The D12C Custom Dual 1x2 optical switch is two S12 Single 1x2 switches in one switch with an extra path in state 1. See Switch Overview for detailed information common to all Luminos switching products.
The following diagrams show the optical connections for the 2 states. The numbers identify the fiber endpoints. If looking at it as 2 single 1x2s, fibers 1, 6 and 5 make up one single 1x2 while fibers 4, 2, and 3 make up the other.
This optical switch is labeled custom because of the extra path between 5 and 2 in state 1. In many applications, this extra path has no effect and in some cases can be used for monitoring.
An example of how a device can monitor itself on the secondary part of a D12C in state 1.