Most deployed optical transport networks are proprietary, behaving as a closed, highly coupled, single-vendor managed domain. Although their control planes and management systems may export high-level and open northbound interfaces (NBI), the internal details and interfaces are not disclosed to the network operator. However, driven by the requirements of telecommunication and data-center operators and the need to keep costs down while supporting sustained traffic increase, a trend known as disaggregation has steadily emerged during the past years. It involves composing and assembling open and available components, devices and sub-systems into optical infrastructures and networks, combining “best-in-class” devices, tailored to the specific needs of the aforementioned operators. It has been motivated by factors such as an increase in hardware commoditization, a perceived different rate of innovation of the different components, a promised acceleration in service deployment, or the consequent reduction in operational and capacity expenses. In practice, disaggregation brings multiple challenges, depending on the level that applies (e.g., partial or total, down to each of the optical components) and is taking place in stages. It is commonly accepted that disaggregation implies a trade-off between: (i) the opportunities due to the new degree of flexibility provided by component migration and upgrades without vendor lock-in and (ii) the potential decrease in performance compared to fully integrated systems and the underlying complexity – including interoperability -, critical in full disaggregation scenarios. From the point of view of control and management, disaggregation heavily relies on the adoption of open interfaces exporting hardware programmability. Disaggregated optical networks are an important use case for the adoption or a unified, model-driven development. In this paper, tutorial in nature, we will introduce the main concepts behind Software Defined Networking (SDN) for disaggregated optical networks, presenting reference architectures and industry common practices related to the adoption of a unified, model driven approach. The second part will cover an overview of selected deployment models (e.g., addressing transceiver and OLS disaggregation) as well as the OpenConfig and OpenROADM optical device models and Transport API (TAPI) interfaces, which constitute the main elements of the implemented SDN control plane. Such control plane targets mainly the metro segment, as defined within the EC Metro-Haul and ONF ODTN projects.