# Analysis of Available Components and Performance Estimation of Optical Multi-Band Systems
## 2 Review of Commercially Available Components
### Amplifiers  
Optical amplification is a critical procedure in optical transmission as it can rectify the signal power attenuated within the optical fiber. There are numerous commercially available optical amplifiers that can be exploited for an OMB system, the most indicative of which are illustrated in Table 3. In particular, the Doped Fiber Amplifier (DFA) is a family of amplification components that shows desirable characteristics for an OMB system, such as the sufficient flat gain over a large spectral extent, the low noise figure, and the high output power. In Figure 1, we illustrate the attainable gain and the noise figure of indicative commercially available amplifiers for the O, S, C, and L-bands, while for the E-band, the experimental neodymium (N) DFA of [13] is considered. Another considerable DFA solution for the E-band can be the bismuth (B) DFA of [14]. As it is evident from Figure 1, the amplification technology for the S, C, and L-bands is more mature compared with the O and E-bands, as it can provide a higher overall gain and a lower noise figure \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type** & **Band** & **Line Rate** & **Distance** & **Output Power** & **Sensitivity** \\ \hline CFP8 Transceiver & O & 400 Gb/s & \(<\)2 km & N/A & N/A \\ CFP4/CFP2 Transceiver & O & 100 Gb/s & \(<\)10 km & N/A & N/A \\
200 G and 400 G & & & & & \\ Coherent Transceiver & C & 400 Gb/s & N/A & \(>\)\(-\)10 dBm & \(-\)30/\(>\)\(-\)20 dBm \\ CFP2-DCO & & & & & \\
100 G Coherent & C & 100 Gb/s & N/A & \(>\)\(-\)5 dBm & \(>\)\(-\)28 dBm \\ Transceiver CFP-DCO & & & & & \\
400 G QSFP-DCO & C & 400 Gb/s & \(<\)120 km & \(-\)10 dBm & \(>\)\(-\)12 dBm \\ Coherent Transceiver & C & 400 Gb/s & \(<\)120 km & \(-\)10 dBm & \(>\)\(-\)12 dBm \\
400 G Transceiver & C & 400 Gb/s & \(<\)120 km & \(-\)10 dBm & \(>\)\(-\)12 dBm \\ DD-QSFP-DCO & & & & & \\
16G-CWDM SFP+ & & & & & \\ Transceiver & & & & & \\ XFP Transceiver & O & 10 Gb/s & \(<\)40 km & \(>\)\(-\)5 dBm & \(-\)16 dBm \\ SFP Transceiver & O, S & 1 Gb/s & \(<\)40 km & \(>\)\(-\)6 dBm & \(-\)23 dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Commercially available transceivers for data center interconnection and access applications. compared with praseodymium (P) DFA and NDFA. These are important drawbacks for the exploitation of the lower bands, as a network operator may resort to a higher number of PDFAs and NDFAs to restore the optical power compared with thulium (T) and erbium (E) DFAs, which will directly lead to higher CapEx and OpEx costs. Furthermore, due to the increased noise figure, the overall physical layer performance of the channels in the O and E-band is expected to be lower compared with channels in the S, C, and L-bands. The second family of optical amplification components is the semiconductor optical amplifier (SOA). SOAs can be exploited in all bands, as shown in Table 3; however, they show some important drawbacks compared with the DFA family, such as the low saturated output power, the poor gain flatness, the significant transient effects, and the high-noise figure. On the other hand, SOAs are more compact and cheaper than EDFAs and a single SOA, as in [15], can restore the power of channels that are extended over 100 nm. Finally, SOAs as well as ytterbium (Y) DFAs can be exploited to unlock the beyond 1 \(\upmu\)m spectral range of transmission. The third category is the Raman amplification. This category can be exploited in all low attenuation bands similarly to SOAs. Raman-type amplifiers can achieve a sufficient flat gain activating several high-power pumps. An advantage of Raman amplifiers is that they can create arbitrary gain profiles at will, using machine learning methods, which can generate the desirable output power even in a channel basis. In this way, the gain can be tailored to each band to ensure an optimal physical layer performance in all bands of an OMB system concurrently [16].