Tiny glass balls are often used as lenses to couple light into and out of optical fibers. The fiber end is located at a distance f from the sphere. For a sphere of radius a - mm and refractive index n-1.8, determine f such that a ray parallel to the optical axis at a distance y 0.7 mm is focused onto the fiber, as illustrated in Fig. P1.2-4.

2a- y Fiber Lens