the drop module is simlar to that of the add mux in technical back ground however..it Drops a WDM channel from a WDM signal.
add drop mux…Equivalent to a subsystem based on the WDM Add and WDM Drop components.
In the drop section, the input signal is divided in two signals. Each signal is filtered by an optical filter. An inverse filter filters the first signal.
In the add section, the input signals are filtered by an optical filter and are combined in one signal. An inverse filter filters the first signal.
The optical filters can be a Rectangle, Gaussian, or Bessel optical filter.
with regards