| IMO, the trend clearly favors a single fiber model down the road, due to economies that mass production and technological improvements will enable. A trend that exemplifies this, although one that supports less capacity at this time, and simpler in nature, can be seen in the evolving fiber to the home (ftth) model, where a simple wdm scheme is enabling the use of a single strand to support multiple applications in both directions, simultaneously. But ftth doesn't demand the same level of mission-critical treatment that many commercial applications do. To partially mitigate the risk of a catastrophic failure in a neighborhood, passive optical network (PON) fiber rings are used in some designs (I suspect that the rings are two strand), with the section that feeds the home fed by a single fiber from the field node (which is a node <similar to the situation of an ADM on a SONET ring, only passive in nature> on the ring). Again, it's a matter of tradeoffs, and tracking the trajectories of price and performance demands. |
