With the roll-out of digital , high definition, and video on demand TV programming, cable TV operators are seeking to expand the capacity of their metro core transmission networks.

In this article, Robin Andrew of BTI Photonic Systems first describes applications of reconfigurable optical add drop multiplexers (ROADMs) at  the metro core and provides a cost analysis.

The meat of the article is in the last section detailing a new class of wavelength division multiplexing (WDM) systems named "Photonic Layer Systems". These are more compact, lower cost systems that connect the metro core to the access network. They have both DWDM and CWDM capability. BTI is a manufacturer of such systems. According to the article:

By combining the economic value of the photonic layer with carrier-grade functionality, an emerging class of photonic-layer products provides a scalable and cost-effective VOD architecture for delivery of GbE connectivity at the network edge. … They also provide the reach required to extend to tier-two cities and markets in a carrier-managed system that integrates with existing architectures and management networks.