Universal coupling of small core optical fiber to large laser foci

It is often desirable to efficiently couple laser foci that are dimensionally large to dimensionally small optical fibers. A fiber fused in a lower refractive index fiber is disclosed. The fiber/ferrule construct is characterized by having no taper of the fiber in the ferrule and a negative lens shape at a fiber/ferrule face. This construct enable the coupling of imparting rays that fall outside of the fiber core into the transmission path of the fiber. Where the laser systems are integrated in a manner that precludes altering the focusing optic, such as in surgical laser systems, or where the laser's beam focal properties are such that reducing the focal spot diameter is impractical for fiber coupling, modification of the optical fiber input geometry offers a means of customizing the laser-to-fiber interface for applications involving different fiber diameters.