The invention taught herein provides a method, device and system for modulating or switching electromagnetic radiation by controlling a state of the radiation, such as a polarization state. Radiation is directed at a reflective or transmissive structure, such that the radiation is incident on the structure. The structure includes a property that can be dynamically switched between two configurations, one of which is asymmetric and is configured to modify the polarization characteristic of the radiation. The dynamically configurable structure can be combined with polarization components to achieve modulation. Embodiments suitable for mode-locking a laser and for cavity dumping a mode-locked laser are also disclosed.