Pure silica core energy transfer preforms are made by melting and shrinking high-purity synthetic silica and fluorine-doped quartz tubes. They feature a step-index refractive index profile, offering excellent optical uniformity,geometric uniformity, and high numerical aperture. This series of preforms can be custom designed to meet user requirements for core ratio and numerical aperture. They are widely used in specialty fiber applications, such as energy transmission fibersfor industrial lasers and medical fibers.