# Design and Analysis of an O+E-Band Hybrid Optical Amplifier for CWDM Systems
## 4 Results and Discussion  
The length of the PDF, doping concentration of Pr\({}^{3+}\), pump wavelength, and injection current were optimized to achieve the optimum performance of the HOA. As mentioned earlier, we used the previously optimized values of the doping concentration of Pr\({}^{3+}\) and PDF length [6; 27], whereas the pump wavelength and injection current were optimized in this study. Figure 3 shows the plots of the pump wavelength versus the amplifier gain and output power by considering the PDF length, Pr\({}^{3+}\) concentration, and SOA injection current of 15.7 m, \(50\times 10^{24}\) m\({}^{-3}\), and 60 mA, respectively, at an input signal power of -15 dBm. It is clear from Figure 3a,b that an average gain and output power of around 24 dB and 9.6 dBm were observed, respectively, over a 1270-1450 nm wavelength range covering the O+E-band for a pump wavelength of 1010 nm, 1030 nm, and 1040 nm. It is evident from Figure 3a,b that the flatness in gain and power was best for a pump wavelength of 1030 nm. Therefore, we use a pump wavelength of 1030 nm for the rest of the results. Figure 4 shows the wavelength versus gain plots as a function of the injection current of the SOA considering a PDF length of 15.7 m, Pr\({}^{3+}\) concentration of \(50\times 10^{24}\) m\({}^{-3}\), and pump wavelength of 1030 nm for an input signal power of \(-15\) dBm. It may appear that the fluctuation in the gain of the HOA was at a minimum for an injection current of 60 mA, particularly in the E-band, compared to 50 mA and 70 mA. Therefore, 60 mA was used as the optimized value of the injection current of the SOA to obtain an overall flat-gain profile for the HOA. Moreover, it can be observed that the gain of the HOA in the E-band increased by increasing the injection current of the SOA. Figure 4: Wavelength versus gain plots as a function of injection current. Figure 3: Wavelength versus (**a**) gain plots as a function of the pump wavelength and (**b**) output power plots as a function of the pump wavelength. To validate the impact of up-conversion on the gain and output power of the HOA, we obtained the wavelength versus gain and output power plots for the HOA by using a PDF length of 15.7 m, Pr\({}^{3+}\) concentration of \(50\times 10^{24}\) m\({}^{-3}\), pump wavelength of 1030 nm, and injection current of 60 mA, respectively. The results are shown in Figure 5 for a signal power of \(-15\) dBm. Figure 5a shows that a penalty of around 4 dB was observed for the gain of the HOA for an O-band wavelength of 1290 nm. Similarly, Figure 5b shows that a penalty of around 1 dB was observed in the output power of the HOA for an O-band wavelength of 1290 nm. These results confirm that up-conversion had a negative impact on the gain and output power of the PDFA owing to the decrement in the population inversion originating when a Pr\({}^{3+}\) ion jumped to an excited manifold, whereas the other was demoted to a low-energy manifold [27; 31]. It is worth mentioning here that up-conversion occurred only in the PDF, which subsequently affected the wavelengths in the O-band only by reducing the gain and output power, whereas the gain and output power remained constant in the E-band because the phenomenon of up-conversion did not happen in the SOAs. We also plotted the wavelength versus the NF as a function of the signal power, as shown in Figure 6a, considering a PDF length of 15.7 m, Pr\({}^{3+}\) concentration of \(50\times 10^{24}\) m\({}^{-3}\), pump wavelength of 1030 nm, pump power of 500 mW, and injection current of 60 mA. The results show that the NF was equal to 4 dB, 4.5 dB, and 5 dB at a signal wavelength of 1270 nm for signal powers of 0 dBm, \(-15\) dBm, and \(-30\) dBm, respectively. The NF increased to around 5.3 dB, 5.8 dB, and 6 dB for a signal wavelength of 1410 nm and signal powers of 0 dBm, \(-15\) dBm, and \(-30\) dBm, respectively. Therefore, it is clear that the NF increased when the power of the signal was low.