A variable refractive index unit (140) includes an optical axis and a first layer (144a, 146a, 146a') of controllably variable refractive index extending in a first predetermined configuration in a first plane transverse the optical axis. A second, different layer (144b, 146b, 146b') of controllably variable refractive index extends in a second predetermined configuration in a second, different plane transverse the optical axis. The second layer (144b, 146b, 146b') overlaps the first layer (144a, 146a, 146a'). |