# Cladding-Pumped Erbium/Ytterbium Co-Doped Fiber Amplifier for C-Band Operation in Optical Networks
## 4 Conclusions  
The performance of the cladding-pumped EYDFA is characterized using the developed measurement data-based simulation framework. Through the analysis of the amplifier's gain, noise figure, and power penalty, we assess its suitability for operation in metro-access optical transport networks where DWDM techniques are normally deployed. First, we experimentally characterize the double cladding Er\({}^{3+}\)/Yb\({}^{3+}\) co-doped fiber used as a gain medium for our amplifier to come up with the realistic model of the EYDF. Next, we test different EYDFA configurations under different operating conditions (including various doped fiber lengths, pump propagation directions, signal input power, etc.) to reveal parameter settings ensuring the best amplification characteristics, namely, high and uniform gain, and low noise figure. Finally, its power penalty is quantified using \(40\times 10\) Gbps NRZ-OOK signals and the DWDM system configuration with and without the EYDFA. The results show that the amplifier configuration with a 3 W pump source at 975 nm requires a 7 m long EYDF (with the obtained physical parameters) and a co-propagation pumping direction for WDM applications. Considering a reasonably low input signal power (\(\sim\!-20\) dBm/channel), the EYDFA can be used to amplify up to 40 DWDM channels across the C-band, ensuring a maximum output power of +22 dBm, a gain of 19.7-28.3 dB, a noise figure of 3.7-4.2 dB, and a power penalty (with respect to a system without amplification) below 0.1 dB at a BER level of \(10^{-9}\). Finally, the performed  
Figure 7: The worst bit error rate (BER) vs. received optical power detected for Ch1 = 191.6 THz, Ch16 = 193.1 THz, Ch26 = 194.1 THz, and Ch40 = 195.5 THz in a 40-channel WDM system (\(\text{p}_{\text{IN}}=-20\) dBm/channel) with and without the EYDFA where inset (**a**) zooms into the area at BER = \(10^{-9}\) and inset (**b**) shows the eye diagram captured for the configuration with the amplifier at BER \(\cong 10^{-9}\).  
sensitivity analysis for EYDF cross-sections shows how the energy transfer from Yb\({}^{3+}\) to Er\({}^{3+}\) ions impacts the amplifier's gain and noise figure values. Specifically, a \(\pm\)30% change in the cross-sections results in minor gain and noise figure changes--0.7 dB and 0.1 dB, respectively. The revealed characteristics are of importance for assembling and testing an in-house-made cladding-pumped EYDFA.  
Conceptualization, A.S., S.O., A.U., R.M., S.S., V.B.; methodology, A.S., S.O., A.U., U.S., D.P., V.B.; software, S.O., A.U., L.G., R.M., J.G., E.E.; validation, U.S., D.P., L.G., J.G., E.E., O.O.; formal analysis, S.O., U.S., D.P., L.G., O.O., V.B.; investigation, A.S., S.O., A.U., R.M., J.G., E.E., S.S., O.O.; resources, S.S., O.O., V.B.; data curation A.S., S.O., A.U., U.S., D.P., L.G.; writing--original draft preparation, A.S., S.O. and A.U.; writing--review and editing, S.O., A.U., R.M., J.G., S.S., O.O., V.B.; visualization, A.S., S.O., A.U., S.S., J.G.; supervision, S.S., O.O., V.B.; project administration S.S., V.B.; funding acquisition S.S., J.G., V.B. All authors have read and agreed to the published version of the manuscript.  
This work has been supported by the European Regional Development Fund project No. 1.1.1.1/18/A/068.  
Not applicable.  
The Institute of Solid State Physics, University of Latvia as a Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART\({}^{2}\).  
The authors declare no conflict of interest.