A display system 100 includes a light source 110 and a color wheel 114. One embodiment of the optical device includes having at least two light sources entering an aperture and being substantially aligned by a light refraction element. Prior to or upon handover of the client from said first radio layer node to the second radio layer node, a request including the client identifier is sent from said second to said first radio layer node or to another node if the central mobility database is maintained in that other node. The spin barrier layer suppresses diffusion of spin-polarized electrons and is provided on the side of the storage layer opposite the fixed magnetization layer.