A high efficiency optical combiner minimizes core region distortions in the area where fusion splicing between an input tapered fiber bundle (or any other type of “cladding-less” input fiber) and output fiber are joined. The thickness of the output fiber's glass cladding layer in the splice region is reduced (if not removed altogether) so that a core-to-core splice is formed and any necked-down region where the glass flows to join the core regions (while also joining the outer diameters) is essentially eliminated. The reduction of distortions in the core region of the splice improves the transmission efficiency between an input tapered fiber bundle and output fiber, reaching a level of about 99%. This high efficiency optical combiner is particularly well-suited for applications where a number of pump sources are combined and applied as an input to a fiber laser or amplifier.