Hi Atul Sharma,
Are you talking about WDM add component.
as we know that WDM Add Adds a WDM channel and a WDM signal.
The input signals are filtered by an optical filter and are combined in one signal. The first signal is filtered by an inverse filter.
The optical filters can be a Rectangle, Gaussian, or Bessel optical filter.
The level of crosstalk for both MUX and DEMUX components, is defined by bandwidth, ripple, and depth of the filter. These 3 factors will determine how much power, from neighboring channels, will act as crosstalk terms when calculating the performance of a specific channel. The most important parameter is depth, as it will play the most significant role in determining the power levels of the neighboring channels.
If we go through wdm subsystem we will see different signals at input gets first filtered and then combined together and then attenuated.