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Swift and dynamic reconfigurability of network topology, even at the optical layer, is essential for satisfying the various requirements of future networks in diverse areas (e.g., data centers, 5G/Beyond-5G/Local-5G/6G, factory-related networks, and telecom networks) and for addressing issues arising during a disaster. Because of recent efforts to disaggregate optical transport networks, various compact disaggregate blades (e.g., wavelength selective switches and optical amplifier blades) have become commercially available. In principle, such disaggregation technology enables network operators to optimize their networks precisely at the blade level according to their distinctive needs, although the management complexity can increase with the number and diversity of the managed equipment. This paper presents transformation algorithms for mapping between a reconfigurable optical add/drop multiplexer (ROADM)-based model and a disaggregate-blade-based model to realize a flexible and agile optical physical layer based on disaggregation technology without increasing control plane complexity. In this study, a disaggregate-blade-based model named functional block-based disaggregation (FBD) is used, in which the switching functionalities of individual optical components are defined by the integer linear programming (ILP) method using machine-readable GNU MathProg modeling language. By computing the ILP formula, the switching functionalities of whole nodes/networks can be analyzed; that is, the FBD model can form the ROADM-level nodal model by aggregating the individual blade models. With the developed transformation algorithms, automated network operations, including optical path establishment/removal and node structure updates, are experimentally demonstrated on a field testbed. After physically plugging in the new components, the node structure update including the logical topology information is automatically recognized within 5 min. Multi-domain cooperative optical path recovery triggered by the update is also performed.

Disaggregated computing has been widely investigated to support the continuous progress in computing performance and overcome the slowdown of Moore’s law. It involves a flexible and optimal interconnection of heterogeneous compute nodes, such as the CPU, GPU, xPU, memory, and storage, to offer an efficient computing environment for various applications. Such a scheme inherently requires high network performance, including low latency, high capacity, determinism, and energy efficiency, all of which are simultaneously achieved through the introduction of optical-layer switching. This paper presents the application of optical-layer-switching architectures to disaggregated computing. Networks associated with disaggregated computing are classified into intra- and interserver networks. Focusing on the intraserver network, a holistic concept of optically composable disaggregated computing (OCDC) is discussed, along with its technological direction toward future digital infrastructure (i.e., the computing continuum). To realize OCDC, scalable and flexible optical switch technologies, as well as their dynamic and automatic control and management mechanisms, are indispensable. Previous studies have reported 32 × 32 silicon photonic switches that can form a nine-stage Clos topology with a radix of 131,072 and a machine-processable function description model for optical-layer switching, called the functional block-based disaggregation model (FBD model) that is capable of automating the operation, administration, and management of any optical physical topology in cooperation with upper-layer operating systems. This study examines their applicability to OCDC. The superior energy performance and scaling of an OCDC system equipped with optical matrix switches, such as silicon photonic switches, with respect to the conventional one big electrical packet-switching approach based on the reported wall-plug power consumption is also presented. The potential applicability of the FBD model as an essential control and management system for the optical layer of OCDC is evaluated through numerical experiments.

To cope with the capacity increase and diversification of information services, enhancing efficiency, flexibility, and agility in optical transport networks is becoming increasingly important. Quick reconfiguration of the optical physical layer, such as changing optical node architectures or optical physical network topologies, provides additional adaptability to requirement or environment changes. This paper proposes a new topology description scheme to support optical physical layer resource management at the granularity of optical functionality blocks in a machine-processible manner. The proposed scheme specifies intra-node structures as well as inter-node fiber connections (links). Furthermore, different switching functionalities of individual optical components are specified in a common format using integer linear programming (ILP) formulas. The ILP formulas are described in a machine-readable GNU MathProg modeling language so as to be directly introduced to the path computation mechanisms. Based on the proposed topology description scheme, a path computation engine named PathFinder is prototyped and demonstrated for optical networks consisting of various optical components with different switching functionalities. The computational feasibility of PathFinder is evaluated through numerical experiments in terms of elapsed time for path computation and the proposed scheme is successful while retaining reasonable time ranges. Operating topology and node architecture changes based on the proposed scheme are also successfully demonstrated over a multi-granular hierarchical optical network testbed with real hardware.

We investigated the switching dynamics of optical modulators consisting of a Si waveguide with a VO2 cladding layer by utilizing the photothermal effect, which induces a metal–insulator transition in VO2. The devices exhibited stable optical switching with a high extinction ratio exceeding 16 dB. The switching time of the insulator-to-metal transition (heating process) ranged from tens of nanoseconds to microseconds depending on the incident light power, and that of the metal-to-insulator transition (cooling process) was several microseconds regardless of the incident light power. The heat transfer in the devices was numerically simulated to reproduce the switching characteristics and revealed that the temperature change in the first few micrometers of the VO2/Si waveguide governed the switching time. The thermal structural design of the device is thus of key importance to improve the switching speed of the device.

Co-employment of node level and component level model is essential to achieve both SDNcontroller scalability and accurate path computation for functional block-based disaggregation networks.A proposed control system is prototyped and optical path provisioning within 30 seconds is demonstratedon an optical network testbed., Grant numbers : ADRENALINE testbed ® - Experimental research testbed on high-performance and large-scale intelligent optical transport networks and AURORAS - Autonomic and disaggregated optical networks leveraging edge computing and photonic technologies (RTI2018-099178-B-I00) projects.

Updating an OpenROADM node and subsequent re-routing were automated using a mathematical component-based model, triggered by the addition of node components. This process required only five minutes on an orchestrated testbed using SINET5 and a field optical network.