If I have a laser beam of width larger than the core of the single mode fiber, and I use a lens to focus the light such that the entrance of the fiber sits at the focal point of the lens, does the fiber emit light in a cone of light with equal incident and exit angles?
Lets say I've been careful to choose my lens such that the incoming cone of laser light has a narrower angle than the maximum angle of acceptance, then is the angular/spatial structure of my light field preserved?