Non-circular core optical preforms are provided whose core-cladding interface edge has a sharpness that can be accurately controlled according to application-specific needs. Preform design and fiber fabrication is handled such that precisely edged fiber cores are maintained in the drawn fibers. This provides for markedly improved fiber functions, which rely on the non-circular structure of the core. In short, optical fibers having non-circular wave-guiding regions with precise, controlled edges are provided. By using selected manufacturing techniques that employ lower temperatures than commonly used, prior art techniques and by choosing proper materials with appropriate viscosities for core and cladding, the rounding of the edges of the wave-guiding region is precisely maintained in the final optical fibers.