Modeling and analysis of transient response for cascaded WSS-based ROADMs

Wavelength selective switch (WSS)-based reconfigurable optical add/drop multiplexers (ROADMs) are key elements in current operator´s optical networks since they route signals directly in the optical domain. WSS-based ROADMs use a controller per site to guarantee a target power per channel over time following a distributed approach. The simultaneous and independent operation of the cascaded ROADMs´ controllers quickly increase optical power fluctuations (or abrupt power losses) leading to undesired overshoots that impair system operation. This paper first reviews different controllers for both industrial applications and optical devices. Second, the overshoot problem is stated and experimentally validated when such controllers are used for ROADMs deployed in cascade. Third, enhancement techniques for the reviewed controllers are proposed to overcome the overshoot problem in current distributed network scenarios. Finally, trade-offs between transient amplitude response and convergence time are analyzed using a cost function approach.