Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2001-03-17
2002-10-29
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S796000, C359S619000, C359S621000, C359S626000
Reexamination Certificate
active
06473238
ABSTRACT:
BACKGROUND OF THE INVENTION
DESCRIPTION OF THE RELATED ART
Stereoscopic systems provide a viewer with a three-dimensional representation of a scene (or an object), using two or more, two-dimensional representations of the scene. The two-dimensional representations of the scene are taken from slightly different angles. The goal of stereoscopic systems is to produce one or more binocular views of a scene to the viewer. A full-parallax view accurately simulates depth perception irrespective of the viewer's motion, as it would exist when the viewer observes a real scene.
Stereoscopic systems include autostereoscopic systems and non-autostereoscopic systems. Non-autostereoscopic systems require a viewer to use a device, such as viewing glasses, to observe the three-dimensional view, while the three-dimensional effect of autostereoscopic systems may be observed by viewing the system directly.
Early stereoscopic devices used prismatic, total internal reflection (TIR) to simultaneously present two views of a scene, such as the Swan Cube. Prismatic TIR allowed the views to be presented to the viewer such that each of the viewer's eyes was presented one of the two images, thus creating a perception of depth. Prismatic devices simulate depth perception for only a single viewing angle.
After the introduction of transparent plastic optics, autostereoscopic devices using one-dimensional arrays of cylindrical lenses (known as lenticular lenses) were created. A lenticular lens array has an associated array of composite strip images. Each lenticular lens presents the viewer a selected portion of its strip image such that the combined presentation of all of the lenticular lenses presents a three-dimensional view of the scene.
Devices using lenticular lenses have several shortcomings. First, because the lenticular lenses are cylindrical (i.e., they have optical power in a single dimension), they produce parallax only on a horizontal viewing axis. If the viewer's viewing angle departs from the horizontal viewing axis, the three-dimensional representation ceases to exist. Second, the lenticular lenses are highly astigmatic, and therefore, the viewer cannot bring the three-dimensional representation fully into focus. Third, if the two-dimensional images require illumination through the lenticular arrays (i.e., the images are not self-radiant, or the images are not printed on a transparent or translucent material that is capable of backlighting), the three-dimensional presentation will have uneven radiance resulting from uneven distribution within the array.
Another autostereoscopic system uses an array of spherical (or aspherical) lenses. Spherical lens array systems have an associated two-dimensional array of microimages. Each microimage is a two-dimensional view of a scene, captured from a slightly different angle. Unlike lenticular lenses, spherical lenses have optical power in two dimensions, thus allowing the viewer to maintain a three-dimensional representation of a scene despite departing from the horizontal viewing axis.
Each spherical lens presents the viewer a selected portion of a corresponding microimage such that the combined presentation of all of the spherical lenses presents a three-dimensional view of a scene. An advantage of spherical (or aspherical) arrays of lenses is their ability to capture arrays of microimages for use with three-dimensional viewing systems. The process of capturing arrays of microimages is known as integral imaging. An image captured by a spherical lens array is initially pseudoscopic, but may be made orthoscopic by reproduction of a captured image using a second array.
The shortcomings of spherical arrays have included that lenses in a lens arrays have excessive aberrations and a tendency to transmit light from multiple microimages. Both of these shortcomings have resulted in reduced image quality.
A difficulty encountered in capturing and reproducing images is optical crosstalk between lens systems of the array. Crosstalk causes overlap of adjacent images, resulting in degradation of the microimages. Solutions to crosstalk have ranged from modifications of the scene when creating the microimages, to optomechanical modifications of the lens arrays. Optomechanical modifications of the lens arrays have included baffles that limit the field of the lens systems comprising a lens array. The baffled lens systems are said to be field-limited. And a field-limited system whose field does not overlap the field of adjacent lens systems is said to be “isolated.” Solutions to crosstalk have been costly to implement.
SUMMARY OF THE INVENTION
In general, it has been found that the above recited optical goals may be achieved by the use of two arrays, the two arrays typically including three active optical boundaries and a planar surface disposed at the focal length of the array. In the invention, a first boundary is convex and substantially spherical, a second boundary is concave and usually oblate, and a third boundary is prolate and predominantly convex. The internal surfaces of the second and third optical boundaries may, in some embodiments, also be employed as efficient angle-selective reflectors. In preferred embodiments of the invention, the two array layers are joined using bonding agents of specific optical characteristics. The two preferred compositions are 1) a light-absorbing bonding agent, and 2) a low-index UV-curing fluoropolymer. Two embodiments of the microlens may be conceived of as roughly analogous to, in the first case, an aspheric doublet with an internal aperture, and in the second case, an aspheric cemented triplet.
The invention includes arrays in which the outer spherical lens surfaces are imbricated, i.e. having a polygonal aspect when viewed on-axis, as well as embodiments in which the convex outer lens surfaces are formed as independent features on a continuous planar background, as suits their application. Other specific embodiments will be understood by way of the following figures and description.
The improvement of the array optics generally relies on a low-index region of highly aspheric geometry located within an array of higher-index optical material, such as acrylic, polycarbonate or polyetherimide. The region is typically created by permanently bonding two discrete arrays such that the low-index material is entrapped between the bonded arrays. Each microlens cell therefore has three significant optical boundaries, and a continuous planar rear surface. The general family of geometries illustrated in this document have been found to greatly reduce spherical aberration, while also eliminating the preponderance of field curvature. Because the performance of these arrays is not implicitly degraded at short focal lengths, a continuous, full-parallax image field of 60° or more can be attained.
The arrays generally fall into two categories. The first type of array uses air as the low-index material. The distinctive equiangular geometry of these arrays allows the optical pathway to be confined to a central angular zone; because of this ability to restrict light, these arrays will be referred to as field-limited arrays. This type of array may be used, for example, in illuminated displays electronic image detection, machine vision, and real-time 3D video capture. A second type of array uses a fluoropolymer as the low-index material, and conveys a great preponderance all incident light to the image plane. These arrays are referred to as open-field arrays, and may be used to produce high-brightness images for viewing under arbitrary ambient illumination, or for imaging lenses with increased optical gain or reduced lens flare.
By exploiting TIR, the field-limited arrays can be fashioned to eliminate image overlap and confine the converged real microimages to the region of the focal plane immediately associated with their respective microlenses. This light restriction on acceptance allows a set of coplanar microimages to be captured without significant overlap. The array may be used to eliminate the formation of parasitic latent image
Epps Georgia
Spector David N.
Testa Hurwitz & Thibeault LLP
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