Passive Germanium-Doped Preform is a fiber preform designed and developed specifically for a range of specialty optical fibers. Produced using an in-tube chemical vapor deposition process, this preform exhibits excellent optical and geometric uniformity, low hydroxyl content, and high numerical aperture. This preform can be customdesigned to meet user requirements for numerical aperture, mode field diameter, cutoff wavelength, and bend sensitivity. It is widely used in fiber optic sensing, fiber lasers, and other fields.