Hi Khaled

There are several options:

• The slide surface or object is a transparent object and uses an image to filter light so that could be used both in sequential and non-sequential mode.
• You could use a coating to define the filter.
  Normally, OpticStudio assumes the coating thickness is uniform across the entire optical surface. But there is an option to create a tapered coating. Have a look at the polynomial options under The Libraries Tab > Coatings Group > Defining Coatings > The TAPR Data Section

  

  You can find an example in the default coating file:
   

  

   

• In sequential mode, you can define a user-defined surface and there are examples of surfaces that modifies the transmission. Have a look at the surfaces called us_filt*.dll.
• In non-sequential, it could also be done via dlls.

Let us know if you need further help on any of these options.