Focusing a light beam more than thirty focal depths from the aplanatic point with a plano-convex lens
AssigneeU.S. Philips Corporation
InventorsBernardus H. W. Hendriks, Josephus J. M. Braat
Life of this patent
Estimating the term…
Abstract
A device is described for optically scanning a record carrier with a radiation beam having a high numerical aperture. The radiation beam is focused on the record carrier by means of an objective lens and a plano-convex lens. The plano-convex lens has a gap with the record carrier of several tens of micrometers. It focuses the radiation beam to a point at least 30 focal depths away from an aplanatic point of the plano-convex lens. As a consequence, the lens has a relatively large tolerance for sideways movements.
Claims14
An optical scanning device for optically scanning a record carrier comprising an information layer and a transparent layer, the device comprising an objective lens and a plano-convex lens for converging a radiation beam through the transparent layer to a focus on the information layer, the plano-convex lens having a convex surface facing the objective lens, and a planar surface facing the transparent layer, the objective lens and plano-convex lens are designed for forming a focus point at a distance of more than thirty focal depths of the converging radiation beam from an aplanatic point of the plano-convex lens.
An optical scanning device for optically scanning a record carrier comprising an information layer and a transparent layer having a refractive index n1, the device comprising an objective lens and a plano-convex lens for converging a radiation beam through the transparent layer to a focus on the information layer, the plano-convex lens having a convex surface facing the objective lens, a planar surface facing the transparent layer, a magnifying power and a refractive index n2, the value of n1 is larger than the value of n2 and the magnifying power of the plano-convex lens is substantially equal to 1/n1.
An optical scanning device for optically scanning a first and second type of record carrier, the first type of record carrier comprising a first information layer and a first transparent layer having a first thickness, the second type of record carrier comprising a second information layer and a second transparent layer having a refractive index n1 and a second thickness larger than the first thickness, the device comprising an objective lens and a plano-convex lens for converging a radiation beam through the first or second transparent layer to a focus spot on the information layer, the plano-Convex lens having a convex surface facing the objective lens, a planar surface facing the transparent layer, a magnifying power and a refractive index n2, the magnifying power of the plano-convex lens is substantially equal to 1/n1.
An optical scanning device for optically scanning a record carrier comprising at least two adjacent information layers and a transparent spacer layer having a refractive index n1 arranged between the information layers, the device comprising an objective lens and a plano-convex lens for converging a radiation beam to a focus spot on one of the information layers, the plano-convex lens having a convex surface facing the objective lens, a planar surface facing the transparent layer, a magnifying power and a refractive index n2, the magnifying power of the plano-convex lens is substantially equal to 1/n1.
Dependencies are inferred from the claim text.