Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 15

Suppose we have two 2 × 2 waveguide couplers (couplers A and B) that have identical channel geometries and spacings, and are formed on the same substrate material. If the index of refraction of coupler A is larger than that of coupler B, which device has a larger coupling coefficient k What does this imply about the device lengths needed in each case to form a 3-dB coupler