Hologram and holographic viewing device incorporating it

#The present invention relates generally to a hologram and a holographic viewing device incorporating it, and more particularly to a holographic viewing device with a built-in computer-generated hologram set up in the form of a transmission type Fourier transform hologram.

#Patent Publication 1 comes up with holographic eyeglasses constructed as shown in the perspective view of FIG. 16(a). More specifically, two transmission type holograms 2 and 3 are fitted in a binocular framework of an eyeglass frame 1. As a scene containing light sources 4, 5, 6 and 7, each of small area, as shown in FIG. 16(b), is viewed with the eyeglasses using the transmission type holograms 2 and 3, for instance, it looks as shown in FIG. 16(c). In other words, it looks as if the small-area light sources 4, 5, 6 and 7 in the actual scene of FIG. 16(b) were replaced with pre-selected words “NOEL” 8, 9, and 11, respectively. For the transmission holograms 2 and 3 having such features, Fourier transform (Fraunhofer) holograms having the aforesaid words “NOEL” are used in the form of computer-generated holograms.

#A little more explanation is given of the transmission holograms 2 and 3. Suppose now that transmission type hologram 21 stands for the transmission type holograms 2 and 3, and a (small-area) point light source 23 is located behind the transmission type hologram 21, as shown in FIG. 14(a). Then, as the point light source 23 is viewed with an eye 22 through the transmission type hologram 21, one image is reconstructed corresponding to the point light source 23 behind that transmission type hologram 21. FIG. 14(b) is a plan view of a unit hologram 24 that forms a part of the transmission type hologram 21. As shown, nine element holograms 241, each comprising a transmission type Fourier transform hologram, are lined up parallel with one another into the unit hologram 24, and the transmission type hologram 21 is assembled by arranging a multiplicity of such unit holograms 24 in rows and columns. FIG. 14(c) is illustrative of one exemplary reconstructed image 25 reconstructed upon viewing the point light source 23 through the transmission type hologram 21, which corresponds to the word “NOEL” in FIG. 16(b). In this case, the image has a crescent form.

#FIG. 1(a) is a flowchart of one hologram fabrication process according to the invention, and FIG. 1(b) is illustrative in schematic of that flowchart.

#FIG. 2 is illustrative of how to reconstruct images with the hologram fabricated according to FIG. 1.

#FIG. 3 is illustrative of the positions of point light sources at which each image reconstructed from the hologram can be seen and a region in which each reconstructed image can be seen.

#FIG. 1(a) is a flowchart illustrative of one hologram fabrication process according to the invention, and FIG. 1(b) is illustrative in schematic of that flowchart. First of all, a plurality of input images 41 and 42 are fabricated on a computer (step 101). For instance, the input image 41 has a crescent pattern a, and the input image 42 has a stellar pattern b.

#Then, on the computer, Fourier transform is applied to each input image 41, 42 to fabricate a Fourier transform image 51, 52 (step 102). Each Fourier transform image 51, 52 is binarized or multi-digitalized (step 103). In FIG. 1(b), numeral reference 61 is a Fourier transform image that is multi-digitalized in correspondence to the input image 41 (a diffraction optical element; an element hologram), and 62 is a Fourier transform image (a diffraction optical element; and element hologram) that is multi-digitalized in correspondence to the input image 42.

#Then, the image to be reconstructed is simulated (step 104). For this simulation, inverse Fourier transform is applied to the multi-digitalized Fourier transform images 61, 62 to obtain the respective Fourier transform images 71, 72, whereby whether or not appropriate processing has occurred at each step is checked out.