A microstructured optical fiber has periodically arranged high-index rods embedded in a low-index background, a high-index ring surrounding the high-index rods, and a high-index core located at the center. The high-index rods and the low-index background forms a microstructured cladding region which supports the guidance of supermodes. The fundamental and the highest supermodes form a cladding-mode band, wherein at least the effective index of a core mode lies in the cladding-mode band. Also provided is

a technique for selectively filtering the fiber modes, to selectively filter out one or some of the high-order modes with the other modes still guided in the core with low loss. The cascade of optical fibers can filter out a group of fiber modes, marking guidance of a single high-order mode in a few-mode optical fiber possible.

A method of drawing a material into sheet form includes forming a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is much greater than a second transverse dimension substantially perpendicular to the first transverse dimension. A furnace having substantially linearly opposed heating elements one spaced from the other is provided and the heating elements are energized to apply heat to the preform to create a negative thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a central plane of the preform. The preform is drawn in such a manner that the material substantially maintains its first transverse dimension and deforms across its second transverse dimension.