# The Multiband over Spatial Division Multiplexing Sliceable Transceiver for Future Optical Networks
## 6 Experimental Assessment
### MB Transmission Assessment  
In a first use case, MB transmission is assessed considering the experimental setup described in Section 5. The signal-noise ratio (SNR) profiles in a B2B configuration are depicted in Figure 7. From the figure, it can be seen that the three slices, working in different bands, present similar performance in terms of SNR per subcarrier. Mainly, the degradation of the higher frequencies, corresponding to the higher subcarrier numbers, is due to the limited bandwidth of the DAC, which is around 13 GHz bandwidth. In particular, the electrical OFDM signal occupies 20 GHz bandwidth, corresponding to 512 subcarriers. Considering a SSMF path of 25 km length, the SNR profiles present different performance per each band, as seen in Figure 8d. The DSB L-band contribution is more affected by CD, showing two attenuation peaks within the signal bandwidth at around 11 GHz (subcarrier 281) and 19 GHz (subcarrier 488). This translates to a CD coefficient of 19.4 ps/(nmkm) at 1600 nm, according to Equation (4):  
\[f_{CD}^{n}=\sqrt{\frac{c(2n-1)/2\lambda^{2}}{LD}}. \tag{4}\]  
\(D\) is the dispersion coefficient parameter, \(c\) the speed of light and \(f_{CD}^{n}\) the \(n\)-th attenuation peak due to CD. The C- and L-band contributions are more resilient against CD, due to SSB modulation showing a flatter SNR profile. However, they present lower SNR values within the lower frequencies/subcarriers due to the setup implementation. In particular, different lasers, filter and amplification technology are used to set up the 3 BVTs conforming the MB S-BVT. BPL is applied to compensate the SNR degradation that specific subcarriers present in order to ensure the transmission at the target BER.  
Figure 7: SNR profile of the S-, C-, and L-band contributions in B2B configuration.  
The received spectra after amplification and applying BPL are depicted in Figure 8. From the DSB L-band spectrum, depicted in Figure 8c, it could be seen that the implemented BPL algorithm has set to 0 the subcarriers with lower SNR. The SSB C-band and L-band spectra, in Figure 8a,b, show 5 dB power attenuation due to fibre transmission over a 25 km path in comparison with the B2B spectra of Figure 6. The achieved performance in terms of maximum data rate is depicted in Figure 9, for different SSMF lengths. In the B2B configuration, an aggregated capacity of 212 Gb/s is achieved ensuring the target BER. After 25 km SSMF, this data rate decreases to 134 Gb/s, and thanks to the implementation of BPL algorithms, the 3 contributions still present similar performance. After 50 km and 75 km path, the aggregated capacity decreases to 107 Gb/s and 73 Gb/s, respectively. Due to setup implementations, the L-band contributions can achieve higher OSNR values. However, the DSB transmission is more affected by CD. This effect can be seen in terms of achieved data rate in Figure 9, where the C-band contributions outperforms L-band contribution after transmission over the fibre with lower OSNR values.  
Regarding the transceiver scalability, the modular architecture of the MB(oS-BVT) S-BVT enables the use of more slices in the different bands, in order to enable higher capacities. Specifically, by considering the full population of the analysed bands with 25 GHz (S+C) and 50 GHz (L-band) channel bandwidths, a total aggregated capacity of 47 Tb/s is envisioned in B2B configuration. This corresponds to 23 Tb/s for the S-band (350 channels), 12 Tb/s for the C-band (175 channels), and 12 Tb/s for the L-band (150 channels).  
Figure 8: OSA captures after applying BPL and after 25 km of SSMF of the (**a**) S-band (**b**) C-band, and (**c**) L-band slices. (**d**) SNR profile of the S-, C-, and L-band contributions after 25 km of SSMF.