## 4 Optical and Radio Frequency Measurement Analysis
### Optical Measurements Analysis
The dashed lines in the respective colors represent the experimental and theoretical results when the HPLS is OFF, i.e., when the system is not under the effect of Raman optical amplification. For the RF gain (Figure 7a), there is a good match between theory and experiment. The maximum \(\mathrm{G}_{\mathrm{RF}}^{\mathrm{M}}\) for the Raman-based link is 21.3 dB at an input HPLS power of 35 dBm, whereas for the EDFA-based link, the \(\mathrm{G}_{\mathrm{RF}}^{\mathrm{M}}\) is 20.9 dB at an input HPLS power of 36 dBm. Figure 7: Theoretical and measured RF metrics for the 10 km Raman-based and EDFA-based links for 5 GHz: (**a**) RF gain; (**b**) noise figure; (**c**) spurious-free dynamic range. Figure 7b shows the measured and theoretical NF. For the Raman-based link, NFM is 49.1 dB at an input HPLS power of 35 dBm, whereas for the EDFA-based link, NFM is 31 dB at an input HPLS power of 36 dBm. For the Raman-based link, a noticeable increase in the NF occurs between 33 dBm and 35 dBm. This rise is attributed to the noise components \(\mathrm{n}_{\mathrm{T}}^{\mathrm{rim}}\) and \(\mathrm{n}_{\mathrm{T}}^{\mathrm{rim}}\), whose influence becomes more significant at high optical power levels [9]. In the EDFA-based link, the increase in NF is less intense due to the low RIN of the HPLS (\(\mathrm{n}_{\mathrm{T}}^{\mathrm{HPLS}}\)) used in the link [2; 9]. Between NFM and NFT, there is a mismatch of 2 dB for a power of 35 dBm on the Raman-based link. This difference is not observed for noise when Equation (5) is applied to a backward and forward link separately, as is usually the case in the literature [9; 11], and has no influence at low noise levels, as seen for the EDFA-based link, which has a good match between the curves. Figure 7c presents the measured and theoretical SFDRM. For the Raman-based link, the theoretical SFDR is 75.8 dB.Hz\({}^{2/3}\) at an input HPLS power of 35 dBm, whereas for the EDFA-based link, it is 89.4 dB.Hz\({}^{2/3}\) at an input HPLS power of 36 dBm. A discrepancy of approximately 2 dB between SFDRM and SFDRT for the Raman-based link at an input optical power of 35 dBm can be attributed to the mismatch in the NF. As indicated in Equation (6), the SFDR is directly influenced by the NF. Despite a slight mismatch between the experimental and theoretical results at higher power levels, particularly for the Raman-based link, the overall agreement between the observed results was good. To better visualize the noise impact generated by optical Raman amplification on the RoF system, the RF signal spectrum is measured at the LNA2 output for different HPLS power levels over the 10 km fiber length. Figure 8 shows the output RF spectrum for the Raman-based HPLS. An RF output power of \(-\)7.2 dBm was measured for an input HPLS power of 35 dBm, with a signal-to-noise ratio (SNR) of approximately 65 dB. A significant power increase of 37 dB in the noise floor was observed when the maximum HPLS power of 35 dBm was compared with the HPLS power off. Figure 9 shows the measured output RF spectrum for the EDFA-based HPLS, with an RF signal power of \(-\)7.3 dBm and an SNR of approximately 81 dB for an input power of 36 dBm. The difference in noise floor power level between the HPLS off and the HPLS powered at 36 dBm is 20.5 dB. The RoF noise floor output power difference between the two systems is 16.2 dB, considering the highest HPLS power for each PoF system. Although the EDFA-based link requires more power to reach the same RF signal level, the noise generated by the optical amplification is considerably lower. Figure 8: Electrical spectra of the Raman links for different HPLS powers. Table 1 presents the RF metrics and the power provided at the PPC input (\(P_{PPC}\)) as a function of both HPLS and different link lengths, with a focus on the lowest measured \(NF^{M}\). The lowest measured NF for the EDFA-based HPLS case is 31 dB at an input HPLS power of 36 dBm for a fiber length of 10 km. For the Raman-based HPLS, the lowest NF is 41.8 dB at an input HPLS power of 35 dBm and for a fiber length of 5 km.