Some embodiments of the present invention provide a waveguide apparatus for transferring light to a weld area. The waveguide apparatus can include a waveguide comprising a material having a first index of refraction and having at least one wall defining at least one cavity. The assembly can also include a filler material positioned within the at least one cavity and having a second index of refraction less than the first index of refraction. Also, some embodiments of the present invention provide a laser welding assembly in which a waveguide apparatus is used to weld materials, a method of laser welding materials using a waveguide, and a method of manufacturing such a waveguide.