## 3 Results and Discussion
### Transmission Properties Using Green Light as a Function of Fiber Length
Notice that the width increase was quite smooth for the measurements obtained for GH and BH, but had an irregular trend for MH that we attribute to the effect of end polishing over its double-cladding structure. Figure 5c,d shows the 3-dB bandwidth and the data rate for a BER of 10\({}^{-6}\) as functions of fiber length, respectively. Both graphs illustrate how the MH fiber presents superior performance with the highest bandwidths and bit rates for all fiber lengths, consistently with its reduced modal dispersion due to its lower NA. In fact, this fiber can support Gigabit data rates at up to 50 m. However, error-rates below 10\({}^{-6}\) cannot be obtained with this fiber above 100 m, because of the low received power due to its higher attenuation. For all fibers, the maximum data rates with BER of 10\({}^{-6}\) are higher than 100 Mb/s at 100 m, and the maximum is exactly this bit rate for the GH fiber at 130 m, confirming that standard POFs are suitable for industrial and avionics data networks. In addition, even the high-aperture fibers are able to sustain 1 Gb/s for links of 30 m or less, and thus, to meet the typical requirements for domestic and automotive applications. Moreover, these bit rates could be raised by introducing modulation formats to increase spectral efficiency and forward error correction (FEC) techniques to permit BER values of up to 10\({}^{-3}\), whereas the link reach could be pushed farther using receivers with higher responsivity at 520 nm. Although previous results showed that the performance for the standard GH fiber was significantly better than for the heat-resistant BH [22], here we found only small differences between GH and BH, even with slight superiority of BH that we attribute to their different launching conditions, which was illustrated before by the differences between their 1-m EAFs. Another possible reason is that, in this work, we tested a recently acquired spool of BH fiber with improved characteristics. In addition, the duplex reel configuration can also affect the fiber properties, as it is necessary to split a segment at both ends, which can introduce additional disturbances in the power distribution of the GH fiber. The lower graphs (see Figure 5c,d) show that there were small differences in the frequency domain performances obtained for red and green light with the GH fiber. From 50 m downwards, the fiber bandwidths obtained at 650 nm were always higher than those obtained at 520 nm, with the differences increasing for shorter fiber lengths. For 15 m, bandwidths of 729 and 1390 MHz were obtained for green and red light, respectively. Moreover, the maximum data rate was also higher with red light below 70 m, although the red link did not work above 85 m due to the low received power. From these results, we cannot discard that the causes of the differences between red and green were their diverse launching conditions and high variability, increased by the fiber duplex configuration. Therefore, we carried out the control experiment previously described to determine if there are significant differences between the frequency responses for 650 nm and 520 nm measured under the same conditions. The results are shown in the next subsection.