However, it has some mismatch: slides 15 and 16 in Lecture 14 do contain this information. Sure, I understand that the higher delta-n, the wider the resonance. Actually, I need not theory but the result (numerical or simple formula).
I am assuming that is a thick grating. You may refer to coupled wave theory (CWT). Eq. ~58-59 in reference: Kogelnik, Herwig. "Coupled wave theory for thick hologram gratings." Bell System Technical Journal 48.9 (1969): 2909-2947.
Thank you for your answer. We are just performing the calculation with Kogelnik expressions using different parameters to obtain the needing spectrum selectivity. However, it seems I have seen a paper with the direct dependence of spectral selectivity width from the grating modulation (numerical or simple formula).
As I mentioned, we made the calculation spectral (and also angular) selectivity using different parameters to obtain the needing value. The result is in our paper: https://www.researchgate.net/publication/318205293_Optical_elements_containing_semitransparent_wavelike_films?_iepl%5BviewId%5D=rEhlMlmNFLe1oUJ0q7VT6mKkvyAtmrySdHoN&_iepl%5Bcontexts%5D%5B0%5D=prfhpi&_iepl%5Bdata%5D%5BstandardItemCount%5D=2&_iepl%5Bdata%5D%5BuserSelectedItemCount%5D=0&_iepl%5Bdata%5D%5BtopHighlightCount%5D=1&_iepl%5Bdata%5D%5BtopHighlightIndex%5D=1&_iepl%5Bdata%5D%5BfeaturedItem1of1%5D=1&_iepl%5BtargetEntityId%5D=PB%3A318205293&_iepl%5BinteractionType%5D=publicationTitle