Currently optical networks are reaching their maximum transport capacity. Several solutions, in particular, space division multiplexing (SDM) can be used to overcome this capacity limit. To use SDM, the reconfigurable optical add/drop multiplexers (ROADMs) need to be adapted to support this multiplexing. In this work, four switching strategies used in
SDM ROADMs and the respective SDM ROADM architectures to implement these strategies are explained and analyzed, for
uncoupled scenarios, in terms of cost and power consumption. The impact of the physical layer impairments (PLIs), namely,
amplified spontaneous emission noise, non-linear interference, passband narrowing due to optical filtering and in-band crosstalk is also assessed, considering a cascade of SDM ROADMs with spatial and spatial-wavelength switchinggranularities. The in-band crosstalk in networks with a single
spatial channel or in a SDM network with the ROADM architecture with spatial granularity has an insignificant impact, but in a SDM network with spatial wavelength
granularity can lead to an OSNR penalty of around 2 dB, when the number of spatial channels is high. The other PLIs have
similar impacts in all networks studied.