# Design and Analysis of an O+E-Band Hybrid Optical Amplifier for CWDM Systems
## 3 Proposed Design of Hybrid Optical Amplifier  
Figure 2a shows the schematic of the proposed design of an HOA for O+E-band amplification based on a parallel combination of a PDFA and an SOA. Figure 2b illustrates the implementation of the proposed HOA in a typical eight-channel CWDM transmission link. The HOA consists of a wavelength division multiplexer (WDM) used to combine the O- and E-band signals, a reflective-type WFBG filter used to separate the O- and E-band wavelengths for amplification, a laser diode pump, and two optical isolators used to block any light reflected back into the system. The O- and E-band wavelengths are combined using a WDM coupler and then applied to the WFBG, whose center wavelength is adjusted to 1310 nm. The WFBG reflects all E-band signals and transmits all O-band signals, as shown in Figure 2. The O-band signal is coupled with a pump laser with a wavelength and power of 1030 nm and 500 mW, respectively, and injected into the PDF. Similarly, the E-band signal is applied to the input of the SOA for amplification. The injection current of the SOA is adjusted such that the gain fluctuation in the E-band is minimum. The injection current used to drive the SOA in this work is 60 mA. The O- and E-band signals are combined after amplification using an optical coupler. A two-port WDM analyzer, an optical power meter (OPM), and an optical spectrum analyzer (OSA) are employed in the simulation for the observation and analysis of the results. Figure 2b shows eight CW lasers centered at wavelengths of \(\lambda_{1}=1270\) nm, \(\lambda_{2}=1290\) nm, \(\lambda_{3}=1310\) nm, \(\lambda_{4}=1370\) nm, \(\lambda_{5}=1390\) nm, \(\lambda_{6}=1410\) nm, \(\lambda_{7}=1430\) nm, and \(\lambda_{8}=1450\) nm, each modulated by non-return-to-zero (NRZ) data at a rate of 10 Gbps. A pseudo-random bit-sequence generator (PRBS) inputs the logical data to the NRZ generator that converts the data into an electrical signal. After modulation with a Mach-Zehnder modulator (MZM), the resultant optical signals are multiplexed (MUX) and transmitted over a standard SMF of 60 km. The combined 80 Gbps CWDM signal is amplified using the proposed O+E-band HOA. At the receiving end, the optical CWDM signal is demultiplexed (DEMUX). Each of the outputs of the DEMUX is photodetected using a PIN photodiode, low-pass filtered (LPF) to remove the band noise and harmonics, and given to bit-error rate (BER) estimators. Table 3 shows the values of the important parameters used in our study. \begin{table}
\begin{tabular}{l l} \hline \hline
**Symbol** & **Description** \\ \hline \(\sigma_{ap}\), \(\sigma_{ep}\) & Pump absorption and emission cross-sections \\ \(\sigma_{ns}\), \(\sigma_{es}\) & Signal absorption and emission cross-sections \\ \(\sigma_{al}\), \(\sigma_{el}\) & Pump and signal absorption and emission cross-sections for length \(l\) \\ \(\Phi_{p}\) & Quantum efficiency of pump \\ \(\Upsilon\) & Lifetime of the metastable state \\ \(L\) & PDF length \\ \(A\) & Effective area of fiber core \\ \(\alpha\) & Effective loss coefficient \\ \(\Gamma\) & Optical confinement factor \\ \(R(n)\) & Recombinition rate \\ \(I\), \(I_{sp}\) & Intensities of signal and spontaneous emission \\ \(e\) & Electron charge \\ \(E\) & Photon energy \\ \(\beta\) & Spontaneous emission coefficient \\ \(V\) & Active volume \\ \(c\) & Light velocity \\ \(N_{m}\) & Material index \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._Figure 2: Schematic of (**a**) the proposed HOA and (**b**) the system-level integration of the HOA in an eight-channel CWDM transmission system.