Optical fibers that possess the characteristics of both conventional cladded fibers and of a new type of fiber have been drawn and evaluated. The core has an equilateral triangular cross section with slightly bulging curved sides. The rounded vertices are in contact with the inside of the cladding tube of lower refractive index. Most of ther periphery of the core is surrounded by air. The cavity-like waveguide modes of this new type of fiber can be described as due to skew rays being reflected systematically from the glass–to–air interfaces as they propagate along the fiber. Near-field and far-field radiation patterns have been photographed and are presented. A new type of laser based on these cavity-like waveguide modes is proposed, in which the triangular core is made of a material (e.g., neodymium-doped glass, YAG, etc.) that can be optically pumped. The normal mode of operation of the laser consists of six diverging, spatially separated output beams; it can be optically pumped axially from both ends simultaneously, while being pumped from the sides.
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