Preform
From Wikipedia, the free encyclopedia
A preform is material that has undergone preliminary shaping but is not yet in its final form.
Contents |
[edit] Fiber optics
In fiber optics, a preform is a piece of glass used to draw an optical fiber. The preform may consist of several pieces of a glass with different refractive index, to provide the core and cladding of the fiber. The shape of the preform may be circular, although for some applications such as double-clad fibers another form is preferred.[1] In fiber lasers based on double-clad fiber, an asymmetric shape improves the filling factor for laser pumping.
Due to the surface tension, the shape is smoothed during the drawing process, and the shape of the resulting fiber does not reproduce the sharp edges of the preform. Nevertheless, the careful polishing of the preform is important, any defectes of the preform surface affect the optical and mechanical properties of the resulting fiber. In particular, the preform for the test-fiber shown in the figure was not polished well, and the cracks are seen with confocal optical microscope.
[edit] Archeology
In archeology, a preform is the rough, incomplete and unused basic form of a stone tool formed by lithic reduction. Typically, a preform is the shaped remnant of a lithic core. Larger and thicker than the intended tool, it lacks the final trimming and refinement that is present in the completed artifact. Sometimes basic features such as stems and notches have been initiated. In most cases, the term refers to incomplete projectile point.
[edit] See also
[edit] References
- ^ Kouznetsov, D.; Moloney, J.V. (2003). "Highly efficient, high-gain, short-length, and power-scalable incoherent diode slab-pumped fiber amplifier/laser". IEEE Journal of Quantum Electronics 39 (11): 1452–1461. DOI:10.1109/JQE.2003.818311.
