# Analysis of Available Components and Performance Estimation of Optical Multi-Band Systems
## 4 Discussion  
Our analysis revealed that the transceivers based on the application can be decoupled into two categories, the long-reach applications and access/intra-data center applications. In the first category, there are available transceivers for 100 G to 800 G line rates. However, in order to increase the line rate per channel, we can either consume more optical bandwidth, which will result in a lower number of channels, or migrate to a higher modulation format, which will require a higher OSNIR to attain the same BER, limiting the optical reach. The most suitable solution depends solely on the high-level objective set by the network operator. Furthermore, from the category of the SFP transceivers, there are various commercially available solutions mainly for O and C-bands, as these bands are the main bands for access and short-reach transmission. Finally, the most desirable characteristics \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Bands** & **PM-QPSK** & **PM-16 QAM** & **PM-64 QAM** \\ \hline \multirow{2}{*}{S\({}_{1}\) band} & L = 2250 km & L = 450 km & L = 150 km \\  & C = 9.2 Tb/s & C = 18.4 Tb/s & C = 27.6 Tb/s \\ \hline \multirow{2}{*}{S\({}_{2}\) band} & L = 2250 km & L = 750 km & L = 150 km \\  & C = 8.9 Tb/s & C = 17.8 Tb/s & C = 267 Tb/s \\ \hline \multirow{2}{*}{C band} & L = 2250 km & L = 750 km & L = 150 km \\  & C = 11.6 Tb/s & C = 23.2 Tb/s & C = 34.8 Tb/s \\ \hline \multirow{2}{*}{L band} & L = 2250 km & L = 750 km & L = 150 km \\  & C = 14.1 Tb/s & C = 28.2 Tb/s & C = 42.3 Tb/s \\ \hline Total (C \(\times\) L) & 98.55 (Pb/s)-km & 60.18 (Pb/s)-km & 19.71 (Pb/s)-km \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Attainable reach and capacity per band when PM-QPSK, PM-16 QAM, and PM-64 QAM are considered. Figure 4: OSNIR for different wavelengths when S, C, and L-bands are employed. for optical transceivers are the high output power and the low receiver sensitivity, as both can lead to a longer transmission length and/or number of supported users. Based on our study, the commercially available technology of band filters seems to be mature. By placing a number of these filters, e.g., in tandem, we can obtain a filter that can multiplex/demultiplex the desirable bands. The most important characteristics of a band filter are (a) the wavelength range, in order to exploit optimally the low-loss spectrum of the SMF, (b) the insertion loss, which has to be as low as possible to minimize the total losses, (c) the isolation, to be as high as possible, in order to avoid crosstalk, and (d) the return loss, which has to be kept in a high level to avoid the filter reflections. Next, the amplification technology is mature in S, C, and L-bands, as there, the majority of the optical amplifiers exists. On the other hand, the technology at both the component and system level has to be developed further in O and E-bands in order to exploit the whole extent of the low-attenuation spectrum of the fiber. Our study revealed that SOAs can be employed to attain a wider amplification range; however, they suffer from low gain per channel, low gain flatness, transient effects, and the high noise figure. Furthermore, using Raman amplifiers, we can obtain the desirable gain profiles, which can tune the desirable output power in a channel basis. One significant disadvantage of Raman amplification is the low attainable gain, which compared with DFAs may require a larger number of amplifiers to restore the power of the optical channel. Finally, the rare earth amplification is designated as the winning amplification technology, as it (a) is a well-known technology due to the extensive use of EDFAs in the C-band, (b) allows for a modular engineering, allowing to introduce amplifiers on an as-needed basis, and (c) provides the desirable characteristics such as low noise figure, gain flatness, and high output power.