Passive muxes, as the name implies, are unpowered, unmonitored devices
Sometimes called filters (more technically accurate) or prisms (more conceptual)
Passive muxes allow you to take one fiber pair and break it out into channelized ports allowing for many channelized optics to be used on on pair of fiber
Types of Passive Filters
Fiber Bragg Grating
Thin Film Filter
Arrayed Waveguide Grating
CWDM Example
Example diagram:
Add/Drop Design Example
Example diagram
In this example each location on the add/drop path has two circuits - one east and one west (color coded)
Each lateral is folded, so keep in mind that
A fiber cut on a lateral would take down the location served by the lateral AND all other locations served on the add/drop path would see one of their two paths go down
