Mainly by the core, cladding, and coating layer; the core is made of a highly transparent material; slightly less than the refractive index of the cladding of the fiber [1] of the core, resulting in an optical waveguide effect, so that the majority of The electromagnetic field is bound in the core transmission; the role of the coating layer is to protect the optical fiber from corrosion and mechanical abrasion moisture, while increasing the flexibility of the optical fiber. In the outer coating layer, often added plastic jacket. According to the raw materials of the same below the fiber, the fiber can be divided into the following types: (1) silica-based optical fiber (2) multi-component glass fiber (3) plastic clad fiber (4) all plastic optical fiber according to the fiber cross-section of refraction Distributions in the case of classification, can be divided into step-index optical fiber type and graded index (also known as gradient index type). For step-index optical fiber, the refractive index in the core distribution is uniform, mutations occur at the interface between the refractive index of the core and cladding; and for a graded-index optical fiber, the refractive index changes continuously in the core. n1> n2 (refractive index n1 n2 core refractive index cladding) is a necessary condition for fiber optic guided lightwave transmission in the core, for step-index fiber is concerned, it can make waves in the core and cladding cross total reflection at the interface is formed, the forward guide wave propagation along the core; for a graded-index optical fiber is concerned, it can produce a continuous wave refracted through the fiber axis formed like a sine wave of light rays in the core, the light wave guide forward propagation along the core. According to the optical fiber transmission mode quantitative classification, fiber can be divided into multi-mode fiber and single-mode fiber. Under certain operating wavelength. Multi-mode fiber is capable of transmitting dielectric waveguides many patterns and single-mode fiber transmission only the fundamental mode. Multimode step-index profile optical fiber may be employed, graded-index profile can also be used; use of a step index singlemode fiber profile. Therefore, in general may be used quartz fiber multimode step-index fiber, multimode graded index fiber and single step-index fiber three.