capable of a high degree of functional integration. For ROADMs of today and the
near future, such integration is provided by PLC (Chapter 9 in Volume A), MEMS
(Chapter 19 in Volume A), and LC tech nologies [28]. The PLCs of greatest
interest for ROADMs are made up of index-guided waveguides fabricated on
silica or related glassy materials. Passive devices such as fixed waveguide
DMUXs and power splitters built from PLCs offer excellent accuracy, reliability,
and fiber coupling. Tuning and switching functions are typically integrated as
thermo-optic elements driven by microheaters integrated onto the PLC. A wave-
length multiplexer with an integrated array of VOAs (often called a VMUX) is an
example of a successful PLC product. In very large-scale