Dear all

I design multi-mode fiber which consists of INF3 CORE & CLADDING to see how the light propagate inside of optical fiber.

My target wavelength is 3.3 um. So, RI of INF3CORE (diameter 100 um) - INF3CLADDING (diameter 192 um) is 1.489 and 1.467, respectively. Calculated NA of fiber is about 0.255 by following equation

So, I set the cone angle of my source (Source Point Object) as 14.774, displacing it in front of INF3 fiber by 0.01 mm to make light propagate with angle smaller than arcsin(0.255).
But a large amount of power get lost at the AIR-CORE interface although Nesting rule and NA are considered.

My Ray trace controls & NSC 3D layout settings are as follows

If I set the cone angle of souce as 2 or 5, coupling efficiency is about 95%. 

Is there any problem on NA of source? I want to get some advice for reducing Fresnel reflection of my fiber. Also, there is my zmx file attached.

Thank you.