# The Multiband over Spatial Division Multiplexing Sliceable Transceiver for Future Optical Networks
## 1 Introduction
Together, MB and SDM technologies are capable of addressing the scalability challenges presented by 6G applications and services [20; 21]. Specifically, the convergence of these two advanced technologies is anticipated to shape the landscape of optical networks in the 6G era by achieving:  
1. Enhanced bandwidth and spectral efficiency: MB enables to maximize the spectral resources, allowing for efficient data transmission across a wide range of frequencies/bands, while SDM exploits the spatial dimension such as cores/modes, dramatically increasing the network's capacity. 2. Enhanced network resilience and flexibility: by transmitting data simultaneously across various bands the systems will be more adaptable to dynamic network conditions. Additionally, the spatial diversity will also contribute to the resilience of optical networks. In the event of a failure in one spatial channel, the network can dynamically redistribute resources to maintain service continuity. Together, the convergence of MB and SDM technologies provides a comprehensive approach to fortifying optical networks against disruptions, ensuring robustness and adaptability. 3. Higher network scalability: Multiband over spatial division multiplexing (MBoSDM) technology addresses scalability challenges by efficiently utilizing available bandwidth across diverse bands and exploiting spatial diversity to increase network capacity. The combined effect of MB and SDM technologies is particularly relevant to meet the scalability demands and accommodate the ever-expanding volume of data traffic expected from the diverse range of applications and services anticipated in the 6G era. Therefore, MBoSDM implies a transformation towards achieving unparalleled levels of efficiency, flexibility, and scalability in the 6G era harnessing the strengths of both technologies to address the evolving demands of data-intensive applications and services for the long-term period adoption within optical networks. On this regard, the adoption of advanced transceiver architectures which can exploit MB and SDM technologies is fundamental in order to take advantage of the full potential of the networks. MB(oSDM) sliceable bandwidth/bitrate variable transceivers (S-BVTs) are proposed as an interesting transceiver option, based on a modular and scalable approach that can create a MB high-capacity flow that can be transmitted over different spatial channels [22]. On the one hand, thanks to the transceiver modularity different building blocks can be enabled and disabled according to the network needs and traffic demand, enhancing network efficiency and flexibility. Specifically, this will allow network operators to dynamically allocate and adjust bandwidth and resources on-the-fly as needed. This flexibility maximizes the efficient use of available bandwidth, distributed to match the actual demand, reducing resource wastage and enhancing network performance. With the provision of transceiver scalability, additional slices/bandwidth can be added as necessary, ensuring the network can keep up with increasing demand. By enabling more dynamic and flexible network operation, sliceable transceivers can contribute to better network resilience. In the event of a failure in one slice, resources can be quickly redistributed to maintain service continuity. Finally, the efficient bandwidth utilization and the ability to scale as needed together with the possibility to adopt photonic integration approaches, that MB(oSDM) S-BVTs can offer, can lead to reduced power consumption and a smaller carbon footprint [23; 24]. This work focuses on the design, implementation and experimental assessment of a MB(oSDM) S-BVT enabling up to 3 slices/flows within the C-, L-, and S-bands. The proposed transceiver approach exploits MB and SDM technologies and arises as a key solution to enhance overall network flexibility, efficiency, programmability and scalability toward meeting the stringent 6G capacity/bandwidth targets. In particular, Section 2 provides an overview of MB and SDM technologies.