A side pumped, fiber optic amplifier comprises an optical fiber, having a first refractive index, formed of a laser material, such as Nd:YAG. A jacket, which surrounds the optical fiber, has a second refractive index, lower than the first refractive index. This jacket is cone shaped and tapers from a large end to a small end. High power laser diodes are mounted on the large end to introduce pump light to pump the optical fiber material. The cone-shaped jacket focuses this pump light to an interaction region at the small end, where the jacket material is quite thin, e.g. on the same order of magnitude as the diameter of the optical fiber. The focused light is absorbed by the optical fiber in this interaction region, and causes an electronic population inversion in the laser fiber material. A signal propagating through the optical fiber stimulates spontaneous emission from the optically excited laser material, thereby resulting in amplification of the signal.