Recent advances in high-density and large-scale AWG multi/demultiplexers with higher index-contrast silica-based PLCs

This paper reviews recent progress on high-density and large-scale arrayed-waveguide-grating (AWG) multi/demultiplexers, which have been developed for wavelength division multiplexing (WDM)-based photonic networks. The AWG has been the key to the construction of flexible and large-capacity WDM networks. This is because, compared with conventional filters consisting of thin-film interference filters and microoptics, the AWG offers the advantages of low loss, high port counts, and mass productivity. To improve such characteristics further, low-loss, higher index-contrast (super-high /spl Delta/) planar lightwave circuits (PLCs) with a bending radius of 2 mm have recently been developed. It has been shown that these PLCs are effective for use in constructing a compact AWG module with 1/5 the volume of a conventional module and large-scale AWGs with 256 and 400 channels. Three techniques for low-loss fiber connection with spot-size converters have also been developed for the super-high /spl Delta/ PLCs, and it has been confirmed that these techniques can be applied to the fabrication of AWG modules. Furthermore, two-stage tandem AWG-type multi/demultiplexers with more than 1000 channels have been demonstrated. This paper describes the progress that has been made on these high-density and large-scale AWGs, which are expected to contribute greatly to the construction of future photonic networks including optical add/drop multiplexing systems and optical crossconnect systems.

I. Introduction

The EXPLOSION in demand for Internet services is promoting the rapid development of high-speed and broad-and optical networks such as fiber to the home (FTTH) and dense wavelength division multiplexing (DWDM) systems [1], [2]. Such networks require a variety of optical components including microoptics-, fiber-,and planar-type elements [3]. Planar lightwave circuits (PLC) fabricated using silica-based waveguides are employed in various devices because of their excellent design flexibility, stability, and mass-producibility [4]. Of the PLC-type devices, arrayed waveguide gratings (AWGs) are superior to other types of wavelength multi/demultiplexers, such as dielectric multilayered filters, in terms of compactness and multichanneling [5]. This is because multiple-interference makes it possible to form an AWG in a single device regardless of its channel count. So, 16- to 64-channel AWGs have already been marketed and are widely used as multi/demultiplexers in DWDM systems employed in core networks in such areas as North America and Japan.