# The Multiband over Spatial Division Multiplexing Sliceable Transceiver for Future Optical Networks
## 3 MB(oSDM) S-BVT Architecture and Definition  
The proposed MB(oSDM) S-BVT architecture is depicted in Figure 1 and it is based on multiple bandwidth/bitrate variable transceivers (BVTs) that can be enabled/disabled based on traffic demands, following a modular and adaptable \"pay-as-you-grow\" framework. The envisioned architecture also facilitates MB point-to-point (PtP) and point-to-multipoint (PtMP) connectivity, by incorporating several BVTs designed to operate across various transmission bands, such as C-, L-, S-, O-, U-, and E-bands, as depicted in Figure 1. PtMP operation is achieved by the transceiver architecture's ability to manage multiple BVTs concurrently, enabling multiple network destinations or end-points to be served with a single S-BVT. This capability is especially valuable in scenarios where diverse and evolving communication requirements exist among various network destinations, including variations in path length and data rate requirements [38; 39]. Whether addressing varying transmission distances or accommodating different data rate requirements, the transceiver architecture seamlessly adapts to these diverse needs. This flexibility is key in scenarios where a central node needs to communicate with multiple remote locations, each characterized by unique communication parameters. In this context, the advantage of utilizing a single MB(oSDM) S-BVT for P2 MP operations lies in its ability to streamline networkinfrastructure, reduce complexity, and enhance operational efficiency. Rather than deploying multiple transceivers to address individual communication links, the S-BVT optimizes resource utilization by managing multiple connections with a single, adaptable and programmable device. This not only simplifies the network architecture but also contributes to cost-effectiveness and ease of maintenance. Thanks to its scalable and modular architecture, it can easily accommodate the integration of new features and capabilities, thereby extending the useful lifespan of the equipment. At the digital signal processing (DSP) transmitter side of each BVT, adaptive loading based on orthogonal frequency division multiplexing (OFDM) is implemented, increasing the overall transceiver flexibility. Several operations are performed to generate the OFDM signals, such as data parallelization and mapping, insertion of training symbols (TS), implementation of the inverse fast Fourier transform, insertion of cyclic prefix (CP), serialization, and radio frequency (RF) up-conversion. The implementation of bit and power loading (BPL) algorithms enable to dynamically adjust the power values and modulation format of each ODFM subcarrier to the specific profile of the channel, as depicted in Figure 1[22]. This not only enhances the versatility of the transceiver, but also contributes to enhancing its overall performance. In the inset of Figure 1, it can be seen an example of the BPL operation, considering a C-band BVT based on intensity modulation (IM) and direct detection (DD) in a back-to-back (B2B) configuration, which assigns high modulation formats to the subcarriers that present highest performance/SNR. After DSP, digital-to-analogue conversion by means of a digital-to-analogue converter (DAC) is performed to generate an analogue OFDM signal. Different configurations can be adopted at the transmitter front-end of each MB S-BVT building block for modulation of the MB OFDM signals, such as IM, amplitude modulation or even IQ modulation [40]. Additionally, either external modulation (i.e., adopting Mach-Zehnder modulators--MZMs--and tuneable laser sources--TLSes) or direct modulation (i.e., using vertical cavity surface emitting lasers--VCSELs) can be adopted, trading-off performance versus cost/power consumption [22; 41; 42]. Finally, the different contributions are aggregated/distributed by means of an optical aggregator/distributor capable to allow operation across all the considered bands. This device is a key element of the MB S-BVT  
Figure 1: MB(oSDM) S—BVT architecture.