Imaging by Flat Lens
Negative refarcation can be exploted to make novel lenses having flat surfaces. All conventional lenses have curved surfaces due to positive index of refraction. However, negative index of refraction allows a flat slab of a material to behave as a lens and focus electromagnetic waves as well as produce a real 3-D image. We have demonstrated this unique feature of imaging by a flat lens, using the phenomenon of all-angle negative refraction in a photonic crystalline material.
Conventional optical systems have a single optical axis, limited aperture and cannot focus light onto an area smaller than a square wavelength. In contrast the present flat lens does not have a unique optical axis and is not restricted by the aperture size. We have demonstrated both these features by moving the object by 4 cm: the image moves by a corresponding amount in the same direction (see Figure on right) Note that for the sub-wavelength source we have observed an image of similar size. The unique properties of the flat lens lead to entirely new perspectives on imaging and potentially new applications. A particular advantage of the photonic crystalline material is its scalability to sub-micron dimensions ensuring several possible applications from microwave to optical frequencies.