step index fiber (fiber optics) (SIF)
The step index fiber( SIF) gets its name from the step-like increase in the refractive index from the core glass to the cladding glass. In this optical fiber, the refractive index is constant within the core and characterized by an abrupt transition at the interface between the core glass and cladding glass. The core glass and cladding glass are made of fused silica.
The step fiber has a high mode dispersion of 50 ns/km to 100 ns/km, which leads to large travel time differences of the light beams and thus to strong pulse broadening. This results in a relatively low transmission bandwidth of about 100 MHz x km.
The step index fiber is hardly used any more, if at all, then for short distances over a few hundred meters. The core diameter of modern step index fibers is between 25 µm and 1,500 µm, the cladding diameter between 125 µm and 1,650 µm. The lowest values for the numerical aperture are around 0.10.
The step index fiber is relatively easy to manufacture, it can be used in a wide temperature range up to 130 °C and above, but it has limited transmission properties.