the key components for the WDM networks are narrow-band filters and switches. Three kinds of optical filter are described in this paper: thin-film interference filters, fiber grating filters and arrayed-waveguide-grating (AWG) filters. The optical switches reviewed here are mechanical fiber-type switches, thermo-optic switches made using planar-lightwave-circuit technologies, total-internal-reflection switches and micro-electromechanical-system switches. Each device has its own advantages, and has been or will be used in point-to-point WDM, optical add/drop multiplexing systems and optical crossconnect systems. Further advances in optical components and technologies are expected to contribute greatly to the construction of future photonic networks.