# Design and Analysis of an O+E-Band Hybrid Optical Amplifier for CWDM Systems
## 4 Results and Discussion
The reason behind this trend is that the optical signal-to-noise ratio (OSNR) was reduced when the signal power was weak, which, in turn, increased the NF of the HOA [6]. We also plotted the signal wavelength versus the ASE as a function of the signal power in Figure 6b by 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. It can be observed from the spectral plot in Figure 6b that the average ASEs over a 1270-1450 nm wavelength range were around \(-39\) dBm, \(-33.7\) dBm, and \(-28\) dBm for signal powers of \(-30\) dBm, \(-15\) dBm, and \(0\) dBm, respectively. Moreover, it is also evident that the ASE increased by increasing the signal power. The reason behind this trend is that by increasing the signal power, the photon population due to spontaneous emission relatively increased, which consequently resulted in an increase in the ASE [6]. Figure 5: Wavelength versus (**a**) gain plots considering the up-conversion effect and (**b**) output power plots considering the up-conversion effect. To observe the performance of the proposed O+E-band HOA in a transmission link, we employed it in a CWDM system and measured the BER of the signals transmitted over the link. The BER was computed by observing the statistical distribution of the eye diagrams of the received signals obtained after the low-pass filter (LPF) shown in Figure 2b. The optical power received for each channel at the PIN photodetectors was varied by using optical attenuators to observe the impact on the BER values. The minimum detected optical power necessary to obtain a BER of \(10^{-9}\) is called the receiver sensitivity [32]. Figure 7 shows the BER versus the received optical power plots for channels \(2,3,5,6\), and \(7\), where each channel had a data rate of \(10\) Gbps. We have chosen a limited number of channels to make the results easy to visualize. It is clear that the receiver sensitivities of channels \(5\), \(6\), and \(7\) were around \(-21\) dBm, which is the minimum among all the channels, whereas the receiver sensitivity of channel \(3\) was around \(-18\) dBm, which was the maximum we obtained. The receiver sensitivity of channel \(2\) was equal to \(-19\) dBm. The reason behind this variation in the receiver sensitivities of the different channels is the variation in the gain for the different signal wavelengths, as shown in Figure 3a. In telecommunication systems, an eye diagram is obtained by overlapping the bit periods of the signal over each other on the oscilloscope to obtain a plot of the signal amplitude with respect to time [33]. Since the shape of the resulting plot is similar to an eye, therefore, the name eye diagram is generally used [33]. Eye diagrams instantly provide visual information to a telecommunication system designer to check the received signal quality and predict the system BER [33]. There are two types of noise that can impact system performance, which are amplitude noise and timing jitter. Therefore, the eye  
Figure 6: Wavelength versus (**a**) NF plots as a function of signal power and (**b**) ASE plots as a function of signal power. Figure 7: BER versus detected optical power plots of different channels. diagram is another important alternative to BER measurements, which readily measure the extent of the amplitude noise and timing jitter in received signals. To further evaluate the performance of the channels, the eye diagrams of channels 2, 3, 5, and 7 were obtained at the output of the LPF by considering data rates of 5 Gbps, 7.5 Gbps, and 10 Gbps, as shown in Figure 8. As the data rate increased, the opening of the eye diagrams of channels 2, 3, 5, and 7 decreased due to the intensity fluctuation, timing jitter, and intersymbol interference (ISI). However, the eye diagrams of the channels had enough openings for the easy detection of ones and zeros [2].