The aperture of a perfect lens is divided into several concentric circular zones. The effects of the different zones having different phase retardations are studied. The following conditions are found by a straightforward consideration: When the aperture is divided into two zones, with the inner zone having a phase retardation of π rad with respect to the outer zone, the diffraction pattern in the focal plane of the lens has the smallest central bright spot; this assumes that the same irradiance is always produced at the focus. Conversely, for a given radius of the central bright spot in the diffraction pattern, the greatest irradiance at the focus of the lens is produced when the lens aperture is divided into two concentric circular zones, with the inner zone having a phase retardation of π rad. Such a lens also possesses the same advantages over a perfect lens with a circular stop in its center. It may also possess an effective focal depth greater than that of the latter. It may have one or two foci depending on the value of the radius of the circle that divides its aperture.
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