An optical node comprising: a ROADM core (140, 600), the ROADM core (140, 600) being a reconfigurable optical add drop multiplexer core device including a bidirectional network interface, a light distributor for distributing a multiple-wavelength optical signal containing all the wavelengths received from a network by the network interface via subtending outputs thereof, and a light combiner for receiving multiple-wavelength optical signals via subtending inputs thereof, for combining the received optical signals for transmission to the network interface for outputting to the network; and at least two ROADM add-on devices (542, 544, 546, 548, 602, 604), each bidirectionally connected to the ROADM core (140, 600) by one of the subtending inputs and one of the subtending outputs, configured to process optical signals of multiple wavelengths, and being different types of devices from one another, characterized in that: each ROADM add-on device (542, 544, 546, 548, 602, 604) has a receiving element for receiving on one of the subtending outputs the optical signal containing all of the wavelengths received from the network interface and a transmitting element for transmitting on one of the subtending inputs a multiple-wavelength signal to the ROADM core (140, 600), and each ROADM add-on device being one of a colored optical add/drop device, a colorless optical add/drop device, an optical spur, and a further ROADM core. a ROADM core (140, 600), the ROADM core (140, 600) being a reconfigurable optical add drop multiplexer core device including a bidirectional network interface, a light distributor for distributing a multiple-wavelength optical signal containing all the wavelengths received from a network by the network interface via subtending outputs thereof, and a light combiner for receiving multiple-wavelength optical signals via subtending inputs thereof, for combining the received optical signals for transmission to the network interface for outputting to the network; and a bidirectional network interface, a light distributor for distributing a multiple-wavelength optical signal containing all the wavelengths received from a network by the network interface via subtending outputs thereof, and a light combiner for receiving multiple-wavelength optical signals via subtending inputs thereof, for combining the received optical signals for transmission to the network interface for outputting to the network; and at least two ROADM add-on devices (542, 544, 546, 548, 602, 604), each bidirectionally connected to the ROADM core (140, 600) by one of the subtending inputs and one of the subtending outputs, configured to process optical signals of multiple wavelengths, and being different types of devices from one another, characterized in that: each ROADM add-on device (542, 544, 546, 548, 602, 604) has a receiving element for receiving on one of the subtending outputs the optical signal containing all of the wavelengths received from the network interface and a transmitting element for transmitting on one of the subtending inputs a multiple-wavelength signal to the ROADM core (140, 600), and each ROADM add-on device being one of a colored optical add/drop device, a colorless optical add/drop device, an optical spur, and a further ROADM core. each ROADM add-on device (542, 544, 546, 548, 602, 604) has a receiving element for receiving on one of the subtending outputs the optical signal containing all of the wavelengths received from the network interface and a transmitting element for transmitting on one of the subtending inputs a multiple-wavelength signal to the ROADM core (140, 600), and each ROADM add-on device being one of a colored optical add/drop device, a colorless optical add/drop device, an optical spur, and a further ROADM core.