Silica-Based Planar Lightwave Circuits and Their Applications
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Silica-Based Planar
Lightwave Circuits and Their Applications Yoshinori Hibino
Abstract This article reviews the fabrication technologies and optical characteristics of silicabased planar lightwave circuits (PLCs) on Si developed for photonic networks based on wavelength-division multiplexing (WDM). While there have been various planar optical waveguides made with different materials, silica-based PLCs are the most suitable for constructing practical devices because of their excellent design flexibility, stability, and reproducibility. These advantages mainly result from their material characteristics, that is, silica glass is chemically and physically stable. The article also describes the basic characteristics and recent development of arrayed waveguide grating (AWG) multiplexers/demultiplexers as a device application. Since AWGs offer the advantages of low-loss, high-output port counts and mass producibility, they have played a pivotal role in the construction of flexible, large-capacity WDM networks. Keywords: arrayed waveguide gratings (AWGs), optical communications, photonic materials, planar lightwave circuits (PLCs), waveguides, wavelength-division multiplexing (WDM).
Introduction The recent rapid growth in Internet services has promoted the rapid development of high-speed and broad-band optical networks. Dense wavelength-division multiplexing (DWDM) systems have been widely installed in the backbone networks,1,2 and fiber to the home (FTTH) systems have recently emerged as high-speed access networks.3 These network innovations have been supported by newly developed technologies for constructing not only semiconductor devices such as laser diodes and photodetectors, but also passive optical devices. These passive optical devices are becoming important as multiplexers/ demultiplexers in DWDM systems and optical splitters in FTTH systems. Various passive optical components including micro-optic, fiber, and planar-type elements have been developed for WDMbased photonic networks,4 and some have already been installed in commercial communications networks. Micro-optic devices
MRS BULLETIN/MAY 2003
have a long history, and in terms of optical performance, they have advantages such as low loss and low wavelength dependence.5 However, it is rather difficult to construct a large-scale device because device size and assembly cost generally increase with output port count. Fiber-type optical devices usually have excellent performance with respect to loss and polarization dependence. Planar-type optical devices have the advantages of excellent design flexibility, stability, and mass producibility, although their insertion loss (ratio of input to output power) and polarization dependence are relatively high, compared with other types of devices. Moreover, since it is possible to integrate optical circuits with various functions on a compact planar substrate, optical devices based on planar waveguides have been extensively developed. This article reviews the materials and characteristics for such passive planar opti
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