Hi Soibam,
By default, the transmission curves show codirectional coupling, while contradirectional coupling will be shown in the reflection curves.
If you’re only seeing codirectional coupling, it’s probably because the default grating period is set to that of long-period grating, which only couples codirectionally. If you want contradirectional coupling, you need to change the grating period to that of a short-period grating.
To test this, you can select a shorter default grating period by opening the Grating Manager dialog box, double clicking on the grating, and selecting a shorter period under the Period parameter in the Grating Definition dialog box.
Amine