i am posting this question again the first answer was not helpfull for me... the expert doesnot answer " how is the coupling loss is controlled in an optical fiber network controlled by TIR.

and the part "b" is also not answer clearly for me... please solve it accurately this time

Q#5 A) What is meant by Total Internal Reflection and how is the coupling loss in an optical fiber network controlled by TIR? B) What is meant by modal distortion and what media is greatly affected by it