## 3 Results and Discussion
### Transmission Properties Using Green Light as a Function of Fiber Length
A comparison of the graphs reveals that the MH had the flattest frequency responses at all lengths, which is consistent with its reduced NA of 0.3. The GH and the BH fibers displayed similar frequency responses, although the BH fiber responses were clearly better for 15 and 20 m. We argue that the cause of the difference is that the GH responses were measured with overfilled launch, which was made plain by its wider EAF for 1 m (Figure 2). In the overfilled launch, power is injected at high propagation angles, increasing modal dispersion, which degrades the frequency response, particularly for shorter fiber lengths. Finally, the measurements of transmission performance were carried out by analyzing the bit error rate for a simple data transmission, varying the data rate. Results in terms of BER versus data rate in Mb/s are shown in Figure 4 in the same way as in the previous figures. The curves are shown for the same lengths as for the frequency responses, except that the BER for 10 m is shown instead of that for 15 m.  
Figure 3: Normalized frequency response at selected fiber lengths. (**a**) MH fiber, (**b**) GH fiber, and (**c**) BH fiber. For the three fibers, the link worked even for the longest measured length, although in the cases of MH and GH, only at very low bit rates and with a high BER value. When decreasing the fiber length, the curves were pushed to the right, and the link can work at higher bit rates. For a 10-m MH fiber, the link shows no penalty to the back-to-back (B2B) condition. The B2B curve was obtained with a very short fiber segment and describes the system's limitation due to the transmitter and receiver. For the GH and BH fibers, link length has to be shortened to below 5 m to cancel the penalty, consistently with their lower frequency responses. Figure 5 illustrates the evolutions with length of the fiber transmission parameters extracted from the measurements obtained for all fiber types. In all graphs, the data obtained using the LD520 are represented for the MH fiber with blue circles; for GH with green upright triangles; and for the BH with cyan squares. To compare the properties obtained with red and green light, the data obtained for the other GH fibers in the duplex reel using the LD650 are represented with red inverted triangles. Figure 4: BER as function of bit rate in Mb/s at selected fiber lengths. (**a**) MH fiber, (**b**) GH fiber, and (**c**) BH fiber. Figure 5: Transmission parameters as a function of fiber length for the MH, GH and BH fibers: (**a**) optical power; (**b**) 3-dB bandwidth; (**c**) EAF width at 50% and 95% power; (**d**) data rate for BER = \(10^{-6}\). In Figure 5a, received power versus fiber length is shown for the three fibers with the LD520, and for the GH additionally with the LD650. The symbols represent the averages and the error bars the standard deviations of the measurements. The straight lines show the linear fits to the experimental data. Their slopes represent the fiber attenuation at that wavelength and are: 0.09 dB/m for GH and BH, and 0.15 dB/m for MH at 520 nm. The attenuation obtained at 650 nm for GH is 0.15 dB/m, clearly above the value obtained at 520 nm. The attenuations at 650 nm for MH and BH, stated in their characteristics sheets, are 0.16 dB/m and less than 0.2 dB/m, respectively, which confirms the lower attenuation for all fibers at 520 nm. For MH, the difference is less significant than for the higher NA fibers, but data for this fiber have higher variability, as demonstrated by its larger error bars. Figure 5b shows the EAF width for both 50% and 95% encircled power, as a function of fiber length. The graph shows how MH's spatial distribution is the narrowest with an EAF width at 50% power of 16\({}^{\circ}\), consistent with its lower aperture, whereas for the other fibers, this value is slightly above 20\({}^{\circ}\). The differences between GH and BH, and between the red and green results for GH, are not significant.