Tuning the polarization state of light via time retardation with a microstructured surface

We report here an approach to tune efficiently the phase difference of light in two orthogonal directions, Δφ, by controlling the time retardation with a microstructured surface made of L-shaped metallic patterns. The time retardation through the judicious microstructures can be adjusted on the femtosecond level, and Δφ can be linearly tuned accurately from -180^∘ to 180^∘ by changing the frequency of incident light. Particularly, the amplitudes in two orthogonal directions are identical, so that the polarization state always locates on a meridian of a Poincar\'e sphere. Near-field measurement confirms that there is indeed time retardation between the oscillations in the orthogonal directions of the L-shaped patterns. This approach offers an alternative way to manipulate the polarization state of light.