Dear Mohammed,

You can get nonlinear coefficient X^(3) by either third harmonic generation or four-wave mixing techique. For third harmonic generation to extract x^(3), you can read a reference below

https://www.researchgate.net/publication/265257947_Wang_XH_West_DP_McKeown_NB_King_TA_close_1998_Determining_the_cubic_susceptibility_chi3_of_films_or_glasses_by_the_Maker_fringe_method_a_representative_study_of_spin-coated_films_of_copper_phthalocyan

For other techniques, there are many references available. Hope it helps.

Xuhua

n2 is around 2.4E-15 cm2/W at 1550 nm.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-16-17-12987&id=170498

All these properties are highly dependent on the deposition technique. Please refer to the wafer production company's data sheet to get a clear idea.

In the following paper there is a nice table. I hope it will be useful.

Article Nonlinear silicon nitride waveguides based on a PECVD deposi...