## 4 Optical and Radio Frequency Measurement Analysis  
### Optical Measurements Analysis  
The experiments were carried out using three different fiber lengths: 5 km, 10 km, and 15 km. All the measurements were performed with a fixed TLS optical power of 0 dBm and with the HPLS optical power starting at 30 dBm. * Raman amplification The total Raman gains of the links obtained via Raman-based and EDFA-based HPLS are shown in Figure 2, and they are the sums (in dB) of the forward and backward gains. The forward gains were measured by taking the optical power measured from points F1 and F2, and the backward gains were measured from points B1 and B2 (Figure 1). Figure 2: Experimental Raman gains for 5 km, 10 km, and 15 km SMF-28. The Raman-based HPLS revealed that the measured maximum Raman gains for fiber lengths of 5 km, 10 km, and 15 km were 29.1 dB, 28.5 dB, and 30.9 dB, respectively. For the EDFA-based HPLS, the maximum gains were 21 dB, 29.7 dB, and 31.2 dB, respectively. As expected, theoretically, the Raman gain is greater for longer fibers [4]. Therefore, with long fibers, less input HPLS power is needed to achieve similar optical gain values [5]. However, in both HPLS setups, a limitation is observed in the amount of HPLS optical power that can be transmitted over lengths of 10 km and 15 km. For the link with the Raman-based HPLS, the limits are 35.6 dBm and 34.3 dBm for lengths of 10 km and 15 km, respectively. For the link with the EDFA-based HPLS, the limits are 36.4 dBm and 35.2 dBm, respectively. Increasing the HPLS optical power above these levels causes instabilities in the optical power output of the link, followed by a huge drop in the Raman amplification and the availability of optical power on the PPC at the remote station. These effects are associated with HPLS pump depletion, a phenomenon in which a substantial portion of the optical energy is transferred to the Stokes wave [5; 21]. In the depletion regime, nonlinear interactions between the pump and Stokes waves become more pronounced, potentially causing instabilities. If the HPLS pump fails to sustain a stable energy transfer to the Stokes wave, fluctuations and irregularities may arise. Consequently, this leads to time-dependent variations in both the TLS signal and the entire ASE spectrum, which cannot maintain a constant optical power [5; 21]. As an example, Figure 3 shows the optical spectrum measurements at the output point B2 of the optical fiber shown in Figure 1.  
The spurious peaks observed in both the EDFA-based link (Figure 3a) and the Raman-based link (Figure 3b) degrade the optical and RF performance, causing fluctuations in the Raman optical gain and the RF metrics. For this reason, the limits presented above are used for the different lengths and types of HPLS. * Power over Fiber Analysis  
Considering the Vbias controller and LNA1, the electrical power required to supply electronic devices is approximately 263 mW. An experiment to validate the energy system was carried out with a 5 km Raman-based link. With a 1 \(\times\) 8 optical splitter in the PPC module and an input power limit of 190 mW per PPC, a conversion efficiency of approximately 22% was achieved. As a result, with an HPLS optical power of 35.7 dBm, which guarantees safe operation of PPCs, the PPC module produced a maximum electrical  
Figure 3: Optical spectrum for the measured point B2 for (**a**) 10 km of SMF\(-\)28 for the EDFA\(-\)based link at an input HPLS of 36 dBm and 37 dBm; (**b**) 10 km of SMF\(-\)28 for the Raman-based link at an input HPLS of 35 dBm, 36 dBm and 37 dBm. output of 356 mW. Figure 4 shows the measured electrical power at the output of the PPC module (8_PPCs) for a 5 km fiber length. The DC/DC converter is used to match the voltage and current required by the Vbias controller and the LNA1. Its minimum efficiency is 90%, which results in approximately 320 mW of electrical power. More than enough to keep the system running.