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, Delta phi, 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 Delta phi can be linearly tuned accurately from -180 degrees to 180 degrees by changing the frequency of incident light. Particularly, the amplitudes in two orthogonal directions are identical, so that the polarization state always locates on ameridian of a Poincare 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.