Autostereoscopic three-dimensional display technologies using novel optical imaging systems based on retro-reflection with mirror arrays, a dihedral corner reflector array (DCRA) and a roof mirror array (RMA) are described. The proposed methods can generate a low-distortion aerial 3-D image with high numerical aperture on the basis of retro-reflection imaging. As the examples of 3-D displays based on retro-reflective imaging, a multi-view stereoscopic display using a DCRA and a volumetric display using a RMA were described. The multi-view stereoscopic display can achieve not only aerial image formation of display images but also that of the pupils of projectors around viewing position using a DCRA. This feature is effective in keeping consistency between accommodation and convergence cues for stereoscopic display. The volumetric display using a RMA can generate a 3-D image with natural depth information by light points are arranged in a 3-D volume using relatively simple optical configuration. This method can provide natural perception of depth and accessibility to an image. Experimental demonstrations of the generation of floating autostereoscopic images are presented to verify the validity of our proposed methods.
We propose a floating volumetric display system using a novel imaging element whose aperture is large and can be made
easily at low cost. Diffuse rays in a horizontal direction for an observer are formed by a 90º prism sheet, which has a shape
of an array of 90º V-grooves, as a result of twice total internal reflection. On the other hand, the diffuse rays in a longitudinal
direction for the observer are formed by a linear Fresnel lens. A formed image by the proposed imaging element does not
distort in the horizontal direction because the rays in the horizontal direction converge by retroreflection. The proposed
imaging element can be produced easier than a conventional distortion-free imaging element and display a larger floating
image. A floating three-dimensional image was displayed by a volumetric display system based on optical scanning of an
inclined image plane. A position of a two-dimensional real image formed by the proposed imaging element was moved by
an optical scanner at a faster rate than the duration time of persistence of vision. A stack of moved images created the
floating three-dimensional volume image.
We propose to use a rotational optical scanning method for a volumetric three-dimensional (3D) display based on optical scanning of an inclined image plane. The image plane was moved by an image rotator and formed by a dihedral corner reflector array, which is a distortion free imaging element forming a real image at a plane-symmetrical position. A stack of the moved and formed image planes of a two-dimensional (2D) display created displayable space of a 3D image, which satisfies all the criteria of stereoscopic vision and can be seen by the naked eyes. The image rotator used in this study was constructed of prism sheets and planar mirrors. The image plane was moved rotationally by rotating the proposed image rotator on an axis parallel to the mirror plane. Enlargement of the displayable space is achieved by just extending the distance between the 2D display and the mirror, so that the proposed scanning method is effective to display a large 3D image for our volumetric display system. We made a prototype display and observed a moved image plane to measure the displayable space of the 3D image. The size of the displayable space was 1200 [cm3] that is approximately six times as large as our previous display using a translational optical scanning method.
A volumetric display system using a roof mirror grid array (RMGA) is proposed. The RMGA consists of a
two-dimensional array of dihedral corner reflectors and forms a real image at a plane-symmetric position. A
two-dimensional image formed with a RMGA is moved at thigh speed by a mirror scanner. Cross-sectional images of a
three-dimensional object are displayed in accordance with the position of the image plane. A volumetric image can be
observed as a stack of the cross-sectional images by high-speed scanning. Image formation by a RMGA is free from
aberrations. Moreover, a compact optical system can be constructed because a RMGA doesn't have a focal length.
An experimental volumetric display system using a galvanometer mirror and a digital micromirror device was
constructed. The formation of a three-dimensional image consisting of 1024 × 768 × 400 voxels is confirmed by the
experimental system.
We have proposed a new passive imaging optics which consists of a grid array of micro roof mirrors working as dihedral corner reflectors. Although this element forms mirror-like images at opposite side of objects, the images are real. Because the imaging principle of the proposed element is based on accumulation of rays, the design of each light path makes many kinds of devices possible. So, we propose two variations of such a device. One device consists of an array of micro retroreflectors and a half mirror, and it can also form real mirror-like images. The advantage of this device is wide range of view, because the displacement of each retororeflector is not limited on a plane unlike the roof mirror grid array. The other consists of an array of long dihedral corner reflectors. Although this structure has been already known as a roof mirror array, it can be used for imaging. This device forms two heterogeneous images. One is real at the same side of an object, and the other is virtual at the opposite side. This is a conjugate imaging optics of a slit mirror array whose mirror surface is perpendicular to the device surface. The advantage of a roor mirror array is that the real image has horizontal parallax and can be seen in air naturally.
We propose a new imaging optics called the Transmissive Mirror Device (TMD). It consists of numerous micromirrors
placed perpendicular to the surface of a flat, thin metal plate. The micro-mirror array is implemented
by the inner walls of minute square holes, which are densely pitted on the device. The basic mode of operation
is based on two reflections by a pair of adjacent mutually perpendicular mirrors, i.e., a dihedral corner reflector.
Although the principal of operation is based on reflection by mirrors, the device is also transmissive and deflects
light. Since this imaging system forms a real image at a plane symmetric point, the depth of the 3D image is
inverted. Its optical defects are low optical transmittance and stray light caused by non-reflected light and that
reflected once. We manufactured the device experimentally with nano-precision machining technology and also
evaluated it.
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