According to the different core skin refractive index distribution, plastic Optical fiber can be divided into step index (SI) distributed plastic optical fiber (si-pof) and graded index (GI) distributed plastic optical fiber (GI-POF).

Si-pof has obvious core skin interface. The refractive index of plastic optical fiber changes suddenly at the core skin interface, that is, the refractive index of core material of plastic optical fiber within the core diameter is N1, and the refractive index of cortex with sudden change in cortex is N2, and N1 > N2. The incident light is totally reflected at the core skin interface, and the transmission of light in the fiber core depends on this total reflection to move forward in a sawtooth shape. Due to the different incident angles of the incident light, the time of each mode light reaching the receiver is different, and the pulse broadening phenomenon occurs. Under the condition of limited broadening, the incident angle of the incident light transmitted by si-pof is limited, resulting in the limited bandwidth. The refractive index of GI-POF decreases gradually from the axis center to the edge, and changes in a parabola along the radial direction. Because the refractive index of GI-POF is no longer a constant, the transmission speed of each mode light is different, and their arrival time at the receiver is almost the same, and the output pulse broadening is not large, so the bandwidth of GI-POF is much larger than that of si-pof.