The FDTD simulation is performed with a system in which the front-surface is a concave lens, the inside of bulk is a zero refractive index medium in which positive and negative refractive index cells are randomly arranged, and a reflector is placed over the back-surface plane. In a zero-index medium, an outgoing wavefront is always parallel to the outgoing-surface, is independent of either the incident wavefront or the shape of the incoming-surface. After waiting for a while after entering pulsed light into this structure, the light reflected from the back-surface is focused at the focal point of the concave lens over the front-surface.
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