Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 9

A GaAs optical source that has a refractive index of 3.600 is closely coupled to a step-index fiber that has a core refractive index of 1.465. If the source size is smaller than the fiber core, and the small gap between the source and the fiber is filled with a gel that has a refractive index of 1.305, what is the power loss in deci­bels from the source into the fiber